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A Persistent High-Energy Flux from the Heart of the Milky Way : Integral's view of the Galactic Center

A Persistent High-Energy Flux from the Heart of the Milky Way : Integral's view of the Galactic Center

Publication date: 05 August 2005

Authors: Bélanger, G., et al.

Year: 2005

The IBIS/ISGRI imager on Integral detected for the first time a hard X-ray source, IGR J17456-2901, located within 1' of Sgr A* over the energy range 20-100 keV. Here we present the results of a detailed analysis of ~7x106s of Integral observations of the Galactic Centre. With an effective exposure of 4.7x106s we have obtained more stringent positional constraints on this high-energy (HE) source and constructed its spectrum in the range 20-400 keV. Furthermore, by combining the Isgri spectrum with the total X-ray spectrum corresponding to the same physical region around SgrA* from XMM data, and collected during part of the Integral observations, we constructed and present the first accurate wide band HE spectrum for the central arcmins of the Galaxy. Our complete analysis of the emission properties of IGR shows that it is faint but persistent with no variability above 3 sigma contrary to what was alluded to in our first paper. This result, in conjunction with the spectral characteristics of the X-ray emission from this region, suggests that the source is most likely not point-like but, rather, that it is a compact, yet diffuse, non-thermal emission region. The centroid of IGR is estimated to be R.A.=17h45m42.5s, decl.=-28°59'28'', offset by 1' from the radio position of Sgr A* and with a positional uncertainty of 1'. Its 20-400 keV luminosity at 8 kpc is L=5.4x1035 erg/sec. Very recently, Hess detected of a source of ~TeV gamma-rays also located within 1' of Sgr A*. We present arguments in favor of an interpretation according to which the photons detected by Integral and Hess arise from the same compact region of diffuse emission near the central black hole and that the supernova remnant Sgr A East could play an important role as a contributor of very HE gamma-rays to the overall spectrum from this region.

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