Comprehensive modelling of pulse shape formation in binary X-ray pulsars

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High energy radiation from X-ray binary pulsars originates from the accretion of ionized gas onto strongly magnetized rotating neutron stars. If the magnetic and rotation axes are disaligned, pulsed emission is observed. Accreting X-ray pulsars display a large variety of pulse shapes, that are characteristic for each source. In recent years an increasing wealth of high quality observational data on spectra and pulse shapes has been obtained thanks to the outstanding observations of several satellites. However, after almost four decades of research, there is still no compelling model that one could apply to infer the geometric and physical parameters of X-ray pulsars from their pulse shapes. In this project we aim at a better understanding of the mechanisms of pulse shape formation. We will develop and study a set of comprehensive phenomenological models and compare them to broadband observational data. These models will take full account of relativistic light deflection and will include a number of important effects that have so far been included in few models (and then separately) or have been discussed only in a qualitative way: halo formation, accretion stream eclipses, reprocessing of halo radiation, and different accretion stream geometries. Eventually we expect not only to reach a deep understanding of the mechanisms relevant to accreting pulsar emission but also to set constraints on key physical parameters of such systems like mass, radius, magnetic moment and magnetic field configuration of the neutron star, accretion rate, offset between magnetic and rotation axes, accretion mound geometry.