Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.1093/pasj/psab013

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.3847/1538-4357/abde38

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/abde38/pdf

Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

© 2020 SPIE The XRISM is the X-ray astronomical mission led by JAXA/NASA/ESA with international participation, plan to be launched in 2022 (Japanese fiscal year), to quickly recover the high-resolution X-ray spectroscopy of astrophysical objects using the micro-calorimeter array after the failure of Hitomi. To enhance the scientific outputs of the mission, the Science Operations Team (SOT) is structured independently from the instrument teams and the mission operation team (MOT). The responsibilities of the SOT are summarized into four categories: 1) Guest observer program and data distributions, 2) Distribution of the analyses software and calibration database, 3) Guest observer supporting activities, and 4) the performance verification and optimization (PVO) activities. Before constructing the Operations Concept of the XRISM mission, the lessons on the Science Operations learned from the past Japanese X-ray missions (ASCA, Suzaku, and Hitomi) are reviewed, and 16 kinds of lessons are identified by the above categories: lessons on the importance of avoiding nonpublic (“animal”) tools, coding quality of public tools both on the engineering viewpoint and the calibration accuracy, tight communications with instrument teams and operations team, well-defined task division between scientists and engineers etc. Among these lessons, a) importance of the early preparations of the operations from the ground stage, b) construction of the independent team for the Science Operations from the instrument developments, and c) operations with well-defined duties by appointed members are recognized as the key lessons for XRISM. Then, i) the task division between the Mission and Science Operations and ii) the subgroup structure within the XRISM team are defined in detail as the XRISM Operations Concept. Then, following the Operations Concept, the detail plan of the Science Operations is designed as follows. The Science Operations tasks are shared among Japan, US, and Europe operated by three centers, the Science Operations Center (SOC) at JAXA, the Science Data Center (SDC) at NASA, and European Space Astronomy Centre (ESAC) at ESA. The SOT is defined as a combination of the SOC and SDC; the SOC is designed to perform tasks close to the spacecraft operations, such as spacecraft planning of science targets, quick-look health checks, pre-pipeline data processing, etc., and the SDC covers the tasks on the data calibration processing (pipeline processing), maintenance of the analysis tools etc. The data-archive and users-support activities are planned to be covered both by the SOC and SDC. Finally, the details of the Science Operations tasks and the tools for the Science Operations are also described in this paper. This information would be helpful for a construction of Science Operations of future X-ray missions.

DOI： 10.1117/12.2560861

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Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

© 2020 SPIE The X-Ray Imaging and Spectroscopy Mission, XRISM, is currently scheduled to launch in 2022 with the objective of building on the brief, but significant, successes of the ASTRO-H (Hitomi) mission in solving outstanding astrophysical questions using high resolution X-ray spectroscopy. The XRISM Science Operations Team (SOT) consists of the JAXA-led Science Operations Center (SOC) and NASA-led Science Data Center (SDC), which work together to optimize the scientific output from the Resolve high-resolution spectrometer and the Xtend wide-field imager through planning and scheduling of observations, processing and distribution of data, development and distribution of software tools and the calibration database (CaldB), support of ground and in-flight calibration, and support of XRISM users in their scientific investigations of the energetic universe. Here, we summarize the roles and responsibilities of the SDC and its current status and future plans. The Resolve instrument poses particular challenges due to its unprecedented combination of high spectral resolution and throughput, broad spectral coverage, and relatively small field-of-view and large pixel-size. We highlight those challenges and how they are being met.

DOI： 10.1117/12.2560840

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

<title>Abstract</title>
We report on multi-wavelength monitoring observations of an M-dwarf flare star AD Leonis with the Seimei Telescope (6150–7930 Å), SCAT (Spectroscopic Chuo-university Astronomical Telescope; 3700–7500 Å), and NICER (Neutron Star Interior Composition Explorer; 0.2–12.0 keV), with the collaboration of the OISTER (Optical and Infrared Synergetic Telescopes for Education and Research) program. Twelve flares are detected in total, including ten Hα, four X-ray, and four optical-continuum flares; one of them is a superflare with a total energy of ∼2.0 × 1033 erg. We found that: (1) during the superflare, the Hα emission line full width at 1/8 maximum dramatically increases to 14 Å from 8 Å in the low-resolution spectra (R ∼ 2000) accompanied by large white-light flares, (2) some weak Hα/X-ray flares are not accompanied by white-light emissions, and (3) the non-flaring emissions show clear rotational modulations in X-ray and Hα intensity in the same phase. To understand these observational features, one-dimensional hydrodynamic flare simulations are performed using the RADYN code. We find the simulated Hα line profiles with hard and high-energy non-thermal electron beams to be consistent with the initial phase line profiles of the superflares, while those with a softer and/or weak-energy beam are consistent with those in decay phases, indicating the changes in the energy fluxes injected to the lower atmosphere. Also, we find that the relation between the optical continuum and Hα intensity is nonlinear, which can be one cause of the non-white-light flares. The flare energy budget exhibits diversity in the observations and models, and more observations of stellar flares are necessary for constraining the occurrence of various emission line phenomena in stellar flares.

DOI： 10.1093/pasj/psaa051

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.3847/1538-4357/ab7207

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/ab7207

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We present the results from the Hitomi Soft Gamma-ray Detector (SGD) observation of the Crab nebula. The main part of SGD is a Compton camera, which in addition to being a spectrometer, is capable of measuring polarization of gamma-ray photons. The Crab nebula is one of the brightest X-ray / gamma-ray sources on the sky, and, the only source from which polarized X-ray photons have been detected. SGD observed the Crab nebula during the initial test observation phase of Hitomi. We performed the data analysis of the SGD observation, the SGD background estimation and the SGD Monte Carlo simulations, and, successfully detected polarized gamma-ray emission from the Crab nebula with only about 5 ks exposure time. The obtained polarization fraction of the phase-integrated Crab emission (sum of pulsar and nebula emissions) is (22.1% +/- 10.6%), and, the polarization angle is 110.degrees 7 + 13.degrees 2 /-13.degrees 0 in the energy range of 60-160 keV (The errors correspond to the 1 sigma deviation). The confidence level of the polarization detection was 99.3%. The polarization angle measured by SGD is about one sigma deviation with the projected spin axis of the pulsar, 124.degrees 0 +/- 0.degrees 1.

DOI： 10.1093/pasj/psy118

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On the basis of various data such as ALMA, JVLA, Chandra, {\it Herschel}, and
{\it Spitzer}, we confirmed that two protostellar candidates in Oph-A are bona
fide protostars or proto-brown dwarfs (proto-BDs) in extremely early
evolutionary stages. Both objects are barely visible across infrared (IR, i.e.,
near-IR to far-IR) bands. The physical nature of the cores is very similar to
that expected in first hydrostatic cores (FHSCs), objects theoretically
predicted in the evolutionary phase prior to stellar core formation with gas
densities of $\sim$ 10$^{11-12}$ cm$^{-3}$. This suggests that the evolutionary
stage is close to the FHSC formation phase. The two objects are associated with
faint X-ray sources, suggesting that they are in very early phase of stellar
core formation with magnetic activity. In addition, we found the CO outflow
components around both sources which may originate from the young outflows
driven by these sources. The masses of these objects are calculated to be $\sim
0.01-0.03$ $M_\odot$ from the dust continuum emission. Their physical
properties are consistent with that expected from the numerical model of
forming brown dwarfs. These facts (the X-ray detection, CO outflow association,
and FHSC-like spectral energy distributions) strongly indicate that the two
objects are proto-BDs or will be in the very early phase of protostars which
will evolve more massive protostars if they gain enough mass from the
surroundings. The ages of these two objects are likely to be within $\sim 10^3$
years after the protostellar core (or second core) formation, taking into
account the outflow dynamical times ($\lesssim$ 500 yrs).

DOI： 10.3847/1538-4357/aae153

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arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.3847/1538-4365/aad1ef

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4365/aad1ef

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.1093/pasj/psy027

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS  

The Hitomi (ASTRO-H) mission is the sixth Japanese x-ray astronomy satellite developed by a large international collaboration, including Japan, USA, Canada, and Europe. The mission aimed to provide the highest energy resolution ever achieved at E > 2 keV, using a microcalorimeter instrument, and to cover a wide energy range spanning four decades in energy from soft x-rays to gamma rays. After a successful launch on February 17, 2016, the spacecraft lost its function on March 26, 2016, but the commissioning phase for about a month provided valuable information on the onboard instruments and the spacecraft system, including astrophysical results obtained from first light observations. The paper describes the Hitomi (ASTRO-H) mission, its capabilities, the initial operation, and the instruments/spacecraft performances confirmed during the commissioning operations for about a month. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.

DOI： 10.1117/1.JATIS.4.2.021402

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We present the first MAXI/GSC X-ray source catalog in the low-Galactic-latitude sky vertical bar b vertical bar < 10 degrees outside the Galactic center region (vertical bar b vertical bar < 5 degrees, l < 30 degrees, and l > 330 degrees) based on 7-year data from 2009 August 13 to 2016 July 31. To overcome source confusion in crowded regions, we have accurately calibrated the position-dependent shape of the point-spread function of the MAXI/GSC by analyzing onboard data. We have also taken into account the Galactic ridge X-ray emission. Using a maximum likelihood image fitting method, we have detected 221 sources with a significance threshold >6.5 sigma, 7 of which are transients only detected in 73-day time-sliced images. The faintest source has a flux of 5.2 x 10(-12) erg cm(-2) s(-1) (or an intensity of 0.43 mCrab) in the 4-10 keV band. We have identified the counterparts for about 81% of the detected sources, by cross-matching with the Swift, Uhuru, RXTE, XMM-Newton, MCXC, and ROSAT all-sky survey catalogs. Our catalog contains the source name, position and its error, flux and detection significance in the 3-4. keV, 4-10. keV, and 10-20. keV bands, hardness ratios, and information on the likely counterpart for the individual detected sources. We have obtained 73-day bin light curves of all the cataloged sources over 7 years and have calculated their periodograms. On the basis of the mean properties of time variability and spectral hardness, we suggest that the majority of the unidentified sources are low-mass X-ray binaries or blazars. Finally, we present the log N-log S relations at different Galactic longitudes and for different source populations.

DOI： 10.3847/1538-4365/aaa89c

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.1093/pasj/psx154

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

J-GLOBAL

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

J-GLOBAL

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

J-GLOBAL

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

J-GLOBAL

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

J-GLOBAL

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

J-GLOBAL

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Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

The present paper explains the temperature structure of X-ray emitting plasma in the core of the Perseus cluster based on 1.8-20.0 keV data obtained with the Soft X-ray Spectrometer (SXS) on board the Hitomi Observatory. A series of four observations was carried out, with a total effective exposure time of 338 ks that covered a central region of similar to 7&#039; in diameter. SXS was operated with an energy resolution of similar to 5 eV (full width at half maximum) at 5.9 keV. Not only fine structures of K-shell lines in He-like ions, but also transitions from higher principal quantum numbers were clearly resolved from Si through Fe. That enabled us to perform temperature diagnostics using the line ratios of Si, S, Ar, Ca, and Fe, and to provide the first direct measurement of the excitation temperature and ionization temperature in the Perseus cluster. The observed spectrum is roughly reproduced by a single-temperature thermal plasma model in collisional ionization equilibrium, but detailed line-ratio diagnostics reveal slight deviations from this approximation. In particular, the data exhibit an apparent trend of increasing ionization temperature with the atomic mass, as well as smal

DOI： 10.1093/pasj/psy004

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Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Extending the earlier measurements reported in Hitomi collaboration (2016, Nature, 535, 117), we examine the atmospheric gas motions within the central 100 kpc of the Perseus cluster using observations obtained with the Hitomi satellite. After correcting for the point spread function of the telescope and using optically thin emission lines, we find that the line-of-sight velocity dispersion of the hot gas is remarkably low and mostly uniform. The velocity dispersion reaches a maxima of approximately 200 km s(-1) toward the central active galactic nucleus (AGN) and toward the AGN inflated northwestern &quot;ghost&quot; bubble. Elsewhere within the observed region, the velocity dispersion appears constant around 100 km s(-1). We also detect a velocity gradient with a 100 km s(-1) amplitude across the cluster core, consistent with large-scale sloshing of the core gas. If the observed gas motions are isotropic, the kinetic pressure support is less than 10% of the thermal pressure support in the cluster core. The well-resolved, optically thin emission lines have Gaussian shapes, indicating that the turbulent driving scale is likely below 100 kpc, which is consistent with the size of the

DOI： 10.1093/pasj/psx138

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Nature Publishing Group  

The metal abundance of the hot plasma that permeates galaxy clusters represents the accumulation of heavy elements produced by billions of supernovae(1). Therefore, X-ray spectroscopy of the intracluster medium provides an opportunity to investigate the nature of supernova explosions integrated over cosmic time. In particular, the abundance of the iron-peak elements (chromium, manganese, iron and nickel) is key to understanding how the progenitors of typical type Ia supernovae evolve and explode(2-6). Recent X-ray studies of the intracluster medium found that the abundance ratios of these elements differ substantially from those seen in the Sun(7-11), suggesting differences between the nature of type Ia supernovae in the clusters and in the Milky Way. However, because the K-shell transition lines of chromium and manganese are weak and those of iron and nickel are very close in photon energy, highresolution spectroscopy is required for an accurate determination of the abundances of these elements. Here we report observations of the Perseus cluster, with statistically significant detections of the resonance emission from chromium, manganese and nickel. Our measurements, combined with the latest atomic models, reveal that these elements have near-solar abundance ratios with respect to iron, in contrast to previous claims. Comparison between our results and modern nucleosynthesis calculations(12-14) disfavours the hypothesis that type Ia supernova progenitors are exclusively white dwarfs with masses well below the Chandrasekhar limit (about 1.4 times the mass of the Sun). The observed abundance pattern of the iron-peak elements can be explained by taking into account a combination of near-and sub-Chandrasekhar-mass type Ia supernova systems, adding to the mounting evidence that both progenitor types make a substantial contribution to cosmic chemical enrichment(5,15,16).

DOI： 10.1038/nature24301

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of similar to 1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg(2) at a luminosity distance of 40(-8)(+8) Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 M-circle dot. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at similar to 40 Mpc) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over similar to 10 days. Following early non-detections, X-ray and radio emission were discovered at the transient's position similar to 9 and similar to 16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.

DOI： 10.3847/2041-8213/aa91c9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

X-ray spectroscopy with Hitomi was expected to resolve the origin of the faint unidentified E approximate to 3.5 keV emission line reported in several low-resolution studies of various massive systems, such as galaxies and clusters, including the Perseus cluster. We have analyzed the Hitomi first-light observation of the Perseus cluster. The emission line expected for Perseus based on the XMM-Newton signal from the large cluster sample under the dark matter decay scenario is too faint to be detectable in the Hitomi data. However, the previously reported 3.5 keV flux from Perseus was anomalously high compared to the sample-based prediction. We find no unidentified line at the reported high flux level. Taking into account the XMM measurement uncertainties for this region, the inconsistency with Hitomi is at a 99% significance for a broad dark matter line and at 99.7% for a narrow line from the gas. We do not find anomalously high fluxes of the nearby faint K line or the Ar satellite line that were proposed as explanations for the earlier 3.5 keV detections. We do find a hint of a broad excess near the energies of high-n transitions of S XVI (E similar or equal to 3.44 keV rest-frame)-a possible signature of charge exchange in the molecular nebula and another proposed explanation for the unidentified line. While its energy is consistent with XMM pn detections, it is unlikely to explain the MOS signal. A confirmation of this interesting feature has to wait for a more sensitive observation with a future calorimeter experiment.

DOI： 10.3847/2041-8213/aa61fa

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Czech Technical University in Prague  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：CAMBRIDGE UNIV PRESS  

We report the results of the stellar wind measurement for two colliding wind binaries. The X-ray spectrum is the best measurement tool for the hot postshock gas. By monitoring the changing of the the X-ray luminosity and column density along with the orbital phases, we derive the mass-loss rates of these stars.

DOI： 10.1017/S1743921317003325

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Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We present multi-epoch X-ray spectral observations of three Type IIn supernovae (SNe), SN 2005kd, SN 2006jd, and SN 2010jl, acquired with Chandra, XMM-Newton, Suzaku, and Swift. Previous extensive X-ray studies of SN. 2010jl have revealed that X-ray spectra are dominated by thermal emission, which likely arises from a hot plasma heated by a forward shock propagating into a massive circumstellar medium (CSM). Interestingly, an additional soft X-ray component was required to reproduce the spectra at a period of similar to 1-2 years after the SN explosion. Although this component is likely associated with the SN, its origin remained an open question. We find a similar, additional soft X-ray component from the other two SNe IIn as well. Given this finding, we present a new interpretation for the origin of this component; it is thermal emission from a forward shock essentially identical to the hard X-ray component, but directly reaches us from a void of the dense CSM. Namely, the hard and soft components are responsible for the heavily and moderately absorbed components, respectively. The co-existence of the two components with distinct absorptions as well as the delayed emergence of th

DOI： 10.3847/0004-637X/832/2/194

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Language：English   Publishing type：Research paper (scientific journal)  

© 2016 The Author. Published by Oxford University Press on behalf of the Astronomical Society of Japan. All rights reserved. Twenty-three giant flares from thirteen active stars (eight RS CVn systems, one Algol system, three dMe stars, and one young stellar object) were detected during the first two years of our all-sky X-ray monitoring with the gas propotional counters (GSC) of the Monitor of All-sky X-ray Image (MAXI). The observed parameters of all these MAXI/GSC flares are found to be at the upper ends for stellar flares with the luminosity of 1031-34 erg s-1 in the 2-20 keV band, the emission measure of 1054-57 cm-3, the e-folding time of 1 hr to 1.5 d, and the total radiative energy released during the flare of 1034-39 erg. Notably, the peak X-ray luminosity of 5+4-2 × 1033erg s-1 in the 2-20 keV band was detected in one of the flares on II Peg, which is one of the, or potentially the, largest-ever-observed in stellar flares. X-ray flares were detected from GT Mus, V841 Cen, SZ Psc, and TWA-7 for the first time in this survey. Whereas most of our detected sources are multiple-star systems, two of them are single stars (YZ CMi and TWA-7). Among the stellar sources within 100 pc distance, the MAXI/GSC sources have larger rotation velocities than the other sources. This suggests that the rapid rotation velocity may play a key role in generating large flares. Combining the X-ray flare data of nearby stars and the sun, taken from literature and our own data, we discovered a universal correlation of τ LX0.2 for the flare duration τ and the intrinsic X-ray luminosity LX in the 0.1-100 keV band, which holds for 5 and 12 orders of magnitude in τ and LX, respectively. The MAXI/GSC sample is located at the highest ends of the correlation.

DOI： 10.1093/pasj/psw081

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Nature Publishing Group  

J-GLOBAL

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

DOI： 10.1093/pasj/psw016

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.71.1.0_503

CiNii Books

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

The light from celestial objects includes four important quantities; images, time variation, energy spectrum, and polarization. In the field of X-ray astronomy, the capabilities of the former three have remarkably developed. On the other hand, the progress for the polarimetry is considerably delayed because of technical difficulties. In order to make a breakthrough in the field of X-ray polarimetry, we have developed a new type of optics for X-ray polarimetry. The system is collecting Bragg crystal with large area and very high sensitivity for the polarization dedicated to Fe-K lines. We adopt the 400 reflection of Si(100) crystals with high sensitivity for the polarization around Fe-K lines (6 similar to 7 keV), and bent the crystals with the wide X-ray band and high S/N ratio. Furthermore, to install small area of CCD to non-focal plane, it also has the spectroscopic capability with the better resolution than that of general X-ray CCD.
Our previous development was to bent Si crystals to the cylindrical shape of circle and parabola with the DLC deposition. However, for the better optics for the X-ray polarimetry, the shape should be the paraboloid of revolution to collect X-rays with high S/N ratio. We searched for the method to bent the Si crystals to the shape of the paraboloid of revolution. We devised the method to mold the crystal and the CFRP substrate simultaneously pushed to the sophisticated foundation with the paraboloid of revolution. We developed the prototype of about 8 inch in radius of one-quater size. The crystals was also bent in the circumferential direction. Therefore, the image capability examined with optical parallel beam is 0.6 degree. In this thesis, we discussed the new design for X-ray spectroscopic polarimetry, the evaluation of image capability.

DOI： 10.1117/12.2231166

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Suzaku observations of theWolf-Rayet (W-R) binaryWR 140 (WC7pd+O5.5fc) were made at four different times around periastron passage in 2009 January. The spectra changed in shape and flux with the phase. As periastron approached, the column density of the low-energy absorption increased, which indicates that the emission from the wind-wind collision plasma was absorbed by the dense W-R wind. The spectra can be mostly fitted with two different components: a warm component with k(B)T = 0.3-0.6 keV and a dominant hot component with k(B)T similar to 3 keV. The emission measure of the dominant, hot component is not inversely proportional to the distance between the two stars. This can be explained by the O star wind colliding before it has reached its terminal velocity, leading to a reduction in its wind momentum flux. At phases closer to periastron, we discovered a cool plasma component in a recombining phase, which is less absorbed. This component may be a relic of the wind-wind collision plasma, which was cooled down by radiation, and may represent a transitional stage in dust formation.

DOI： 10.1093/pasj/psv099

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

DOI： 10.1093/pasj/psu063

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Publishing type：Research paper (scientific journal)  

MAXI started its operation in 2009 August. Owing to its unprecedentedly high sensitivity as an all-sky X-ray monitor and to its capability of real-time data transfer, we have detected 56 strong flares from twenty-one active stars (eleven RS CVn systems, one Algol system, seven dMe stars, one dKe star and one Young Stellar Object). These flares have large X-ray luminosity of 6 × 1030 -5 × 1033 ergs s-1 in the 2-20 keV band. The flares can be thought to be high ends among their own categories. During the flare from AT Mic on 2012 April 18th, one of the largest X-ray luminosities was recorded as a dMe star, 6 × 1032 ergs s -1 in the 2-20 keV band. It is larger than its bolometric luminosity by 4 times. The total energy emitted during the flare is 1036 ergs in the same band. Such total energy can be obtained on large flares from RS CVn system, but not on any other flares from dMe stars. In this proceeding, we report on the present situation in characteristics of hyper X-ray flares on each stellar categories. © International Astronomical Union 2014.

DOI： 10.1017/S1743921314002075

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

In our multi-epoch observation of the star-forming region NGC 2264 with the VLBI Exploration of Radio Astrometry, we detected two water maser features. We have measured the annual parallax of the maser sources for the first time in NGC 2264 and derived 1.356 +/- 0.098 mas, corresponding to the distance of 738(-50)(+57) pc, which is consistent with its previously reported photometric observations. One of the maser features is located near a dust continuum core, CMM4S, positionally corresponding to the X-ray source FMS2-1269 listed in Flaccomio et al. Re-analyzing Chandra X-ray data, we found that FMS2-1269 is still surrounded by a dense envelope of a H-2 column density, 5.4 x 10(23) cm(-2). We suggest that the maser detected near the CMM4S core is most likely associated with the X-ray-emitting Class 0 candidate FMS2-1269. The other maser feature is found to emerge from a high-velocity outflow of 150 km s(-1) and is associated with the 3.6 cm radio continuum source NGC 2264 VLA 3 located close to IRS1.

DOI： 10.1088/0067-0049/211/2/18

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

WF-MAXI is a soft X-ray transient monitor proposed for the ISS/JEM. Unlike MAXI, it will always cover a large field of view (20 % of the entire sky) to detect short transients more efficiently. In addition to the various transient sources seen by MAXI, we hope to localize X-ray counterparts of gravitational wave events, expected to be directly detected by Advanced-LIGO, Virgo and KAGRA in late 2010's. The main instrument, the Soft X-ray Large Solid Angle Cameras (SLC) is sensitive in the 0.7-12 keV band with a localization accuracy of similar to 0.1 degrees. The Hard X-ray Monitor (HXM) covers the same sky field in the 20 keV-1 MeV band.

DOI： 10.1117/12.2057188

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.1088/0004-637x/779/2/118

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Other Link： http://stacks.iop.org/0004-637X/779/i=2/a=118?key=crossref.d6cfdf46d5ae0a9b50ed717d620008c2

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.1088/0067-0049/207/2/36

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Other Link： https://iopscience.iop.org/article/10.1088/0067-0049/207/2/36

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We report on the spectral evolution of a new X-ray transient, MAXI J0556-332, observed by MAXI, Swift, and RXTE. The source was discovered on 2011 January 11 (MJD = 55572) by the MAXI Gas Slit Camera all-sky survey at (l, b) = (238 degrees.9, -25 degrees.2), relatively away from the Galactic plane. Swift/XRT follow-up observations identified it with a previously uncatalogued bright X-ray source, which led to optical identification. For more than one year since its appearance, MAXI J0556-332 has been X-ray active, with a 2-10 keV intensity above 30 mCrab. The MAXI/GSC data revealed rapid X-ray brightening in the first five days, and a hard-to-soft transition in the meantime. For the following similar to 70 days, the 0.5-30 keV spectra, obtained by the Swift/XRT and the RXTE/PCA on an almost daily basis, show a gradual hardening, with large flux variability. These spectra are approximated by a cutoff power-law with a photon index of 0.4-1 and a high-energy exponential cutoff at 1.5-5 keV, throughout the initial 10 months where the spectral evolution is mainly represented by a change of the cutoff energy. To be more physical, the spectra are consistently explained by thermal emission from an accretion disk plus Comptonized emission from a boundary layer around a neutron star. This supports the source identification as being a neutron-star X-ray binary. The obtained spectral parameters agree with those of neutron-star X-ray binaries in the soft state, whose luminosity is higher than 1.8 x 10(37) erg s(-1). This suggests a source distance of > 17 kpc.

DOI： 10.1093/pasj/65.3.58

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We report on the first observation of an X-ray outburst of a Be/X-ray binary pulsar, LS V +44 17/RX.10440.9+4431, and the discovery of an absorption dip structure in the pulse profile. An outburst of this source was discovered by MAXI GSC in 2010 April. It was the first detection of transient activity of LS V +44 17 since the source was identified as a Be/X-ray binary in 1997. From the data of a follow-up RXTE observation near the peak of the outburst, we found a narrow dip structure in its pulse profile, which was clearer in the lower-energy bands. The pulse-phase-averaged energy spectra in the 3-100 keV band could be fitted with a continuum model containing a power-law function with an exponential cutoff and a blackbody component, which are modified at low energy by an absorption component. A weak iron K alpha emission line was also detected in the spectra. From the pulse-phase-resolved spectroscopy we found that the absorption column density at the dip phase was much higher than those in the other phases. The dip was not seen in subsequent RXTE observations at lower flux levels. These results suggest that the dip in the pulse profile originates from the eclipse of the radiation from the neutron star by the accretion column.

DOI： 10.1093/pasj/64.4.79

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We report on an X-ray spectral analysis of the black hole candidate XTE J1752-223 in the 2009-2010 outburst, utilizing data obtained with the MAXI/Gas Slit Camera (GSC), the Swift/XRT, and Suzaku, which work complementarily. As already reported by Nakahira et al. (2010, PASJ, 62, L27), MAXI monitored the source continuously throughout the entire outburst for about eight months. All of the MAXI/GSC energy spectra in the high/soft state, lasting for 2 months, are well represented by a multi-color disk plus power-law model. The innermost disk temperature changed from similar to 0.7 keV to similar to 0.4 keV and the disk flux decreased by an order of magnitude. Nevertheless, the innermost radius is constant at similar to 41 D-3.5(cos i)(-1/2) km, where D-3.5 is the source distance in units of 3.5 kpc and i the inclination. The multi-color disk parameters obtained with the MAXI/GSC are consistent with those with the Swift/XRT and Suzaku. The Suzaku data also suggest a possibility that the disk emission is slightly Comptonized, which could account for broad iron-K features reported previously. Assuming that the obtained innermost radius represents the innermost stable circular orbit for a non-rotating black hole, we estimate the mass of the black hole to be 5.51 +/- 0.28 M-circle dot D-3.5(cos i)(-1/2), where the correction for the stress-free inner boundary condition and color hardening factor of 1.7 are taken into account. If the inclination is less than 49 degrees, as suggested from radio monitoring of transient jets, and the soft-to-hard transition in 2010 April occurred at 1%-4% of Eddignton luminosity, the fitting of the Suzaku spectra with a relativistic accretion-disk model derives constraints on the mass and the distance to be 3.1-55 M-circle dot and 2.3-22 kpc, respectively. This confirms that the compact object in XTE J1752-223 is a black hole.

DOI： 10.1093/pasj/64.1.13

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We are developing a Bragg crystal polarimeter which has high modulation factor. The point we aim is to bend the crystal; by using bent crystal, we can reflect X-ray emission with broadened energy width, focus it on a small detector, which increases S/N ratio, and obtain imaging capability. We bent Si (100) crystal sheets by depositing Diamond-Like Carbon (DLC) on the backside of reflection surface. They are bent by the residual stress between the DLC and crystal. We can control the curvature by changing the DLC thickness. The angular reflectivity was measured with the line emission at 8.04 keV (Cu-K alpha). We confirmed that the angular width is broadened to 1 degree, which is equivalent to the energy width of 0.5 keV. The integrated reflectivity becomes larger, as the curvature radius of crystal becomes small. The modulation factor of bent Si is 0.74, which is higher than that of the flat Si of 0.51. Having the wide energy band with the high modulation factor, the bent Si crystal can be a new tool for the X-ray polarimeter. We have also made the bent Ge(111) crystal and measured the same performances. The modulation factor of both the flat and the bent Ge were 0.99, when using the 8.04 keV (Cu-K alpha) beam, as we expected. This means that by choosing crystals, we can make efficient observations with aimed energy band. We report the status of our development.

DOI： 10.1117/12.926053

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

We report a development of a bent crystal for use of X-ray polarimeter. We deposited Diamond-Like Carbon (DLC) on the back side of reflection surface of a Si(400) crystal sheet, and bent the crystal sheet by the residual stress between the DLC and Si. We confirmed that the curvature can be controlled with the thickness of DLC. An angular reflectivity of the crystal was measured with the line emission at 8 keV (Cu-Ka). The angular width is broadened to 2 degree, centered at the Bragg angle expected for the (400) plane of Si(100). The angular width is equivalent to the energy width of 0.5 keV. We found that as the curvature radius of Si becomes small, the integrated reflectivity becomes larger. The modulation factor was measured to be about 0.8 for 8 keV. For the Fe-K lines (similar to 7 keV), which are very important for X-ray astronomy, higher modulation factor close to 1 is expected. The large sensitivity in wide energy band with the high modulation factor indicates that the bent crystal can be a new tool for the X-ray imaging polarimeter. A preliminary design of the polarimetric optics composed by the Si(100) crystal and a small-size imaging detector (e. g. X-ray CCD camera) is proposed in our presentation. Since any kind of crystals can be bent with our method, higher performance will be obtained with changing the crystal.

DOI： 10.1063/1.3696181

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Language：English   Publishing type：Research paper (scientific journal)  

We present a large X-ray flare from a nearby weak-lined T Tauri star TWA-7 detected with the Gas Slit Camera (GSC) on the Monitor of All-sky X-ray Image (MAXI). The GSC captured X-ray flaring from TWA-7 with a flux of 3 × 10-9 erg cm-2 s-1 in 2-20 keV band during the scan transit starting at 2010-09-07 18:24:30 (UT). The estimated X-ray luminosity at the scan in the energy band is 3 × 1032 erg s-1, indicating that the event is among the largest X-ray flares from T Tauri stars. Since MAXI GSC monitors a target only during a scan transit of about a minute per 92 min orbital cycle, the luminosity at the flare peak might have been higher than that detected. At the scan transit, we observed a high X-ray-to-bolometric luminosity ratio, logLX=Lbol = -0.1+0.2-0.3; i.e., the X-ray luminosity is comparable to the bolometric luminosity. Since TWA-7 has neither an accreting disk nor a binary companion, the observed event implies that none of those are essential to generate such big flares in T Tauri stars. © 2011. Astronomical Society of Japan.

DOI： 10.1093/pasj/63.sp3.S713

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We present the first unbiased source catalog of the Monitor of All-sky X-ray Image (MAXI) mission at high Galactic latitudes (vertical bar b vertical bar > 10 degrees), produced from the first 7-month data (2009 September 1 to 2010 March 31) of the Gas Slit Camera in the 4-10 keV band. We have developed an analysis procedure to detect faint sources from the MAXI data, utilizing a maximum likelihood image fitting method, where the image response, background, and detailed observational conditions are taken into account. The catalog consists of 143 X-ray sources above the 7 sigma significance level with a limiting sensitivity of similar to 1.5 x 10(-11) erg cm(-2)s(-1) (1.2 mCrab) in the 4-10 keV band. Among them, we have identified 38 Galactic/LMC/SMC objects, 48 galaxy clusters, 39 Seyfert galaxies, 12 blazars, and 1 galaxy. Four other sources are confused with multiple objects, and one remains unidentified. The log N-log S relation of extragalactic objects is in good agreement with the HEAO-1 A-2 result, although the list of the brightest AGNs in the entire sky has significantly changed since that produced 30 yr ago.

DOI： 10.1093/pasj/63.sp3.S677

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

The monitor of the all-sky X-ray image (MAXI) Gas Slit Camera (GSC) on the International Space Station (ISS) detected a gamma-ray burst (GRB) on 2009, September 26, GRB 090926B. This GRB had extremely hard spectra in the X-ray energy range. Joint spectral fitting with the Gamma-ray Burst Monitor on the Fermi Gamma-ray Space Telescope shows that this burst had a peculiarly narrow spectral energy distribution, which can be represented by a Comptonized blackbody model. This spectrum can be interpreted as photospheric emission from a low baryon-load GRB fireball. Calculating the parameter of the fireball, we found the size of the base of the flow to be r(0) = (4.3 +/- 0.9) x 10(9) Y'(-3/2) cm, the Lorentz factor of the plasma is Gamma = (110 +/- 10) Y'(1/4), where Y' is a ratio between the total fireball energy and the energy in the blackbody component of the gamma-ray emission. This r(0) is a factor of a few times larger, and the Lorentz factor of 110 is smaller by also factor of a few than other bursts that have blackbody components in the spectra.

DOI： 10.1093/pasj/63.sp3.S1035

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We constructed a new X-ray (2-10 keV) luminosity function of Compton-thin active galactic nuclei (AGNs) in the local universe, using the first MAXI/GSC source catalog surveyed in the 4-10 keV band. The sample consists of 37 non-blazar AGNs at z = 0.002-0.2, whose identification is highly (>97%) complete. We confirmed the trend that the fraction of absorbed AGNs with N-H > 10(22) cm(-2) rapidly decreases against the luminosity (L-X), from 0.73 +/- 0.10 at L-X = 10(42-43.5) erg s(-1) to 0.12 +/- 0.08 at L-X = 10(43.5-45.5) erg s(-1). The obtained luminosity function was well-fitted with a smoothly connected double power-law model whose indices are gamma(1) = 0.84 (fixed) and gamma(2) = 2.0 +/- 0.2 below and above the break luminosity, L-* = 10(43.3 +/- 10-4) erg s(-1), respectively. While the result of the MAXI/GSC agrees well with that of HEAO-1 at L-X greater than or similar to 10(43.5) erg s(-1), it gives a larger number density at the lower luminosity range. A comparison between our luminosity function in the 2-10 keV band and that in the 14-195 keV band obtained from the Swift/BAT survey indicates that the averaged broad-band spectra in the 2-200 keV band should depend on the luminosity, approximated by Gamma similar to 1.7 for L-X less than or similar to 10(44) erg s(-1), while Gamma - 2.0 for L-X greater than or similar to 1044 erg s(-1). This trend was confirmed by the correlation between the luminosities in the 2-10 keV and 14-195 keV bands in our sample. We argue that there is no contradiction in the luminosity functions between above and below 10 keV once this effect is taken into account.

DOI： 10.1093/pasj/63.sp3.S937

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We report on the MAXI GSC X-ray monitoring of the Crab nebula and pulsar during the GeV gamma-ray flare for the period of 2010 September 18-24 (MJD 55457-55463), detected by AGILE and Fermi-LAT. There were no significant variations on the pulse phase averaged and pulsed fluxes during the gamma-ray flare on time scales from 0.5 to 5 days. The pulse profile also showed no significant change during this period. The upper limits on the variations of the pulse phase averaged and pulsed fluxes for the period MJD 55457.5-55462.5 in the 4-10 keV band were derived to be 1% and 19%, respectively, at the 90% confidence limit of the statistical uncertainty. The lack of variations in the pulsed component over the multi-wavelength range (radio, X-ray, hard X-ray, and gamma-ray) supports not a pulsar, but a nebular origin for the gamma-ray flare.

DOI： 10.1093/pasj/63.sp3.S821

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

We report the preliminary results of the Suzalcu observations of the W-R binary WR 140 (WC7+O5I). We executed the observations at four different epochs around periastron passage in Jan. 2009 to understand the W-R stellar wind as well as the wind-wind collision shocks. The total exposure was 210 ksec. We detected hard X-ray excess in the HXD band (&gt; 10 keV) for the first time from a W-R binary. Another notable discovery was a soft component which is not absorbed even by the dense wind. The spectra can be fitted by three different components; one is for the stationary cool component with kT similar to 0.1 key, one for a dominant high temperature component with kT similar to 3 keV and one for the hardest power-low component with Gamma similar to 2. The column density at periastron is 30 times higher than that at pre-periastron, which can be explained as self-absorption by the W-R wind. The emission measure of the dominant, high temperature component is not inversely proportional to the distance between the two stars.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

WR 140 is one of the best known examples of a Wolf-Rayet stars. We executed the Suzaku X-ray observations at four different epochs around periastron passage in Jan. 2009 to understand the W-R stellar wind as well as the wind-wind collision shocks. The column density at periastron is about 30 times higher than that at pre-periastron, which can be explained as self-absorption by the Wolf-Rayet wind. The spectra are dominated by a line and continuum emission from a optically thin-thermal plasma. The strong Ne-K lines are evidence that the thermal plasma is shock-heated W-R wind materials by the interaction with the wind from the companion O star. We present the parameters of the wind, such as a mass-loss rate, which were calculated with the absorption and line emission in the spectra.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Suzaku X-ray observations of a young supernova remnant, Cassiopeia A, were carried out. K-shell transition lines from highly ionized ions of various elements were detected, including Chromium (Cr-K alpha at 5.61 keV). The X-ray continuum spectra were modeled in the 3.4-40keV band, summed over the entire remnant, and were fitted with a simplest combination of the thermal bremsstrahlung and the non-thermal cut-off power-law models. The spectral fits with this assumption indicate that the continuum emission is likely to be dominated by non-thermal emission with a cut-off energy at &gt; 1 keV. The thermal-to-non thermal fraction of the continuum flux in the 4-10 keV band is best estimated as similar to 0.1. Non-thermal-dominated continuum images in the 4-14 keV band were made. The peak of the non-thermal X-rays appears at the western part. The peak position of the TeV gamma-rays measured with HEGRA and MAGIC is also shifted at the western part with the I-sigma confidence. Since the location of the X-ray continuum emission was known to be presumably identified with the reverse shock region, the possible keV-TeV correlations give a hint that the accelerated multi-TeV hadrons in Cassiopeia A are dominated by heavy elements in the reverse shock region.

DOI： 10.1093/pasj/61.6.1217

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We report an observation of X-ray emission from the exciting region of Cepheus A with the Chandra/ACIS instrument. What had been an unresolved X-ray source comprising the putative power sources is now resolved into at least three point-like sources, each with similar X-ray properties and differing radio and submillimeter properties. The sources are HW9, HW3c, and a new source that is undetected at other wavelengths "h10." They each have inferred X-ray luminosities &gt;= 10(31) erg s(-1) with hard spectra, T &gt;= 10(7) K, and high low-energy absorption equivalent to tens to as much as a hundred magnitudes of visual absorption. The star usually assumed to be the most massive and energetic, HW2, is not detected with an upper limit about seven times lower than the detections. The X-rays may arise via thermal bremsstrahlung in diffuse emission regions associated with a gyrosynchrotron source for the radio emission, or they could arise from powerful stellar winds. We also analyzed the Spitzer/IRAC mid-IR observation from this star formation region and present the X-ray results and mid-IR classifications of the nearby stars. HH 168 is not as underluminous in X-rays as previously reported.

DOI： 10.1088/0004-637X/704/2/1495

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We present the Suzaku results of eta Carinae in the 5-50 keV range conducted twice around the apastron in 2005 August for 50 ks and in 2006 February for 20 ks. The X-ray Imaging Spectrometer (XIS) produced hard (5-12 keV) band spectra, resolving K shell lines from highly ionized Fe and Ni. The Hard X-ray Detector yielded a significant detection in the super-hard (15-50 keV) band, which was uncontaminated by near-by sources. We constrained the temperature of the optically thin thermal plasma emission dominant in the hard band to be 3-4 keV using the K-shell line features with the XIS. We found significant excess emission above the thermal emission in the super-hard band with the PIN, confirming the previous INTEGRAL ISGRI report. The entire 5-50 keV spectra were fitted by a combination of a thermal plasma model plus a flat power-law, or a very hot thermal bremsstrahlung model for the excess emission. No significant change of the excess emission was found at different epochs within the systematic and statistical uncertainties, and no flare-like flux amplification was seen in the hard band, indicating that the excess emission is a steady phenomenon. We argue that the super-hard emission is attributable to the inverse Compton of stellar UV photons by non-thermal electrons or to the thermal bremsstrahlung of very hot plasma, and not to the bremsstrahlung by non-thermal electrons colliding with cold ambient matter.

DOI： 10.1093/pasj/61.4.629

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We report the discovery of a cluster of Class I protostars in GGD 27. One of these protostars is the previously known, centrally located, GGD 27-ILL, which powers a massive bipolar outflow. We show that GGD 27-ILL, which is known to be the bright infrared (IR) source, IRAS 18162-2048, and a compact radio continuum source, is also the newly discovered hard X-ray source, GGD 27-X. The observations were made with the ACIS instrument on the Chandra X-ray Observatory. The X-rays from GGD 27-X are variable when compared with 4 years earlier, with an unabsorbed 2-10 keV X-ray luminosity in this observation of 1.5-12 x 10(31) erg s(-1) and a plasma temperature of &gt;= 10(7) K. The X-rays are probably associated with the underlying B0 star (rather than outflowing material), providing a rare glimpse in hard X-rays of an optically obscured massive protostar with an outflow. The X-ray luminosity and spectrum appear to be consistent with stars of its type in other star formation regions. Several other variable X-ray sources are also detected in the IR cluster that contains GGD 27-X. We also discuss another nearby cluster. In each of the clusters there is an object that is X-ray hard, highly absorbed at low energies, in a blank optical/IR/radio field, and variable in X-ray intensity by a factor of &gt;= 10 on a timescale of 4 years. These latter objects may arise from more recent episodes of star formation or may be "hidden" Class III sources.

DOI： 10.1088/0004-637X/690/1/850

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：EDP SCIENCES S A  

We present XMM-Newton observations of the WC binary theta Muscae (WR 48), the second brightest Wolf-Rayet binary in optical wavelengths. The system consists of a short-period (19.1375 days) WC5/WC6 + O6/O7V binary and possibly has an additional O supergiant companion (O9.5/B0Iab) which is optically identified at a separation of similar to 46 mas. Strong emission lines from highly ionized ions of C, O, Ne, Mg, Si, S, Ar, Ca and Fe are detected. The spectra are fitted by a multi-temperature thin-thermal plasma model with an interstellar absorption N(H) = 2-3 x 10(21) cm(-2). Lack of nitrogen line indicates that the abundance of carbon is at least an order of magnitude larger than that of nitrogen. A Doppler shift of similar to 630 km s(-1) is detected for the O VIII line, while similar shifts are obtained from the other lines. The reddening strongly suggests that the emission lines originated from the wind-wind shock zone, where the average velocity is similar to 600 km s(-1). The red-shift motion is inconsistent with a scenario in which the X-rays originate from the wind-wind collision zone in the short-period binary, and would be evidence supporting the widely separated O supergiant as a companion. This may make up the collision zone be lying behind the short-period binary. In addition to the emission lines, we also detected the RRC (radiative recombination continuum) structure from carbon around 0.49 keV. This implies the existence of additional cooler plasma.

DOI： 10.1051/0004-6361:20079302

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DOI： 10.1093/pasj/60.sp1.S49

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

We report on results from Suzaku broadband X-ray observations of the southwest part of the galactic supernova remnant (SNR) RXJ1713.7-3946 with an energy coverage of 0.4-40keV. The X-ray spectrum, presumably of synchrotron origin, is known to be completely lineless, making this SNR ideally suited for a detailed study of the X-ray spectral shape formed through efficient particle acceleration at high-speed shocks. With a sensitive hard X-ray measurement from the HXD PIN aboard Suzaku, we determined the hard X-ray spectrum in the 12-40keV range to be described by a power law with photon index of Γ = 3.2 ± 0.2, significantly steeper than the soft X-ray index of Γ = 2.4 ± 0.05 measured previously with ASCA and other missions. We find that a simple power law fails to describe the full spectral range of 0.4-40 keV, and instead a power-law with an exponential cutoff with a hard index of Γ = 1.50 ± 0.09 and a high-energy cutoff of εc = 1.2 ± 0.3 keV formally provides an excellent fit over the full bandpass. If we use the so-called SRCUT model, as an alternative model, it gives a best-fit rolloff energy of εroll = 0.95 ± 0.04 keV. Together with the TeV γ-ray spectrum, ranging from 0.3 to 100TeV, recently obtained by HESS observations, our Suzaku observations of RX J1713.7-3946 provide stringent constraints on the highest-energy particles accelerated in a supernova shock. © 2008. Astronomical Society of Japan.

DOI： 10.1093/pasj/60.sp1.s131

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We present the results of a Suzaku spectroscopic study of soft extended X-ray emission in the H II region of M 17. The spectrum of the extended emission was obtained with a high signal-to-noise ratio in a spatially resolved manner using the X-ray Imaging Spectrometer (XIS). We established that contamination by unresolved point sources, the Galactic Ridge X-ray emission, the cosmic X-ray background, and the local hot bubble emission is negligible in the background-subtracted XIS spectrum of the diffuse emission. Half a dozen emission lines were clearly resolved for the first time, including K alpha lines of highly ionized O, Ne, and Mg as well as L-series complex of Fe at 0.5-1.5keV. Based on diagnosis of these lines, we obtained the following results: (1) the extended emission is an optically thin thermal plasma, represented well by a single temperature of similar to 3.0 +/- 0.4 MK, (2) the abundances of elements with emission lines in the diffuse spectrum are 0.1-0.3 solar, while those of bright discrete sources are 0.3-1.5 solar, (3) the metal abundances relative to each other in the diffuse emission are consistent with solar, except for a Ne enhancement of a factor of similar to 2, (4) both the plasma temperature and the chemical composition of the diffuse emission show no spatial variation across the studied spatial scale of similar to 5 pc.

DOI： 10.1093/pasj/60.sp1.S85

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Language：Japanese   Publishing type：Research paper (scientific journal)  

SN 1006 is one of the supernova remnants (SNRs) with relatively low-temperature electrons, considering the young age of just 1000 years. We carried out SN 1006 mapping observations with the X-ray Imaging Spectrometers (XIS) and the Hard X-ray Detector (HXD) onboard Suzaku, the fifth Japanese X-ray satellite. Thanks to the excellent spectral resolution of XIS in the soft X-ray band, H-like and He-like oxygen emission lines were clearly detected, and we could make a map of the line intensity, and as well as a flux and the photon index of nonthermal component. We found that these parameters have spatial dependences from region to region in the SNR; the north region is bright in nonthermal, while dim in thermal; the east region is bright in both nonthermal and thermal; the inner region shows dim nonthermal and bright thermal emission. The photon index is the smallest in the north region. © 2007.

DOI： 10.1016/j.asr.2007.03.055

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

We report in-flight status of the X-ray detectors on board the Suzaku observatory, the 5th X-ray astronomy satellite of Japan launched on July 10, 2005. Suzaku is equipped with two types of Instruments: one is the X-ray Imaging Spectrometers (XISs) and the other is Hard X-ray Detector (HXD). XIS utilizes the X-ray CCD camera in combination with the grazing-incidence X-ray telescope. HXD is a non-imaging, hybrid detector utilizing Si PIN diodes and GSO/BGO phoswich counters. Suzaku takes a low-earth, circular orbit with an altitude of 560 km and an inclination of 31 deg. This means that Suzaku goes through the south atlantic anomaly about 1/3 of its revolutions. This has a large impact on the in-flight performance of XIS and HXD, which is reported in detail in the present paper. © 2007 IEEE.

DOI： 10.1109/NSSMIC.2007.4436667

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

During an observation of the Galactic plane in the Scutum region with the Suzaku satellite, we discovered a new X-ray transient source, designated Suzaku J1844-0404. Compared with previous Chandra observations of the same field, four Chandra X-ray sources exist within the current positional uncertainty of Suzaku J1844-0404. A firm identification is not possible. From the beginning of the observation, the X-ray intensity was significant at similar to 5 x 10(-14) erg s(-1) cm(-2) (2-10 keV), which may be a possible precursor. Later, the source exhibited a flare with a peak flux of similar to 10(-12) erg s(-1) cm(-2) (2-10 keV). A strong and narrow emission line at similar to 6.66 keV was observed during the flare, most likely the He-like Fe line. The spectrum in 1-10 keV is consistent with a heavily absorbed (N-H similar to 3 x 10(22) H cm(-2)) thin thermal emission with kT as high as similar to 7 keV. A single short flare, as observed, is rather unlikely for a cataclysmic variable. The source is probably an active binary star or a young stellar object.

DOI： 10.1093/pasj/59.sp1.S215

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Suzaku observed the molecular cloud MBM 12 and a blank field less than 3 degrees away to separate the local and distant components of the diffuse soft X-ray background. Towards MBM 12, a local (D less than or similar to 275 pc) O VII emission line was clearly detected with an intensity of 3.5 photons cm(-2) s(-1) sr(-1) (or line units, LU), and the O VIII flux was &lt; 0.34 LU. The origin of this O VII emission could be hot gas in the Local Hot Bubble (LHB), charge exchange within the heliosphere with oxygen ions from the solar wind (SWCX), or both. If entirely from the LHB, the emission could be explained by a region with emission measure of 0.0075 cm(-6) pc and a temperature of 1.2 x 10(6) K. However, this temperature and emission measure implies 1/4 keV emission in excess of observations. There is no evidence in the X-ray light curve or solar wind data for a significant contribution from geocoronal SWCX, although interplanetary SWCX is still possible. In any case, the observed O VII flux represents an upper limit to both the LHB emission and interplanetary SWCX in this direction. The blank field was observed immediately afterwards. The net off-cloud O VII and O VIII intensities were (respectively) 2.34 +/- 0.33 and 0.77 +/- 0.16 LU, after subtracting the on-cloud foreground emission. If this more distant O VII and O VIII emission is from a thermal plasma in collisional equilibrium beyond the Galactic disk, we infer it has a temperature of (2.1 +/- 0.1) x 10(6) K with an emission measure of (4 +/- 0.6) x 10(-3) cm(-6) pc.

DOI： 10.1093/pasj/59.sp1.S141

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We studied extended X-ray emission from the Carina Nebula taken with the Suzaku CCD camera XIS on 2005 August 29. The X-ray morphology, plasma temperature, and absorption to the plasma are consistent with the earlier Einstein results. The Suzaku spectra newly revealed emission lines from various species, including oxygen, but not from nitrogen. This result restricts the N/O ratio to be significantly low, compared with evolved massive stellar winds, suggesting that the diffuse emission originated in an old supernova remnant or a super shell produced by multiple supernova remnants. The X-ray spectra from the north and south of eta Car showed distinct differences between 0.3-2 keV. The south spectrum shows strong L-shell lines of iron ions and K-shell lines of silicon ions, while the north spectrum shows them weak in intensity. This means that the silicon and iron abundances are a factor of 2-4 higher in the south region than in the north region. The abundance variation may be produced by an SNR ejecta, or related to dust formation around the star-forming core.

DOI： 10.1093/pasj/59.sp1.S151

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We have observed the diffuse X-ray emission from the Galactic Center (GC) using the X-ray Imaging Spectrometer (XIS) on Suzaku. The high-energy resolution and the low-background orbit provided excellent spectra of the GC diffuse X-rays (GCDX). The XIS found many emission lines in the GCDX near the energy of K-shell transitions of iron and nickel. The most pronounced features are Fe I K alpha at 6.4 keV and K-shell absorption edge at 7.1 keV, which are from neutral and/or low ionization states of iron, and the K-shell lines at 6.7 keV and 6.9 keV from He-like (Fe XXV K alpha) and hydrogenic (Fe XXVI Ly alpha) ions of iron. In addition, K alpha lines from neutral or low ionization nickel (Ni I K alpha) and He-like nickel (Ni XXVII K alpha), Fe I K beta, Fe XXV K beta, Fe XXVI Ly beta, Fe XXV K gamma, and Fe XXVI Ly gamma were detected for the first time. The line center energies and widths of Fe XXV K alpha and Fe XXVI Ly alpha favor a collisional excitation plasma for the origin of the GCDX. The electron temperature determined from the line flux ratio of Fe XXV K alpha/Fe XXV K beta is similar to the ionization temperature determined from that of Fe XXV K alpha/Fe XXVI Ly alpha. Thus it would appear that the GCDX plasma is close to ionization equilibrium. The 6.7 keV flux and temperature distribution to the galactic longitude is smooth and monotonic, in contrast to the integrated point source flux distribution. These facts support the hypothesis that the GCDX is truly diffuse emission rather than the integration of the outputs of a large number of unresolved point sources. In addition, our results demonstrate that the chemical composition of Fe in the interstellar gas near the GC is constrained to be about 3.5 times solar abundance.

DOI： 10.1093/pasj/59.sp1.S245

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Publishing type：Research paper (international conference proceedings)  

SN 1006 is the milestone of understanding the acceleration mechanism of cosmic rays, and this year is the millennium year for the remnant. We carried out SN 1006 mapping observations with the X-ray Imaging Spectrometers (XIS) onboard Suzaku satellite. Thanks to the excellent spectral response of XIS, K emission lines from highly ionized oxygen were clearly resolved. The intensity maps of these lines have been made additional to the intensity and photon index maps of the nonthermal component. We discovered that regions with strong and hard nonthermal component has weak thermal emission. The north rim of the SNR has the hardest nonthermal component. These facts might have information of efficient cosmic ray acceleration and background plasma.

DOI： 10.1143/PTPS.169.142

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：UNIV CHICAGO PRESS  

We present the results of X-ray and near-infrared (NIR) observations of L1448, a star-forming region in the Perseus cloud complex using the Chandra X-Ray Observatory and the 4 m telescope at the Kitt Peak National Observatory. We detect 72 X-ray sources in a similar to 17' x 17' region with a similar to 68 ks ACIS exposure down to the X-ray flux limit of similar to 10(-15) ergs s(-1) cm(-2) (0.5 - 8 keV), for which we conduct follow-up NIR imaging observations in a concentric similar to 11' x 11' region with FLAMINGOS down to m(KS) similar to 17 mag. Twelve X-ray sources have NIR or optical counterparts. By plotting X-ray mean energy versus the NIR-to-X-ray flux ratio, the X-ray sources are clearly separated into two groups. The X-ray spectral and temporal features, as well as NIR magnitudes and colors, indicate that one group mainly consists of young stellar objects (YSOs) in the cloud and the other of background extragalactic sources. Ten X-ray-emitting YSO candidates are thus newly identified as low-mass or brown dwarf mass sources from their NIR magnitudes. In addition, a possible X-ray signal is found from a midinfrared protostar, L1448 IRS 3( A). The lack of detection of this source in our deep NIR images indicates that this source has a very steep spectral slope of greater than or similar to 3.2 in the 2 - 10 mu m wavelength range.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：UNIV CHICAGO PRESS  

We present the result of a systematic search for the iron K alpha fluorescent line at similar to 6.4 keV among 1616 X-ray sources detected by ultradeep Chandra observations of the Orion Nebula Cluster and the obscured Orion Molecular Cloud 1 population as part of the Chandra Orion Ultradeep Project ( COUP). Seven sources are identified to have an excess emission at similar to 6.4 keV among 127 control sample sources with significant counts in the 6.0 - 9.0 keV band. These seven sources are young stellar objects (YSOs) characterized by intense flarelike flux variations, thermal spectra, and near-infrared (NIR) counterparts. The observed equivalent widths of the line cannot be attributed to the florescence by interstellar or circumstellar matter along the line of sight. The X-ray spectral fits and NIR colors of the 6.4 keV sources show that these sources have X-ray absorption of greater than or similar to 1 x 10(22) cm(-2) and NIR excess emission, which is not expected when the fluorescence occurs at the stellar photosphere. We therefore conclude that the iron fluorescent line of YSOs arises from reflection off of circumstellar disks, which are irradiated by the hard X-ray continuum emission of magnetic reconnection flares.

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：UNIV CHICAGO PRESS  

We report the discovery of X-rays from both components of Cepheus A, East and West, with the XMM-Newton observatory. HH 168 joins the ranks of other energetic Herbig-Haro objects that are sources of T &GE; 10(6) K X-ray emission. The effective temperature of HH 168 is T = 5.8(-2.3)(+3.5) x 10(6) K, and its unabsorbed luminosity is 1: 1; 10(29) ergs s(-1), making it hotter and less luminous than other representatives of its class. We also detect prominent X-ray emission from the complex of compact radio sources believed to be the power sources for Cep A. We call this source HWX, and it is distinguished by its hard X-ray spectrum, T = 1.2(-0.5)(+1.2) 10(8) K, and its complex spatial distribution. It may arise from one or more protostars associated with the radio complex, the outflows, or a combination of the two. We detect 102 X-ray sources, many presumed to be pre-main-sequence stars on the basis of the reddening of their optical and IR counterparts.

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：EUROPEAN SPACE AGENCY  

We present the result of a coherent search for the iron K. fluorescent line at similar to 6.4 keV among 1616 X-ray sources detected by ultradeep Chandra observations of the Orion Nebula Cluster (ONC) -Chandra Orion Ultra-deep Project (COUP). Seven sources are identified to have an excess emission at similar to 6.4 keV among 127 control sample sources with significant counts in the 6.0-9.0 keV band. These seven sources axe considered to be young stellar objects (YSOs) belonging to ONC from their flare-like flux variation, thermal spectra, and near-infrared (NIR) or centimeter identifications. We discuss that the observed equivalent widths of the fluorescent line can not be accounted with the reflection by interstellar or circumstellar matter in the line of sight. The X-ray spectral fittings and NIR colors of the 6.4 keV sources show that these sources preferentially have X-ray absorption of &gt; 1x10(22) cm(-2) and NIR excess emission, which are not expected when the reflection occurs at the stellar photosphere. We therefore conclude that the iron fluorescent line of YSOs arises at disks, which are photoionized by the strong continuum emission from X-ray flares.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TERRA SCIENTIFIC PUBL CO  

Almost all young stellar objects (YSOs) are now known to emit X-rays driven by the magnetic activity. The solar-type dynamo is the plausible mechanism to generate the magnetic fields, but it does not work properly on protostars or intermediate-mass YSOs due to the difference of their stellar inner structure. To find an alternative mechanism, the structure and energy of magnetic fields surrounding stars should be investigated. In this sence, a stellar X-ray flare gives us important information because it directly traces an activity of one magnetic loop. With this motivation, we searched for stellar X-ray flares using the ASCA satellite and detected seven flares from low-mass and intermediate-mass YSOs. By comparing flare parameters with the absorption column density (NH), we found that younger stars tend to have higher plasma temperature and larger emitting volumes. Furthermore, the flare loop size should be far larger than the solar radii in low-mass protostars and Herbig Ae/Be stars (HAEBEs). These facts suggest that the magnetic fields of low-mass protostars and HAEBEs far extend from the stellar main body and probably connect to the circumstellar disks, and that the magnetic reconnection by the star-disk differential rotation should energize the X-ray flares. We also present supporting evidence of quasi-periodic flares detected on the ClassI protostar YLW15.

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Language：English   Publisher：UNIV CHICAGO PRESS  

We report detections of X-rays from HH 80 and HH 81 with the ACIS instrument on the Chandra X-Ray Observatory. These are among the most luminous Herbig-Haro ( HH) sources in the optical, and they are now the most luminous known in X-rays. These X-rays arise from the strong shocks that occur when the southern extension of this bipolar outflow slams into the ambient material. There is a one-to-one correspondence between regions of high X-ray emission and high Halpha emission. The X-ray luminosities of HH 80 and HH 81 are 4.5 and 4.3 x 10(31) ergs s(-1), respectively, assuming that the measured low-energy absorption is not in the sources. The measured temperature of the HH plasma is not as large as that expected from the maximum velocities seen in the extended tails of the optical emission lines. Rather, it is consistent with the similar to 10(6) K temperature of the "narrow'' core of the optical lines. There is no observed emission from HH 80 North, the northern extension of the bipolar flow, based on a measurement of lower sensitivity. We imaged the central region of the bipolar flow revealing a complex of X-ray sources, including one near but not coincident with the putative power source in the radio and infrared. This source, CXOPTM J181912.4 - 204733, has no counterparts at other wavelengths and is consistent in luminosity and spectrum with a massive star with A(V) similar to 90 mag. It may contribute significantly to the power input to the complex. Alternatively, this emission might be extended X-rays from outflows close to the power source. We detect 94 X-ray sources overall in this area of star formation.

DOI： 10.1086/382220

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Language：English   Publisher：OXFORD UNIV PRESS  

We report on the results of a systematic study of X-ray flares from low-mass young stellar objects, using two deep exposure Chandra observations of the main region of the rho Ophiuchi star-forming cloud. From 195 X-ray sources, including class I-III sources and some young brown dwarfs, we detected a total of 71 X-ray flares. Most of the flares have the typical profile of solar and stellar flares, fast rise and slow decay, while some bright flares show unusually long rise timescales. We derived the time-averaged temperature (&lt;kT&gt;), luminosity (&lt;L-X&gt;), rise and decay timescales (tau(r) and tau(d)) of the flares, finding that (1) class I-II sources tend to have a high &lt;kT&gt;, which sometimes exceeds 5 keV, (2) the distribution of &lt;L-X&gt; during flares is nearly the same for all classes from similar to 10(29.5) to similar to 10(31.5) ergs(-1), although there is a marginal hint of a higher &lt;L-X&gt; distribution for class I than class II-III, and (3) positive and negative log-linear correlations are found between tau(r), and tau(d), and &lt;kT&gt; and tau(r). In order to explain these relations, we used the framework of magnetic reconnection model with heat conduction and chromospheric evaporation to formulate the observational parameters (tau(r), tau(d), and &lt;kT&gt;) as a function of the pre-flare (coronal) electronic density (n(c)), the half-length of the reconnected magnetic loop (L), and magnetic field strength (B). The observed correlations are well reproduced if loop lengths are nearly the same for all classes, regardless of the existence of an accretion disk. The estimated loop length is almost comparable to the typical stellar radius of these objects (10(10)-10(11) cm), which indicates that the observed flares are triggered by solar-type loops, rather than larger ones (similar to 10(12) cm) connecting the star with its inner accretion disk. The higher &lt;kT&gt; observed for class I sources may be explained by a slightly higher magnetic field strength (approximate to 500G) than for class II-III sources (200-300 G).

DOI： 10.1093/pasj/55.3.653

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Language：English   Publisher：OXFORD UNIV PRESS  

We report on the results of a systematic study of X-ray flares from low-mass young stellar objects, using two deep exposure Chandra observations of the main region of the rho Ophiuchi star-forming cloud. From 195 X-ray sources, including class I-III sources and some young brown dwarfs, we detected a total of 71 X-ray flares. Most of the flares have the typical profile of solar and stellar flares, fast rise and slow decay, while some bright flares show unusually long rise timescales. We derived the time-averaged temperature (&lt;kT&gt;), luminosity (&lt;L-X&gt;), rise and decay timescales (tau(r) and tau(d)) of the flares, finding that (1) class I-II sources tend to have a high &lt;kT&gt;, which sometimes exceeds 5 keV, (2) the distribution of &lt;L-X&gt; during flares is nearly the same for all classes from similar to 10(29.5) to similar to 10(31.5) ergs(-1), although there is a marginal hint of a higher &lt;L-X&gt; distribution for class I than class II-III, and (3) positive and negative log-linear correlations are found between tau(r), and tau(d), and &lt;kT&gt; and tau(r). In order to explain these relations, we used the framework of magnetic reconnection model with heat conduction and chromospheric evaporation to formulate the observational parameters (tau(r), tau(d), and &lt;kT&gt;) as a function of the pre-flare (coronal) electronic density (n(c)), the half-length of the reconnected magnetic loop (L), and magnetic field strength (B). The observed correlations are well reproduced if loop lengths are nearly the same for all classes, regardless of the existence of an accretion disk. The estimated loop length is almost comparable to the typical stellar radius of these objects (10(10)-10(11) cm), which indicates that the observed flares are triggered by solar-type loops, rather than larger ones (similar to 10(12) cm) connecting the star with its inner accretion disk. The higher &lt;kT&gt; observed for class I sources may be explained by a slightly higher magnetic field strength (approximate to 500G) than for class II-III sources (200-300 G).

DOI： 10.1093/pasj/55.3.653

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Language：English   Publisher：UNIV CHICAGO PRESS  

We report the X-ray detection of the brown dwarf (BD) companion TWA 5B in an similar or equal to12 Myr old pre-main-sequence binary system. We clearly resolve the faint companion (35 photons) separated from the X-ray luminous primary by 2" in a Chandra ACIS image. TWA 5B shows a soft X-ray spectrum with a low plasma temperature of only 0.3 keV and a constant flux during the 3 hr observation, of which the characteristics are commonly seen in the solar corona. The X-ray luminosity is 4 x 10(27) ergs s(-1) (0.1-10 keV band) or log (L-x/L-bol) = -3.4 Comparing these properties to both younger and older BDs, we discuss the evolution of the X- ray emission in BDs. During their first few megayears, they exhibit high levels of X-ray activity, as seen in higher mass pre-main-sequence stars. The level in TWA 5B is still high at t similar or equal to 12 Myr in log L-x/L-bol, while kT has already substantially cooled.

DOI： 10.1086/375017

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Language：English   Publisher：UNIV CHICAGO PRESS  

We conducted deep near-infrared (NIR) imaging observations of Orion molecular clouds 2 and 3 using the Quick Infrared Camera on the 88 inch (2.2 m) telescope of the University of Hawaii. Our purposes were (1) to generate a comprehensive NIR source catalog of these star-forming clouds and ( 2) to identify the NIR counterpart of the Chandra X-ray sources that have no counterpart in the Two Micron All Sky Survey (2MASS) catalog. Our J-, H-, and K-band observations are similar to2 mag deeper than those of 2MASS and match the current Chandra observation well. We detected 1448 NIR sources, for which we derived the position, the J-, H-, and K-band magnitude, and the 2MASS counterpart. Using this catalog, we identified the NIR counterpart for similar to42% of the 2MASS unidentified Chandra sources. The nature of these Chandra sources are discussed using their NIR colors and spatial distributions, and a dozen protostar and brown dwarf candidates are identified.

DOI： 10.1086/346277

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Language：English   Publisher：UNIV CHICAGO PRESS  

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Language：English   Publisher：ASP Conference Series  

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Language：English   Publisher：IOP PUBLISHING LTD  

We obtained near-infrared (NIR) imaging with the Subaru Telescope of the class 0 protostar candidates in the Orion molecular cloud 3, two of which were discovered to have X-ray emission by the Chandra X-Ray Observatory. We found strong evidence for the class 0 nature of the X-ray sources. First, our deep K-band image shows no emission brighter than 19.6 mag from both of these X-ray sources. Since class I protostars or class II T Tauri stars should be easily detected in the NIR with this sensitivity, the lack of K-band detection suggests that they are likely much more obscured than class I protostars. Second, our H-2 v = 1-0 S(1) image shows a bubble-like feature from one of the X-ray class 0 protostar candidates, which reinforces the idea that this is a class 0 protostar. We also discuss the nature of nine NIR sources found in our deep image based on their colors, spatial coincidence with millimeter cores, and the properties of their X-ray counterparts.

DOI： 10.1086/340559

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Language：English   Publishing type：Book review, literature introduction, etc.   Publisher：IOP PUBLISHING LTD  

The Orion Nebula Cluster and the molecular cloud in its vicinity have been observed with the ACIS-I detector on board the Chandra X-ray Observatory with 23 hr exposure in two observations. We detect 1075 X-ray sources, most with subarcsecond positional accuracy. Ninety-one percent of the sources are spatially associated with known stellar members of the cluster, and an additional 7% are newly identified deeply embedded cloud members. This provides the largest X-ray study of a premain-sequence stellar population and covers the initial mass function from brown dwarfs up to a 45 M. O star. Source luminosities span 5 orders of magnitude from log L-X similar or equal to28.0 to 33.3 ergs s(-1) in the 0.5-8 keV band, plasma energies range from 0.2 to &gt;10 keV, and absorption ranges from log N-H &lt; 20.0 to similar to 23.5 cm(-2). Comprehensive tables providing X-ray and stellar characteristics are provided electronically.
We examine here the X-ray properties of Orion young stars as a function of mass; other studies of astrophysical interest will appear in companion papers. Results include: ( a) the discovery of rapid variability in the 09.5 31 M. star theta(2)A Ori, and several early B stars, inconsistent with the standard model of X-ray production in small shocks distributed throughout the radiatively accelerated wind; (b) support for the hypothesis that intermediate-mass mid-B through A type stars do not themselves produce significant X-ray emission; (c) confirmation that low-mass G through M type T Tauri stars exhibit powerful flaring but typically at luminosities considerably below the saturation level; (d) confirmation that the presence or absence of a circumstellar disk has no discernable effect on X-ray emission; (e) evidence that T Tauri plasma temperatures are often very high with T &gt;= 100 MK, even when luminosities are modest and flaring is not evident; and (f) detection of the largest sample of pre-main-sequence very low-mass objects showing flaring levels similar to those seen in more massive T Tauri stars and a decline in magnetic activity as they evolve into L and T type brown dwarfs.

DOI： 10.1086/340936

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：日本経済新聞社  

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：日本天文学会  

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Language：English   Publisher：ARI  

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Language：English   Publisher：UNIV CHICAGO PRESS  

We report X-ray results of the Chandra observation of OMC-2 and OMC-3. A deep exposure of similar to100 ks detects similar to400 X-ray sources in the field of view of the ACIS array, providing one of the largest X-ray catalogs in a star-forming region. Coherent studies of the source detection, time variability, and energy spectra are performed. We classify the X-ray sources into Class I, Class II, and Class III + MS based on the J-, H-, and K-band colors of their near-infrared counterparts and discuss the X-ray properties (temperature, absorption, and time variability) along these evolutionary phases.

DOI： 10.1086/338110

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Language：English   Publisher：Astronomical Society of the Pacific  

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Language：English   Publisher：MACMILLAN PUBLISHERS LTD  

Herbig-Haro (HH) objects have been known(1,2) for 50 years to be luminous condensations of gas in star-forming regions, but their underlying physical nature is still being elucidated. Previously suggested models encompass newborn stars(3), stellar winds clashing with nebular material(4), dense pockets of interstellar gas excited by shocks from outflows(5), and interstellar 'bullets' (ref. 6). Recent progress has been made with the jet-induced shock model(7), in which material streams out of young stellar objects and collides with the surrounding interstellar medium. A clear prediction of this model is that the most energetic Herbig-Haro objects will emit X-rays, although they have not hitherto been detected(8). Here we report the discovery of X-ray emission from one of the brightest and closest Herbig-Haro objects, HH2, at a level consistent with the model predictions. We conclude that this Herbig-Haro object contains shock-heated material located at or near its leading edge with a temperature of about 10(6) K.

DOI： 10.1038/35099508

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Language：English   Publisher：OXFORD UNIV PRESS  

DOI： 10.1093/pasj/53.5.885

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Language：English   Publisher：Astronomical Society of the Pacific  

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Language：English   Publisher：UNIV CHICAGO PRESS  

We observed a 17 ' x 17 ' region of the rho Oph molecular cloud, using the ACIS-I array on board the Chandra X-Ray Observatory. A 100 ks exposure observation revealed similar to 100 X-ray sources above the detection limit of similar to 10(28) ergs s(-1). About two-thirds of the X-ray sources are identified with an optical and/or IR counterpart, including significant numbers of class I, II, and III sources and a few brown dwarfs. The X-ray detection rate of class I sources is a surprisingly high 70%. Many X-ray flares, possibly because of the magnetic activity, are found from all of the classes. We make systematic spectral studies of the quiescent and flare X-rays for all the X-ray sources. The X-ray temperatures and absorptions of class I sources are generally larger than those of class II and III sources. In addition, X-ray flares from class I sources show slightly higher duty ratio, temperature, and luminosity than those of more evolved classes. We further give brief results on brown dwarfs, sources in a younger phase than class I, unclassified, and unidentified sources. Details for several selected young stellar objects, including the first detection of a neutral iron line (6.4 keV) from a class I source (YLW 16A), are separately addressed.

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Language：English   Publisher：UNIV CHICAGO PRESS  

We observed a 17 ' x 17 ' region of the rho Oph molecular cloud, using the ACIS-I array on board the Chandra X-Ray Observatory. A 100 ks exposure observation revealed similar to 100 X-ray sources above the detection limit of similar to 10(28) ergs s(-1). About two-thirds of the X-ray sources are identified with an optical and/or IR counterpart, including significant numbers of class I, II, and III sources and a few brown dwarfs. The X-ray detection rate of class I sources is a surprisingly high 70%. Many X-ray flares, possibly because of the magnetic activity, are found from all of the classes. We make systematic spectral studies of the quiescent and flare X-rays for all the X-ray sources. The X-ray temperatures and absorptions of class I sources are generally larger than those of class II and III sources. In addition, X-ray flares from class I sources show slightly higher duty ratio, temperature, and luminosity than those of more evolved classes. We further give brief results on brown dwarfs, sources in a younger phase than class I, unclassified, and unidentified sources. Details for several selected young stellar objects, including the first detection of a neutral iron line (6.4 keV) from a class I source (YLW 16A), are separately addressed.

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Language：English   Publisher：UNIV CHICAGO PRESS  

We have observed the Orion Molecular Clouds 2 and 3 (OMC-2 and OMC-3) with the Chandra X-Ray Observatory (CXO). The northern part of OMC-3 is found to be particularly rich in new X-ray features; four hard X-ray sources are located in and along the filament of cloud cores. Two sources coincide positionally with the submillimeter-millimeter dust condensations of MMS 2 and 3 or an outflow radio source VLA 1, which are in a very early phase of star formation. The X-ray spectra of these sources show an absorption column of (1-3) x 10(23) H cm(-2). Assuming a moderate temperature plasma, the X-ray luminosity in the 0.5-10 keV band is estimated to be similar to 10(30) ergs s(-1) at a distance of 450 pc. From the large absorption, positional coincidence, and moderate luminosity, we infer that the hard X-rays are coming from very young stellar objects embedded in the molecular cloud cores. We found another hard X-ray source near the edge of the dust filament. The extremely high absorption of 3 x 10(23) H cm(-2) indicates that the source must be surrounded by dense gas, suggesting that it is either a young stellar object in an early accretion phase or a Type II AGN (e.g., a Seyfert 2), although no counterpart is found at any other wavelength. In contrast to the hard X-ray sources, soft X-ray sources are found spread around the dust filaments, most of which are identified with IR sources in the T. Tauri phase.

DOI： 10.1086/321392

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Language：English   Publisher：Astronomical Society of the Pacific  

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Language：English   Publisher：Astronomical Society of the Pacific  

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Language：English   Publisher：ASTRONOMICAL SOC PACIFIC  

Follow-up observations of the X-ray emitting class 0 candidates were performed in the near infrared hand using the SUBARU telescope. We set the upper limit on the K-band magnitude of these candidates, and found a jet-like feature in H-2 v = 1-0 S(1) band, originating from one of these candidates. These sources, therefore, arc, more likely to be class 0s, and thus are the first discoveries of the X-ray emitting class 0 objects.

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Language：English   Publisher：ASTRONOMICAL SOC PACIFIC  

We observed a 17' x 17' region of the p Oph molecular cloud, using the ACIS-I array onboard the Chandra X-ray Observatory (CXO). A 100-ks exposure observation revealed similar to hundred X-ray sources above the detection limit of similar to 10(28) ergs s(-1), of which 18 are class I sources and 29 have no counterpart in any other wave lengths. The X-ray detection rate of class 1 sources is a surprisingly high 70 %. Many X-ray flares, possibly due to the magnetic activity, are found from all of the classes. Difference in X-ray property between class I and class II/III sources, X-ray detection from brown dwarfs, and possible nature of unidentified sources are also discussed. More information is available from Imanishi et al. (2001 ApJ in press, astro-ph/0104190).

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Language：English   Publisher：ASTRONOMICAL SOC PACIFIC  

This paper reports discovery of X-ray emission from Class 0 protostar candidates, which are youngest X-ray stars ever detected. Class 0 is thought to be the evolutionary phase just after the birth of a star, and the ages are less than 10(5) years. The central stars are deeply embedded in dust condensations and thus never detected in any other wavelengths. The X-ray spectra are heavily absorbed, possibly by large amounts of gas and dust around the central stars. This high absorption proves that the X rays come really from the center of the dust condensations, i.e. from the central stars. Assuming a moderate temperature plasma, the X-ray luminosities in the 0.5-10 keV band are all similar to10(30) erg s(-1) at a distance of 450 pc, which are common in the older Class 1, 11 and III phases.

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Language：English   Publisher：ASTRONOMICAL SOC PACIFIC  

We report ASCA observations of two molecular cloud cores in the Perseus molecular cloud complex, Barnard I and the core containing a Class 0 protostar, IRAS 03282+3035. We detected 4 X-ray sources and found counterparts for two of them. We found no X-ray emission from young IRAS sources, IRAS 03282+3035 and IRAS 03301+3057, and obtained upper limits of their X-ray emissions.

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Language：English   Publisher：ASTRONOMICAL SOC PACIFIC  

We observed a 17' x 17' region of the p Oph molecular cloud, using the ACIS-I array onboard the Chandra X-ray Observatory (CXO). A 100-ks exposure observation revealed similar to hundred X-ray sources above the detection limit of similar to 10(28) ergs s(-1), of which 18 are class I sources and 29 have no counterpart in any other wave lengths. The X-ray detection rate of class 1 sources is a surprisingly high 70 %. Many X-ray flares, possibly due to the magnetic activity, are found from all of the classes. Difference in X-ray property between class I and class II/III sources, X-ray detection from brown dwarfs, and possible nature of unidentified sources are also discussed. More information is available from Imanishi et al. (2001 ApJ in press, astro-ph/0104190).

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Language：English   Publisher：ASTRONOMICAL SOC PACIFIC  

We present the ASCA observational results of intermediate mass to high mass pre-main-sequence stars. Seven objects in five fields were observed. Most sources exhibited significant time variability including flaring events, which suggests some magnetic activities on these stars. In the spectral analysis, younger sources in about 10(5)-years-old have higher plasma temperatures than 2keV whereas older sources have lower ones in our limited samples. The possible magnetic amplification mechanism is also discussed.

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Language：English   Publisher：UNIV CHICAGO PRESS  

About 1000 X-ray emitting young pre-main-sequence (PMS) stars distributed in mass from similar to 0.05 M. brown dwarfs to a similar to 50 M. O star are detected in an image of the Orion Nebula obtained with the Advanced CCD Imaging Spectrometer on board the Chandra X-Ray Observatory. This is the richest field of sources ever obtained in X-ray astronomy. Individual X-ray luminosities in the Orion Nebula cluster range from the sensitivity limit of 2 x 10(28) ergs s(-1) to similar to 10(32) ergs s(-1). ACIS sources include 85%-90% of V &lt; 20 stars, plus a lower but substantial fraction of deeply embedded stars with extinctions as high as A(V) similar or equal to 60. The relationships between X-ray and other PMS stellar properties suggest that X-ray luminosity of lower-mass PMS stars depends more on mass, and possibly stellar rotation, than on bolometric luminosity, as widely reported. In a subsample of 17 unabsorbed stars with mass similar or equal to 1 M., X-ray luminosities are constant at a high level around L-x similar or equal to 2 x 10(30) ergs s(-1) for the first similar or equal to 2 Myr while descending the convective Hayashi track, but diverge during the 2-10 Myr phase with X-ray emission plummeting in some stars but remaining high in others. This behavior is consistent with the distribution of X-ray luminosities on the zero-age main sequence and with current theories of their rotational history and magnetic dynamos.
The sources in the Becklin-Neugebauer/Kleinman-low region of massive star formation are discussed in detail. They include both unabsorbed and embedded low-mass members of the Orion Nebula cluster, the luminous infrared Source n, and a class of sources without optical or infrared counterparts that may be new magnetically active embedded PMS stars. Several X-ray sources are also variable radio emitters, an association often seen in magnetically active PMS stars. Faint X-ray emission is seen close to, but apparently not coincident with, the Becklin-Neugebauer object. Its nature is not clear.

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：日本天文学会  

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Language：English   Publisher：IOP PUBLISHING LTD  

The ASCA satellite has recently detected variable hard X-ray emission from two class I protostars in the rho Oph cloud, YLW 15 (IRS 43) and WL 6, with a characteristic timescale of similar to 20 hr. In YLW 15, the X-ray emission is in the form of quasi-periodic energetic flares, which we explain in terms of strong magnetic shearing and reconnection between the central star and the accretion disk. The flare modeling, based on the solar analogy, gives us access to the size of the magnetic structures, which in turn allows us to calculate the rotation parameters of the star and the disk. In WL 6, X-ray flaring is rotationally modulated and appears to be more like the solar-type magnetic activity ubiquitous on T Tauri stars. On the basis of these observations, we find that YLW 15 is a fast rotator (near break-up), while WL 6 rotates with a significantly longer period. We thus use X-ray flaring as a "clock" to measure the rotation of protostars. With the help of the mass-radius relation on the stellar "birthline," we derive masses of M-* similar to 2 M-circle dot and less than or similar to 0.4 M-circle dot for the central stars of YLW 15 and WL 6, respectively. YLW 15 thus appears to be a future A star. In the long term, the magnetic interactions between the star and the disk result in magnetic braking and angular momentum loss of the star. A comparison of the rotation behavior of YLW 15 and WL 6 confirms that for solar-mass stars magnetic braking takes place on timescales t(br) similar to a few x 10(5) yr, i.e., of the same order as the estimated duration of the class I protostar stage. The main parameter determining t(br) turns out to be the stellar mass, so that close to the birthline there must be a mass-rotation relation, t(br) similar to proportional to M-*, such that stars with M-* greater than or similar to 1-2 M-circle dot are fast rotators, while their lower mass counterparts have had the time to spin down and reach synchronous rotation with the inner surrounding accretion disk. The rapid rotation and strong star-disk magnetic interactions of YLW 15 also naturally explain the observation of "superflares" of X-ray luminosities as high as L-X greater than or similar to 10(33)-10(34) ergs s(-1) during a few hours, while at the WL 6 stage the lower X-ray luminosities are likely to be of purely stellar origin. The mass-rotation relation through magnetic braking may also explain why so few class I protostars have been detected in X-rays to date, and why they all lie in clusters. In the case of YLW 15, and perhaps also in other protostars, a hot coronal wind (T similar to 10(6) K) may be responsible for the VLA thermal radio emission. This paper thus proposes the first clues to the magnetic properties of protostars, which govern their rotation status and evolution.

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Language：English   Publisher：IOP PUBLISHING LTD  

With ASCA, we have detected three X-ray flares from the class I protostar YLW 15. The flares occurred every similar to 20 hr and showed an exponential decay with time constant 30-60 ks. The X-ray spectra are explained by a thin thermal plasma emission. The plasma temperature shows a fast rise and slow decay for each flare with kT(peak) similar to 4-6 keV. The emission measure of the plasma shows this time profile only for the first flare, and remains almost constant during the second and third flares, at the level of the tail of the first flare. The peak flare luminosities, L-X,L-peak, were similar to 5-20 x 10(31) ergs s(-1), which are among the brightest X-ray luminosities observed to date for class I protostars. The total energy released in each flare was 3-6 x 10(36) ergs. The first flare is well reproduced by the quasi-static cooling model, which is based on solar flares, and it suggests that the plasma cools mainly radiatively, confined by a semicircular magnetic loop of length similar to 14 R-circle dot with diameter-to-length ratio similar to 0.07. The two subsequent flares were consistent with the reheating of the same magnetic structure and the periodicity of the flares imply that the reheating events of the same magnetic loop originate in an interaction between the star and the disk due to the differential rotation.

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Language：English   Publisher：PERGAMON PRESS LTD  

We detected three intermittent X-ray flares from a protostar YLSY15. Each flare occurred every similar to 20 hours, and showed an exponential decay of time constant 30-60 ks. The time-sliced X-ray spectra are all explained by a thin thermal plasma emission. The plasma temperature shows a fast-rise and a slow-decay for each flare, while the emission measure of the plasma increases only at the beginning of the first flare and is almost constant during the second and third hares. Thus the X-rays are attributable to a single plasma produced by the first large flare, then the plasma is re-heated quasi-periodically. The re-heating interval is significantly shorter than the spin periods known on T Tauri stars (2-3 days at minimum), but comparable to the Keplerian rotation period of inner accretion disk at a distance of r similar to 5 R-circle dot (M/M-circle dot)(1.5) Assuming that the temperature decrease is due to radiative cooling, and the plasma geometry is a solar-like flare loop of an aspect ratio (= length/diameter) of 10, we estimate that the plasma loop length is about 10 Ro. Possible origin for the quasi-periodic flaring, magnetic activity produced in a star and inner disk interacting region, is briefly discussed. (C) 2000 COSPAR. Published by Elsevier Science Ltd.

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Language：English   Publisher：PERGAMON PRESS LTD  

We report on the hard X-ray detection from the core of the Monoceros R2 giant molecular cloud. The temperature is extremely high of about 5.5 keV in quiescent state. The strongest source among hard sources is associated with molecular core and suffered deep absorption. A hard X-ray flare near the core is also observed. The temperature is also extremely high. Strong Ca and Fe lines are observed in flare spectrum, and the energies are significantly lower than those of usual plasma model. The flare spectrum show some differences from those of low-mass young stars. It might be evidence of the X-rays from a high-mass protostar. (C) 2000 COSPAR. Published by Elsevier Science Ltd.

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Language：English   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：Central Bureau for Astronomical telegrams  

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Language：English   Publisher：野辺山電波観測所  

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Language：English   Publisher：MAX-Planck 研究所  

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Language：English   Publisher：野辺山電波観測所  

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Language：English   Publisher：Max-Planck 研究所  

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Language：English   Publisher：Wiley-VCH Verlag  

With ASCA, we detected hard X-rays from low-mass and high-mass Young Stellar Objects (YSOs), deeply embedded in dense molecular cloud cores. The X-rays from YSOs possessed line emissions from highly ionized ions of heavy elements, and were well fitted with thin-thermal plasma model. Some of them exhibited time valiabilities like solar flares, while their luminosities were at least 3-5 orders of magnitude larger than those from the Sun. These results support a scenario that stars in very young stage always emit magnetic-powered X-rays independently of the mass.

DOI： 10.1002/1521-3994(199908)320:4/5<175::AID-ASNA175>3.0.CO;2-O

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Language：English   Publisher：WILEY-V C H VERLAG GMBH  

With ASCA, we detected hard X-rays from low-mass and high-mass Young Stellar Objects (YSOs), deeply embedded in dense molecular cloud cores. The X-rays from YSOs possessed line emissions from highly ionized ions of heavy elements, and were well fitted with thin-thermal plasma model. Some of them exhibited time valiabilities like solar flares, while their luminosities were at least 3-5 orders of magnitude larger than those from the Sun. These results support a scenario that stars in very young stage always emit magnetic-powered X-rays independently of the mass.

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Language：English   Publisher：IOP PUBLISHING LTD  

We present results of a approximate to 40 ks ASCA observation of the active weak-lined T Tauri star V773 Tau (HD 283447) and the surrounding Barnard 209 dark cloud, obtained in 1995 February. During this observation, V773 Tau exhibited a dramatic X-ray flare, with the X-ray count rate increasing rapidly by a factor of similar to 20, then decreasing exponentially with an e-folding timescale of approximate to 2.3 hr. The peak flare luminosity was at least similar to 10(33) ergs s(-1) (0.7-10 keV; distance = 150 pc), which is among the highest X-ray luminosities observed to date for T Tauri stars. The total energy release was similar to 10(37) ergs. However, the most spectacular aspect of this hare was its temperature, which reached a maximum value of at least 100 million K. Spectral fits near flare maximum give a temperature of similar to 10 keV, which slowly declined to a value similar to 6 keV at the end of the observation. These temperature measurements are based on high signal-to-noise ratio spectra, and provide the first unambiguous evidence for superhot flaring plasma at temperatures of similar to 10(8) K in T Tauri stars. A simple cooling-loop model gives electron densities that are similar to those of solar flares, but requires loop sizes that are comparable to or larger than the star itself. The flare showed other interesting behavior, including a high (and possibly variable) absorption column density, N-H = 4 x 10(22) cm(-2), and an apparent increase in the global metal abundance during the flare.

DOI： 10.1086/306024

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Language：English   Publisher：The Astronomical Society of the Pacific  

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Language：English   Publisher：IOP PUBLISHING LTD  

We have obtained high signal-to-noise ratio 0.5-10 keV band X-ray spectra of the peculiar, extremely luminous star eta Carinae with the Advanced Satellite for Cosmology and Astrophysics (ASCA) X-ray observatory during Cycle 4 observations in mid-1996. These data comprise the best X-ray spectra to date of the cool source (kT similar to 0.3 keV) surrounding the homunculus and of the hot source (kT similar to 5 keV) associated with eta Car itself. We identify line emission from ions of N, Mg, Si, and S and numerous strong transitions of Fe in a variety of ionization stages, including the first clear identification of a fluorescent Fe line produced by photoionization of cool material by the X-ray continuum from the hot source. The line strengths are consistent with thermal equilibrium models, though abundances of some important elements are nonsolar. Our analysis suggests that Fe is slightly underabundant and S and Si somewhat overabundant. Most importantly, we confirm the high N enrichment derived by Tsuboi et al. from their analysis of a shorter ASCA observation obtained during the performance verification (PV) phase in 1993 August. The O/N abundance ratio derived from the ASCA spectra is consistent with an upper limit from optical/UV spectral analysis (Davidson et al.) and with predictions of evolutionary models for extremely massive stars. Comparison of the Cycle 4 and PV-phase spectra shows that the X-ray luminosity increased by similar to 50% during this 3 year interval. Using the ASCA spectral model as a template, we reevaluate the spectrum of II Car obtained by the Rontgen Satelite (ROSAT) in late 1992 and construct an X-ray light curve for the 1992.4-1996.6 interval. We present spectra from the Intel national Ultraviolet Explorer (IUE) satellite obtained at nearly the same time as the Cycle 4 ASCA spectra and show that the observed X-ray variability is reflected in changes of some important UV spectral features. Our data suggest that the X-ray emission and state of the stellar wind are intimately connected, though the exact mechanism of coupling is not known. We suggest two alternatives: an underlying photospheric change of undetermined origin in eta Car itself, or a collision between a dense stellar wind from eta Car and the wind or photosphere of a companion.

DOI： 10.1086/305190

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Language：English   Publisher：KLUWER ACADEMIC PUBL  

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Language：English   Publisher：KLUWER ACADEMIC PUBL  

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Language：English   Publisher：イタリア天文学会  

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Language：English   Publisher：イタリア天文学会  

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Language：English   Publisher：UNIV CHICAGO PRESS  

We report CO (J = 2-1, J = 1-0) outflows from four X-ray-emitting protostars (EL29, IRS44, WL6, WL10) in the rho Ophiuchi cloud core which have been firmly identified with the X-ray satellite ASCA. The common feature of these outflows is that the blue and red lobes are largely overlapped, which indicates that the inclination angle between the outflow axis and line of sight is smaller than 30 degrees (nearly pole-on configuration). Taking account of the hard X-ray transparency (N-H similar to 10(23) cm(-2)) and the column density of a circumstellar disk (N-H&gt;10(24) cm(-2)), it is naturally understood that hard X-rays emitted near the surface of protostars or the inner part of the disk are observed in the nearly pole-on configuration. The outflow detection rate (4/5) in the present observations shows that a low-mass protostar emits X-rays even in the outflow phase of early stellar evolution.

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Language：English   Publisher：OXFORD UNIV PRESS  

This paper presents a comprehensive study with the Japanese X-ray astronomical satellite ASCA on X-rays from the main body of the rho Ophiuchi dark cloud. We have constructed separate X-ray images using 3 energy bands and 12 time-sliced data, and thereby detected 19 X-ray sources, doubling the previous ASCA results of II X-ray sources. Three of the sources are associated with class-I infrared sources, which precede the T Tauri phase. Half of the 19 sources were found to be time variable, and 5 flare-like events with an averaged energy of &gt; 3 x 10(35) erg were observed. With the analogy of solar flares, we estimated the flare loop height and plasma density to be 3 x 10(11) cm and 3 x 10(11) cm(-3), respectively. Among these sources, a flare from the class-I source EL 29 exhibited an order-of-magnitude larger absorption (N-H) than in quiescence states, which may indicate the exsistence of a dense protostellar disk.

DOI： 10.1093/pasj/49.4.461

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Language：English   Publisher：Universal Academy Press  

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Language：English   Publisher：OXFORD UNIV PRESS  

We present ASCA results on the peculiar star eta Car in the center of the Carina Nebula. The X-ray emission from eta Car was found to be attributable to two thermal components: the high-temperature component (kT similar to 5 keV) is consistent with a point source, and is highly absorbed, while the low-temperature plasma (kT similar to 0.7 keV) is extended, and shows no significant circumstellar absorption. We found a line-like structure around 0.5 keV, which is probably due to the Ly alpha line of nitrogen. Using a variable-abundance coronal plasma model, we found that the relative abundance of nitrogen to oxygen is extremely large in comparison with the solar value. This may be the first X-ray evidence of the enrichment of CNO-processed material in an evolved massive star.

DOI： 10.1093/pasj/49.1.85

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：日本天文学会  

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Language：English   Publisher：AIP PRESS  

ASCA is the first satellite which has an imaging capability in high energies up to 10 keV, hence can peer deeply into the molecular cloud where protostar candidates may reside. We have carried out a systematic survey of hard X-rays from the core of molecular clouds, and discovered hard X-rays from protostar candidates (Class I objects) in the core of Rho Oph dark cloud. Two of them showed clear time variability; one (EL29) is flare-like and the other (WL6) is sinusoidal flux variation.
On the other hand, in Taurus dark cloud, we have detected a giant flare of a weak-lined TTS, V773 Tau in hard X-ray band. The plasma temperature was extremely high, about 8 keV, at the maximum flux, then it decreased as the flux decreased. The decay time and estimated electron density were found to be comparable to those of the sun, but the geometrical flare size was equal or even larger than the stellar size. The absorption column during the flare was large, about 3.6 x 10(22) H cm(-3), and it makes impossible to detect the flare in soft X-ray band. Interestingly, in the decay phase, we found the apparent change of the metal abundance.

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Language：English   Publisher：Universal Academy Press  

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Language：English   Publisher：Kluwer Academic Press  

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Language：English   Publisher：Universal Academy Press  

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Language：English   Publisher：KLUWER ACADEMIC PUBL  

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Language：English   Publisher：KLUWER ACADEMIC PUBL  

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Language：English   Publisher：KLUWER ACADEMIC PUBL  

The Japan-U.S. satellite ASCA was launched in February 1993 and provides a new capability to obtain high-resolution X-ray spectra of Wolf-Rayet stars in the 0.5 - 10 keV band. We present spectra of the wide binary HD 193793 (WC7+O4-5) obtained three months after periastron with the WC7 star in front, and of the WN7 star HD 93162 in Carina. The spectrum of HD 193793 is heavily absorbed below 2 keV by the WC7 wind and shows a prominent emission line from He-like iron at 6.7 keV. Acceptable fits were obtained using a Raymond-Smith model with kT approximate to 3 keV and non-solar abundances. In contrast, the spectrum of HD 93162 is softer and shows very little emission above approximate to 2 keV. The relatively low signal-to-noise precludes emission line analysis, and an acceptable spectral fit was obtained using a simple Bremsstrahlung model with kT approximate to 1.6 keV. No significant variability was detected in the X-ray light-curves of either star.

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Language：English   Publisher：ASTRONOMICAL SOC JAPAN  

Using the ASCA satellite we have discovered a new transient X-ray source at the position of RA(2000)= 18(h)45(m)2(s), Dec(2000) = -4 degrees 33'31'' (uncertainty = 1'), designated as AX 1845.0-0433. The NH-corrected X-ray flux was similar to 3 x 10(-12) erg s(-1) cm(-2) in the 0.7-10 keV region at the beginning of the observation; the X-ray source then suddenly flared up to a level of about 1 x 10(-9) erg s(-1) cm(-2) in the 0.7-10 keV region after N-H-correction within less than a few hours. It exhibited flare-like activity on the minimum time scale of a few ten minutes; the activity lasted until the end of the observation. The X-ray spectra in the quiescent and flare states resemble those of binary X-ray pulsars. However, no coherent pulsation was found in the range from 125 ms to 4096 s.

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Language：English   Publisher：Universal Academy Press  

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