Thursday, 4 November 2010
Rapid QSO shutdown in Hanny's Voorwerp
Schawinski et al (2010, http://arxiv.org/abs/1011.0427) presents interesting X-ray observations of Hanny's Voorwerp. They argue that the light from the Voorwerp (the green fuzz above) is caused by ionizing radiation from an AGN in the center of the host galaxy IC 2497. However their X-ray data show only a weak AGN, much too weak to explain the emission lines in the Voorwerp they argue (by 2-4 orders of magnitude). The inference is thus that the Voorwerp is a light echo of a QSO phase that terminated < 70,000 years ago. This is a rapid turn-off and more extreme than what you would expect by scaling up an X-ray binary for instance.