X-ray Beaming in the High Magnetic Field Pulsar GX 1+4

Abstract

Pulse profiles from X-ray pulsars often exhibit strong energy dependence and both periodic and aperiodic variations with time. The great variety of profiles observed in various sources, and even from individual sources, makes it difficult to separate the numerous factors influencing the phase-dependence of the X-ray emission. These factors include the system geometry and particularly the photon energy and angle dependence of emission about the neutron star poles. Comptonisation may play an important role in determining beam patterns and hence pulse profiles in X-ray pulsars. A Monte Carlo simulation is used to investigate the beaming due to Comptonisation in a simple accretion column geometry. We apply the model to the extremely variable pulse profiles of the high-magnetic field pulsar GX 1+4.