Determination of intergalactic magnetic fields from gamma ray data

TL;DR

This study measures intergalactic magnetic fields using gamma-ray data from Cherenkov and Fermi telescopes, revealing field strengths between 0.01 and 30 femtoGauss depending on cosmic-ray assumptions.

Contribution

It introduces a method to estimate intergalactic magnetic fields solely from spectral gamma-ray data, accounting for cosmic-ray interactions and source spectral properties.

Findings

Intergalactic magnetic fields are constrained between 0.01 and 30 femtoGauss.

The spectral data alone can determine magnetic field limits independent of source intrinsic spectra.

Cosmic-ray interactions significantly influence the observed gamma-ray spectra and magnetic field estimates.

Abstract

We report a measurement of intergalactic magnetic fields using combined data from Atmospheric Cherenkov Telescopes and Fermi Gamma-Ray Space Telescope, based on the spectral data alone. If blazars are assumed to produce both gamma rays and cosmic rays, the observed spectra are not sensitive to the intrinsic spectrum of the source, because, for a distant blazar, secondary photons produced in line-of-sight cosmic-ray interactions dominate the signal. In this case, we find 0.01 fG < B < 30 fG. If one excludes the cosmic-ray component, the 0.01 fG lower limit remains, but the upper limit depends on the spectral properties of the source. We present the allowed ranges for a variety of model parameters.