Shock interaction has been argued to play a role in powering a range of optical transients , including supernovae ( particularly the superluminous class ; SLSNe ) , classical novae , stellar mergers , tidal disruption events ( TDEs ) , and fast blue optical transients ( FBOTs ) .
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 non-relativistic transients to their maximal neutrino and gamma-ray fluence ( i.e .
assuming their optical luminosity is entirely shock-powered ) .
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 energies E _ { max } \mathrel { \hbox { \hbox to 0.0 pt { \hbox { \lower 4.0 pt \hbox { $ \sim$ } } } % \hbox { $ > $ } } } 10 ^ { 16 } eV , sufficient to contribute to the IceCube astrophysical background .
Furthermore , several of the considered sources - particularly hydrogen-poor supernovae - may serve as “ hidden ” gamma-ray sources due to the high gamma-ray opacity of their ejecta , evading constraints imposed by the non-blazar Fermi -LAT background .
However , adopting an ion acceleration efficiency \epsilon _ { nt } \sim 0.3 - 1 \% motivated by nova observations , we find that currently known classes of non-relativistic , potentially shock-powered transients contribute at most a few percent of the total IceCube background .