ROSAT/Chandra observations of a bright transient in M 81

We present a 10-year X-ray light curve and the spectra of a peculiar X-ray transient in the spiral galaxy M 81. The source was below the detection lim it of ROSAT PSPC before 1993, but it brightened substantially in 1993, with luminosities exceeding the Eddington limit of a 1.5-M-. compact accretor. It then faded and was not firmly detected in the ROSAT HRI and PSPC observa tions after 1994. The Chandra image obtained in 2000 May, however, shows an X-ray source at its position within the instrumental uncertainties. The Ch andra source is coincident with a star-like object in the Digitized-Sky-Sur vey. A Hubble image suggests that the optical object may be extended. While these three observations could be of the same object, which may be an X-ra y binary containing a black-hole candidate, the possibility that the ROSAT and Chandra sources are two different objects in a dense stellar environmen t cannot be ruled out. The Hubble data suggests that the optical object may be a globular cluster yet to be identified.