The effects of high-velocity supernova kicks on the orbital properties and sky distributions of neutron-star binaries

We systematically investigate the effects of high supernova kick velocitieson the orbital parameters of post-supernova neutron-star binaries. Using Monte-Carlo simulations, we determine the post-supernova distributions of orbitalparameters for progeneitors of HMXBs and LMXBs. With the recent distribution ofpulsar birth velocities by Lyne and Lorimer (1994), only about 27% of massivesystems remain bound after the supernova, of which about 26% immediatelyexperience dynamical mass transfer and possibly merge to become Thorne-Zytkowobjects. The correlations between various orbital parameters can be comparedwith observational samples to yield information about supernova kick velocitiesand pre-supernova orbital-period distributions. After the supernova, the spinsof most stars in massive systems have large inclinations with respect to theirorbital axes, and a significant fraction of systems (about 20%) contain starswith retrograde spins. In the case of low-mass companions, we find that about19% of systems remain bound after the supernova, of which about 57% experienceimmediate dynamical mass transfer. There is a tight correlation between theeccentricity and the post-supernova orbital period in LMXB progeneitors. AllLMXBs with post-supernova periods longer than a few days initially have largeeccentricities (e.g. Cir X-1 is discussed in this context). We use the resultsof these calculations to simulate the sky distributions of HMXBs and LMXBs. Thesimulated distributions agree with observed samples. Most importantly, thedistribution of Galactic LMXBs is consistent with an ordinary Galactic diskpopulation which has been widened because of large supernova kicks and does notrequire a special population of progenitors