Supernova axions convert to gamma-rays in magnetic fields of progenitor stars

Abstract

It has long been established that axions could have been produced within the nascent proto-neutron-star formed following the type II supernova SN1987A, escaped the star due to their weak interactions, and then converted to gamma-rays in the Galactic magnetic fields; the non-observation of a gamma-ray flash coincident with the neutrino burst leads to strong constraints on the axion-photon coupling for axion masses $m_a\lesssim 10^{-10}$ eV. In this work we use SN1987A to constrain higher mass axions, all the way to $m_a\sim 10^{-3}$ eV, by accounting for axion production from the Primakoff process, nucleon bremsstrahlung, and pion conversion along with axion-photon conversion on the still-intact magnetic fields of the progenitor star. Moreover, we show that gamma-ray observations of the next Galactic supernova, leveraging the magnetic fields of the progenitor star, could detect quantum chromodynamics axions for masses above roughly 50 $\mu$eV, depending on the supernova. We propose a new full-sky gamma-ray satellite constellation that we call the GALactic AXion Instrument for Supernova (GALAXIS) to search for such future signals along with related signals from extragalactic neutron star mergers.

Comments: 10+18 pages, 3+20 figures, video abstract at https://youtu.be/QiNonlkARps; v2: updated to journal version, minor analysis issues fixed for SMM, conclusions unchanged