Population X: Are the super-Eddington X-ray sources beamed jets in microblazars or intermediate mass black holes?
Abstract
Recent X-ray observations reveal an increasing number of X-ray sources in nearby galaxies exceeding luminosities of Lx > 2 1039 erg/s. Assuming isotropic emission, the Eddington limit suggests a population of intermediate-mass black holes of Mbh >> 10 Msun. However, Markoff, Falcke, & Fender (2001) proposed that jets may be contributing to the X-ray emission from X-ray binaries (XRBs), implying that some X-ray sources may be relativistically beamed. This could reduce the required black hole masses to standard values. To test this hypothesis, we investigate a simple X-ray population synthesis model for X-ray point sources in galaxies with relativistic beaming and compare it with an isotropic emission model. The model is used to explain a combined data set of X-ray point sources in nearby galaxies. We show that the current distributions are consistent with black hole masses Mbh <=10 Msun and bulk Lorentz factors for jets in microquasars of gammaj ~ 5. Alternatively, intermediate mass black holes up to 1000 Msun are required which are distributed in a powerlaw with roughly dN/dM ~ M-2.
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