Hiroshi Murakami

ASCA X-Ray Source Catalog in the Galactic Center Region

The ASCA satellite made 107 pointing observations on a 5 × 5 deg2 region around the center of our Galaxy from 1993 to 1999. In the X-ray images of the 0.7-3 keV or 3-10 keV bands, we found 52 point sources and a dozen diffuse sources. All the point sources are uniformly fitted with an absorbed power-law model. For selected bright sources, Sgr A*, AX J1745.6-2901, A1742-294, SLX 1744-300, GRO J1744-28, SLX 1737-282, GRS 1734-292, AX J1749.2-2725, KS 1741-293, GRS 1741.9-2853, and an unusual flare source XTE J1739-302, we present further detailed spectral and timing analyses and discuss their nature. The dozen extended X-ray sources comprise radio supernova remnants, giant molecular clouds, and some new discoveries. Most show emission lines from either highly ionized atoms or low-ionized irons. The X-ray spectra were fitted with either a thin thermal or power-law model. This paper summarizes the results and provides the ASCA X-ray source catalog in the Galactic center region.

ASCA Observations of the Sagittarius B2 Cloud: An X-Ray Reflection Nebula

We present the ASCA results of imaging spectroscopy of the giant molecular cloud Sgr B2. The X-ray spectrum is found to be very peculiar; it exhibits a strong emission line at 6.4 keV, a low-energy cutoU below about 4 keV, and a pronounced edge structure at 7.1 keV. The X-ray image is extended, and its peak position is shifted from the core of the molecular cloud toward the Galactic center by about 1@¨2@. The X-ray spectrum and the morphology are well reproduced by a scenario that X-rays from an external source located in the Galactic center direction are scattered by the molecular cloud Sgr B2 and come into our line of sight. Thus, Sgr B2 may be called an X-ray re—ection nebula. Possible implications of the Galactic center activity related to this unique source are presented. Subject headings: Galaxy: abundancesGalaxy: centerISM: clouds ¨ ISM: individual (Sagittarius B2) ¨ X-rays: ISM

ASCA Detection of a Superhot 100 Million K X‐Ray Flare on the Weak‐lined T Tauri Star V773 Tauri

We present results of a ≈ 40 ks ASCA observation of the active weak-lined T Tauri star V773 Tau (HD 283447) and the surrounding Barnard 209 dark cloud, obtained in 1995 February. During this observation, V773 Tau exhibited a dramatic X-ray flare, with the X-ray count rate increasing rapidly by a factor of ~20, then decreasing exponentially with an e-folding timescale of ≈ 2.3 hr. The peak flare luminosity was at least ~1033 ergs s-1 (0.7-10 keV; distance = 150 pc), which is among the highest X-ray luminosities observed to date for T Tauri stars. The total energy release was ~1037 ergs. However, the most spectacular aspect of this flare was its temperature, which reached a maximum value of at least 100 million K. Spectral fits near flare maximum give a temperature of ~10 keV, which slowly declined to a value ~6 keV at the end of the observation. These temperature measurements are based on high signal-to-noise ratio spectra, and provide the first unambiguous evidence for superhot flaring plasma at temperatures of ~108 K in T Tauri stars. A simple cooling-loop model gives electron densities that are similar to those of solar flares, but requires loop sizes that are comparable to or larger than the star itself. The flare showed other interesting behavior, including a high (and possibly variable) absorption column density, NH = 4 × 1022 cm-2, and an apparent increase in the global metal abundance during the flare.

Chandra Observations of Diffuse X-Rays from the Sagittarius B2 Cloud

We present the first Chandra results of the giant molecular cloud Sagittarius B2 (Sgr B2), located about 100 pc away from the Galactic center. Diffuse X-rays are clearly separated from one-and-a-half-dozen resolved point sources. The X-ray spectrum exhibits pronounced iron K-shell transition lines at 6.40 keV (Kα) and 7.06 keV (Kβ), deep iron K-edge at 7.11 keV, and large photoelectric absorption at low energy. The absorption-corrected X-ray luminosity is ~1 × 1035 ergs s-1, 2 orders of magnitude larger than the integrated luminosity of all the resolved point sources. The diffuse X-rays come mainly from the southwest half of the cloud with a concave shape pointing to the Galactic center direction. These results strongly support the ASCA model that Sgr B2 is irradiated by an X-ray source at the Galactic center side.

CHANDRA HIGH-RESOLUTION SPECTROSCOPY OF THE ABSORPTION-LINE FEATURES IN THE LOW-MASS X-RAY BINARY GX 13+1

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 Kabsorption 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 � 400 km s � 1 corrected for the proper motion, with a line-of-sight velocity dispersion of 490 þ110 � 140 km s � 1 . The plasma is photoionized with an ionization parameter of log� 4:1 4:7. The inferred mass outflow rate is 0:7 ; 10 18 gs � 1 or higher, comparable to the mass accretion rate (10 18 gs � 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 � 10 10 -10 11 cm with a density k10 13 cm � 3 . Subject headings: stars: individual (GX 13+1) — X-rays: binaries — X-rays: stars

Characteristics of genomic breakpoints in TLS-CHOP translocations in liposarcomas suggest the involvement of Translin and topoisomerase II in the process of translocation

Fusion of TLS/FUS and CHOP gene by reciprocal translocation t(12;16)(q32;q16) is a common genetic event found in myxoid and round-cell liposarcomas. Characterization of this genetic event was performed by three methods, Southern blot, RTu2009–u2009PCR, and genomic long-distance PCR in nine myxoid and three round-cell liposarcomas. All but one tumors showed genetic alternations indicating the fusion of TLS/FUS and CHOP gene. Two novel types of fusion transcripts were found, of which one lacked exon 2 sequence of CHOP gene, and the other lacked 3′ half of exon 5 of TLS gene. The latter case was caused by a cryptic splicing site which was created by the genomic fusion. Detailed analyses genomic fusion points revealed several sequence characteristics surrounding the fusion points. Homology analyses of breakpoint sequences with known sequence motifs possibly involve in the process of translocation uncovered Translin binding sequences at both of TLS/FUS and CHOP breakpoints in two cases. Translocations were always associated with other genetic alterations, such as deletions, duplications, or insertions. Short direct repeats were almost always found at both ends of deleted or duplicated fragments some of which had apparently been created by joining of sequences that flank the rearrangement. Finally, consensus topoisomerase II cleavage sites were found at breakpoints in all cases analysed, suggesting a role of this enzyme in creating staggered ends at the breakpoint. These data suggested that sequence characteristics may play an important role to recruit several factors such as Translin and topoisomerase II in the process of chromosomal translation in liposarcomas.

High incidence of SV40-like sequences detection in tumour and peripheral blood cells of Japanese osteosarcoma patients

Recent studies have revealed the evidence for the significance of SV40 genome in human malignancies. In this paper, the presence of SV40-like sequences was investigated in 54 Japanese osteosarcomas in which mutations of the retinoblastoma (Rb), p53, MDM2, and CDK4 genes had been already analysed. Using polymerase chain reaction and Southern hybridization, SV40-like sequences were detected in 25 cases (46.3%). In most cases, only a part of SV40 genome was detected, and the regulatory region containing enhancer sequences was most frequently found (21/54, 38.9%). There was no apparent relationship between the presence of SV40-like sequences and tumour suppressor genes mutations in each tumour. The SV40-like sequences were also detected in peripheral blood cells of substantial proportion of the patients (43.3%), whereas the incidence was much lower (4.7%) in normal healthy controls. This difference is statistically highly significant (P< 0.0001), suggesting that the presence of SV40-like sequences, even if only a part, may play some roles to predispose individuals to osteosarcoma.

ASCA Discovery of Diffuse 6.4 keV Emission near the Sagittarius C Complex: A New X-Ray Reflection Nebula

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.

DALI2: A NaI(Tl) detector array for measurements of

A NaI(Tl) detector array called DALI2 (Detector Array for Lo w Intensity radiation 2) has been constructed for in-beam γ-ray spectroscopy experiments with fast radioactive isotope (R I) beams. It consists typically of 186 NaI(Tl) scintillator s covering polar angles from∼15◦ to ∼160◦ with an average angular resolution of 6 ◦ in full width at half maximum. Its high granularity (good angular resolution) enables Doppler-shift correcti ons that result in, for example, 10% energy resolution and 20 % full-energy photopeak e fficiency for 1-MeVγ rays emitted from fast-moving nuclei (velocities of v/c ≃ 0.6). DALI2 has been employed successfully in numerous experiments using fast RI beams wi th velocities ofv/c = 0.3 − 0.6 provided by the RIKEN RI Beam Factory.

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We study the composition of the Galactic interstellar medium (ISM) toward the Galactic center region (5? < |l| < 20?) by utilizing X-ray absorption features of three bright low-mass X-ray binaries (LMXBs), GX 13+1, GX 5-1, and GX 340+0, observed with the Chandra HETGS. We detect X-ray absorption fine structure (XAFS) of the Si K edge, characterized by a narrow and a broad absorption feature at 1846 and ?1865 eV, respectively. Comparison with ground experimental data indicates that most of the ISM Si exists in the form of silicates, although a composition of pure forsterite is ruled out. The XAFS spectra of the sulfur K edge indicate that a significant fraction of S exists in the gas phase. From each source, we derive the column densities of Mg, S, Si, and Fe from the K-edge depth and that of O (or H) from the absorption of the continuum. The elemental abundance ratios are found to be consistent between the three targets: the mean values of O/Si, Mg/Si, S/Si, and Fe/Si are determined to be 0.63 ? 0.17, 1.14 ? 0.13, 1.03 ? 0.12, and 0.97 ? 0.31 solar, respectively (90% error in the mean value). We discuss the origins of the overabundances of the heavy metals relative to O in the Galactic ISM by comparison with the abundance pattern of the intracluster medium in clusters of galaxies. Assuming that most of the Mg and Si atoms are depleted into silicates of either the proxine or olivine family, we estimate that the number ratio of Mg to Fe in olivine is 1.2 and that 15%-37% of the total O atoms in the ISM must be contained in silicate grains.