Parity-odd correlators of diffuse gamma rays and intergalactic magnetic fields

TL;DR

This paper links intergalactic helical magnetic fields to parity odd signatures in diffuse gamma rays, showing how to infer magnetic field properties from gamma ray data and providing estimates consistent with previous findings.

Contribution

It introduces a method to connect gamma ray parity odd correlators with magnetic field spectra and applies it to Fermi-LAT data to estimate magnetic field strength.

Findings

Peak in $Q(R)$ correlator indicates magnetic field strength of ~10^{-14} G.

Observed features support the intergalactic magnetic field hypothesis.

Predictions made for future observational tests.

Abstract

We develop the connection between intergalactic helical magnetic fields and parity odd signatures in the diffuse gamma ray sky. We find that the location and the amplitude of a peak in a parity odd correlator, $Q(R)$, can be used to infer the normal and helical power spectra of the intergalactic magnetic field. When applied to Fermi-LAT data, the amplitude of the observed peak in $Q(R)$ gives $\sim 10^{-14}~{\rm G}$ intergalactic magnetic field strength, which is consistent with an earlier independent estimate that only used the peak location (Tashiro et al. 2014). We discuss features in the observed $Q(R)$ that further support the intergalactic magnetic field hypothesis and make predictions for future tests.