Reprocessing of X rays in low-mass X-ray binaries

We have applied a simple geometric model for the reprocessing of X rays in low-mass X-ray binaries to estimate their absolute visual magnitudes, and the amplitudes of their optical light curves. A comparison with the observed values for these quantities leads to an X-ray albedo in excess of 0.9, i.e., only a small fraction of the X rays incident on the accretion disk are absorbed and transformed into lower-energy photons. We derive an opening (semi-) angle of the disk, as seen from the X-ray source, of similar to 12 degrees.