Modeling the Emission and Polarization Properties of Pulsating Ultraluminous X ‐Ray Sources

Pulsating Ultraluminous X‐ray Sources (PULXs) are a class of extragalactic sources with high X‐ray luminosity, in excess of 10 39 $$ {10}^{39} $$ erg s − 1 $$ {\mathrm{s}}^{-1} $$ , and showing pulsations that associate them with neutron stars accreting at a super‐Eddington rate. A simplified model is presented, which describes the thermal emission from an accreting, highly magnetized neutron star and includes the contributions from an accretion disk and an accretion envelope surrounding the star magnetosphere. Through numerical calculations, we determine the flux, pulsed fractions, polarization degree, and polarization angle considering various viewing geometries. The model is confronted with the XMM‐Newton spectra of M51 ULX‐7, and the best fitting viewing geometries are estimated. A measurement of the polarization observables, which will be available with future facilities, along with spectroscopic data obtained with XMM‐Newton, will provide considerable additional information on these sources.