Evidence for GeV Pair Halos around Low Redshift Blazars

TL;DR

This study provides evidence for GeV pair halos around low-redshift blazars, suggesting the presence of intergalactic magnetic fields influencing gamma-ray propagation.

Contribution

It presents the first stacking analysis of Fermi LAT data showing statistical evidence for pair halos around blazars, supporting models of intergalactic magnetic fields.

Findings

Detection of excess GeV photons around blazars

Bayes factor > 100 indicating strong evidence for extended emission

Consistent with pair halos produced by intergalactic magnetic fields

Abstract

We report on the results of a search for $\gamma$-ray pair halos with a stacking analysis of low-redshift blazars using data from the Fermi Large Area Telescope. For this analysis we used a number of a-priori selection criteria, including the spatial and spectral properties of the Fermi sources. The angular distribution of $\sim$ 1GeV photons around 24 stacked isolated high-synchrotron-peaked BL Lacs with redshift $z<0.5$ shows an excess over that of point-like sources. A statistical analysis yields a Bayes factor of $\mathrm{log}_{10}B_{10}>2$, providing evidence in favor of extended emission against the point-source hypothesis, consistent with expectations for pair halos produced in the IGMF with strength $B_{\mathrm{IGMF}}\sim 10^{-17}-10^{-15}\mathrm{G}$.