Bayesian analysis of neutrinos observed from supernova SN 1987A

We present a Bayesian analysis of the energies and arrival times of the neutrinos from supernova SN 1987A detected by the Kamiokande II, IMB, and Baksan detectors, and find strong evidence for two components in the neutrino signal: a long time scale component from thermal Kelvin-Helmholtz cooling of the nascent neutron star, and a brief (~< 1 s), softer component similar to that expected from emission by accreting material in the delayed supernova scenario. In the context of this model, we show that the data constrain the electron antineutrino rest mass to be less than 5.7 eV with 95% probability. Our analysis takes advantage of significant advances that have occured in the years since the detections in both our understanding of the supernova mechanism and our ability to analyze sparse data. As a result there are substantial differences between our inferences and those found in earlier studies. We find that two-component models for the neutrino signal make the data >100 times more probable than single-component models. In addition, the radius and binding energy of the nascent neutron star implied by single-component models deviates significantly from the values predicted by current neutron star models, whereas those implied by models with an accretion component are in complete agreement with the predictions. As a result, two-component models are hundreds to thousands of times more probable than single-component models. The neutrino data thus provide the first direct observational evidence in favor of the delayed supernova scenario over the prompt scenario. (Abridged abstract)