High-energy neutrinos from fallback accretion of binary neutron star merger remnants

TL;DR

This paper models high-energy neutrino production from fallback accretion in binary neutron star mergers, predicting fluxes that could contribute to IceCube observations and be correlated with gravitational waves.

Contribution

It introduces a numerical simulation of neutrino fluxes from fallback accretion in neutron star mergers, considering different parameter scenarios including an optimistic case.

Findings

Neutrino flux peaks at 10^3-10^4 seconds after merger.

Detection possible only within ~4 Mpc under optimistic conditions.

Fallback neutrino emission could account for up to 10% of IceCube's diffuse flux.

Abstract

Following the coalescence of binary neutron stars, debris from the merger which remains marginally bound to the central compact remnant will fallback at late times, feeding a sustained accretion flow. Unbound winds or a wide-angle jet from this radiatively-inefficient disk may collide with the comparatively slow dense kilonova ejecta released from an earlier phase. Under the assumption that such interaction accelerate cosmic rays to ultra-high energies, we numerically simulate their propagation and interactions through the dynamical ejecta. The hadronuclear and photo-hadronic processes experienced by particles produce isotropic high-energy neutrino fluxes, peaking at times $10^{3-4}\,$s, which we calculate for two sets of parameters. A first set is inspired by the observations of GW170817. In the second scenario, which we call optimistic, parameters are chosen so as to optimize the neutrino flux, within the range allowed by observation and theory. We find that single sources can only be detected with IceCube-Gen2 for optimistic scenarios and if located within $\sim 4\,$Mpc. The cumulative flux could contribute to $\sim 0.5-10\%$ of the diffuse flux observed by the IceCube Observatory, depending on the fall-back power and the cosmic ray composition. The neutrino emission powered by fallback is nearly isotropic, and can be used for future correlation studies with gravitational wave signals.