Discovery of a luminous, variable, off-center source in the nucleus of M82 with the Chandra High-Resolution Camera

We present results from observations of the most famous starburst galaxy M82 with the High-Resolution Camera on board the Chandra X-Ray Observatory. We found nine sources in the central 1' x 1' region, but no source was detected at the galactic center. Comparing the observations on 1999 October 28 and on 2000 January 20, we found that four of the nine sources showed significant time variability. In particular, CXOM82 J095550.2+694047, which is 9 " away from the galactic center, showed extremely large time variability. We conclude that this source is the origin of the hard X-ray time variability of M82 detected with ASCA. Assuming a spectral shape obtained by the ASCA observation, its luminosity in the 0.5-10 keV band changed from 1.2 x 10(40) ergs s(-1) on 1999 October 28 to8.7 x 10(40) ergs s(-1) on 2000 January 20.