VERITAS and multiwavelength observations of the Blazar B3 2247+381 in response to an IceCube neutrino alert

TL;DR

This study investigates the potential link between a blazar and a neutrino alert, using multiwavelength observations, but finds no significant evidence supporting the blazar as the neutrino source, suggesting the neutrino excess is likely a background fluctuation.

Contribution

The paper provides multiwavelength observational data of B3 2247+381 in response to an IceCube neutrino alert and assesses its potential as a neutrino source using spectral modeling and flux comparisons.

Findings

No detection of the blazar with VERITAS during the neutrino alert period.

The blazar was in a low-flux state across multiple wavelengths during the neutrino events.

The neutrino excess is likely a background fluctuation, not associated with the blazar.

Abstract

While the sources of the diffuse astrophysical neutrino flux detected by the IceCube Neutrino Observatory are still largely unknown, one of the promising methods used towards understanding this is investigating the potential temporal and spatial correlations between neutrino alerts and the electromagnetic radiation from blazars. We report on the multiwavelength target-of-opportunity observations of the blazar B3 2247+381, taken in response to an IceCube multiplet alert for a cluster of muon neutrino events compatible with the source location between May 20, 2022 and November 10, 2022. B3 2247+381 was not detected with VERITAS during this time period. The source was found to be in a low-flux state in the optical, ultraviolet and gamma-ray bands for the time interval corresponding to the neutrino event, but was detected in the hard X-ray band with NuSTAR during this period. We find the multiwavelength spectral energy distribution is well described using a simple one-zone leptonic synchrotron self-Compton radiation model. Moreover, assuming the neutrinos originate from hadronic processes within the jet, the neutrino flux would be accompanied by a photon flux from the cascade emission, and the integrated photon flux required in such a case would significantly exceed the total multiwavelength fluxes and the VERITAS upper limits presented here. The lack of flaring activity observed with VERITAS, combined with the low multiwavelength flux levels, and given the significance of the neutrino excess is at 3$\sigma$ level (uncorrected for trials), makes B3 2247+381 an unlikely source of the IceCube multiplet. We conclude that the neutrino excess is likely a background fluctuation.