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Updated: Mar 29, 2026

Visualization of Low-Level Gamma Radiation Sources Using a Low-Cost, High-Sensitivity, Omnidirectional Compton Camera
Published on: January 30, 2020
Search for GeV γ-Ray Pair Halos Around Low Redshift Blazars
Wenlei Chen1, James H Buckley1, Francesc Ferrer1
1Department of Physics and McDonnell Center for the Space Sciences, Washington University in St. Louis, St. Louis, Missouri 63130, USA.
Abstract:
We report on the results of a search for γ-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 ~1 GeV photons around 24 stacked isolated high-synchrotron-peaked BL Lacs with redshift z<0.5 shows an excess over that of pointlike sources. A frequentist test yields a p value of p~0.01 for the extended emission against the point-source hypothesis. A Bayesian estimation provides Bayes factors log_{10}B_{10}>2, consistent with expectations for pair halos produced in the intergalactic magnetic fields with strength B_{IGMF}~10^{-17}-10^{-15} G.
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