The image shows an animation of INTEGRAL/IBIS 20 - 60 keV views of the Galactic
Centre (3.5° x 2°) from 2003 until 2009. Most of the sources are X-ray
binaries and display strong time variability. The black cross gives the position
of the supermassive black hole, Sgr A*. The green circle corresponds to the position
of the molecular cloud Sgr B2. The associated hard X-ray source, IGR J17475-2822,
shows a clear decline in flux during the 7 years of monitoring.
Hard X-rays from the giant molecular cloud Sgr B2 are best interpreted as scattering
of radiation emitted by Sgr A*. INTEGRAL's discovery shows that this fading non-thermal
emission likely traces the end of the past activity of Sgr A* about 100 years ago.
Along with XMM-Newton measurements of the Fe K-line variability from other clouds
of this region this discovery allowed both the strength and duration of this past
activity to be constrained. These results established that the behaviour of Sgr A*
resembles that of a Low Luminosity Active Galactic Nucleus and it might become brighter
again in the future.
Related links:
R. Terrier et al., 2010, ApJ in press, arXiv: 1005.4807 v1
