An unusual brightening of a non-active galaxy nucleus

NGC 247 is a dwarf or intermediate spiral galaxy at a distance of 3.4 Mpc. Past observations suggest that there was no activity of the nuclear black hole. We conducted an XMM observation of NGC 247 on 2014 July 1, which serendipitously detected a bright X-ray source coincident with the nuclear position (within 2 arcsec) with a luminosity of 2E39 erg/s in 0.3-10 keV. The most recent observation before that one was made on 2011 Feb 1 with Chandra. There was no detection in the nuclear region, giving an upper limit of 1E37 erg/s. If the new X-ray source is indeed due to the nuclear black hole activity, its sudden brightening suggests that it may have tidally disrupted a star some time between 2011 and 2014, or start to accrete a stream of gas at a low rate. Either will be of great interest due to its rarity and the small distance. A sub-arcsecond position accuracy is needed to determine if the X-rays arise from the nucleus.