X-RAY-PROPERTIES OF THE NUCLEUS OF M81

Due to the appearance of SN 1993J, the region of M81 (NGC 3031) was ob served with ASCA ten times between 1993 April and 1995 April. Data fro m eight of these observations have been used to study the 0.5-10 keV s pectral and temporal properties of the source designated X-5, coincide nt with the M81 nucleus. The 2-10 keV luminosity of X-5 varied by a fa ctor of 1.7 over a period of two years, around a mean of similar to 2 x 10(40) erg s(-1). Variations by similar to 20% on a time scale of on e day Mere also detected. The average spectrum of X-5 can be represent ed in the 2-10 keV range by a power-law continuum of the photon index, Gamma = 1.85 +/- 0.04, and a relatively low intrinsic absorption colu mn of N-H similar to 1 x 10(21) cm(-2). In the soft (< 2 keV) energy r ange, an additional thermal component with a temperature of 0.6-0.8 ke V has been detected. An apparently broad or complex Fe-K emission line centered at 6.6-6.7 keV was also detected at an equivalent width of 1 70 +/- 60 eV. These results indicate that the M81 nucleus is a low-lum inosity active galactic nucleus, and suggest that similar objects are relatively numerous. A comparison is made between the nucleus of M81 a nd those of Seyfert galaxies.