Detection possibility of the pair-annihilation neutrinos from the neutrino-cooled pre-supernova star

Abstract

The signal produced in neutrino observatories by the pair-annihilation neutrinos emitted from a 20 M pre-supernova star at the silicon burning phase is estimated. The spectrum of the neutrinos with an average energy ∼2 MeV is calculated with the use of the Monte Carlo method. A few relevant reactions for neutrinos and anti-neutrinos in modern detectors are considered. The most promising results are fromν e + p −→ n + e + reaction. During the Si-burning phase we expect 1.38 neutrons/day/kiloton of water to be produced by neutrinos from a star located at a distance of 1 kpc. Small admixture of effective neutron-adsorbers as e.g. NaCl or GdCl 3 makes these neutrons easily visible because of Cherenkov light produced by electrons which were hit by ∼8 MeV photon cascade emitted by Cl or Gd nuclei. The estimated rate of neutron production for SNO and Super-Kamiokande is, respectively, 2.4 and 44 events per day for a star at 1 kpc. For future detectors UNO and Hyper-Kamiokande we expect 6.1 and 7.5 events per day even for a star 10 kpc away. This would make it possible to foresee a massive star death a few days before its core collapse. Importance of such a detection for theoretical astrophysics is discussed.

Probing supernova shock waves and neutrino flavour transitions in next-generation water Cherenkov detectors

“…In the absence of more detailed information, we assume a uniform neutrino flux from silicon burning for two days before t = 0, with emission parameters taken from [30].…”

“…For simplicity, we have taken α = 3 for all flavors for t > 0 [17], and α ≃ 4.3 (from a fit to the spectrum in [30]) for t < 0. For t > 0, the average energies for each flavor are given as a function of time in the LL simulation [27], while for t < 0 they are assumed nearly constant and equal to ∼ 1.8 MeV for all flavors in the OMK evaluation [30]. phase, as derived from [30] with shape parameter α = 4.28 [32].…”

“…For t > 0, the average energies for each flavor are given as a function of time in the LL simulation [27], while for t < 0 they are assumed nearly constant and equal to ∼ 1.8 MeV for all flavors in the OMK evaluation [30]. phase, as derived from [30] with shape parameter α = 4.28 [32]. Right panel: energy spectra associated to the supernova neutrino burst, averaged in the time interval for shock-wave effects (t > 2), as derived from [27] with shape parameter α = 3 [32].…”

“…The upper and lower panels show the neutrino emission rate dN ν /dt and the average neutrino energy E for different flavors. The left panels refer to the silicon burning phase from the OMK calculations [30], while the right panels refer to the supernova neutrino burst from the LL group simulation [27]. According to the LL simulation, all flavors have comparable emission rates (within a factor ∼ 2) in the so-called cooling phase (t > ∼ 0.5 s).…”

The next-generation liquid-scintillator neutrino observatory LENA

“…An increased neutron rate in LENA can signify neutrino emission by thermal processes in the progenitor during its last weeks of pre-SN evolution [88]. While this effect requires the star to be close, the red supergiant Betelgeuse at about 200 pc [89] is a possible candidate.…”