Suzaku Detection of Extended/Diffuse Hard X-Ray Emission from the Galactic Center
Maeda, Yoshitomo; Kokubun, Motohide; Makishima, Kazuo; Nakazawa, Kazuhiro; Takahashi, Tadayuki; Koyama, Katsuji; Ebisawa, Ken; Takahashi, Hiromitsu; Bamba, Aya; Tsuru, Takeshi Go; Yamauchi, Shigeo; Yuasa, Takayuki; Tamura, Ken-Ichi; Hyodo, Yoshiaki; Senda, Atsushi
Japan
Abstract
Five on-plane regions within ±0°.8 of the galactic center were observed with the Hard X-ray Detector (HXD) and the X-ray Imaging Spectrometer (XIS) aboard Suzaku. From all regions, significant hard X-ray emission was detected with HXD-PIN up to 40keV, 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 1mCrab, 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 12-40keV surface brightness of 4×10-10 erg cm-2 s-1 deg-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--40keV 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.