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 ∼ 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 log10B10>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 BIGMF∼10−17−10−15G.
@article{arxiv.1410.7717,
title = {Evidence for GeV Pair Halos around Low Redshift Blazars},
author = {Wenlei Chen and James H. Buckley and Francesc Ferrer},
journal= {arXiv preprint arXiv:1410.7717},
year = {2015}
}