Unusual Properties of X-Ray Emission near the Galactic Center

Y. Tanaka(1,2), K. Koyama(3), Y. Maeda(4), T. Sonobe(5)


(1) The Institute of Space & Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510
(2) Max-Planck Institut für Extraterrestrische Physik, D-85748 Garching, Germany
(3) Dept. of Physics, Kyoto University, Sakyo-ku, Kyoto 606-01
(4) Dept. of Astronomy & Astrophysics, Penn State University, University Park, PA 16802-6305, U.S.A.
(5) Fujitsu Ltd., 4-1-1 Kamikodanaka, Nakahara-ku, Kawasaki, Kanagawa 211-8588

Paper: PASJ, 52, L25-L30 (2000)

EPrint Server: astro-ph/0009445

Abstract:

The X-ray spectrum in a 1o*1o region of the Galactic center observed with the ASCA satellite is examined in detail, following the first report by Koyama et al. (1996, AAA 65.155.208). The observed spectrum contains prominent emission lines from helium-like and hydrogen-like ions of various elements, and is essentially the same all over the region. If the observed spectrum is thermal emission from hot plasmas, it requires multi-temperature plasma components, each at a different degree of ionization and with a different amount of absorption. The absence of adiabatic cooling and of systematic changes in the degree of ionization over the region is against the Galactic center origin of hot plasmas. A significant broadening of the helium-like and hydrogen-like iron K-lines is confirmed. The line width corresponds to a rms velocity of 3300 km s-1, which far exceeds the sound velocity in a plasma of kT 14 keV measured with the Ginga satellite. These facts cast doubt on a thermal origin of the observed X-ray emission.

Preprints available from the authors at maeda@cubic.astro.psu.edu , or the raw TeX (no figures) if you click here.

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