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Conference on the Galactic Center: A Window to the Nuclear Environment of Disk Galaxies, Shanghai : Chine (2009)
Variable Hard X-Ray Emission from the Sgr B2 Molecular Cloud
R. Terrier1, G. Ponti2, G. Belanger3, A. Decourchelle4, V. Tatischeff5, A. Goldwurm1, 4, G. Trap1, 2, 4

The 4 million solar masses black hole at the Galactic centre (GC) is remarkably quiet today. The molecular cloud Sgr B2, among others, emits strong Fe K alpha photons as well as hard X-rays up to 100 keV. This has been interpreted as the result of the illumination of the cloud by a past high luminosity period of Sgr A*. This interpretation is still controversial since irradiation by subrelativistic cosmic rays might also account for the observed spectra. We present here the results of 7 years of INTEGRAL monitoring of Sgr B2 and show that its hard X-ray (20-60 keV) flux has decreased by nearly 40% during that period. This cannot be accounted for by cosmic ray interpretations and support the idea that Sgr A* was more active in the past and has been quiescent since about 100 years.
1 :  APC - UMR 7164 - AstroParticule et Cosmologie
2 :  Université Paris-Sud - Paris 11
3 :  LAPTH - Laboratoire d'Annecy-le-Vieux de Physique Théorique
4 :  IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers (ex DAPNIA)
5 :  CSNSM - Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse
Physique/Astrophysique/Phénomènes cosmiques de haute energie

Planète et Univers/Astrophysique/Phénomènes cosmiques de haute energie