ROSAT/Chandra Observations of a Bright Transient in M81

Abstract

We present a 10-year X-ray light curve and the spectra of a peculiar X-ray transient in the spiral galaxy M81. The source was below the detection limit of ROSAT PSPC before 1993, but it brightened substantially in 1993, with luminosities exceeding the Eddington limit of a 1.5 solar-mass compact accretor. It then faded and was not firmly detected in the ROSAT HRI and PSPC observations after 1994. The Chandra image obtained in 2000 May, however, shows an X-ray source at its position within the instrumental uncertainties. The Chandra source is coincident with a star-like object in the Digitized-Sky-Survey. 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-ray binary containing a black-hole candidate, the possibility that the ROSAT and Chandra sources are two different objects in a dense stellar environment cannot be ruled out. The Hubble data suggests that the optical object may be a globular cluster yet to be identified.

accepted for publication in Astronomy and Astrophysics

References in corpus (5)

• New Evidence for Black Hole Event Horizons from Chandra
• The Ultra-luminous M81 X-9 source: 20 years variability and spectral states
• Properties of the Chandra Sources in M81
• BeppoSAX study of the broad-band properties of luminous globular cluster X-ray sources
• ROSAT X-Ray Observations of the Spiral Galaxy M81

Cited by in corpus (5)

• Chandra X-ray Observations of the Spiral Galaxy M81
• XMM-Newton observations of the spiral galaxy M74 (NGC 628)
• The nature of ultra-luminous X-ray sources in NGC4565
• Multiwavelength study of the bright X-ray source population in the interacting galaxies NGC5774/NGC5775
• Detection of X-ray elongated emission from a ultraluminous X-ray source in the interacting pair of galaxies NGC 5953/5954