Cyclotron resonant scattering model fits to the spectra from gamma-ray burst GB870303

Abstract

We demonstrate that the cyclotron resonant scattering model can account for the spectral lines seen at two epochs, S1 and S2, in the Ginga data for GB870303. Using a Monte Carlo code, we model line formation by injecting continuum photons into a static plane‐parallel slab of electrons threaded by a superstrong magnetic field (B∼1012 G) oriented at an angle Ψ relative to the slab normal. We apply rigorous statistical inference to compare azimuthally‐symmetric models (Ψ=0°) with models having a more general magnetic field orientation. If the burst source is a neutron star with a simple dipole field, these two classes of magnetic field orientations are equivalent to models in which the line forming region lies at the magnetic pole, or elsewhere on the stellar surface. We present the results of separate fits to the spectra for epochs S1 and S2, as well as joint fits to both spectra. The joint fits marginally favor a line forming region with Ψ=90°; i.e., a line forming region at the magnetic equator, assuming ...