A 106-d period in the nuclear source X-8 in M33

Abstract

With an X-ray luminosity of about 10^39 erg/s, the source X-8 coincident with the optical center of M33 is the most luminous X-ray source in the Local Group. However, its nature remains a mystery. We present here new and archival ROSAT observations of X-8 spread over 6 years which show variability and a ~ 106-d periodicity. This implies that (most of) the emission from M33 X-8 arises from a single object, perhaps a binary system with a ~ 10 Msol black hole primary. We suggest that the companion is a giant orbiting with a ~ 10 day period, and that the observed modulation is ``super-orbital'', analogous to that seen in Cyg X-2 and X1820-30.

17 pages, 3 postscript figures, LaTeX, uses aasms4.sty, accepted for publication in ApJ Letters

References in corpus (4)

• Radiation-Driven Warping: The Origin of Warps and Precession in Accretion Disks
• Why Low-Mass Black-Hole Binaries Are Transient
• Transients Among Binaries with Evolved Low-Mass Companions
• The Transient Nature of GRO J1655-40 and its Evolutionary State

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