SN1987A and the properties of the neutrino burst

Abstract

We reanalyze the neutrino events from SN1987A in IMB and Kamiokande-II ͑KII͒ 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 one͒ 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 ͑marginally͒ in energy. The observations give useful information on the astrophysical parameters of the collapse. We find that the mean energy of electron antineutrinos is ͗E͘ϭ12-15 MeV, the total energy radiated around (2 -5)ϫ10 53 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.

Is there a problem with low energy SN1987A neutrinos?

“…This is why we would like to consider the possibility that some of the low energy events in KII are not due toν e p → e + n interactions of supernova neutrinos as usually assumed. The possibility that a few events are due to elastic scattering has been recently reconsidered [11], finding that, although this cannot be excluded, it helps only marginally to explain the presence of low energy events in KII data set. This forced the authors of [11] to admit that a few of these events are of a different origin, and possibly are due to background.…”

Neutrinos from Supernovas and Supernova Remnants

“…The numerical values of k ν = (ψ (1) ν + ψ (2) ν )/ψ γ for several values of Γ, obtained using the spectrum-weighted momenta from figure 5.5 by [17], are reported in table 1 by [4]. 3 In our calculation, we omitted the contribution of ν's produced in other decay modes of π and K, as well as in K 0 's decay chains, and so we introduce and error at several % level. In the calculation made in [16], those contributions are taken into account.…”

“…In 2000 years, the SNR proceeds by ∼ 10 pc. The density is ∼ 0.2 protons/cm 3 , too faint to permit a significant production of secondaries. In the galaxy, the most dense noncollapsed objects are the molecular clouds, whose density can reach 10 4 protons/cm 3 .…”

Neutrino bursts from gravitational stellar collapses with LVD

“…Assuming a model for the neutrino emission and propagation, the detector sensitivity can be expressed in terms of source distance (or emitted neutrino flux). In particular we adopt the following conservative values for the astrophysical parameters of SN1987A (Costantini et al, 2004(Costantini et al, , 2007: averageν e energy <Eν e >=14 MeV; total radiated energy E b =2.4·10 53 erg, assuming energy equipartition; average non-electron neutrino energy 10% higher thanν e (Keil et al, 2003), and concerning neutrino oscillations (see Agafonova et al, 2007, for a discussion), we consider normal mass hierarchy. We calculate the number of inverse beta decay signals expected from a SN1987A-like event occurring at different distances, for E cut =7 and E cut =10 MeV.…”