Suzaku Detection of Extended/Diffuse Hard X-Ray Emission from the Galactic Center
Takayuki Yuasa(1), Ken-ichi Tamura(2,1), Kazuhiro Nakazawa(1), Motohide Kokubun(2), Kazuo Makishima(1,3), Aya Bamba(2), Yoshitomo Maeda(2), Tadayuki Takahashi(2,1), Ken Ebisawa(2,1), Atsushi Senda(3), Yoshiaki Hyodo(4), Takeshi Go Tsuru(4), Katsuji Koyama(4), Shigeo Yamauchi(5), Hiromitsu Takahashi(6)
(1) Department of Physics, School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033
(2) Department of High Energy Astrophysics, Institute of Space and Astronautical Science (ISAS),,Japan Aerospace Exploration Agnency (JAXA), 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510
(3) Cosmic Radiation Laboratory, The Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako, Saitama 351-0198
(4) Department of Physics, Graduate School of Science, Kyoto University, Kita Shirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502
(5) Faculty of Humanities and Social Sciences, Iwate University, 3-18-34 Ueda, Morioka, Iwate 020-8550
(6) Department of Physical Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526
Paper: PASJ, in press
Abstract:
Five on-plane regions within +/- \timeform0o.8 of the Galactic
center
were observed with the Hard X-ray Detector (HXD) and the X-ray Imaging
Spectrometer (XIS) onboard Suzaku.
From all regions,
significant hard X-ray emission was detected with HXD-PIN up to 40 keV,
in addition to the extended plasma emission which is dominant in the XIS band.
The hard X-ray signals are inferred to come
primarily from a spatially extended source,
rather than from a small number of bright discrete objects.
Contributions to the HXD data from catalogued X-ray sources,
typically brighter than 1 mCrab,
were estimated and removed using information from Suzaku and other satellites.
Even after this removal,
the hard X-ray signals remained significant,
exhibiting a typical 12-40 keV surface brightness of
4*10-10 \ergcms \mathrmdeg-2
and power-law-like spectra with a photon index of 1.8.
Combined fittings to the XIS and HXD-PIN spectra confirm
that a separate hard tail component is
superposed onto the hot thermal emission,
confirming a previous report based on the XIS data.
Over the 5-40 keV band,
the hard tail is spectrally approximated
by a power law of photon index 2,
but better by those with somewhat convex shapes.
Possible origins of the extended hard X-ray emission are discussed.
Preprints available from the authors at yuasa@amalthea.phys.s.u-tokyo.ac.jp
,
or the raw TeX (no figures) if you click here.
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