海老沢 研

The Galactic black-hole binary GROJ1655-40, a source harboring superluminal jets, was observed with Suzaku on 2005 September 22-23. The source was detected over a broad and continuous energy range of 0.7-300 keV, with an intensity of similar to 50 mCrab at 20 keV At a distance of 3.2 kpc, the 0.7-300 keV luminosity was similar to 5.2 x 10(36) erg s(-1) (similar to 0.7% of the Eddington luminosity for a 6 M-circle dot black hole). The source was in a typical low/hard state, exhibiting a power-law shaped continuum with a photon index of similar to 1.6. During the observation, the source intensity gradually decreased by 25% at energies above similar to 3 keV, and by 35% below 2 keV. This, together with the soft X-ray spectra taken with the X-ray Imaging Spectrometer (XIS), suggests the presence of an independent soft component that can be represented by emission from a cool (similar to 0.2 keV) disk. The hard X-ray spectra obtained with the Hard X-ray Detector reveal a high-energy spectral cutoff, with an e-folding energy of similar to 200 keV. The entire 0.7-300 keV spectrum cannot be reproduced by a single thermal Comptonization model, even when considering reflection effects. Instead, the spectrum (except the soft excess) can be successfully explained by invoking two thermal-Comptonization components with different y-parameters. In contrast to the high/soft state spectra of this object, in which narrow iron absorption lines are detected with equivalent widths of 60-100 eV, the present XIS spectra bear no such features beyond an upper-limit equivalent width of 23 eV.

Five on-plane regions within +/-0.degrees 8 of the galactic center were observed with the Hard X-ray Detector (HXD) and the X-ray Imaging Spectrometer (XIS) aboard Suzaku. From all regions, significant hard X-ray emission was detected with HXD-PIN up to 40 keV, in addition to the extended plasma emission which is dominant in the XIS band. The hard X-ray signals are inferred to come primarily from a spatially extended source, rather than from a small number of bright discrete objects. Contributions to the HXD data from catalogued X-ray sources, typically brighter than 1 mCrab, were estimated and removed using information from Suzaku and other satellites. Even after this removal, the hard X-ray signals remained significant, exhibiting a typical 12-40keV surface brightness of 4 x 10(-10) erg cm(-2) s(-1) deg(-2) and power-law-like spectra with a photon index of 1.8. Combined fittings to the XIS and HXD-PIN spectra confirm that a separate hard tail component is superposed onto the hot thermal emission, confirming a previous report based on the XIS data. Over the 5-40 keV band, the hard tail is spectrally approximated by a power law of photon index similar to 2, but better by those with somewhat convex shapes. Possible origins of the extended hard X-ray emission are discussed.

In order to carry out a precise spectral study of the Galactic Ridge X-ray Emission using Suzaku, we have observed a typical Galactic plane field at (l, b) = (28 degrees 46, -0 degrees 20), which is already deeply observed with Chandra, and known to be devoid of bright X-ray point sources. Thanks to the low background and high spectral resolution of Suzaku, we were able to resolve three narrow iron K-emission lines from low-ionized (6.41 keV), helium-like (6.67 keV), and hydrogenic ions (7.00 keV). The cosmic-ray ion charge-exchange model or the non-equilibrium ionization plasma model are unlikely to explain these line features, since they require either broad emission lines or lines at intermediate ionization states. Collisional ionization equilibrium plasma is the likely origin for the 6.67 keV and 7.00 keV lines; however, the origin of the 6.41 keV line, which is due to fluorescence from cold material, has not been elucidated. We could also precisely measure the absolute X-ray surface brightness in the direction of the Galactic plane. Excluding point sources brighter than similar to 2 X 10(-13) erg s(-1) cm(-2) (2-10keV), the total surface brightness on the Galactic plane is similar to 6.1 x 10(-11) erg s(-1) cm(-2) deg(-2) (2-10keV), including the contribution of the cosmic X-ray background, which is estimated to be similar to 1.3 x 10(-11) erg s(-1) cm(-2) deg(-2).

An invessel neutron monitor using micro-fission chambers is one of the most important diagnostics to measure the fusion power in ITER. A single micro-fission chamber with 10 mg of 235U to be installed in a gap between a shielding blanket module and a vacuum vessel can cover the range of the fusion power from 100 kW to 1 GW. For the low fusion power operation including D-D operation, a micro-fission chamber bundle consisting of 13 micro-fission chamber units has been designed. Nuclear heating of the micro-fission chamber for high power operations and the micro-fission chamber bundle for low power operation were analyzed by neutron transport calculations using the MCNPX code. Heat transport analyzes for the micro-fission chambers were carried out with a general purpose Finite Element Method code ANSYS 8.1, which indicated that the detector temperature might be kept less than the operational temperature limit by the thermal conduction to the vacuum vessel with the heat transfer coefficient of 100 W/m2 K or larger. © 2007 Elsevier B.V. All rights reserved.

Aims. The Galactic bulge region is a rich host of variable high-energy point sources. Since 2005, February 17 we are monitoring the source activity in the Galactic bulge region regularly and frequently, i.e., about every three days, with the instruments onboard INTEGRAL. Thanks to the large field of view, the imaging capabilities and the sensitivity at hard X-rays, we are able to present for the first time a detailed homogeneous (hard) X-ray view of a sample of 76 sources in the Galactic bulge region. Methods. We describe the successful monitoring program and show the first results from the start of the monitoring up to 2006, April 21, i.e., for a period of about one and a half year, during three visibility seasons. We focus on the short (hour), medium (month) and long-term (year) variability in the hard X-ray bands, i.e., 20-60 keV and 60-150keV. When available, we discuss the simultaneous observations in the soft X-ray, 3-10keV and 10-25keV, bands. Results. Almost all the sources in the Galactic bulge region we detect in the 20-60 keV and 60-150keV bands are variable. During the last two and a half weeks of the third visibility season most of the known persistent (hard) X-ray sources in the Galactic Center region were not detected. Of our sample of sources, per visibility season we detect 32/33 sources in the 20-60 keV band and 8/9 sources in the 60-150 keV band above a signal to noise of 7. On average, we find per visibility season one active bright (≳ 100 mCrab, 20-60 keV) black-hole candidate X-ray transient and three active weaker (≳25mCrab, 20-60 keV) neutron star X-ray transients. Most of the time a clear anti-correlation can be seen between the soft and hard X-ray emission in some of the X-ray bursters. Hard X-ray flares or outbursts in X-ray bursters, which have a duration of the order of weeks are accompanied by soft X-ray drops. On the other hand, hard X-ray drops can be accompanied by soft X-ray flares/outbursts. During the course of our program we found a number of new sources, IGR J17354-3255, IGR 17453-2853, IGR J17454-2703, IGRJ17456-290 Ib, IGRJ17536-2339, and IGRJ17541-2252. We report here on some of the high-energy properties of these sources. Conclusions. The high-energy light curves of all the sources in the field of view, and the high-energy images of the region, are made available through the WWW, as soon as possible after the observations have been performed, at http://isdc.urdge.ch/Science/BULGE/. © ESO 2007.

We report on a Chandra grating observation of the recently discovered hard X-ray transient IGR J17497-2821. The observation took place about 2 weeks after the discovery of the source at a flux level of about 20 mcrab in the 0.8-8 keV range. We extracted the most precise X-ray position of IGR J17497-2821, i.e., αJ2000 = 17h49m38.037s, δJ2000 = -28°21′17.37″ (with a 90% uncertainty of 0.6″). We also report on optical and near-infrared photometric follow-up observations based on this position. With the multiwavelength information at hand, we discuss the possible nature of the source, proposing that IGR J17497-2821 is a low-mass X-ray binary, most likely hosting a black hole, with a red giant K-type companion. © 2007. The American Astronomical Society. All rights reserved.

High-sensitivity wide-band X-ray spectroscopy is the key feature of the Suzaku X-ray observatory, launched on 2005 July 10. This paper summarizes the spacecraft, in-orbit performance, operations, and data processing that are related to observations. The scientific instruments, the high-throughput X-ray telescopes, X-ray CCD cameras, non-imaging hard X-ray detector are also described.

We have developed a framework for the Monte Carlo simulations of X-Ray Telescope (XRT) and X-ray Imaging Spectrometer (XIS) on board Suzaku, mainly for the scientific analysis of spatially and spectroscopically complex celestial sources. A photon-by-photon instrumental simulator is built on the ANL platform, which has been successfully used in ASCA data analysis. The simulator has a modular structure, in which the XRT simulation is based on a ray-tracing library, while the XIS simulation utilizes a spectral "Redistribution Matrix File" (RMF), generated separately by other tools. Instrumental characteristics and calibration results [e.g., XRT geometry, reflectivity, mutual alignments, thermal shield transmission, build-up of the contamination on the XIS optical blocking filters (OBF)] are incorporated as completely as possible. Most of this information is available in the form of FITS (Flexible Image Transport System) files in the standard calibration database (CALDB). This simulator can also be utilized to generate an "Ancillary Response File" (ARF), which describes the XRT response and the amount of OBF contamination. An ARF is dependent on the spatial distribution of the celestial target and the photon accumulation region on the detector, as well as the observing conditions, such as the observation date and satellite attitude. We describe the principles of the simulator and the ARF generator, and demonstrate their performance compared with in-flight data.

Two ultraluminous X-ray sources (ULXs) in the nearby Sb galaxy NGC 1313, named X-1 and X-2, were observed with Suzaku on 2005 September 15. During the observation for a net exposure of 28 ks (but over a gross time span of 90 ks), both objects varied in intensity by about 50%. The 0.4-10 keV X-ray luminosities of X-1 and X-2 were measured as 2.5 x 10(40) erg s(-1) and 5.8 x 10(39) erg s(-1), respectively, with the former exhibiting the highest ever reported for this ULX. The spectrum of X-1 can be explained by the sum of a strong and variable powerlaw component with a high-energy cutoff, and a stable multicolor blackbody with an innermost disk temperature of similar to 0.2 keV. These results suggest that X-1 was in a "very high" state, where disk emission is strongly Comptonized. The absorber within NGC 1313 toward X-1 is suggested to have a subsolar oxygen abundance. The spectrum of X-2 is best represented, in its fainter phase, by a multicolor blackbody model with an innermost disk temperature of 1.2-1.3 keV, and becomes flatter as the source becomes brighter. Hence, X-2 is interpreted to be in a slim-disk state. These results suggest that the two ULXs have black hole masses of some dozens to a few hundred of solar masses.

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.

The Galactic center (GC) region has been known to exhibit strong enhancements of hot diffuse plasma, which is characterized by the highly ionized Fe-K fluorescence line. Based on past X-ray observations with Ginga, ASCA, and RXTE, in the Galactic plane or bulge region, a non-thermal emission, so-called the "hard-tail", has been confirmed to dominate the hard X-ray flux above 10 keV, and an association was found between surface brightnesses of the thermal and non-thermal components despite the completely different emission mechanism. Therefore, it is obviously important to investigate an existence of the hard-tail at GC with the unprecedented sensitivity of the HXD onboard Suzaku. By combining its narrow field-of-view of 30' and X-ray images simultaneously obtained by the XIS below 10 keV, an extensive investigation of spectral and spatial properties of the GC hard X-ray emission can be for the first time realized. We will report on results from seven pointings around GC, with a total exposure of 300 ks, performed in the performance verification phase of Suzaku. Strong hard X-ray signals were clearly detected in every observation by HXD-PIN in 10-70 keV range with a few tenth mCrab level intensities.

We have observed a typical Galactic plane blank field with Suzaku for 100 ksec to carry out spectral study of the Galactic Ridge X-ray Emission (GRXE). The field had been previously studied with Chandra, and is known to be devoid of bright X-ray point sources. We were able to resolve, for the first time, three narrow iron K-emission lines from low-ionized (6.4 keV), helium-like (6.67 keV), and hydrogenic ions (7.0 keV). These line features constrain the GRXE emission mechanisms. The cosmic-ray ion charge exchange model or the non-ionization equirribrium (NIE) plasma model are very unlikely, since they require either broad emission lines or lines at intermediate ionization states. We were able to precisely measure the absolute GRXE flux thanks to the low background and small stray-light contamination of Suzaku. Excluding point sources brighter than 2 x 10(-13) ergs s(-1) cm(-2) (2-10 keV), only similar to 10% of the 2-10 keV GRXE flux is explained by the Chandra point sources brighter than 3 x 10(-15) ergs s(-1) cm(-2).

We report about the Suzaku observation of two ultraluminous X-ray sources (ULXs), X-1 and X-2, in NGC1313, together with their spectra by XMM-Newton. During the observation, both showed intensity-correlated spectral changes. The brighter source, X-1, exhibited the highest luminosity (similar to 3 x 10(40) erg s(-1)) ever recorded from this source. Its spectral variation is ascribed to a strong power-law like component with a mild high energy curvature, while about 10% of the flux is carried by a stable soft component modeled by a cool disk emission. These properties suggest that the source was in the "very high" state, wherein the disk emission is strongly Comptonized and the optically-thick disk is truncated at a large radii or cooled off. The spectrum of X-2 is best represented, in its fainter phase, by a multicolor disk model with the innermost disk temperature of 1.2-1.3 keV, and becomes flatter as the source gets brighter. Hence X-2 is interpreted to be in a slim disk state. These results suggest that the two ULXs host black holes of a few tens to a few hundreds solar masses.

It may seem to be difficult to analyze the Suzaku data, but the data structure and the tools are rather simple. We have constructed the way to process Suzaku FITS data and ftools for over ten years. We have prepared three kinds of manuals to analyze the data; Seven step manual of the XIS and the HXD for beginners, first step manual to walk through the analyses, and the ABC guide as a full manual. In the actual analyses, we have to be careful about events in operation and the limitations in the calibration of instruments. In this paper, the data structure, tools, and manuals with activities of help desks, current status of processing are summarized.

The Galactic black-hole binary GRO J1655-40 was observed with Suzaku on 2005 September 22-23, for a gross time span of similar to 1 day. The source was detected over a wide and continuous energy range of 0.7-300 keV, with an intensity of similar to 50 mCrab in the 1.5 - 12 keV band. At an assumed distance of 3.2 kpc, the 0.7-300 keV luminosity is calculated to be similar to 4.4 x 10(36) ergs s(-1). The source was in a typical low/hard state, since its overall spectrum was dominated by a power-law component with a photon index of similar to 1.7. The source intensity gradually decreased by 20% during the observation, involving little spectral changes above similar to 3 keV. However, at softer energies, the amplitude of variability was somewhat enhanced. This indicates the presence of an independent soft component. The spectra in the hard energy band reveal a high-energy spectral cutoff, with an e-folding energy of similar to 200 keV which is suggested to be higher than those observed from typical black hole binaries in the low/hard state.

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.

We have analyzed the archival XMM-Newton data of the bright ultraluminous X-ray source M82 X-1 with a 105 ks exposure when the source was in the steady state. Thanks to the high photon statistics from the large effective area and long exposure, we were able to discriminate different X-ray continuum spectral models. Neither the standard accretion disk model [where the radial dependency of the disk effective temperature is T(r) proportional to r(-3/4)] nor a power-law model gives a satisfactory fit. In fact, observed curvature of the M82 X-1 spectrum was just between those of the two models. When the exponent of the radial dependence [p in T(r) proportional to r(-p)] of the disk temperature is allowed to be free, we obtained p = 0.61(-0.02)(+0.03). Such a reduction of p from the standard value 3/4 under extremely high mass accretion rates is predicted from the accretion disk theory as a consequence of the radial energy advection. Thus, the accretion disk in M82 X-1 is considered to be in the slim-disk state, where an optically thick advection-dominated accretion flow is taking place. We have applied a theoretical slim-disk spectral model to M82 X-1 and estimated the black hole mass approximate to 19-32(circle dot). We propose that M82 X-1 is a relatively massive stellar black hole that has been produced through evolution of an extremely massive star, shining at a super-Eddington luminosity by several times the Eddington limit.

An open question remains whether Ultraluminous X-ray Sources (ULXs) really contain intermediate-mass black holes (IMBHs). We carefully investigated the XMM-Newton EPIC spectra of four ULXs that were claimed to be strong candidates of IMBHs by several authors. We first tried fitting by the standard spectral model of disk blackbody (DBB) + power-law (PL), finding good fits to all of the data, in agreement with others. We, however, found that the PL component dominates the DBB component at similar to 0. 3 to 10 keV. Thus, the black hole parameters derived solely from the minor DBB component are questionable. Next, we tried to fit the same data by the "p-free disk model" without the PL component, assuming an effective temperature profile of T-eff proportional to r(-p), where r is the disk radius. Interestingly, in spite of one less free-model parameter, we obtained similarly good fits with much higher innermost disk temperatures, 1.8 < kT(in) < 3.2keV. More importantly, we obtained p similar to 0.5, just the value predicted by the slim (super-critical) disk theory, rather than p = 0.75 that is expected from the standard disk model. The estimated black hole masses from the p-free disk model are much smaller; M less than or similar to 40M(circle dot). Furthermore, we applied a more sophisticated slim-disk model by Kawaguchi (2003, ApJ, 593, 69), and obtained good fits with roughly consistent black hole masses. We thus conclude that the central engines of these ULXs are super-critical accretion flows to stellar-mass black holes.

It still remains an open question if the ultraluminous X-ray sources (ULXs) really contain intermediate-mass black holes (IMBHs). To settle this issue, we investigate the XMM-Newton EPIC spectra of NGC 5204 X-1, whose X-ray luminosity is Lx similar to (2 - 6) x 1039 erg s(-1). We first tried the standard spectral model of a disk blackbody (DBB) + power law (PL) and found a good fit to the data (reduced chi-squared is 1.05) with the innermost temperature kT(in) = 0.25 +/- 0.03 keV and the photon index Gamma = 1.92 +/- 0.06. This apparently supports the IMBH interpretation of ULXs, in agreement with Roberts et al. (2005). Next, we tried to fit the data by using the p-free disk model alone, assuming an effective temperature profile of T-eff proportional to r(-p). Surprisingly, we also obtained a good fit (reduced chi-squared is 1.12) with a higher innermost disk temperature kT(in) = 2.54 +/- 0.34 keV. More importantly, we obtained p = 0.50 +/- 0.03, just the value predicted by the slim-disk theory, rather than the value p = 0.75 expected from the standard-disk model. That is, NGC 5204 X-1 should shine at about the Eddington luminosity, and it should contain a stellar-mass black hole of 2.67(cos i)M--1/2(circle dot) (about 10 M-circle dot for i &gt; 80 degrees).

We report on observations of the X-ray pulsar IGR J16320-4751 (also known as AX J1631.9-4752) performed simultaneously with International Gamma-Ray Astrophysics Laboratory (INTEGRAL) and XMM-Newton. We refine the source position and identify the most likely infrared counterpart. Our simultaneous coverage allows us to confirm the presence of X-ray pulsations at similar to 1300 s, that we detect above 20 keV with INTEGRAL for the first time. The pulse fraction is consistent with being constant with energy, which is compatible with a model of polar accretion by a pulsar. We study the spectral properties of IGR J16320-4751 during two major periods occurring during the simultaneous coverage with both satellites, namely a flare and a non-flare period. We detect the presence of a narrow 6.4 keV iron line in both periods. The presence of such a feature is typical of supergiant wind accretors such as Vela X-1 or GX 301-2. We inspect the spectral variations with respect to the pulse phase during the non-flare period, and show that the pulse is solely due to variations of the X-ray flux emitted by the source and not due to variations of the spectral parameters. Our results are therefore compatible with the source being a pulsar in a High Mass X-ray Binary. We detect a soft excess appearing in the spectra as a blackbody with a temperature of similar to 0.07 keV. We discuss the origin of the X-ray emission in IGR J16320-4751: while the hard X-rays are likely the result of Compton emission produced in the close vicinity of the pulsar, based on energy argument we suggest that the soft excess is likely the emission by a collisionally energized cloud in which the compact object is embedded.

Our current theoretical and observational understandings of the accretion disks around Galactic black-holes are reviewed. Historically, a simple phenomenological accretion disk model has been used to interpret X-ray observations. Although such a phenomenological interpretation is still useful, high quality X-ray data from contemporary instruments allow us to test more realistic accretion disk models. In a simple and ideal case, the standard optically thick accretion disk model is successful to explain observations, such that the inner disk radius is constant at three times the Schwarzschild radius over large luminosity variations. However, when disk luminosity is close to or exceeds the Eddington luminosity, the standard disk model breaks, and we have to consider the "slim disk" solution in which radial energy advection is dominant. Recent observations of Ultra-luminous X-ray sources (ULXs), which may not be explained by the standard disk model, strongly suggest the slim disk solution. We compare theoretical X-ray spectra from the slim disk with observed X-ray spectra of ULXs. We have found that the slim disk model is successful to explain ULX spectra, in terms of the massive stellar black-holes with several tens of solar mass and the super-Eddington mass accretion rates. In order to explain the large luminosities (> 10(40) ergs s(-1)) of ULXs, "intermediate black-holes" (>100M(circle dot)) are not required. Slim disks around massive stellar black-holes of up to several tens of solar mass would naturally explain the observed properties of ULXs. (C) 2006 COSPAR. Published by Elsevier Ltd. All rights reserved.

Our current theoretical and observational understandings of the accretion disks around Galactic black-holes are reviewed. Historically, a simple phenomenological accretion disk model has been used to interpret X-ray observations. Although such a phenomenological interpretation is still useful, high quality X-ray data from contemporary instruments allow us to test more realistic accretion disk models. In a simple and ideal case, the standard optically thick accretion disk model is successful to explain observations, such that the inner disk radius is constant at three times the Schwarzschild radius over large luminosity variations. However, when disk luminosity is close to or exceeds the Eddington luminosity, the standard disk model breaks, and we have to consider the "slim disk" solution in which radial energy advection is dominant. Recent observations of Ultra-luminous X-ray sources (ULXs), which may not be explained by the standard disk model, strongly suggest the slim disk solution. We compare theoretical X-ray spectra from the slim disk with observed X-ray spectra of ULXs. We have found that the slim disk model is successful to explain ULX spectra, in terms of the massive stellar black-holes with several tens of solar mass and the super-Eddington mass accretion rates. In order to explain the large luminosities (> 10(40) ergs s(-1)) of ULXs, "intermediate black-holes" (> 100M circle dot) are not required. Slim disks around massive stellar black-holes of up to several tens of solar mass would naturally explain the observed properties of ULXs. (c) 2006 COSPAR. Published by Elsevier Ltd. All rights reserved.

A comparative XMM-Newton archival data spectral study of the ultraluminous X-ray source (ULX) M33 X-8 has been performed by using both the standard disk model and the newly developed slim disk models. The results of this analysis tend to confirm the hypothesis that M33 X-8 is an X-ray binary with a stellar-mass black hole accreting at super-Eddington rate. © 2005 COSPAR.

The Galactic Bulge region is a rich host of variable high-energy point sources. These sources include bright and relatively faint X-ray transients, X-ray bursters, persistent neutron star and black-hole candidate binaries, X-ray pulsars, etc.. We have a program to monitor the Galactic Bulge region regularly and frequently with the gamma-ray observatory INTEGRAL As a service to the scientific community the high-energy light curves of all the active sources as well as images of the region are made available through the WWW. We show the first results of this exciting new program.

Using the Chandra Advanced CCD Imaging Spectrometer Imaging array (ACIS-I), we have carried out a deep hard X-ray observation of the Galactic plane region at (l, b) approximate to (28 degrees.5, 0 degrees.0), where no discrete X-ray source had been reported previously. We have detected 274 new point X-ray sources ( 4 sigma confidence), as well as strong Galactic diffuse emission within two partially overlapping ACIS-I fields (similar to 250 arcmin(2) in total). The point-source sensitivity was similar to 3 x 10(-15) ergs s(-1) cm(-2) in the hard X-ray band (2-10 keV) and similar to 2 x 10(-16) ergs s(-1) cm(-2) in the soft band (0.5-2 keV). The sum of all the detected point-source fluxes accounts for only similar to 10% of the total X- ray flux in the field of view. Even hypothesizing a new population of much dimmer and numerous Galactic point sources, the total observed X- ray flux cannot be explained. Therefore, we conclude that X- ray emission from the Galactic plane has a truly diffuse origin. Removing point sources brighter than similar to 3 x 10(-15) ergs s(-1) cm(-2) (2-10 keV), we have determined the Galactic diffuse X-ray flux to be 6.5 x 10(-11) ergs s(-1) cm(-2) deg(-2) (2-10 keV). Only 26 point sources were detected in both the soft and hard bands, indicating that there are two distinct classes of X- ray sources distinguished by their spectral hardness ratios. The surface number density of the hard sources is only slightly higher than that measured at the high Galactic latitude regions, indicating that the majority of the hard sources are background AGNs. Following up the Chandra observation, we have performed a near-infrared (NIR) survey with SofI at ESO/NTT. Almost all the soft X- ray sources have been identified in the NIR, and their spectral types are consistent with main-sequence stars, suggesting that most of them are nearby X- ray-active stars. On the other hand, only 22% of the hard sources had NIR counterparts, which are presumably Galactic. From X- ray and NIR spectral study, they are most likely to be quiescent cataclysmic variables. Our observation suggests a population of greater than or similar to 10(4) cataclysmic variables in the entire Galactic plane fainter than similar to 2 x 10(33) ergs s(-1). We have carried out a precise spectral study of the Galactic diffuse X- ray emission excluding the point sources. Confirming previous results, we have detected prominent emission lines from highly ionized heavy elements in the diffuse emission. In particular, the central energy of the iron emission line was determined to be 6.52(-0.14)(+0.08) keV ( 90% confidence), which is significantly lower than what is expected from a plasma in thermal equilibrium. The downward shift of the iron line center energy suggests nonequilibrium ionization states of the plasma or the presence of a nonthermal process to produce 6.4 keV fluorescent lines.

We report on an observation of the recently discovered accreting millisecond X-ray pulsar IGR J00291+5934 performed with the RXTE-Proportional Counter Array ( PCA) and Chandra-High Energy Transmission Grating Spectrometer (HETGS). The RXTE data are from a two-week follow-up of the source, while the Chandra observation took place around the end of the follow-up, about 12 days after the discovery of the source, when the source flux had decreased already by a factor of ten. The analysis of the Chandra data allowed us to extract the most precise X-ray position of IGR J00291+5934, RA = 00(h) 29(m) 03.08(s), and Dec = +59 degrees 34' 19.2" (0.6" error), compatible with the optical and radio ones. We find that the spectra of IGR J00291+5934 can be described by a combination of a thermal component and a power-law. Along the outburst detected by PCA, the power-law photon index showed no particular trend, while the thermal component (similar to 1 keV, interpreted as a hot spot on the neutron star surface) became weaker until non-detection. In the simultaneous observation of the weak Chandra/RXTE spectrum, there was no longer any indication of the similar to 1 keV thermal component, while we detected a colder thermal component (similar to 0.4 keV) that we interpret as the emission from the cold disc. A hint of a 6.4 keV iron line was detected, together with an excess around 6.8 keV and absorption feature around 7.1 keV. The last two features have never been detected in the spectra of accretion-driven millisecond pulsars before and, if confirmed, would suggest the presence of an expanding hot corona with high outflow velocities.

We present the study of one year of INTEGRAL data on the neutron star low mass X-ray binary GX 5-1. Thanks to the excellent angular resolution and sensitivity of INTEGRAL, we are able to obtain a high quality spectrum of GX 5-1 from similar to 5keV to similar to 100 keV, for the first time without contamination from the nearby black hole candidate GRS 1758-258 above 20 keV. During our observations, GX 5-1 was mostly found in the horizontal and normal branch of its hardness intensity diagram. A clear hard X-ray emission is observed above similar to 30 keV which exceeds the exponential cut-off spectrum expected from lower energies. This spectral flattening may have the same origin of the hard components observed in other Z sources as it shares the property of being characteristic to the horizontal branch. The hard excess is explained by introducing Compton up-scattering of soft photons from the neutron star surface due to a thin hot plasma expected in the boundary layer. The spectral changes of GX 5-1 downward along the "Z" pattern in the hardness intensity diagram can be well described in terms of monotonical decrease of the neutron star surface temperature. This may be a consequence of the gradual expansion of the boundary layer as the mass accretion rate increases.

We report the discovery of a high-energy transient with the IBIS/ISGRI detector on board the INTEGRAL observatory. The source, namely IGR J00291+5934, was first detected on 2nd December 2004 in the routine monitoring of the IBIS/ISGRI 20- 60 keV images. The observations were conducted during Galactic Plane Scans, which are a key part of the INTEGRAL Core Programme observations. After verifying the basic source behaviour, the discovery was announced on 3rd December. The transient shows a hard Comptonised spectrum, with peak energy release at about 20 keV and a total luminosity of similar to 0.9 x 10(36) erg s(-1) in the 5-100 keV range, assuming a distance of 3 kpc. Following the INTEGRAL announcement of the discovery of IGR J00291+5934, a number of observations were made by other instruments. We summarise the results of those observations and, together with the INTEGRAL data, identifiy IGR J00291+5934 as the 6th member of a class of accreting X-ray millisecond pulsars.

Shell-like supernova remnants (SNRs) are primary candidates for the origin of Galactic cosmic rays. However, among the known SNRs (about 220), only a small fraction has been known to exhibit the synchrotron X-ray spectrum, that is considered to be a piece of evidence for high energy particle acceleration. Synchrotron X-ray emitting SNRs are known to be systematically radio-quiet compared to the SNRs that do not emit synchrotron X-rays. Therefore, most synchrotron X-ray emitting SNR candidates may have escaped detection in the previous systematic radio surveys. On the other hand, hard X-ray surveys are effective to search for synchrotron X-ray emitting SNRs, because of its penetration power. Thus we have searched for SNRs in the ASCA Galactic Plane Survey data, the first Galactic imaging survey in &gt 2 keV, and discovered 14 candidates. Deep follow-up observations with ASCA, XMM, or Chandra on 5 of them revealed 2 sources to be synchrotron X-ray emitting SNRs. Furthermore we confirmed non-thermal X-ray spectra from the other 3 sources, though the origin is yet unknown. We report the observational results and discuss the X-ray origin. © 2006 International Astronomical Union.

We have discovered a number of nonthermal X-ray features within central 40 pc region of the Galactic center by analysing 600-ksec observations of Chandra archival data. Most of the detected X-ray structures exhibit small-scale knot-like morphologies and their spectra are well reproduced by single hard power-law with photon indices of 1-2. Among them, the most outstanding features are the three X-ray knots which are aligned on a straight line from the potition of Sgr A* to north-northwest direction. The X-ray properties of these knots lead us to suspect that they are X-ray jets ejected from Sgr A* in the recent past. In addition, we have obtained an indication that the summed flux of nonthermal diffuse X-rays within 30 pc of the GC seems to be smoothly connected to the 20-100 keV flux detected with INTEGRAL IBIS/ISGRI. These results suggest that the origin of GC hard X-rays (or High energy Gamma-rays) is not (or partly) from the Galactic nucleus. © 2006 International Astronomical Union.

Various X-ray satellites have used the Crab as a standard candle to perform their calibrations in the past. The calibration of XMM-Newton, however, is independent of the Crab nebula, because this object has not been used to adjust spectral calibration issues. In 2004 a number of special observations were performed to measure the spectral parameters and the absolute flux of the Crab with XMM-Newton's EPIC-pn CCD camera. We describe the results of the campaign in detail and compare them with data of four current missions (Integral, Swift, Chandra, RXTE) and numerous previous missions (ROSAT, EXOSAT, Beppo-SAX, ASCA, Ginga, Einstein, Mir-HEXE).

We present the results of high-resolution spectroscopy of absorption-line features of highly ionized ions in the X-ray spectra of GX 13+1 with the Chandra HETGS. We have resolved Kalpha absorption lines of hydrogen-like Fe, Mn, Cr, Ca, Ar, S, Si, and Mg ions and helium-like Fe ions. Applying the Voigt profile to these spectral features, we find that the plasma responsible for the absorption lines has a significant blueshift of 460 +/- 70 km s(-1), indicating an outflow velocity of approximate to 400 km s(-1) corrected for the proper motion, with a line-of-sight velocity dispersion of 490(-140)(+110) km s(-1). The plasma is photoionized with an ionization parameter of log xi similar or equal to 4.1-4.7. The inferred mass outflow rate is 0.7 x 10(18) g s(-1) or higher, comparable to the mass accretion rate ( 10(18) g s(-1)) estimated from the continuum spectrum. This indicates that the mass outflow plays a significant role to determine the whole dynamics of the accretion disk. We consider a simplified radiation-driven disk wind model for the origin of the outflow. Our observations are explained by the wind originating from radii of similar to 10(10) - 10(11) cm with a density greater than or similar to10(13) cm(-3).

This Letter presents the first results of an observational campaign to study the Galactic center with INTEGRAL, the International Gamma-Ray Astrophysics Laboratory. Mosaicked images were constructed using data obtained with ISGRI, the soft gamma-ray instrument of the coded aperture IBIS imager, in the energy ranges 20 - 40 and 40 - 100 keV. These give a yet unseen view of the high-energy sources of this region in hard X-rays and gamma rays with an angular resolution of 12' (FWHM). We report on the discovery of a source, IGR J1745.6 - 2901, coincident with the Galactic nucleus Sgr A* to within 0.'9. Located at R.A. = 17(h)45(m)38(s).5 (J2000.0), decl. = -29degrees01'15"(J2000.0), the source is visible up to about 100 keV with a 20 - 100 keV luminosity at 8 kpc of (2.89 +/- 0.41) x 10(35) ergs s(-1). Although the new INTEGRAL source cannot unequivocally be associated to the Galactic nucleus, this is the first report of significant hard X-ray emission from within the inner 10' of the Galaxy and a contribution from the Galactic supermassive black hole itself cannot be excluded.

Using the Chandra ACIS-I instruments, we have carried out a deep X-ray observation on the Galactic plane region at (l, b) approximate to (28.degrees 5, 0.degrees 0), where no discrete X-ray sources have been known previously. We have detected, as well as strong diffuse emission, 274 new point X-ray sources (4 a confidence) within two partially overlapping fields (similar to 250 arcmin(2) in total down to the flux limit similar to 3 x 10(-15) erg s(-1) cm(-2) (2- 10 keV) and similar to 7x 10(-16) erg s(-1) cm(-2) (0.5 - 2 keV). We clearly resolved point sources and the Galactic diffuse emission, and found that similar to 90 % of the flux observed in our field of view originates from diffuse emission. Many point sources are detected either in the soft X-ray band (below 2 keV) or in the hard band (above 2 keV), and only a small number of sources are detected in both energy bands. On the other hand, most soft X-ray sources are considered to be nearby X-ray active stars. We have carried out a follow-up near-infrared (NIR) observation using SOFI at ESO/NTT. Most of the soft X-ray sources were identified, whereas only a small number of hard X-ray sources had counterparts in NIR. Using both X-ray and NIR information, we can efficiently classify the point X-ray sources detected in the Galactic plane. We conclude that most of the hard X-ray sources are background Active Galactic Nuclei seen through the Milky Way, whereas majority of the soft X-ray sources are nearby X-ray active stars.

Early results from the INTEGRAL Core Program, for a sample of eight persistently bright neutron star low mass X-ray binaries in the energy range from 5 keV to 200 keV, are presented. It is shown that INTEGRAL efficiently detects sources and that spectra may be obtained up to several hundreds of keV by combining data from three of the four INTEGRAL instruments: JEM-X, IBIS and SPI. For the source GX 17+2 it is shown that the spectrum extends well above 100 keV with a flattening above 30 keV. This might suggest a non-thermal comptonisation emission, but uncertainties in the current data reduction and background determination do not allow firm conclusions to be drawn yet.

Ultraluminous compact X-ray sources (ULXs) in nearby spiral galaxies and Galactic superluminal jet sources share the common spectral characteristic that they have unusually high disk temperatures that cannot be explained in the framework of the standard optically thick accretion disk in the Schwarzschild metric. On the other hand, the standard accretion disk around the Kerr black hole might explain the observed high disk temperature, since the inner radius of the Kerr disk becomes smaller and the disk temperature can consequently be higher. However, we point out that the observable Kerr disk spectra become significantly harder than Schwarzschild disk spectra only when the disk is highly inclined. This is because the emission from the innermost part of the accretion disk is Doppler boosted for an edge-on Kerr disk while hardly seen for a face-on disk. The Galactic superluminal jet sources are known to be highly inclined systems; thus, their energy spectra may be explained with the standard Kerr disk with known black hole masses. For ULXs, on the other hand, the standard Kerr disk model seems implausible, since it is highly unlikely that their accretion disks are preferentially inclined, and if the edge-on Kerr disk model is applied, the black hole mass becomes unreasonably large (greater than or similar to300 M-circle dot). Instead, the slim-disk (advection-dominated optically thick disk) model is likely to explain the observed super-Eddington luminosities, hard energy spectra, and spectral variations of ULXs. We suggest that ULXs are accreting black holes with a few tens of solar masses, which is not unexpected from the standard stellar evolution scenario, and that their X-ray emission is from the slim disk shining at super-Eddington luminosities.

We present the first INTEGRAL results on Cyg X-3 from the PV phase observations of the Cygnus region. The source was clearly detected by the JEM-X, ISGRI and SPI. The INTEGRAL observations were supported by simultaneous pointed RXTE observations. Their lightcurves folded over the 4.8 hour binary period are compatible with the mean RXTE/ASM and CGRO/BATSE light curves. We fit our broad-band X-ray/gamma-ray spectra with a physical model, which represents the first such published model for Cyg X-3. The main physical processes in the source are thermal Comptonization and Compton reflection with parameters similar to those found for black-hole binaries at high Eddington rates.

We review highlights of the results obtained from recent Galactic X-ray survey observations, in particular ASCA Galactic center and plane surveys and our Chandra deep survey on the (l, b) approximate to (28.degrees5, 0.degrees0) region. Strong hard X-ray diffuse components are observed from Galactic ridge, center and bulge. and they have both thermal and non-thermal spectral components. Dozens of discrete and extended sources have been discovered on the Galactic plane, which also indicate thermal and/or non-thermal X-ray energy spectra, They are often associated with radio sources and are considered to be SNR candidates. Most of the hard X-ray point sources in the outer part of the Galactic plane are considered to be background AGNs, while fraction of the Galactic hard X-ray sources (such as quiescent dwarf novae) increases toward the Galactic center. Most of the soft X-ray sources on the Galactic plane are presumably nearby active stars.

Ultra-luminous Compact X-ray Sources (ULXs) in,nearby spiral galaxies and Galactic superluminal jet sources share the common spectral characteristic that they have unusually high disk temperatures which cannot be explained in the framework of the standard optically thick accretion disk in the Schwarzschild metric. On the other hand, the standard accretion disk around the Kerr black hole might explain the observed high disk temperature, as the inner radius of the Kerr disk gets smaller and the disk temperature can be consequently higher. However, we point out that the observable Kerr disk spectra becomes significantly harder than Schwarzschild disk spectra only when the disk is highly inclined. This is because the emission from the innermost part of the accretion disk is Doppler-boosted for an edge-on Kerr disk, while hardly seen for a face-on disk. The Galactic superluminal jet sources are known to be highly inclined systems, thus their energy spectra may be explained with the standard Kerr disk with known black hole masses. For ULXs, on the other hand, the standard Kerr disk model seems implausible, since it is highly unlikely that their accretion disks are preferentially inclined, and, if edge-on Kerr disk model is applied, the black hole mass becomes unreasonably large ( &gt;= 300 M-circle dot). Instead, the slim disk (advection dominated optically thick disk) model is likely to explain the observed super-Eddington luminosities, hard energy spectra, and spectral variations of ULXs. We-suggest that ULXs are accreting black holes with a few tens of solar mass, which is not unexpected from the standard stellar evolution scenario, and that their X-ray emission is from the slim disk shining at super-Eddington luminosities.

We report several important results obtained from recent Galactic Xray survey observations, in particular ASCA Galactic center and plane surveys and our Chandra deep survey on the (l, b) approximate to (28 degrees.5, 0 degrees.0) region. Strong hard X-ray diffuse components are observed from Galactic ridge, center and bulge, and they have both thermal and non-thermal spectral components. Dozens of discrete and extended sources have been discovered on the Galactic plane, which also indicate thermal and/or non-thermal X-ray energy spectra. They are often associated with radio sources and are considered to be SNR candidates. Most of the hard Xray point sources in the outer part of the Galactic plane are considered to be background AGNs, while fraction of the Galactic hard X-ray sources (such as quiescent dwarf novae) increases toward the Galactic center. Most of the soft Xray sources on the Galactic plane are presumably nearby active stars.

We present the results from a multiwavelength campaign of GRS 1915+105 performed from 2000 April 16 to April 25. This is one of the largest coordinated set of observations ever performed for this source, covering the wide energy band in radio (13.3-0.3 cm), near-infrared (J, H, and K bands), X-rays, and gamma rays (from 1 keV to 10 MeV). During the campaign GRS 1915+105 was predominantly in the "plateau" (or low/ hard) state but sometimes showed soft X-ray oscillations: before April 20.3, rapid, quasi-periodic (≃45 minutes) flare-dip cycles were observed. In the spectral energy distribution in the plateau state, optically thick synchrotron emission and Comptonization is dominant in the radio and X- to gamma-ray bands, respectively. The small luminosity in the radio band relative to that in X-rays indicates that GRS 1915+105 falls in the regime of "radio-quiet" microquasars. In three epochs we detected faint flares in the radio or infrared bands with amplitudes of 10-20 mJy. The radio flares observed on April 17 shows frequency-dependent peak delay, consistent with an expansion of synchrotron-emitting region starting at the transition from the hard-dip to the soft-flare states in X-rays. On the other hand, infrared flares on April 20 appear to follow (or precede) the beginning of X-ray oscillations with an inconstant time delay of ≃5-30 minutes. This implies that the infrared-emitting region is located far from the black hole by ≳10 13 cm, while its size is ≲1012 cm constrained from the time variability. We find a good correlation between the quasi-steady flux level in the near-infrared band and in the X-ray band. From this we estimate that the reprocessing of X-rays, probably occurring in the outer parts of the accretion disk, accounts for about 20%-30% of the observed K magnitude in the plateau state. The OSSE spectrum in the 0.05-10 MeV band is represented by a single power law with a photon index of 3.1 extending to ∼1 MeV with no cutoff. We can model the combined GIS-PCA-HEXTE spectra covering 1-200 keV by a sum of the multicolor disk model, a broken power law modified with a high-energy cutoff, and a reflection component. The power-law slope above ∼30 keV is found to be very similar between different states in spite of large flux variations in soft X-rays, implying that the electron energy distribution is not affected by the change of the state in the accretion disk.

We report on the results of an ASCA observation of the Galactic jet source GRO J1655-10 performed from 1997 February 25 to February 28 covering a full orbital period (2.62 d). The averaged 2-10 keV flux was about 1.1 Crab. An absorption line feature centered at 6.8 keV was detected both in the GIS and SIS spectra. We interpret this as a blend of two resonance-absorption K alpha, lines from H-like and He-like iron ions. We can consistently explain both the ASCA spectra and the simultaneous RXTE/PCA spectrum by a combination of K-absorption lines and Ii-absorption edges of iron ions. The fact that the absorption line is stably present over the whole orbital phase implies that the distribution of the highly ionized plasma is not affected by the companion star, which is consistent with its presence around the black hole. A curve of growth analysis shows that the plasma contains velocity dispersion along the line-of-sight larger than 300 km s(-1) attributed to bulk motions. It is probably a part of a geometrically thick accretion flow in turbulent motions with velocities of 500-1600 km s(-1) at an estimated radius of similar to 10(10) cm.

We report observation results of the supersoft X-ray sources CAL 87 and RX J0925.7-4758 with the X-ray CCD cameras (Solid-State Imaging Spectrometers [SISs]) on board ASCA. Because of the superior energy resolution of the SIS (DeltaE/E similar to 10% at 1 keV) relative to previous instruments, we could study detailed X-ray spectral structures of these sources for the first time. We have applied theoretical spectral models to CAL 87 and constrained the white dwarf mass and intrinsic luminosity as 0.8-1.2 M. and 4 x 10(37)-1.2 x 10(38) ergs s(-1), respectively. However, we have found the observed luminosity is an order of magnitude smaller than the theoretical estimate, which indicates that the white dwarf is permanently blocked by the accretion disk, and we are observing a scattering emission by a fully ionized accretion disk corona (ADC) whose column density is similar to1.5 x 10(23) cm(-2). Through simulation we have shown that the orbital eclipse can be explained by the ADC model, such that a part of the extended X-ray emission from the ADC is blocked by the companion star filling its Roche lobe. We have found that very high surface gravity and temperature, similar to 10(10) cm s(-2) and similar to 100 eV, respectively, as well as a strong absorption edge at similar to1.02 keV, are required to explain the X-ray energy spectrum of RX J0925.7-4758. These values are only possible for an extremely heavy white dwarf near the Chandrasekhar limit. Although the supersoft source luminosity should be similar to 10(38) ergs s(-1) at the Chandrasekhar limit, the observed luminosity of RX J0925.7-4758 is nearly 2 orders of magnitude smaller, even assuming an extreme distance of similar to 10 kpc. To explain the luminosity discrepancy, we propose a model in which very thick matter that was previously ejected from the system, as a form of jets, intervenes the line of sight and reduces the luminosity significantly because of Thomson scattering.

We report on the development of the ISAS Ginga archive. At ISAS, all the Ginga archive and analysis software were originally developed on the main-frame computers. We are installing them to the UNIX environment with minor modification so that all the analysis will become possible in the modern network computing environment. The archive will be made public from ISAS PLAIN Center (Center for Planning and information systems) in near future.

The Ultra-luminous Compact X-ray Sources (ULXs) in nearby spiral galaxies and the Galactic super-luminal jet sources share the common spectral characteristic that they have extremely high disk temperatures which cannot be explained in the framework of the standard accretion disk model in the Schwarzschild metric. We have calculated an extreme Kerr disk model to examine if the Kerr disk model can instead explain the observed 'too hot' accretion disk spectra. We found that the Kerr disk spectrum becomes significantly harder compared to the Schwarzschild disk only when the disk is highly inclined. For super-luminal jet sources, which are known to be inclined systems, the Kerr disk model may thus work if we choose proper values for the black hole angular momentum. For the ULXs, however, the Kerr disk interpretation will be problematic, as is is highly unlikely that their accretion disks are preferentially inclined.