A geomagnetic filter for the Fermi-LAT background

TL;DR

This paper proposes a novel method using geomagnetic shielding effects to differentiate charged particles from gamma rays in Fermi-LAT data, aiding the study of the extragalactic gamma-ray background's origins.

Contribution

It introduces a geomagnetic filtering technique for gamma-ray data analysis, complementing detector-based methods and applied specifically to Fermi-LAT observations.

Findings

Geomagnetic shielding can partially filter charged particles in gamma-ray data.

Application to Fermi-LAT data demonstrates the method's effectiveness.

Analysis suggests star-forming galaxies contribute to the gamma-ray background.

Abstract

One of the unsolved questions in gamma-ray astronomy is whether the extragalactic gamma-ray background is of the discrete-source origin. To respond to this question, one first needs to reduce the data by differentiating charged particles from gamma rays. This procedure is usually performed on the basis of the detector responses. In this paper, we showed that the geomagnetic shielding effect at GeV energies can, to some extent, be used for this purpose for gamma-ray telescopes in a low Earth orbit. We illustrated this method by applying it to the Fermi-LAT data. To partially decompose the charge-filtered background, we examined the contribution from star-forming galaxies by implying a radio/gamma connection in consideration of next generation radio surveys.