High-energy Neutrinos from Gamma-Ray-faint Accretion-powered Hypernebulae

Abstract

Hypernebulae are inflated by accretion-powered winds accompanying hyper-Eddington mass transfer from an evolved post-main-sequence star onto a black hole or neutron star companion. The ions accelerated at the termination shock—where the collimated fast disk winds and/or jet collide with the slower, wide-angled wind-fed shell—can generate high-energy neutrinos via hadronic proton–proton reactions, and photohadronic (p γ) interactions with the disk thermal and Comptonized nonthermal background photons. It has been suggested that some fast radio bursts (FRBs) may be powered by such short-lived jetted hyper-accreting engines. Although neutrino emission associated with the millisecond duration bursts themselves is challenging to detect, the persistent radio counterparts of some FRB sources—if associated with hypernebulae—could contribute to the high-energy neutrino diffuse background flux. If the hypernebula birth rate follows that of stellar-merger transients and common envelope events, we find that their volume-integrated neutrino emission—depending on the population-averaged mass-transfer rates—could explain up to ∼25% of the high-energy diffuse neutrino flux observed by the IceCube Observatory and the Baikal Gigaton Volume Detector Telescope. The time-averaged neutrino spectrum from hypernebula—depending on the population parameters—can also reproduce the observed diffuse neutrino spectrum. The neutrino emission could in some cases furthermore extend to >100 PeV, detectable by future ultra-high-energy neutrino observatories. The large optical depth through the nebula to Breit–Wheeler (γ γ) interaction attenuates the escape of GeV–PeV gamma rays coproduced with the neutrinos, rendering these gamma-ray-faint neutrino sources, consistent with the Fermi observations of the isotropic gamma-ray background.