The Black Hole Mass Distribution in the Galaxy
  We use dynamical mass measurements of 16 black holes in transient low-mass
X-ray binaries to infer the stellar black hole mass distribution in the parent
population. We find that the observations are best described by a narrow mass
distribution at 7.8 +/- 1.2 Msolar. We identify a selection effect related to
the choice of targets for optical follow-ups that results in a flux-limited
sample. We demonstrate, however, that this selection effect does not introduce
a bias in the observed distribution and cannot explain the absence of black
holes in the 2-5 solar mass range. On the high mass end, we argue that the
rapid decline in the inferred distribution may be the result of the particular
evolutionary channel followed by low-mass X-ray binaries. This is consistent
with the presence of high-mass black holes in the persistent, high-mass X-ray
binary sources. If the paucity of low-mass black holes is caused by a sudden
decrease of the supernova explosion energy with increasing progenitor mass,
this would have observable implications for ongoing transient surveys that
target core-collapse supernovae. Our results also have significant implications
for the calculation of event rates from the coalescence of black hole binaries
for gravitational wave detectors.
