How fast can an AGN shut downquestionMark XMM-Newton observation of IC 2497

We propose to observe IC 2497 with XMMNewton to detect, or rule out, anobscured AGN that might account for the illumination of Hanny.s Voorwerp.. TheVoorwerp is a highly ionised cloud of gas extended over 1525 kpc next to thespiral galaxy IC 2497. There is no source of ionisation within the Voorwerp,implicating a luminous 1E44 erg/s AGN in IC 2497 as the source. Swift XRTobservations do not yield a detection, allowing the presence of a highlyobscured, sufficiently luminous AGN. With 34 ksec of XMM observations, we coulddetect an obscured AGN down to 1E42 erg/s. We can thus either locate an obscuredAGN, or we can for the first time constrain the shutdown time scale for apowerful AGN, as it drops by a factor of 100 in luminosity in 1E5 years. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]