Electron neutrino and antineutrino spectra associated with neutron star formation

The spectra of electron neutrinos and antineutrinos emitted by collapsing stellar nuclei have been calculated. The obtained spectra can be approximated by a simple analytical expression, which at high energies differs from the Fermi-Dirac distribution of zero chemical potential by an additional cutoff factor. The mean electron neutrino and antineutrino energies are found to be about 10 MeV and 13 MeV respectively. It is shown that the spectra are largely due to neutrino and antineutrino absorption by free nucleons.