Investigating IceCube Neutrino Alerts with the HAWC $\gamma$-Ray Observatory

TL;DR

This study searches for gamma-ray and neutrino coincidences using HAWC data and IceCube alerts, finding a 5% coincidence rate consistent with background expectations, including detections from two known AGNs.

Contribution

It presents the first coincidence analysis between HAWC gamma-ray data and IceCube neutrino alerts, utilizing a Bayesian Block algorithm for the search.

Findings

Approximately 5% coincidence rate observed, consistent with background expectations.

Detected neutrino coincidences include known AGNs Markarian 421 and 501.

No significant excess of true astrophysical sources identified.

Abstract

Neutrino emission from astrophysical sources has long been considered a signature of cosmic-ray acceleration. The IceCube neutrino observatory has observed a diffuse flux of TeV-PeV neutrinos, but very few confirmed sources have emerged. With the recent publication of IceCube Event Catalog (IceCat-1), IceCube has released a list of the most promising astrophysical neutrino events since May 2011. Using the archival data from the High Altitude Water Cherenkov (HAWC) $\gamma$-ray observatory, we perform a coincidence search for gamma rays and neutrinos using a Bayesian Block algorithm with the public IceCube alerts from IceCat-1, along with additional alerts issued later. In this work, we consider 368 alerts, up to July 8, 2025, that are within HAWC's field of view. We observe approximately a 5\% coincident detection rate, which is consistent with expectations from background. Two of these detections contain the Active Galactic Nuclei (AGN) Markarian 421 and Markarian 501. We discuss the likelihood that the neutrino/$\gamma$-ray coincidences are false positives and a brief overview of the results.