Revisiting variable gamma-ray sky at 1 GeV with 6 years of Fermi-LAT data

TL;DR

This study conducts a blind search for gamma-ray sky variability above 1 GeV using 6 years of Fermi-LAT data, identifying 8 new variable sources with flaring activity and spectral properties typical of blazars.

Contribution

It introduces a novel blind variability detection method using Kolmogorov-Smirnov tests on Fermi-LAT data, discovering new gamma-ray variable sources.

Findings

Identified 8 previously unknown variable gamma-ray sources.

Detected sources with flaring activity on weekly timescales.

Sources exhibit spectra peaking around GeV, typical of blazars.

Abstract

We perform a blind search for the variability of the gamma-ray sky in the energy range E>1 GeV using 308 weeks of the Fermi-LAT data. We use the technique based on the comparison of the weekly photon counts and exposures in sky pixels by means of the Kolmogorov-Smirnov test. We consider the flux variations in the region significant if statistical probability of uniformity is less than $4\times10^{-6}$, which corresponds to 0.05 false detections in the whole set of 12288 pixels. Close inspection of the detected variable regions result in identification of 8 sources without previous known variability. Two of them are included in the second Fermi LAT source catalogue (FBQS J122424.1+243623 and GB6 J0043+3426) and one (3EG J1424+3734) was reported by EGRET and also was included in the First Fermi LAT source catalogue (1FGL), but is missing in the 2FGL. Possible identifications of five other sources are obtained using NED and SIMBAD databases (1RXS J161939.9+765515, PMN J2320-6447, PKS 0226-559, PKS J0030-0211, PMN J0225-2603). These new variable gamma-ray sources demonstrate recurring flaring activity with time scale ~weeks and have hard spectra. Their spectral energy distributions deviate significantly from a simple power-law shape and often peak around ~GeV. These properties of activity are typical for flaring blazars.