X-ray emission spectrum for axion-photon conversion in magnetospheres of strongly magnetized neutron stars

Abstract

Detecting axionic dark matter (DM) could be possible in an X-ray spectrum from strongly magnetized neutron stars (NSs). We examine the possibility of axion-photon conversion in the magnetospheres of strongly magnetized NSs. In the current work, we investigate how the modified Tolman Oppenheimer Volkoff (TOV) system of equations (in the presence of a magnetic field) affects the energy spectrum of axions and axions-converted photon flux. We have considered the distance-dependent magnetic field in the modified TOV equations. We employ three different equations of states (EoSs) to solve these equations. We obtain the axions emission rate by including the Cooper-pair-breaking formation process (PBF) and Bremsstrahlung process in the core of NSs using the NSCool code. We primarily focus on three NSs: PSR B0531+21, PSR J0538+2817, and one Magnificient seven (M7) star RXJ 1856.5-3754. We further investigate the impact of the magnetic field on the actual observables, such as axion`s energy spectrum and axion-photon flux. We also compare our calculated axion-photon flux from all available archival data from PN+MOS+Chandra. Our predicted axion-photon flux values as a function of axion`s energy closely follow the experimentally archival data, which allows us to put bounds on the axion`s mass for the three different EoS.13