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 bol ∼ 1042–1044 erg s−1). The temperature structure in the hot gas suggests the presence of a bubble or cavity around the fading AGN ( ${{\rm {E}}}_{\rm bub} \sim 10^{54}{--}10^{55}$ 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 bol ∼ 1046 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.