Variable gamma-ray sky at 1 GeV

TL;DR

This study analyzes 168 weeks of Fermi-LAT data to identify long-term gamma-ray flux variability across the sky, discovering 117 variable sources including new variability in 27 sources, notably blazars and Geminga.

Contribution

It presents a full-sky blind search method using Kolmogorov-Smirnov tests to detect gamma-ray flux variability, identifying new variable sources and characterizing their nature.

Findings

117 variable gamma-ray sources identified

27 sources show previously unreported variability

Geminga's flux variability is statistically significant

Abstract

We search for the long-term variability of the \gamma-ray sky in the energy range E > 1 GeV with 168 weeks of Fermi-LAT data. We perform a full sky blind search for regions with variable flux looking for deviations from uniformity. We bin the sky into 12288 bins using Healpix package and use Kolmogorov-Smirnov test to compare weekly photon counts in each bin with a constant flux hypothesis. The weekly exposure of Fermi-LAT for each bin is calculated with the Fermi-LAT tools. We consider flux variations in the bin significant if statistical probability of uniformity is less than 4e-6, which corresponds to 0.05 false detections in the whole set. We identified 117 variable sources, variability of 27 of which has not been reported before. Among the sources with previously unidentified variability there are 25 AGNs belonging to blazar class (11 BL Lacs and 14 FSRQs), one AGN of uncertain type and one pulsar PSR J0633+1746 (Geminga). The observed long term flux variability of Geminga has a statistical significance of 5.1\sigma.