Neutrino follow-up with the Zwicky Transient Facility: Results from the first 24 campaigns

TL;DR

The Zwicky Transient Facility conducted a systematic follow-up of high-energy neutrino alerts, constraining the optical properties of potential neutrino sources and finding limited associations, thus providing new insights into the origins of astrophysical neutrinos.

Contribution

This study presents the first comprehensive constraints on the optical luminosity function of neutrino sources using systematic follow-up data from ZTF.

Findings

No new neutrino source candidates were identified.

Bright transients above magnitude -21 contribute no more than 87% of neutrino flux.

Bright transients above magnitude -22 contribute no more than 58% of neutrino flux.

Abstract

The Zwicky Transient Facility (ZTF) performs a systematic neutrino follow-up program, searching for optical counterparts to high-energy neutrinos with dedicated Target-of-Opportunity (ToO) observations. Since first light in March 2018, ZTF has taken prompt observations for 24 high-quality neutrino alerts from the IceCube Neutrino Observatory, with a median latency of 12.2 hours from initial neutrino detection. From two of these campaigns, we have already reported tidal disruption event (TDE) AT 2019dsg and likely TDE AT 2019fdr as probable counterparts, suggesting that TDEs contribute >7.8% of the astrophysical neutrino flux. We here present the full results of our program through to December 2021. No additional candidate neutrino sources were identified by our program, allowing us to place the first constraints on the underlying optical luminosity function of astrophysical neutrino sources. Transients with optical absolutes magnitudes brighter that $-21$ can contribute no more than 87% of the total, while transients brighter than $-22$ can contribute no more than 58% of the total, neglecting the effect of extinction and assuming they follow the star formation rate. These are the first observational constraints on the neutrino emission of bright populations such as superluminous supernovae. None of the neutrinos were coincident with bright optical AGN flares comparable to that observed for TXS 0506+056/IC170922A, with such optical blazar flares producing no more than 26% of the total neutrino flux. We highlight the outlook for electromagnetic neutrino follow-up programs, including the expected potential for the Rubin Observatory.