THE GALACTIC DISTRIBUTION OF LOW-MASS X-RAY BINARIES

We have analyzed the Galactic distribution of low-mass X-ray binaries (LMXBs) in which the accreting compact object is a neutron star. The rms value of their distances, z, to the Galactic plane equals similar to 1 kpc. This wide z-distribution cannot be explained by systemic velocities that increased as a result of sudden symmetric mass loss at the formation of the neutron star alone. Kick velocities imparted on the neutron star, following the radio pulsar velocity distribution recently derived by Lyne and Lorimer (1994) can account for the LMXB z-distribution. This distribution is consistent with formation of the neutron stars in LMXBs from direct collapse of a helium star and also from accretion-induced collapse of a white dwarf. The triple-star evolution proposed by Eggleton and Verbunt is not a dominant production mechanism for LMXBs.