Search for Galactic PeV Gamma Rays with the IceCube Neutrino Observatory

TL;DR

This study used IceCube data to search for PeV gamma-ray sources in the Galaxy, setting upper limits on gamma-ray fluxes and projecting improved sensitivity with the full detector.

Contribution

First search for Galactic PeV gamma rays with IceCube, establishing upper limits and demonstrating the potential of the full detector for future observations.

Findings

No gamma-ray sources detected in the 1.2-6.0 PeV range.

Set a 90% confidence level upper limit on gamma-ray to cosmic-ray ratio.

Projected over tenfold sensitivity improvement with the full IceCube detector.

Abstract

Gamma-ray induced air showers are notable for their lack of muons, compared to hadronic showers. Hence, air shower arrays with large underground muon detectors can select a sample greatly enriched in photon showers by rejecting showers containing muons. IceCube is sensitive to muons with energies above ~500 GeV at the surface, which provides an efficient veto system for hadronic air showers with energies above 1 PeV. One year of data from the 40-string IceCube configuration was used to perform a search for point sources and a Galactic diffuse signal. No sources were found, resulting in a 90% C.L. upper limit on the ratio of gamma rays to cosmic rays of 1.2 x 10^(-3)for the flux coming from the Galactic Plane region (-80 deg < l < -30 deg; -10 deg < b < 5 deg) in the energy range 1.2 - 6.0 PeV. In the same energy range, point source fluxes with E^(-2) spectra have been excluded at a level of (E/TeV)^2 d\Phi/dE ~ 10^(-12)-10^(-11) cm^2/s/TeV depending on source declination. The complete IceCube detector will have a better sensitivity, due to the larger detector size, improved reconstruction and vetoing techniques. Preliminary data from the nearly-final IceCube detector configuration has been used to estimate the 5 year sensitivity of the full detector. It is found to be more than an order of magnitude better, allowing the search for PeV extensions of known TeV gamma-ray emitters.