Neutrino-inducedγ-ray emission from supernovae

Abstract

During a core-collapse supernova, absorption of {nu}{sub e} emitted from the protoneutron star by protons in the hydrogen envelope produces neutrons and positrons. Neutron capture on protons and positron annihilation then produce {gamma} rays of 2.22 and 0.511 MeV, respectively. We calculate the fluxes of these {gamma} rays expected from a supernova with an 11M{sub {center_dot}} progenitor. The flux from neutron capture on protons exponentially decays on a time scale of 564 s, which is determined by neutron decay and capture on protons and {sup 3}He nuclei. The peak flux is 2.38x10{sup -7} cm{sup -2} s{sup -1} for a supernova at a distance of 1 kpc. In contrast, the {gamma}-ray flux from positron annihilation follows the time evolution of the {nu}{sub e} luminosity and lasts for {approx}10 s. The peak flux in this case is 6.8x10{sup -5} cm{sup -2} s{sup -1} for a supernova at a distance of 1 kpc. Detection of the above {gamma}-ray fluxes is beyond the capability of current instruments, and perhaps even those planned for the near future. However, if such fluxes can be detected, they not only constitute a new kind of signal that occurs during the gap of several hours between the neutrino signalsmore » and the optical display of a supernova, but may also provide a useful probe of the conditions in the surface layers of the supernova progenitor.« less