UCL Discovery

Abstract

Soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are peculiar classes of X-ray sources which share a number of common properties. Among others are: a sporadic bursting activity,slow rotation periods in a narrow range (a few seconds), high secular spindown and a X-ray luminosity of ~1E34-1E36 erg/s. Over the last few years, observations provided increasing evidence that SGRs and AXPs are magnetars: ultra-magnetized neutron stars with surface field in excess of 1E14 G, i.e. well above the threshold at which QED effects become relevant. Spectral analysis is an important tool in magnetar astrophysics since it can provide key information on the emission mechanisms. The first attempts at modelling the soft X-ray (< 10 keV) spectra of AXPs proved that a model consisting of a blackbody (kT~0.3‑0.6 keV) plus a power-law (photon index ~2‑4) could successfully reproduce the observed emission. However, despite the blackbody plus power-law spectral model has been largely applied to the X-ray spectra of magnetar candidates, a convincing physical interpretation is still missing. In this talk, I will present the application of synthetic model spectra, that we calculated with a new magnetic montecarlo radiative code. Our code accounts for resonant cyclotron upscattering of soft thermal photons (emitted by the star surface), by a population of relativistic electrons threated in the magnetosphere. Polarization and QED effects are consistently accounted for. Further applications to the modeling of the hard X-ray magnetar emission are discussed.