辻本 匡弘

We report on a serendipitous detection of an intense X-ray flare from the Tycho reference source on HD 161084 during a Suzaku observation of the galactic center region for similar to 20 ks. The X-ray Imaging Spectrometer recorded a flare from this A1-type dwarf or subgiant star with a flux of similar to 1.4 x 10(-12) erg s(-1) cm(-2) (0.5-10 keV) and a decay time scale of similar to 0.5 hr. The spectrum is hard with a prominent Fe XXV K alpha emission line at 6.7 keV, which is explained by a similar to 5 keV thin-thermal plasma model attenuated by a similar to 1.4 x 10(21) cm(-2) extinction. The low extinction, which is consistent with the optical reddening, indicates that the source is a foreground star toward the galactic center region. Based on a spectroscopic parallax distance of similar to 530 pc, the peak X-ray luminosity amounts to similar to 1 x 10(32) erg s(-1) (0.5-10 keV). This is much larger than the X-ray luminosity of ordinary late-type main-sequence stars, and the X-ray emission is unattributable to a hidden late-type companion that comprises a wide binary system with the A star. We discuss possible nature of HD 161084, and suggest that it is most likely an interacting binary with elevated magnetic activity in the companion, such as the Algol-type system. The flux detected by Suzaku during the burst is similar to 100-times larger than the quiescent level measured using the archived XMM-Newton and Chandra data. The large flux amplification makes this star a unique example among sources of this class.

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).

We report on the detection of a transient X-ray source toward the Small Magellanic Cloud (SMC) using the X-ray Imaging Spectrometer (XIS) on board the Suzaku telescope. The source was detected at the edge of the XIS image during a routine observation of the calibration source 1E0102.2-7219, a supernova remnant in the SMC. We constrained the source position using ray-tracing simulations. No such transient source was found at the position in the other Suzaku observations, nor in all of the available archived images of other X-ray missions for the last similar to 28 years. The XIS spectrum can be explained by a single blackbody with a temperature of similar to 72 eV, and an interstellar extinction of similar to 4.9 x 10(20) H atoms cm(-2), consistent with the value to the SMC. An additional absorption edge at similar to 0.74 keV was also confirmed, which is presumably due to absorption by helium-like oxygen ions. Assuming that the source is at the distance of the SMC, the X-ray luminosity in the 0.2-2.0 keV band is similar to 10(37) erg s(-1) and the radius of the source is similar to 10(8) cm. The XIS light curve shows about a two-fold decline in X-ray flux during the 24 ks observation. Together with the archived data, the X-ray flux in the burst is at least three-orders of magnitude brighter than the undetected quiescent level. All of these properties are often seen among supersoft sources (SSSs). We conclude that the transient source is another example of SSS in the SMC.

We present the results of a Suzaku spectroscopic study of soft extended X-ray emission in the H II region of M17. 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 Kα lines of highly ionized O, Ne, and Mg as well as L-series complex of Fe at 0.51.5 keV. 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 ∼ 3.0 ± 0.4MK, (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 ∼ 2, (4) both the plasma temperature and the chemical composition of the diffuse emission show no spatial variation across the studied spatial scale of ∼ 5 pc. © 2008. Astronomical Society of Japan.

We present the results of a Suzaku study of a bright point-like source in the 6.7 keV intensity map of the Galactic center region. We detected an intense Fe XXV 6.7 keV line with an equivalent width of ∼ 1 keV as well as emission lines of highly ionized Ar and Ca from a spectrum obtained by the X-ray Imaging Spectrometer. The overall spectrum is described very well by a heavily absorbed (∼ 2 × 1023 cm-2) thin thermal plasma model with a temperature of 3.8 ± 0.6keV and a luminosity of ∼ 3 × 1034 erg s_1 (2.0-8.0 keV) at 8 kpc. The absorption, temperature, luminosity, and the 6.7 keV line intensity were confirmed with the archived XMM-Newton data. The source has a very red (J - Ks = 8.2 mag) infrared spectral energy distribution (SED), which was fitted by a blackbody emission of ∼ 1000 K attenuated by a visual extinction of ∼ 31 mag. The high plasma temperature and the large X-ray luminosity are consistent with a wind-wind colliding Wolf-Rayet binary. The similarity of the SED to those of the eponymous Quintuplet cluster members suggests that the source is a WC-type source. © 2008. Astronomical Society of Japan.

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.

We are developing a normal incident X-ray telescope with an adaptive optics system in order to achieve an unprecedented high-angular-resolution. The primary mirror with a diameter of 80mm is a spherical shape with a focal length of 2000 mm, which was coated by Mo/Si multilayer. The secondary mirror is a deformable mirror with 55 mm diameter, which was also coated by Mo/Si multilayer. Optical lights from a pin-hole were measured by a wave-front sensor and used as a reference for a correction of the deformable mirror. All the components were installed in a vacuum chamber. A closed loop control with the wave front sensor and the deformable mirror was successfully performed in the telescope and we confirmed the correction of the wave front. The rms-deviation of a performed wave front from a target shape during the control was ∼30 nm-rms, whereas it without control was more than ∼80 nm-rms. A 13.5 nm X-ray from an electron impact X-ray source was imaged on a backside CCD installed on a focal plane. A mesh made by steel was installed in front of the X-ray source, whose pitch and wire-thickness are 500 micro-m and 50 micro-m. The image of this mesh by optical lights from the X-ray generator is detected by the CCD. The current image quality is ∼2.4 arc-sec and this was comparable to a diffraction limit of an optical wave length with our 80mm primary mirror.

Anaplastic meningiomas recur locally more frequently than benign meningiomas, but pulmonary metastasis by anaplastic meningiomas is uncommon. We report a rare case in which both local recurrence and multiple pulmonary metastases by an intracranial meningioma were clearly demonstrated by gadolinium-enhanced MR imaging after repeated craniotomies and radiotherapies.

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. © 2007. Astronomical Society of Japan.

Detailed models for the density and temperature profiles of gas and dust in protoplanetary disks are constructed by taking into account X-ray and UV irradiation from a central T Tauri star, as well as dust size growth and settling toward the disk midplane. The spatial and size distributions of dust grains are numerically computed by solving the coagulation equation for settling dust particles, with the result that the mass and total surface area of dust grains per unit volume of the gas in the disks are very small, except at the midplane. The H2 level populations and line emission are calculated using the derived physical structure of the disks. X-ray irradiation is the dominant heating source of the gas in the inner disk and in the surface layer, while the UV heating dominates otherwise. If the central star has strong X-ray and weak UV radiation, the H2 level populations are controlled by X-ray pumping, and the X-ray-induced transition lines could be observable. If the UV irradiation is strong, the level populations are controlled by thermal collisions or UV pumping, depending on the dust properties. As the dust particles evolve in the disks, the gas temperature at the disk surface drops because the grain photoelectric heating becomes less efficient. This makes the level populations change from LTE to non-LTE distributions, which results in changes to the line ratios. Our results suggest that dust evolution in protoplanetary disks could be observable through the H2 line ratios. The emission lines are strong from disks irradiated by strong UV and X-rays and possessing small dust grains; such disks will be good targets in which to observe H2 emission. © 2007. The American Astronomical Society. All rights reserved.

We present the results of a joint Suzaku and Chandra X-ray spectroscopic study of the Arches cluster in the Galactic center region. The superb spectroscopic performance of XIS on-board Suzaku brought a tight constraint of the spectrum of the Arches X-rays. We found that the spectrum consists of a thermal plasma, a hard power-law tail, and two Gaussian components. The plasma component with a temperature of～2.2keV is established from highly ionized Ca XIX and Fe XXV Kα emission lines as well as the lack of Fe XXVI Kα line. The two Gaussian lines represent the Kα and Kβ lines from iron at lower ionization stages at～6.4keV and～7.1keV. Both the line centers and the intensity ratio of these two lines are consistent with the neutral iron. The hard power-law tail with a photon index of～0.7 was found to have no pronounced iron K edge feature. In comparison with ACIS spectra constructed separately for point-like and diffuse emission by using the unprecedented spatial capability of Chandra, we conclude that the thermal component is from the ensemble of point-like sources plus thermal diffuse emission concentrated at the cluster center, while the Gaussian and the hard tail components are from the non-thermal diffuse emission extended in a larger scale. In the band-limited images of the XIS field, the distribution of the 7.5-10.0keV emission resembles that of the 6.4keV emission, including the local excess at the Arches cluster. This strongly suggests that the power-law emission is related to the 6.4 and 7.1keV lines in the underlying physics. The full discussion can be found in Tsujimoto et al. [M. Tsujimoto, Y. Hyodo and K. Koyama, Publ. Astron. Soc. Jpn. 59 (2007), S229]. For point-like X-ray emission, three Arches sources are exceptionally bright among cluster members. The brightest spectrum of them requires two temperature plasma with an extinction of 2×10^<23> cm^<-2>. The estimated hard-band luminosity of&ap;10^<35> erg s^<-1>, which is brighter than any known stellar sources in our Galaxy, might be a consequence of colliding wind shocks with an extreme mass loss rate (～10^<-4> M_&029BF yr^<-1>) indicated from near-infrared and radio continuum observations.

We present the results of a high-resolution X-ray imaging study of the stellar population in the Galactic massive star-forming region RCW 49 and its central OB association Westerlund 2. We obtained a ∼40 ks X-ray image of a ∼ 17′ × 17′ field using the Chandra X-Ray Observatory and deep NIR images using the Infrared Survey Facility in a concentric ∼ 8.3′ × 8.3′ region. We detected 468 X-ray sources and identified optical, NIR, and Spitzer MIR counterparts for 379 of them. The unprecedented spatial resolution and sensitivity of the X-ray image, enhanced by optical and infrared imaging data, yielded the following results: (1) The central OB association Westerlund 2 is resolved for the first time in the X-ray band. X-ray emission is detected from all spectroscopically identified early-type stars in this region. (2) Most (∼86%) X-ray sources with optical or infrared identifications are cluster members in comparison with a control field in the Galactic plane. (3) A loose constraint (2-5 kpc) for the distance to RCW 49 is derived from the mean X-ray luminosity of T Tauri stars. (4) The cluster X-ray population consists of low-mass pre-main-sequence and early-type stars as obtained from X-ray and NIR photometry. About 30 new OB star candidates are identified. (5) We estimate a cluster radius of 6′-7′ based on the X-ray surface number density profiles. (6) A large fraction (∼90%) of cluster members are identified individually using complimentary X-ray and MIR excess emission. (7) The brightest five X-ray sources, two Wolf-Rayet stars and three O stars, have hard thermal spectra. © 2007. The American Astronomical Society. All rights reserved.

We present the first high spatial resolution X-ray study of the massive star-forming region NGC 6357, obtained in a 38 ks Chandra/ACIS observation. Inside the brightest constituent of this large H H region complex is the massive open cluster Pismis 24. It contains two of the brightest and bluest stars known, yet remains poorly studied; only a handful of optically bright stellar members have been identified. We investigate the cluster extent and initial mass function and detect ∼800 X-ray sources with a limiting sensitivity of ∼1030 ergs s-1; this provides the first reliable probe of the rich intermediate-mass and low-mass population of this massive cluster, increasing the number of known members from optical study by a factor of ∼50. The high-luminosity end (log Lh[2-8 keV] ≥ 30.3 ergs s-1) of the observed X-ray luminosity function in NGC 6357 is clearly consistent with a power-law relation as seen in the Orion Nebula Cluster and Cepheus B, yielding the first estimate of NGC 6357's total cluster population, a few times the known Orion population. We investigate the structure of the cluster, finding small-scale substructures superposed on a spherical cluster with 6 pc extent, and discuss its relationship to the nebular morphology. The long-standing LX - 10-7 Lbol correlation for O stars is confirmed. Twenty-four candidate O stars and one possible new obscured massive YSO or Wolf-Rayet star are presented. Many cluster members are estimated to be intermediate-mass stars from available infrared photometry (assuming an age of ∼1 Myr), but only a few exhibit K-band excess. We report the first detection of X-ray emission from an evaporating gaseous globule at the tip of a molecular pillar; this source is likely a BO-B2 protostar. © 2007. The American Astronomical Society. All rights reserved.

We have carried out near-infrared (NIR) imaging observations of the Carina Nebula for an area of ∼400 arcmin2 including the clusters Trumpler 14 and Trumpler 16, with 10 σ limits of J ∼ 18.5, H ∼ 17.5, and Ks ∼ 16.5 mag. A total of 544 Class II candidates, 11 Class I candidates, and 40 red (H - Ks > 2) sources have been found. The majority of the Class II candidates are found to be distributed toward the clusters, whereas most of the red NIR sources are concentrated to the southeast of Trumpler 16, along the V-shaped dust lane. We found indications of ongoing star formation near the three MSXsources, G287.51-0.49, G287.47-0.54, and G287.63-0.72, where red NIR sources and X-ray sources are seen. In particular, two hard X-ray sources are identified near G287.47-0.54, one of which does not have an NIR counterpart and may be associated with a Class I/Class 0 object. The color-magnitude diagrams of the clusters suggest very young stellar population (< 3 Myr). The Ks-band luminosity function ( KLF ) of Trumpler 14 shows a sharp peak at the faint end, likely due to the onset of deuterium burning. The KLF of Trumpler 16, in contrast, rises smoothly until it turns over. The slopes of the mass functions derived for the clusters are in agreement with the canonical Salpeter value for the field stars. © 2007. The American Astronomical Society. All rights reserved.

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 η 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. © 2007. Astronomical Society of Japan.

We present the results of a Suzaku study of the Arches cluster in the Galactic center region. A high signal-to-noise ratio spectrum in the 3-12 keV band was obtained with the X-ray Imaging Spectrometer (XIS) onboard the Suzaku observatory. We found that the spectrum consists of a thermal plasma, a hard power-law tail, and two Gaussian line components. The plasma component with a temperature of ∼ 2.2keV is established from the presence of Ca XIX and Fe XXV Kα lines as well as absence of the Fe XXVI Kα line. The two Gaussian lines represent the Kα and Kβ lines from iron at lower ionization stages at ∼ 6.4 and ∼ 7.1 keV. Both the line centers and the intensity ratio of these two lines are consistent with neutral iron. The hard power-law tail with a photon index of ∼ 0.7 was found to have no pronounced iron K edge feature. Compared with the published Chandra spectra constructed separately for point-like and diffuse emission, we conclude that the thermal component is from an ensemble of point-like sources plus thermal diffuse emission concentrated at the cluster center, while the Gaussian and the hard tail components are from non-thermal diffuse emission extended in a larger scale. In band-limited images of the XIS field, the distribution of the 7.5-10.0 keV emission resembles that of the 6.4 keV emission, including local excess at the Arches cluster. This strongly suggests that the power-law emission is related to the 6.4 and 7.1 keV lines in the underlying physics. We discuss two ideas to explain both the hard continuum and the lines: (1) X-ray photoionization that produces fluorescence lines and the Thomson scattering continuum and (2) non-thermal electron impact ionization of iron atoms and bremsstrahlung continuum. However, whichever scenario is adopted, the photon or particle flux from the Arches cluster is too low to account for the observed lines and continuum intensity. © 2007. Astronomical Society of Japan.

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.

We report the current status of the "X-mas" (X-ray milli-arcsecond) project. X-mas is an application of the AO technology to the X-ray optics, aiming to obtain high-resolution defraction-limited X-ray images. Our X-ray telescope employs the Newton optics with a paraboloid primary and a 31-element deformable secondary mirrors. The aperture of the primary mirror is 80 millimeters with the focal length of 2 meters. Multi-layer coating of the mirrors by silicon and molybdenum realizes a large reflectivity of ∼60% for the primary and 30-50% for the secondary mirror at 13.5 nm, which enables us to construct a normal incidence optics at this wavelength. We use a laser guide source and a wave front sensor to optimize the form of the secondary deformable mirror for the purpose of offsetting the large-scale figure errors in the X-ray optics. A back-side illumination X-ray CCD detector manufactured by Hamamatsu Photonics is used for X-ray detections. We have assembled all these elements and started to accumulate data. Closed-loop AO is in operation for the laser guide source. Likely X-ray images are obtained through the telescope. The results in 2005-2006 are presented.

The Cepheus B (Cep B) molecular cloud and a portion of the nearby Cep OB3b OB association, one of the most active regions of star formation within 1 kpc, have been observed with the ACIS detector on board the Chandra X-Ray Observatory. We detect 431 X-ray sources, of which 89% are confidently identified as clustered pre-mainsequence (PMS) stars. Two main results are obtained. First, we provide the best census to date for the stellar population of the region. We identify many members of two rich stellar clusters: the lightly obscured Cep OB3b association and the deeply embedded cluster in Cep B, whose existence was previously traced only by a handful of radio sources and T Tauri stars. Second, we find a discrepancy between the X-ray luminosity functions of the Cep OB3b and the Orion Nebula cluster. This may be due to the different initial mass functions of the two regions (an excess of ≃0.3 M ⊙ stars) or different age distributions. Several other results are obtained. A diffuse X-ray component seen in the field is attributed to the integrated emission of unresolved low-mass PMS stars. The X-ray emission from HD 217086 (O7n), the principle ionizing source of the region, follows the standard model, involving many small shocks in an unmagnetized radiatively accelerated wind. X-ray source 294 joins a number of similar superflare PMS stars for which long magnetic structures may connect the protoplanetary disk to the stellar surface. © 2006. The American Astronomical Society. All rights reserved.

We report the Chandra detection of hard X-ray emission from the Welch ring in W49A, an organized structure of ultracompact (UC) H II regions containing a dozen nascent early-type stars. Two UC H II regions are associated with hard X-ray emission in a deep Advanced CCD Imaging Spectrometer (ACIS) image exposed for ∼96.7 ks. One of the two X-ray sources has no near-infrared counterpart and is extended by ∼5″, or ∼0.3 pc, at a distance of ∼11.4 kpc, which is spatially aligned with the cometary radio continuum emission associated with the UC H II region. The X-ray spectrum of the emission, when fit with a thermal model, indicates a heavily absorbed plasma with extinction of ∼5 × 1023 cm-2, temperature ∼7 keV, and X-ray luminosity in the 3.0-8.0 keV band of ∼3×133 ergs s-1. Both the luminosity and the size of the emission resemble the extended hard emission found in UC H II regions in Sagittarius B2, yet they are smaller by an order of magnitude than the emission found in massive star clusters such as NGC 3603. Three possibilities are discussed for the cause of the hard extended emission in the Welch ring: an ensemble of unresolved point sources, shocked interacting winds of the young O stars, and a wind-blown bubble interacting with ambient cold matter. © 2006. The American Astronomical Society. All rights reserved.

We report a new type X-ray imaging polarimeter: a multi-layer-coated CCD. When the X-rays are detected by the CCD, with the incident angle of 45 deg, through the coated multi-layer, the transmissions of the P and S polarized photons are different from each other and we can get an image with a selected position angle of the polarization.By the simulation of the transmission of the multi-layer, we designed an optimal number of the layer-pair and their thickness. The target wave length is 135 angstrom, because the Mo/Si multi-layer has a good performance in this energy range. If the dead layer of the back-side CCD is 1000 angstrom, nine layer-pairs make the largest difference between the P and S transmission.We deposited the Mo/Si multi-layer directly on a back-side CCD. The CCD was exposed to the polarized photons from synchrotron radiation with 45 deg incident angle. The detected intensity is measured as a function of the photon energy and of the rotation angle around the photon beam. The detection of the polarization is confirmed. However the measured performance is lower than expected. Some possibilities of the cause are discussed.

We present the result of a coherent search for the iron K α fluorescent line at ∼6.4 keV among 1616 X-ray sources detected by ultra-deep Chandra observations of the Orion Nebula Cluster (ONC) - Chandra Orion Ultra-deep Project (COUP). Seven sources are identified to have an excess emission at 6.4 keV among 127 control sample sources with significant counts in the 6.0-9.0 keV band. These seven sources are 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 >1 × 1022 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.

We are developing a soft x-ray telescope with an adaptive optics system for future astronomical observation with very fine angular resolution of an order of milli-arc-second. From a technical point of view, we are trying to develop a normal incident telescope with multi layers. Thus the wave length is limited to be around 13.5 nm with a band pass of roughly 1nm. Since the x-ray telescope must be installed on a satellite, a stable conditions of temperature, gravity etc, can not be expected. Therefore, we investigate to use an adaptive optics system using an optical light source attached in the telescope. In this paper, we report our present status of the development. The primary mirror is an off-axis paraboloid with 80 mm effective diameter and 2 m focal length. This mirror has been coated with Mo/Si multi-layers. The reflectivity of the 13.5 nm x rays is ranging from 35% to 55%. We use a deformable mirror for the secondary mirror, which has also been coated with Mo/Si multi-layers. This mirror consists of 31 element-bimorph-piezo electrodes. The surface roughness of the mirror is ∼6 nm rms. The reflectivity of the 13.5 nm x rays is roughly 65%. The adaptive optics system using an optical laser and a wave front sensor has been performed. We are using a shack-hartmann sensor (HASO 32) with a micro-lens array and a CCD. A pin hole with one micron diameter is used for the optical light source. The precision of the measurement of the wave front shape is a few nm. X-ray exposure test is now conducting, although the optical adaptive optics system is not yet installed. The x-ray detector is a back illumination CCD. The quantum efficiency for 13.5 nm x ray is ∼50%. The pixel size is 24 micron square. X-ray source is an electron impact source with an Al/Si alloy target. We confirmed that the x-ray intensity around 13.55 nm is bright enough for our experiment. The imaging performance is now trying to improve and the adaptive optics system will be installed in this year.

We present new velocity-resolved spectra of the [Fe II] λ1.644 μm line emission toward the L1551 IRS 5 outflow. The spectra were taken toward the bright [Fe II] knots PHK 1 and PHK 2 with the slit positions perpendicular to the northern jet. We have two major conclusions: (1) At PHK 1, located 1″.2 away from the L1551 IRS 5 VLA sources, the spatial profile of the low radial velocity component at VLSR ∼ -110 km s -1 shows two spatial subcomponents with their FWHMs of 0″.83 and 2″.84. The wide subcomponent has an wide opening angle of ∼ 100°, which is consistent with the opening angle suggested by the broad velocity width of the narrow one. It favors the interpretation that both subcomponents of the low-velocity component arise from the same outflow. The gas corresponding to the wide subcomponent fills the space between the optical jet and the shell of the CO molecular outflow and may be sweeping up envelope material in the vicinity of the protostars. (2) At PHK 2, located ∼4″.2 away from the VLA sources, we confirmed that the northern jet has two radial velocity components: VLSR ∼ -270 and -140 km s-1. The former velocity component is highly collimated because it has the same spatial width of 0″.78 at both of the two [Fe II] knots.

We present a description of the data reduction methods and the derived catalog of more than 1600 X-ray point sources from the exceptionally deep 2003 January Chandra X-Ray Observatory (Chandra) observation of the Orion Nebula Cluster and embedded populations around OMC-1. The observation was obtained with Chandra's Advanced CCD Imaging Spectrometer (ACIS) and has been nicknamed the Chandra Orion Ultradeep Project (COUP). With an 838 ks exposure made over a continuous period of 13.2 days, the COUP observation provides the most uniform and comprehensive data set on the X-ray emission of normal stars ever obtained in the history of X-ray astronomy © 2005. The American Astronomical Society. All rights reserved.

We present the result of a systematic search for the iron Kα fluorescent line at ∼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 ∼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 ≳ 1 × 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. © 2005. The American Astronomical Society. All rights reserved.

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 ∼ 17′ × 17′ region with a ∼ 68 ks ACIS exposure down to the X-ray flux limit of ∼10 -15 ergs s -1 cm -2 (0.5-8 keV), for which we conduct follow-up NIR imaging observations in a concentric ∼11′ × 11′ region with FLAMINGOS down to m Ks ∼ 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 ≳3.2 in the 2-10 μm wavelength range. © 2005. The American Astronomical Society. All rights reserved.

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) ≈ (28°5.0°0), where no discrete X-ray source had been reported previously. We have detected 274 new point X-ray sources (4 σ confidence), as well as strong Galactic diffuse emission within two partially overlapping ACIS-I fields (∼250 arcmin2 in total). The point-source sensitivity was ∼3 × 10-15 ergs s-1 cm -2 in the hard X-ray band (2-10 keV) and ∼2 × 10 -16 ergs s-2 cm-2 in the soft band (0.5-2 keV). The sum of all the detected point-source fluxes accounts for only ∼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 ∼3 × 10-15 ergs s-1 cm-2 (2-10 keV), we have determined the Galactic diffuse X-ray flux to be 6.5 × 10 -11 ergs s-1 cm-2 deg-2 (2-10keV). 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 mainsequence 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 ≳104 cataclysmic variables in the entire Galactic plane fainter than ∼2 × 1033 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. © 2005. The American Astronomical Society. All rights reserved.

We report the results of a search for 6.4 keV Fe fluorescent emission in Young Stellar Objects (YSOs) with measured accretion luminosities in the ρ Oph cloud, using the existing Chandra and XMM-Newton observations of the region. A total of nine such YSOs have X-ray data with sufficiently high S/N for the 6.4 keV line to be potentially detected if present. A positive detection of the Fe 6.4 keV line is reported for one object, Elias 29, in both the XMM-Newton and the Chandra data. The 6.4 keV line is detected in Elias 29 both during quiescent and flaring emission, unlikely all previously reported detections of 6.4 keV Fe fluorescence in YSOs which were made during intense flaring. The observed equivalent width of the fluorescent line is large, Wα ≃ 160 eV, ruling out fluorescence from diffuse circumstellar material. It is also larger than expected for simple reflection from a solar-composition photosphere or circumstellar disk, but it is compatible with being due to fluorescence from a centrally illuminated circumstellar disk. The X-ray spectrum of Elias 29 is also peculiar in terms of its high (ionized) Fe abundance, as evident from the very intense Fe XXV 6.7 keV line emission; we speculate on the possible mechanism leading to the observed high abundance. © ESO 2005.

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.

We propose a new type of wide band X-ray imaging spectrometer as a focal plane detector of the super mirror onboard on future X-ray missions including post Astro-E2. This camera is realized by the hybrid of back illumination CCDs and a back supportless CCD for 0.05-10 keV band, and a Micro Pixel Gas Chamber detecting X-rays at 10-80 keV. © 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

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 counter-part 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 ∼2 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 ∼42% 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.

We present the Chandra Advanced CCD Imaging Spectrometer and ASCA Gas Imaging Spectrometer results for a series of four long-term observations on DoAr 21, ROXs 21, and ROXs 31, the X-ray-brightest T Tauri stars in the ρ Ophiuchi cloud. In the four observations with a net exposure of ∼600 ks, we found six, three, and two flares from DoAr 21, ROXs 21, and ROXs 31, respectively; hence, the flare rate is fairly high. The spectra of DoAr 21 are well fitted with a single-temperature plasma model, while those of ROXs 21 and ROXs 31 need an additional soft plasma component. Since DoAr 21 is younger (∼105 yr) than ROXs 21 and ROXs 31 (∼106 yr), these results may indicate that the soft component gradually increases as T Tauri stars age. The abundances are generally subsolar and vary from element to element. Both high first ionization potential (FIP) and low-FIP elements show enhancement over the mean abundances. An unusual giant flare is detected from ROXs 31. The peak luminosity and temperature are ∼1033 ergs s-1 and ∼10 keV, respectively. The temperature reaches its peak value before the flux maximum and is nearly constant (4-5 keV) during the decay phase, indicating successive energy release during the flare. The abundances and absorption show dramatic variability from the quiescent to flare phase.

We report X-ray results of the Chandra observation of OMC-2 and OMC-3. A deep exposure of ∼100 ks detects ∼400 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.

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 H2 v = 1-0 S(l) 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.

We present a new method for estimating the thickness of the depletion layer of an X-ray CCD without a calibrated X-ray source. It is known that a high-energy particle continuously loses its energy when it passes through a material, and that its total-energy loss in a thin material depends on the thickness of the material. We irradiated a Hamamatsu-CCD (CCD-CREST Deep 1) with a conversion β-ray source 207Bi which emits monoenergetic β-rays, then obtained an energy-loss distribution. In comparison with an energy-loss distribution simulated with Geant4, we found that the CCD-CREST has a depletion layer thickness of ∼6.7 μm, which is consistent with the result using a calibrated X-ray source. Since it is difficult to obtain a calibrated X-ray source, our method is useful for estimating a depletion layer thickness. © 2002 Elsevier Science B.V. All rights reserved.

We present results of an X-ray search from bona fide and candidate brown dwarfs in the ρ Ophiuchi cloud cores with the Chandra X-ray Observatory. The selected areas are two fields near the cloud center and are observed with the ACIS-I array of a 17′ × 17′ size and a ∼ 100 ks exposure. Among 18 bona fide and candidate brown dwarfs listed by the infrared spectroscopy, we find X-ray emission from seven sources above 99.9% confidence level. Therefore, ∼ 40% of the infrared-selected brown dwarfs in this cloud emit X-rays. For the brightest four sources, the X-ray spectra are made and are fitted with a thin-thermal plasma model of a temperature 1-2.5 keV. The X-rays are also time variable with rapid flares from two of the brown dwarfs. Assuming 2 keV temperature and using the empirical relation of Av versus NH, we estimate the X-ray luminosity or its upper limit of the other faint or non-X-ray sources. The X-ray luminosity (Lx) of the X-ray-detected sources is in the range of 0.3-90 × 1028 ergs s-1, while the luminosity ratio of X-ray to bolometric (Lx/Lbol) is 10-5 -10-3, similar to those of low-mass premain-sequence and dMe stars. All these results suggest that the X-ray origin of brown dwarfs is the same as low-mass stars; strong magnetic activity at the stellar surface.

We present an ASCA discovery of diffuse hard X-ray emission from the Sgr C complex with its peak in the vicinity of the molecular cloud core. The X-ray spectrum is characterized by a strong 6.4 keV line and large absorption. These properties suggest that Sgr C is a new X-ray reflection nebula that emits fluorescent and scattered X-rays via irradiation from an external X-ray source. We found no adequately bright source in the immediate Sgr C vicinity to fully account for the fluorescence. The irradiating source may be the Galactic nucleus Sgr A*, which was brighter in the past than it is now, as is suggested from observations of the first X-ray reflection nebula Sgr B2.

The Advanced Satellite for Cosmology and Astrophysics (ASCA) has made multiple observations of the Small Magellanic Cloud (SMC). X-ray mosaic images in the soft (0.7-2.0 keV) and hard (2.0-7.0 keV) bands are separately constructed, and the latter provides the first hard X-ray view of the SMC. We extract 39 sources from the two-band images with a criterion of S/N > 5 and conduct timing and spectral analyses for all of these sources. Coherent pulsations are detected from 12 X-ray sources, five of which are new discoveries. Most of the 12 X-ray pulsars are found to exhibit long-term flux variabilities; hence they are likely to be X-ray binary pulsars (XBPs). On the other hand, we classify four supernova remnants (SNRs) as thermal SNRs, because their spectra exhibit emission lines from highly ionized atoms. We find that XBPs and thermal SNRs in the SMC can be clearly separated by their hardness ratio (the ratio of the count rate between the hard and soft bands). Using this empirical grouping, we find many XBP candidates in the SMC, although no pulsations have yet been detected from these sources. Possible implications on the star formation history and evolution of the SMC are presented by a comparison of the source populations in the SMC and our Galaxy.