Constraints on Minute-Scale Transient Astrophysical Neutrino Sources

TL;DR

This paper sets limits on the neutrino emission from short-lived astrophysical transients like GRBs, using IceCube data, and constrains their contribution to the overall astrophysical neutrino flux.

Contribution

It provides the first generic bounds on neutrino fluxes from transient sources, constraining their energy output and occurrence rate based on IceCube observations.

Findings

Neutrino flux from rare sources like long GRBs is constrained to less than 5% of the astrophysical flux.

Median energy released in neutrinos by a bright GRB-like source is less than 10^52.5 erg.

Transient sources must be more common than 10^-5 Mpc^-3 yr^-1 to explain the total neutrino flux.

Abstract

High-energy neutrino emission has been predicted for several short-lived astrophysical transients including gamma-ray bursts (GRBs), core-collapse supernovae with choked jets and neutron star mergers. IceCube's optical and X-ray follow-up program searches for such transient sources by looking for two or more muon neutrino candidates in directional coincidence and arriving within 100s. The measured rate of neutrino alerts is consistent with the expected rate of chance coincidences of atmospheric background events and no likely electromagnetic counterparts have been identified in Swift follow-up observations. Here, we calculate generic bounds on the neutrino flux of short-lived transient sources. Assuming an $E^{-2.5}$ neutrino spectrum, we find that the neutrino flux of rare sources, like long gamma-ray bursts, is constrained to <5% of the detected astrophysical flux and the energy released in neutrinos (100GeV to 10PeV) by a median bright GRB-like source is $<10^{52.5}$erg. For a harder $E^{-2.13}$ neutrino spectrum up to 30% of the flux could be produced by GRBs and the allowed median source energy is $< 10^{52}$erg. A hypothetical population of transient sources has to be more common than $10^{-5}\text{Mpc}^{-3}\text{yr}^{-1}$ ($5\times10^{-8}\text{Mpc}^{-3}\text{yr}^{-1}$ for the $E^{-2.13}$ spectrum) to account for the complete astrophysical neutrino flux.