Search for GeV and X-ray flares associated with the IceCube track-like neutrinos

TL;DR

This study searched for gamma-ray and X-ray flares associated with IceCube track-like neutrino events using Fermi-LAT data, but found no significant counterparts, providing upper limits on possible source fluxes and implications for neutrino source density.

Contribution

First systematic search for gamma-ray and X-ray counterparts to IceCube track-like neutrinos with Fermi-LAT, setting upper limits and constraining source models.

Findings

No significant GeV gamma-ray excess detected

Upper limits established for gamma-ray fluxes during neutrino events

No associated X-ray transients found

Abstract

Dozens of high-energy neutrinos have been detected by the IceCube neutrino telescope, but no clear association with any classes of astrophysical sources has been identified so far. Recently, Kadler et al. (2016) report that a PeV cascade-like neutrino event occurs in positional and temporal coincidence with a giant gamma-ray flare of the blazar PKS B1424-418. Since IceCube track-like events have much better angular resolution, we here search for possible short-term gamma-ray flares that are associated with the IceCube track-like events with Fermi Large Area Telescope (LAT) observations. Among them, three track-like neutrino events occur within the field of view of Fermi-LAT at the time of the detection, so search for the {\em prompt} gamma-ray emission associated with neutrinos are possible. Assuming a point source origin and a single power law spectrum for the possible gamma-ray sources associated with neutrinos, a likelihood analysis of 0.2-100 GeV photons observed by Fermi-LAT on the timescales of $\sim 12$ hours and one year are performed, and for the three special neutrinos, the analysis are also performed on the timescales of thousand of seconds before and after the neutrino detection. No significant GeV excesses over the background are found and the upper limit fluxes at 95\% confidence level are obtained for different timescales. We also search for possible hard X-ray transient sources associated with the IceCube track-like neutrino events, but the search also yields null results. We discuss the implication of the non-detection of gamma-ray flares for the constraints on the neutrino source density.