Recent X-ray observations reveal an increasing number of X-ray sources in nearby galaxies exceeding luminosities of L _ { x } \ga 2 \cdot 10 ^ { 39 } \mbox { erg } \mbox { s } ^ { -1 } .
Assuming isotropic emission , the Eddington limit suggests a population of intermediate-mass black holes of M _ { \bullet } \gg 10 M _ { \odot } .
However , ? ) 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 M _ { \odot } \la 10 and bulk Lorentz factors for jets in microquasars of \gamma _ { j } \sim 5 .
Alternatively , intermediate mass black holes up to 1000 M _ { \odot } are required which are distributed in a powerlaw with roughly \frac { dN } { dM } \sim M ^ { -2 } .