Deep X-Ray Observations of Supernova Remnants G359.1-0.5 and G359.0-0.9 with ASCA

We present the results of deep ASCA observations of two shell-like radio supernova remnants (SNRs) located in the direction to the Galactic center (GC) region. Unlike the radio morphology, G359.1-0.5 shows center-filled X-rays with prominent K-alpha lines of He-like silicon and H-like sulfur. The plasma requires at least two temperature components: a silicon-dominated cool plasma of 0.6keV temperature and a sulfur-dominated higher temperature plasma of 4.4keV. Because the absorption column is ~ 6x10^22 H cm^-2, this SNR would be near to the GC. The spherical plasma is attributable to supernova ejecta with the total mass of Si and S being about 0.1 solar mass and 0.3 solar mass, respectively. X-rays from G359.0-0.9 trace the partial shell structure of the radio emission. The spectrum is well fitted to a single-temperature plasma of 0.4keV with a non-solar abundance of magnesium or iron. Because the absorption column is not very large, ~ 1.8x10^22 H cm^-2, G359.0-0.9 would be in front of the GC region. The total supernova energy, interstellar density near to the X-ray emitting shell and age of the SNR are estimated to be 1.2x10^51erg, 0.5cm^-3, and 1.8x10^4yr, respectively. We also discuss possible implications on the origin of the large-scale hot plasma surrounding the GC.Comment: 8 pages, 7 postscript figures, uses PASJ95.sty and PASJadd.sty; accepted for publication in PASJ 52 April 2000; changed one of figure

The discovery of a new non-thermal X-ray filament near the Galactic Centre

We report the discovery by XMM-Newton and Chandra of a hard extended X-ray source (XMM J174540-2904.5) associated with a compact non-thermal radio filament (the Sgr A-E `wisp'=1LC 359.888-0.086= G359.88-0.07), which is located within ~4 arcmin of the Galactic Centre. The source position is also coincident with the peak of the molecular cloud, M -0.13-0.08 (the `20 km/s' cloud). The X-ray spectrum is non-thermal with an energy index of 1.0 (+1.1 -0.9) and column density of 38 (+7 -11) x 10^22 H/cm2. The observed 2--10 keV flux of 4 x 10^-13 erg/s/cm2 converts to an unabsorbed X-ray luminosity of 1 x 10^34 erg/s assuming a distance of 8.0 kpc. The high column density strongly suggests that this source is located in or behind the Galactic Centre Region. Taking account of the broad-band spectrum, as well as the source morphology and the positional coincidence with a molecular cloud, we concluded that both the radio and X-ray emission are the result of synchrotron radiation. This is the first time a filamentary structure in the Galactic Centre Region. has been shown, unequivocally, to have a non-thermal X-ray spectrum.Comment: 5 pages, 4 figures, Accepted for publication in MNRAS, also found in http://www.star.le.ac.uk/~mas/research/paper/#Sakano2002mnra

Unusual X-ray transients in the Galactic Centre

We report the discovery in the Galactic Centre region of two hard X-ray sources, designated as XMM J174457-2850.3 and XMM J174544-2913.0, which exhibited flux variations in the 2--10 keV band in excess of a factor of 100 in observations spanning roughly a year. In both cases the observed hydrogen column density is consistent with a location near to the Galactic Centre, implying peak X-ray luminosities of ~5 x 10^34 erg/s. These objects may represent a new population of transient source with very different properties to the much more luminous Galactic Centre transients associated with neutron star and black-hole binary systems. Spectral analysis shows that XMM J174457-2850.3 has relatively weak iron-line emission set against a very hard continuum. XMM J174544-2913.0, on the other hand, has an extremely strong K-line from helium-like iron with an equivalent width of ~2.4keV. The nature of the latter source is of particular interest. Does it represent an entirely new class of object or does it correspond to a known class of source in a very extreme configuration?Comment: 9 pages, 5 figures, to appear in MNRAS, figures with full resolution are available at http://www.star.le.ac.uk/~mas/research/paper/#Sakano2004mnra

Discovery of a Slow X-Ray Pulsator, AX J1740.1-2847, in the Galactic Center Region

We report the discovery of an X-ray pulsar AX J1740.1-2847 from the Galactic center region. This source was found as a faint hard X-ray object on 7--8 September 1998 with the ASCA Galactic center survey observation. Then, coherent pulsations of P=729 +/- 14 sec period were detected. The X-ray spectrum is described by a flat power-law of ~= 0.7 photon index. The large absorption column of log NH ~= 22.4 (cm^-2) indicates that AX J1740.1-2847 is a distant source, larger than 2.4 kpc, and possibly near at the Galactic center region. The luminosity in the 2--10 keV band is larger than 2.5 x 10^33 erg/s, or likely to be 3.2 x 10^34 erg/s at the Galactic center distance. Although the slow pulse period does not discriminate whether AX J1740.1-2847 is a white dwarf or neutron star binary, the flat power-law and moderate luminosity strongly favor a neutron star binary.Comment: To appear in PASJ Dec. 25, 2000 issue, Vol.52 No.6; 5 pages LaTeX files, uses PASJ95.sty, PASJadd.sty, psfig.sty; also available at http://www-maxi.tksc.nasda.go.jp/%7Esakano/work/paper/index-e.htm

Estimation of Central Black Hole Masses in LowLuminosity Active Galactic Nuclei

Abstract We analyzed six low-luminosity active galactic nuclei (hereafter LLAGNs), which consist of two bright LINERs (low-ionization nuclear emission line region) with broad Hα, and of four bright low-luminosity Seyferts observed by the X-ray satellite ASCA. We examined the time variabilities of these targets, and found that most targets show no significant time variabilities, although these galaxies belong to LLAGNs. By applying Fourier analysis to their light curves in the 2-10 keV band, we obtained the lower limits of their time variability scales, which correspond to their central black hole masses greater than several times 10 6 M . Our result suggests that these LLAGNs are harbors of super-massive black holes, but the emitting powers are only < 1% of the Eddington luminosities of the central engines in the LLAGNs due to their small accretion rates. Since a black hole would grow by mass accretion, it is hard to create such a super-massive black hole under a small accretion rate. Therefore, the mass-accretion rates in the past must have been larger than those at present, and the galaxies have probably been as luminous as QSOs. This will be a hint to find out the cause of the lack of QSOs in the local universe

ASCA Observations of the Sgr 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 cutoff 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 arcminute. 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 reflection nebula. Possible implications of the Galactic center activity related to this unique source are presented.Comment: 15 pages, 8 figures, AAS LaTeX, To be published in The Astrophysical Journa

Treatment of refractory acute leukemia with aclacinomycin-A.

Twelve patients with refractory acute leukemia (7 patients with acute myelocytic leukemia and 5 patients with acute lymphocytic leukemia) were treated with a new anthracycline antibiotic, aclacinomycin-A (ACM). ACM was administrated by intravenous drip infusion at a dose of 20 mg/day for 7 or 14 days and this was repeated after at least 7 days. Four of 12 patients (33.3%) achieved a complete remission; 3 of 7 acute myelocytic leukemia (42.8%) and 1 of 5 acute lymphocytic leukemia (20.0%). The days required for achieving the complete remission ranged from 23 to 78 days (median: 61) and the total doses of ACM used from 180 to 500 mg (median: 310), and the durations of complete remission from 11 to 28+ weeks (median: 21+). The untoward effects on digestive organs, such as nausea, vomiting and anorexia, and hematological toxicities were frequently seen; however, they were controlled by supportive treatment. Alopecia was not observed. Arrythmia was recognized in one patient at the initiation of ACM infusion with complete remission without withdrawal of ACM. These results suggest that ACM is a potentially effective anthracycline antibiotic in the clinical management of acute leukemia.</p

Treatment of refractory acute leukemia with aclacinomycin-A.

Twelve patients with refractory acute leukemia (7 patients with acute myelocytic leukemia and 5 patients with acute lymphocytic leukemia) were treated with a new anthracycline antibiotic, aclacinomycin-A (ACM). ACM was administrated by intravenous drip infusion at a dose of 20 mg/day for 7 or 14 days and this was repeated after at least 7 days. Four of 12 patients (33.3%) achieved a complete remission; 3 of 7 acute myelocytic leukemia (42.8%) and 1 of 5 acute lymphocytic leukemia (20.0%). The days required for achieving the complete remission ranged from 23 to 78 days (median: 61) and the total doses of ACM used from 180 to 500 mg (median: 310), and the durations of complete remission from 11 to 28+ weeks (median: 21+). The untoward effects on digestive organs, such as nausea, vomiting and anorexia, and hematological toxicities were frequently seen; however, they were controlled by supportive treatment. Alopecia was not observed. Arrythmia was recognized in one patient at the initiation of ACM infusion with complete remission without withdrawal of ACM. These results suggest that ACM is a potentially effective anthracycline antibiotic in the clinical management of acute leukemia.</p