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We present a 10-year X-ray light curve and the spectra of a peculiar X-raytransient in the spiral galaxy M81. The source was below the detection limit ofROSAT PSPC before 1993, but it brightened substantially in 1993, withluminosities exceeding the Eddington limit of a 1.5 solar-mass compactaccretor. It then faded and was not firmly detected in the ROSAT HRI and PSPCobservations after 1994. The Chandra image obtained in 2000 May, however, showsan X-ray source at its position within the instrumental uncertainties. TheChandra source is coincident with a star-like object in theDigitized-Sky-Survey. A Hubble image suggests that the optical object may beextended. While these three observations could be of the same object, which maybe an X-ray binary containing a black-hole candidate, the possibility that theROSAT and Chandra sources are two different objects in a dense stellarenvironment cannot be ruled out. The Hubble data suggests that the opticalobject may be a globular cluster yet to be identified.Comment: accepted for publication in Astronomy and Astrophysic

ROSAT/Chandra observations of a bright transient in M 81