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[17.36] CXOU J013651.1+154547: An Extremely Variable ULX in M74

M.I. Krauss (MIT), R.E. Kilgard (Harvard-Smithsonian CfA, U. of Leicester), M.R. Garcia (Harvard-Smithsonian CfA), T.P. Roberts (U. of Leicester), A.H. Prestwich (Harvard-Smithsonian CfA)

We present an investigation into a newly discovered ultraluminous X-ray source (ULX) in M74, CXOU J013651.1+154547. It varies in luminosity by more than an order of magnitude (from 5 x 10³⁸ to 1 x 10⁴⁰ erg s^-1) in only 30 minutes, and flares on a characteristic timescale of around 4000 s. It has neither a radio nor optical counterpart, which suggests that it resides in M74 and is not a background AGN. It most closely resembles Galactic microquasars, in particular GRS 1915+105, in its temporal variability and spectral components. However, CXOU J013651.1+154547 resides near several prominent OB associations, suggesting that it may be associated with recent star formation. We discuss the spectral, spatial, and temporal characteristics of this intriguing source in the context of known Galactic sources as well as other ULXs.

Bulletin of the American Astronomical Society, 35#2
© 2003. The American Astronomical Soceity.