Limits to the radiative decays of neutrinos and axions from γ-ray observations of SN 1987A

Using γ-ray observations made by the Solar Maximum Mission Gamma Ray Spectrometer in the energy range 4.1 to 6.4 MeV we limit the possible radiative decays of neutrinos and axions emitted by SN 1987A. For neutrinos less massive than about 20 eV our constraint is tau/sub nu//m/sub nu/ greater than 1.7 x 1015 B/sub γ/ sec/eV; and for masses between 20 and 275 eV our constraint is tau/sub nu/ greater than 3.4 x 1016 B/sub γ/γ/sub GRS//sup -1/2/ sec, where B/sub γ/ is the branching ratio for the radiative decay mode and γ/sub GRS/ is the yet undetermined instrument background count rate in units of 0.1 sec-1. The first limit is some 2 orders-or-magnitude better than the previous limit based upon the integrated γ-ray flux from all supernovae. The axion limit is less interesting: m/sub α/ less than 55γ/sub GRS//sup 11/94/ eV. 15 refs