ENERGY-DEPENDENT EFFECTS OF SCATTERING ATMOSPHERES ON X-RAY PULSAR PULSE PROFILES

We propose that radiation-supported scattering atmospheres near accret ing X-ray pulsars can explain energy-dependent features observed in th e pulse profiles of 4U 1626-67, 4U 1538-52,4U 1907+09 and Vela X-1. Th ese atmospheres provide a physical model for the phenomenological annu lar emitting regions employed by Leahy to fit X-ray pulsar pulse profi les. We examine the effects of the scattering atmospheres under the as sumption that stable, optically thick atmospheres exist in a region wh ere the optically thin resonant radiation force exceeds the force of g ravity on ionized hydrogen. We predict that less complex pulse profile s will be observed at higher photon energies because the scattering at mospheres, which are supported by resonant Compton radiation pressure, become transparent to photons with energies greater than the cyclotro n energy at the neutron star surface.