X-ray emission from M 82.

An X-ray study of M82 with the Einstein Observatory imaging instruments is presented. Observations with the High Resolution Imager show a luminous, extended X-ray source centered on M82. The most intense feature in the X-ray image has dimensions of about 30-60 arcsec and corresponds quite closely to the optically brightest region near the nucleus of the galaxy. Several discrete unresolved sources are detected in this central region. Outside the central region a diffuse X-ray halo is detected which extends for several arcminutes along the minor axis of the galaxy both north and south of the nucleus. The X-ray halo shows substantial spatial correlation with the H-alpha filamentary structure within the optical halo. These results are interpreted in the context of the current 'starburst' models for the nuclear activity in M82, and the importance of the discovery of the X-ray halo in distinguishing between alternative hypotheses for the origin of the optical halo is discussed.