A Multi-messenger Search for Ultra-high-energy Gamma Rays in Coincidence with Neutrinos

TL;DR

This study investigates the correlation between ultra-high-energy gamma rays and neutrinos using multimessenger data, finding potential associations but highlighting the need for more sensitive instruments for definitive source identification.

Contribution

The paper introduces a new metric for selecting high-quality UHE events and applies it to search for correlations between HAWC gamma-ray data and IceCube neutrino alerts.

Findings

24 spatial coincidences found, exceeding random expectations

Potential associations between gamma rays and neutrinos suggested

Current angular resolutions limit definitive source identification

Abstract

The last five years have shown us that ultra-high-energy (UHE; $>$100 TeV) gamma-ray sources are ubiquitous, but the nature of these sources remain highly uncertain. UHE gamma rays can be produced via either leptonic (Inverse compton) or hadronic (pion decay) emission mechanisms. To decisively determine the emission mechanisms, multimessenger searches are essential. Neutrinos are of particular interest as they are only created via hadronic channels. In this work, we describe a metric to select high-quality UHE events from the High Altitude Water Cherenkov (HAWC) Observatory. We use this metric to search for correlations between HAWC archival data and IceCube public neutrino alerts. 24 spatial coincidences are found, which is higher than the number of events expected by random chance. Therefore, we conclude that there are likely associations between HAWC gamma rays and IceCube neutrinos, but the angular resolutions of the two instruments prevent us from conclusively making any definitive associations between the coincidences and specific astrophysical sources. More sensitive detectors are needed.