Energy-dependent effects of scattering atmospheres on X-ray pulsar pulse profiles

We propose that radiation-supported scattering atmospheres near accreting X-ray pulsars (XRPs) can explain energy-dependent features observed in the pulse profiles of 4U 1626-67, 4U 1538-52, 4U 1907+09 and Vela X-1. These atmospheres provide a physical model for the phenomenological annular emitting regions employed by Leahy to fit X-ray pulsar pulse profiles. We examine the effects of the scattering atmospheres under the assumptions that stable, optically thick atmospheres exist in a region where the optically thin resonant radiation force exceeds the force of gravity on ionized hydrogen. We predict that less complex pulse profiles will be observed at higher photon energies because the scattering atmospheres, which are supported by resonant Compton radiation pressure, become transparent to photons with energies greater than the cyclotron energy at the neutron star surface.