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M.C. Weisskopf (Space Sciences Department, NASA/MSFC), K. Wu (MSSL, University College London), A.F. Tennant (Space Sciences Department, NASA/MSFC), D.A Swartz (USRA, MSFC)
The X-ray spectrum and light curve of the bright source CG X-1 in the field of the Circinus galaxy are re-examined.Previous analyses have concluded that the source is an accreting black hole of about 50 solar masses although it was noted that the light curve resembles that of an AM Her-type system.Here we show that the light curve and orbital dynamics constrain the mass of the compact object to less than 30 solar masses and the mass of the companion to less than 1 solar mass.Combining the mass constraints with the observed X-ray flux, we show that an accreting object must either radiate anisotropically or strongly violate the Eddington limit.If the emission is beamed, then the companion star, which intercepts this flux during eclipse, will be driven out of thermal equilibrium and evaporate within ~103 yr.We find, therefore, that the observations are most consistent with the interpretation of CG X-1 as a bright, long-period, AM Her system in the Milky Way.
Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.