Traces of Past Activity in the Galactic Centre

Abstract

The Milky Way centre hosts a supermassive Black Hole (BH) with a mass of ∼ 4 × 1{0}⁶ M_{⊙}. Sgr A^∗, its electromagnetic counterpart, currently appears as an extremely weak source with a luminosity L∼10^-9L_Edd. The lowest known Eddington ratio BH. However, it was not always so; traces of "glorious" active periods can be found in the surrounding medium. We review here our current view of the X-ray emission from the Galactic Center (GC) and its environment, and the expected signatures (e.g. X-ray reflection) of a past flare. We discuss the history of Sgr A^∗'s past activity and its impact on the surrounding medium. The structure of the Central Molecular Zone (CMZ), a highly flattened toroid, has not changed significantly since the last active phase of Sgr A^∗. This relic torus provides us with the opportunity to image the three-dimensional structure of an AGN torus in exquisite detail.