Monte-Carlo modeling of cyclotron resonant scattering features

Abstract

Cyclotron resonant scattering features (CRSFs) exhibit the fundamental physical processes in the line-forming region of highly magnetized neutron stars and allow for a direct measurement of a neutron star's magnetic field. The multiplicity of CRSFs seen in many sources - with 4U 0115+63 being the record holder showing a fundamental line plus 4 harmonics - and the complex shape of the fundamental line can provide unique insights into the physical properties and B-field geometry of the accretion column. The strong coupling of a photon's angle and energy due to relativistic effects are leading to a coupling of the seed photons spectral distribution and the accretion geometry and therefore hinder comprehension. The model presented here is using a Monte-Carlo approach to the problem by propagating individual photons through different kinds of cyclotron resonant scattering media. We produce tables of the simulated data allowing the fast creation of output spectra by convolution of the input continuum with the corresponding Green's functions. An XSPEC implementation of this model and an initial set of tables will soon be available to the community. While this model follows similar physical assumptions and the same Green's functions strategy as previous work, the Monte-Carlo code has been completely redone from scratch. The new code not only provides new geometries, the possibility to trace every single photon during its way through the medium and the flexibility to introduce new simulation parameters easily as necessary for a feasible comparison to data but also yields corrected scattering profiles. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.