Spectropolarimetric simulations of localized magnetar twist

The spectra of magnetars in soft X-rays are typically well fitted by the superposition of a thermal component and a power-law tail that extends to higher energies. The current model used to explain such emission is based on a reprocessing of the thermal radiation via resonant cyclotron scattering (RCS) onto moving magnetospheric charges. Due to the cross section increase at the cyclotron frequency of these charges, which stream along the closed field lines to sustain the twisted magnetic field, the magnetosphere becomes optically thick. In literature, the vast majority of the theoretical models developed so far rely on globally twisted configurations. However, a realistic magnetic field topology could be more complicate; specifically, the twist could be localized. While a self-consistent spectro-polarimetric emission model does not exist as yet, in this work a simplified model will be considered to study the possible observational effects of local twists. To do so, I used a Monte Carlo code to simulate the spectral and polarization properties of soft X-ray emission from magnetars. The local twist configuration was approximated starting from the self-similar, globally twisted model already discussed in literature. I analyzed the obtained results and characterized the main features that arise due to this specific magnetic field topology. A representative simulated measurement, performed considering the observational features of the space-based X-ray spectropolarimeter IXPE, is also discussed.