Black hole hyperaccretion in collapsars. I. MeV neutrinos

As the plausible central engine of gamma-ray bursts (GRBs), a black hole (BH) hyperaccretion disk should be in a state of neutrino-dominated accretion flow (NDAF) if the accretion rate is larger than the ignition rate of an NDAF. A rotating stellar-mass BH surrounded by a hyperaccretion disk might be born in the center of a massive core collapsar. In the initial hundreds of seconds of the accretion process, the mass supply rate of the massive progenitor is generally higher than the ignition accretion rate, but the jets are generally choked in the envelope. Thus, neutrinos can be emitted from the center of a core collapsar. In this paper, we study the effects of the masses and metallicities of progenitor stars on the time-integrated spectra of electron neutrinos from NDAFs. The peak energies of the calculated spectra are approximately 10-20 MeV. The mass of a collapsar has little influence on the neutrino spectrum, and a low metallicity is beneficial to the production of low-energy ($\lesssim$ 1 MeV) neutrinos. We also investigate the differences in the electron neutrino spectra between NDAFs and proto-neutron stars. Combining with the electromagnetic counterparts and multi-messenger astronomy, one may verify the possible remnants of the core collapse of massive stars with future neutrino detectors.