SN1987A and the properties of the neutrino burst

Abstract

We reanalyze the neutrino events from SN1987A in IMB and Kamiokande-II (KII) detectors, and compare them with the expectations from simple theoretical models of the neutrino emission. In both detectors the angular distributions are peaked in the forward direction, and the average cosines are 2 sigma above the expected values. Furthermore, the average energy in KII is low if compared with the expectations; but, as we show, the assumption that a few (probably one) events at KII have been caused by elastic scattering is not in contrast with the ``standard'' picture of the collapse and yields more satisfactory distributions in angle and (marginally) in energy. The observations give useful information on the astrophysical parameters of the collapse. We find that the mean energy of electron antineutrinos is $〈E〉=12--15\mathrm{MeV},$ the total energy radiated around $(2--5)\ifmmode\times\else\texttimes\fi{}{10}^{53}\mathrm{erg},$ and there is a hint for a relatively large radiation of nonelectronic neutrino species. These properties of the neutrino burst are not in disagreement with those suggested by the current theoretical paradigm, but the data leave wide space to nonstandard pictures, especially when neutrino oscillations are included.