http://arxiv.org/abs/1908.10882
We study high-energy neutrino emissions from tidal disruption remnants around supermassive black holes (SMBHs). The neutrinos are produced by the decay of charged pions originated in ultra-relativistic protons which are accelerated there. In the standard theory of tidal disruption events (TDEs), there are four distinct phases from the circularization of stellar debris to super- and sub-Eddington accretion flows to radiatively inefficient accretion flows (RIAFs). In addition, we consider the magnetically arrested disk (MAD) state in both the super-Eddington accretion and RIAF phases. We find that there are three promising cases to produce neutrino emissions: the super-Eddington accretion phase with the MAD state and the RIAF phase with both non-MAD and MAD states. In the super-Eddington MAD state, the enhanced magnetic field makes it possible to accelerate the protons up to an energy of E_{p,max}~0.35 PeV (M_{bh}/10^{7.7}M_sun)^{41/48} with the other given appropriate parameters. The neutrino energy estimated at the peak of the energy spectrum is then E_{nu, pk}~67TeV(M_bh/10^{7.7}Msun)^{41/48}. For M_bh>~10^{7.7}Msun, the neutrino light curve is proportional to t^{-65/24}, while it follows the standard t^{-5/3} decay rate for M_{bh}<10^{7.7}M_sun. In both cases, the neutrino luminosity is nearly Eddington. Such a high luminosity and characteristic light curve diagnose the MAD state in TDEs. In the RIAF phase, we find E_{p, max}~0.45PeV(M_bh/10^7Msun)^{5/3} and E_{nu,pk}~0.35PeV(M_bh/10^7Msun)^{5/3}, and its light curve is proportional to t^{-10/3}. This indicates one can identify if the existed RIAFs are the TDE origin or not. Although E_{p,max}~25PeV(M_bh/10^7Msun)^{-1/12} in the RIAF with the MAD state, the resultant neutrino luminosity is too weak to be detected with IceCube. The tidal disruption remnants are potentially a population of hidden neutrino sources invisible in gamma rays.
K. Hayasaki and R. Yamazaki
Fri, 30 Aug 19
31/58
Comments: 41 pages, 2 figures, accepted for publication in ApJ; comments are welcomed
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