Speaker
Description
We investigate axion emission from canonical $1.4\,M_\odot$ neutron stars using the APR and SLy equations of state, with particular emphasis on axion production through nucleon-nucleon bremsstrahlung and Cooper pair breaking and formation (PBF) processes in the stellar core. The background stellar structure is constructed by solving the Tolman-Oppenheimer-Volkoff equations in the presence of a radially dependent internal magnetic field, allowing a direct comparison between magnetized and non-magnetized configurations. The thermal evolution is then computed with an NSCool-based numerical framework including neutrino, photon, and axion emission under an iron-envelope heat-blanketing boundary. A central ingredient of this work is the implementation of different nucleonic pairing models in PBF process of axion production through density-dependent critical temperatures, which determine the onset and strength of neutron and proton superfluidity/superconductivity and strongly influence the PBF axion emissivity. For each stellar configuration, we compute the axion luminosity and spectrum arising from bremsstrahlung and PBF processes and subsequently evaluate the probability of axion-photon conversion in the magnetosphere. The conversion of axion to photon flux from the magnetosphere of neutron stars has been obtained. Finally, the converted axion-to-photon flux is compared with the observed Chandra, XMM-Newton/MOS, and NuSTAR data. On comparison, we find that the constraint on the axion mass and corresponding coupling constant vary significantly on the basis of pairing models in the PBF process of axion production.