Magnetic Turbulence Boosts Supernova Signals of Axion-Photon Conversion

Abstract

Magnetic fields between a supernova (SN) and Earth convert axions into gamma rays. The absence of such a signal in coincidence with SN 1987A neutrinos, using the coherent Milky Way field, provides well-studied constraints on $g_{ap}\times g_{aγ}$ (axion-proton times axion-photon couplings) and on $g_{aγ}$ alone. We show that the small-scale power of the turbulent magnetic field component boosts axion-photon conversion and, crucially, extends sensitivity to larger masses. The turbulent field components of the Milky Way and of the Large Magellanic Cloud (hosting SN 1987A) yield improvements of up to two orders of magnitude in $g_{ap}\times g_{aγ}$. Turbulence should likely impact the sensitivity of other searches based on other axion-photon conversion sites, such as starburst galaxies.