Moving on in the same paper ..
Quote:
However, IC 2497 poses a challenge: the optical image reveals no strong point source, the nuclear spectrum shows very weak optical line emission (Lintott et al. 2009), and it also has a weak (∼ 10⌃38 ergs−1) nuclear radio source (J ́ozsa et al. 2009). These observations are difficult to reconcile with the presence of a currently active L(bol) ∼ 10⌃46 ergs−1 quasar. There are two possible scenarios that can account for these apparently contradictory observations as argued by Lintott et al. (2009):
1) the quasar in IC 2497 features a novel geometry of obscuring material and is obscured at an unprecedented level only along our line of sight, while being virtually unobscured towards the Voorwerp;
or 2) the quasar in IC 2497 has shut down within the last 70,000 years, while the Voorwerp remains lit up due to the light travel time from the nucleus.
If the latter is the case, the IC 2497–Voorwerp system gives for the first time an upper limit of the shutdown timescale of an individual quasar central engine. In this Letter, we present observations to distinguish these two scenarios.
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Interesting that these guys are sticking to the shut down occurring only 70,000 years ago, whereas the GalaxyZoo guys are saying that it stopped less than about 200,000 years ago (bit of a difference there .. but probably not that significant).
Cheers