1997/10/01 by G. Dubus, Guillaume Dubus, P. A. Charles +5 · 4 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Galaxies: Formation, Evolution, Phenomena #astro-ph
paper · pdf · doi:10.1086/311013
17 pages, 3 postscript figures, LaTeX, uses aasms4.sty, accepted for publication in ApJ Letters
arxiv created 1997/10/01 · openalex publication_date 1997/11/20 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
With an X-ray luminosity of about 1039 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.