New Method for Investigating the Presence of Extragalactic Magnetic Fields

TL;DR

This paper introduces a novel method to detect extragalactic magnetic fields by analyzing gamma-ray asymmetries around blazars, providing new constraints on magnetic field strength.

Contribution

It proposes a new signature based on gamma-ray distribution asymmetry and applies it to constrain magnetic field strengths using observational data.

Findings

Excluded magnetic field range from 10^{-16} to 10^{-14} G

Used gamma-ray asymmetry as a new detection signature

Analyzed a sample of the 10 brightest BL Lacs

Abstract

The extragalactic magnetic field could be detected by searching for signatures of the electromagnetic cascade initiated by high-energy photons on the intergalactic radiation and deflected by the field. This process produces a time delay and an extended gamma-ray halo around the source, which are looked for. We propose a new signature of electromagnetic echoes: the asymmetry of the gamma-ray distribution around blazars. As a measure of asymmetry, we use the offset of the gamma-ray distribution to the location of the blazar. This offset is due to the tilt of the jet of the blazar relative to the line of sight. Using a subsample of the 10 brightest BL Lacs, we exclude the range of extragalactic magnetic fields from $10^{-16}$ to $10^{-14}$ G, assuming that these objects have maintained a constant average luminosity over hundreds of thousands of years.