January 13, 1999

RXTE observers Paul Nandra and Rick Edelson have found suggestive similarities in the timing properties of NGC 3516, an AGN suspected of harboring a supermassive black hole, and Cygnus X-1, the prototypical galactic black hole. The flickering properties of the two objects are different by a factor of about one million, the same factor by which NGC 3516 is brighter than Cygnus X-1 in luminosity. If luminosity scales with mass, the result implies a mass for NGC 3516 of 10 million solar masses, in line with earlier estimates based on spectroscopic measurements.