High-energy Neutrinos and Gamma Rays from Nonrelativistic Shock-powered Transients

Abstract

Shock interaction has been argued to play a role in powering a range of optical transients, including supernovae, classical novae, stellar mergers, tidal disruption events, and fast blue optical transients. These same shocks can accelerate relativistic ions, generating high-energy neutrino and gamma-ray emission via hadronic pion production. The recent discovery of time-correlated optical and gamma-ray emission in classical novae has revealed the important role of radiative shocks in powering these events, enabling an unprecedented view of the properties of ion acceleration, including its efficiency and energy spectrum, under similar physical conditions to shocks in extragalactic transients. Here we introduce a model for connecting the radiated optical fluence of nonrelativistic transients to their maximal neutrino and gamma-ray fluence. We apply this technique to a wide range of extragalactic transient classes in order to place limits on their contributions to the cosmological high-energy gamma-ray and neutrino backgrounds. Based on a simple model for diffusive shock acceleration at radiative shocks, calibrated to novae, we demonstrate that several of the most luminous transients can accelerate protons up to 1016 eV, sufficient to contribute to the IceCube astrophysical background. Furthermore, several of the considered sources—particularly hydrogen-poor supernovae—may serve as “gamma-ray-hidden” neutrino sources owing to the high gamma-ray opacity of their ejecta, evading constraints imposed by the nonblazar Fermi Large Area Telescope background. However, adopting an ion acceleration efficiency of ∼0.3%–1% motivated by nova observations, we find that currently known classes of nonrelativistic, potentially shock-powered transients contribute at most a few percent of the total IceCube background.

A concordance scenario for the observed neutrino from a tidal disruption event

“…We conclude that TDEs might be a promising class of neutrino emitters. While we have presented only one model here, other possibilities are conceivable, such as the interaction of an isotropic outflow with UV photons 17 , non-relativistic shocks forming in the environment 29 or a neutrino production from the accretion disk itself, especially radiatively inefficient accretion flows or magnetically arrested disk states 14 ; the neutrino production may also happen in a hot corona similar to that of an active galactic nucleus (AGN) 30 . Our model is unique in that we have emphasized the connection to the X-ray observations, we have described the late, post-peak neutrino observation, and we have obtained a sufficiently high neutrino fluence to describe the observations in spite of a relatively small assumed SMBH mass.…”

Radio Observations of an Ordinary Outflow from the Tidal Disruption Event AT2019dsg

“…AT 2019dsg also exhibited X-ray emission and radio emission in the first few months following discovery (Cannizzaro et al 2020;Stein et al 2021). Additionally, Stein et al (2021) claim a potential coincident high-energy neutrino with the spatial location of AT 2019dsg, but several months after discovery (on 2019 October 1); the emission mechanism for such a neutrino is debated (Fang et al 2020;Winter & Lunardini 2020;Liu et al 2020;Murase et al 2020).…”

Tidal Disruption Events and High-Energy Neutrinos

“…Given this wealth of new data, one can consider where TDEs falls in the broader 'zoo' of optical transient populations. While TDEs are intrinsically rare phenomena, with rates less than 1% of the core-collapse supernova rate, each individual TDE can be extremely bright, reaching optical outputs one thousand times brighter than a typical supernova [19]. In aggregate, TDEs thus output enormous rates of energy into the universe.…”