Letter to the Editor
Population X: Are the super-Eddington X-ray sources beamed jets in microblazars or intermediate mass black holes?
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
Corresponding author: E. Körding, körding@mpifr-bonn.mpg.de
Accepted: 12 December 2001
Recent X-ray observations reveal an increasing number of X-ray sources in nearby galaxies exceeding luminosities of . Assuming isotropic emission, the Eddington limit suggests a population of intermediate-mass black holes of . However, Markoff et al. ([CITE]) 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 and bulk Lorentz factors for jets in microquasars of . Alternatively, intermediate mass black holes up to 1000 are required which are distributed in a powerlaw with roughly .
Key words: X-rays: binaries / accretion, accretion disks / black hole physics / radiation mechanisms: non-thermal
© ESO, 2002