Extended X-ray emission in the IC 2497 - Hanny's Voorwerp system: energy
  injection in the gas around a fading AGN
  We present deep Chandra X-ray observations of the core of IC 2497, the galaxy
associated with Hanny's Voorwerp and hosting a fading AGN. We find extended
soft X-ray emission from hot gas around the low intrinsic luminosity
(unobscured) AGN ($L_{\rm bol} \sim 10^{42}-10^{44}$ erg s$^{-1}$). The
temperature structure in the hot gas suggests the presence of a bubble or
cavity around the fading AGN ($\mbox{E$_{\rm bub}$} \sim 10^{54} - 10^{55}$
erg). A possible scenario is that this bubble is inflated by the fading AGN,
which after changing accretion state is now in a kinetic mode. Other
possibilities are that the bubble has been inflated by the past luminous quasar
($L_{\rm bol} \sim 10^{46}$ erg s$^{-1}$), or that the temperature gradient is
an indication of a shock front from a superwind driven by the AGN. We discuss
the possible scenarios and the implications for the AGN-host galaxy
interaction, as well as an analogy between AGN and X-ray binaries lifecycles.
We conclude that the AGN could inject mechanical energy into the host galaxy at
the end of its lifecycle, and thus provide a source for mechanical feedback, in
a similar way as observed for X-ray binaries.
