Magnetar hard X-ray emission from axion-like particle conversion

We explore the possibility that axion-like-particles (ALPs), which would be produced in the core of magnetars and would then convert in the magnetosphere into photons, can explain magnetar hard X-ray spectra. We remark that this scenario would also provide answers to some questions related to magnetar heating. Indeed, considering that magnetars have: 1) hard X-ray spectra that are difficult to explain with known mechanisms; 2) large photon luminosities that force high core temperatures; 3) high core temperatures that imply large neutrino emissivities; 4) and large neutrino emissivities that lead to small magnetar lifetimes in contradiction to observations - explaining the hard X-ray spectra with ALPs could decrease the core temperatures and thus the neutrino emissivities, allowing for longer magnetar lifetimes as expected from observations. In this work, we initiate the study of this scenario for three magnetars with extreme luminosities, and conclude that the general idea is likely worth investigating in more detail.

Automated summary

This study explores the possibility of using ALPs to explain magnetar hard X-ray spectra and suggests that this scenario could also provide answers to magnetar heating related questions. The research finds that explaining the hard X-ray spectra with ALPs could decrease the core temperatures and neutrino emissivities of magnetars, allowing for longer lifetimes as expected from observations.