The nuclear X-ray source in M81

Abstract

The Einstein Observatory High Resolution Imager has detected a pointlike X-ray source coincident with the radio and optical nucleus of the nearby galaxy M81 (NGC 3031). It has a luminosity of approx.1.7 x 10/sup 40/ ergs s/sup -1/ (0.5--4.5 keV). We discuss the evidence that this is a low-luminosity Seyfert 1 galaxy from comparisons of X-ray, optical, and radio data and conclude that this is very likely the case. If this is so, it implies that the active galaxy X-ray luminosity function extends two orders of magnitude below its previous observed limit.