A search for pair halos around active galactic nuclei through a temporal analysis of Fermi-LAT data

TL;DR

This paper introduces a novel temporal analysis method to search for pair halos around active galactic nuclei using Fermi-LAT gamma-ray data, but finds no evidence of such halos and provides a way to reconstruct the instrument's PSF.

Contribution

The paper presents a new method for detecting pair halos via temporal and spatial analysis of gamma-ray data and demonstrates its effectiveness in reconstructing the Fermi-LAT PSF.

Findings

No evidence for pair halos in the analyzed data.

Upper limits set on the photon fraction from pair halos.

Reconstructed PSF agrees with previous measurements.

Abstract

We develop a method to search for pair halos around active galactic nuclei (AGN) through a temporal analysis of gamma-ray data. The basis of our method is an analysis of the spatial distributions of photons coming from AGN flares and from AGN quiescent states and a further comparison of these two spatial distributions. This method can also be used for a reconstruction of a point spread function (PSF). We found no evidence for a pair halo component through this method by applying it to the Fermi-LAT data in the energy bands of 4.5-6, 6-10, and >10 GeV and set upper limits on the fraction of photons attributable to a pair halo component. An illustration of how to reconstruct the PSF of Fermi-LAT is given. We demonstrate that the PSF reconstructed by using this method is in good agreement with that which was obtained by using the gamma-ray data taken by LAT in the direction of the Crab pulsar and nebula.