On the measurement of handedness in Fermi Large Area Telescope data

TL;DR

This study updates the measurement of photon arrival direction handedness in Fermi-LAT data over 10 years, revealing that previous signals suggesting intergalactic magnetic field helicity are not statistically significant after improved uncertainty analysis.

Contribution

It provides a refined analysis of handedness in Fermi-LAT data using extensive simulations to accurately estimate uncertainties, challenging earlier indications of a magnetic field helicity signal.

Findings

Previous signals are rendered non-significant with improved analysis.

Simulations show earlier uncertainties were underestimated.

Updated data analysis over 10 years refines the magnetic field helicity measurement.

Abstract

A handedness in the arrival directions of high-energy photons from outside our Galaxy can be related to the helicity of an intergalactic magnetic field. Previous estimates by arXiv:1310.4826 and arXiv:1412.3171 showed a hint of a signal present in the photons observed by the Fermi Large Area Telescope (LAT). An update on the measurement of handedness in Fermi-LAT data is presented using more than 10 years of observations. Simulations are performed to study the uncertainty of the measurements, taking into account the structure of the exposure caused by the energy-dependent instrument response and its observing profile, as well as the background from the interstellar medium. The simulations are required to accurately estimate the uncertainty and to show that previously the uncertainty was significantly underestimated. The apparent signal in the earlier analysis of {\em Fermi}-LAT data is rendered non-significant.