Presupernova ultralight axionlike particles

We calculate the production of ultralight axionlike particles (ALPs) in a nearby supernova progenitor. Once produced, ALPs escape from the star and a part of them is converted into photons during propagation in the Galactic magnetic field. It is found that the MeV photon flux that reaches Earth may be detectable by γ -ray telescopes for ALPs lighter than ∼1 neV when Betelgeuse undergoes oxygen and silicon burning. The dependence of the γ -ray flux on the stellar mass is much smaller than the uncertainty that originates from the Galactic magnetic field. If ALPs are lighter than ∼0.1 neV and the supernova progenitor is close enough to the Solar System, the γ -ray flux is insensitive to the distance d because the ALP-photon conversion probability is proportional to d². (Non)detection of γ rays from a supernova progenitor with next-generation γ -ray telescopes just after presupernova neutrino alerts would lead to an independent constraint on ALP parameters as stringent as a SN 1987A limit.