Multimessenger ms- to decades-long transients from hyper-accreting compact objects

“Hypernebulae” are a potential new class of objects that are inflated by accretion-powered winds accompanying hyper-Eddington mass transfer from an evolved post-main sequence star onto a stellar-mass black hole or neutron star companion. It has been suggested that some fast radio bursts (FRBs) may be powered by such short-lived (decades-millenia), jetted, accreting engines, and the surrounding hypernebula could generate persistent radio emission and contribute large and time-variable rotation measure to the bursts. Hypernebulae can be discovered independently of an FRB association in radio surveys, such as VLASS, as off-nuclear point sources whose fluxes can evolve significantly on timescales as short as years, possibly presaging energetic transients from common-envelope mergers. The ions accelerated at the hypernebula termination shock can generate high-energy neutrinos via photohadronic (pγ) interactions with the disk thermal and Comptonized nonthermal background photons. Although detecting neutrino emission associated with the ms-duration bursts themselves is untenable, 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 steller-merger transients and common envelope events, their volume-integrated neutrino emission could explain ≳25% of the high-energy diffuse neutrino flux observed by the IceCube Observatory and the Baikal-GVD Telescope.