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

It has long been established that axions could have been produced through the Primakoff process 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 mₐ 10⁻¹⁰ eV. In this work we use SN1987A to constrain, for the first time, higher mass axions, all the way to mₐ ~ 10⁻³ eV, by accounting for 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 $50$ μeV, 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.