Axions from SN1987A

Axion emission from SN1987A by nucleon-nucleon axion bremsstrahlung is considered. On the basis of the neutrino observations the axion luminosity must be ≲${10}^{53}$ erg ${\mathrm{s}}^{\mathrm{-}1}$. This occurs if (1) axions couple very weakly: $m_a$≲0.75×${10}^{\mathrm{-}3}$ eV; or (2) axions couple strongly enough to be ‘‘trapped’’ and radiated from an ‘‘axion sphere’’ with $T_a$≲8 MeV: $m_a$≳2.2 eV. In general, ‘‘axion trapping’’ occurs for $m_a$≳0.016 eV. Our mass constraints are at best reliable to within a factor of ≃3.