paper

Constraints on the Intergalactic Magnetic Field with Gamma-Ray Observations of Blazars

arXiv:1510.02485 · doi:10.1088/0004-637X/814/1/20

Abstract

Distant BL Lacertae objects emit rays which interact with the extragalactic background light (EBL), creating electron-positron pairs, and reducing the flux measured by ground-based imaging atmospheric Cherenkov telescopes (IACTs) at very-high energies (VHE). These pairs can Compton-scatter the cosmic microwave background, creating a -ray signature at slightly lower energies observable by the \fermi\ Large Area Telescope (LAT). This signal is strongly dependent on the intergalactic magnetic field (IGMF) strength () and its coherence length (). We use IACT spectra taken from the literature for 5 VHE-detected BL Lac objects, and combine it with LAT spectra for these sources to constrain these IGMF parameters. Low values can be ruled out by the constraint that the cascade flux cannot exceed that observed by the LAT. High values of can be ruled out from the constraint that the EBL-deabsorbed IACT spectrum cannot be greater than the LAT spectrum extrapolated into the VHE band, unless the cascade spectrum contributes a sizable fraction of the LAT flux. We rule out low values ( G for \ Mpc) at in all trials with different EBL models and data selection, except when using GeV spectra and the lowest EBL models. We were not able to constrain high values of .

18 pages, 11 figures, 2 tables. Accepted by ApJ

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