Search for neutrino emission from blazar $\gamma$-ray flares accounting for possible neutrino time delays

TL;DR

This study searches for high-energy neutrino emissions from blazar gamma-ray flares, considering potential time delays, and finds a tentative correlation that is consistent with random chance after statistical correction.

Contribution

It introduces a method to account for neutrino time delays relative to gamma-ray flares in blazars and applies it to existing data sets, exploring possible neutrino-emission correlations.

Findings

A ~2σ pre-trial correlation at ~1000 days delay

Correlation is consistent with null hypothesis after trial correction

No statistically significant neutrino-flare association found

Abstract

We report the results of the search for the high-energy neutrino emission associated with blazar flares, accounting for a possible lag of neutrinos with respect to the electromagnetic emission, either due to the slowness of the proton energy losses in $p\gamma$ collisions and/or proton acceleration. We perform two tests, cross-matching neutrinos with energies $E_{\nu} \gtrsim 100$ TeV from the public catalogue of neutrino alerts IceCat-1 with active galactic nuclei from two source samples based on 1) the MOJAVE database and 2) the CGRaBS catalogue, and utilising Fermi-LAT light curves from the public light curve repository. We scan over a wide range of values of the jet-frame time delay $t^{\prime}_{\mathrm{delay}}$ between the neutrino arrival and the time of the prior major $\gamma$-ray flare and find a pre-trial $\sim 2\sigma$ correlation at $t^{\prime}_{\mathrm{delay}} \sim 10^{3}$ d, which is consistent ($p_{\mathrm{post-trial}} \sim 0.1$) with expectations under the null hypothesis after trial correction.