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From: Yoshitomo Maeda  maeda@cubic.astro.psu.edu 
To: gcnews@aoc.nrao.edu
cc: ytanaka@mpe.mpg.de
Mime-Version: 1.0
Date: Wed, 27 Sep 2000 14:58:30 -0400

%astro-ph/0009445
\title{Unusual Properties of X-Ray Emission near the Galactic Center}
\author{Y. Tanaka(1,2), K. Koyama(3), Y. Maeda(4), T. Sonobe(5)}
\institute{The Institute of Space \& Astronautical Science, 3-1-1 
Yoshinodai,
	   Sagamihara, Kanagawa 229-8510 (2) Max-Planck Institut f\"{u}r 
	   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}


\begin{abstract}
The X-ray spectrum in a $1^{\circ}\times1^{\circ}$ 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
$\sim3300$ km~s$^{-1}$, which far exceeds the sound velocity in a plasma of
$kT\sim14$ keV measured with the Ginga satellite.
These facts cast doubt on a thermal origin of the observed X-ray emission.
\end{abstract}


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