Suzaku Detection of Extended/Diffuse Hard X-Ray Emission from the Galactic Center

Abstract

Five on-plane regions within +/- 0.8deg 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 4E-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--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.

13 pages, 18 figures

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• In-Orbit Performance of the Hard X-ray Detector on board Suzaku
• Iron and Nickel Line Diagnostics for the Galactic Center Diffuse Emission
• Hard X-ray emission from the Galactic ridge
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• On the contribution of point sources to the Galactic ridge X-ray emission
• First broad band study of the mysterious source 1E 1743.1-2843
• Hard X-ray diffuse emission from the Galactic Center seen by INTEGRAL

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