Search for variable gamma-ray emission from the Galactic plane in the Fermi data

TL;DR

This study systematically analyzes Fermi gamma-ray data to identify variable sources in the Galactic plane, revealing several regions with significant variability, including pulsars and the Galactic ridge, suggesting pulsar wind nebulae as a potential origin.

Contribution

The paper introduces a method to detect long-term variability in gamma-ray sources along the Galactic plane using variability maps, highlighting regions with significant variability.

Findings

Several regions along the Galactic plane show significant variability.

Variable sources include known pulsars, blazars, and the Galactic ridge.

Variability on months timescale may be common in pulsars.

Abstract

High-energy gamma-ray emission from the Galactic plane above ~100 MeV is composed of three main contributions: diffuse emission from cosmic ray interactions in the interstellar medium, emission from extended sources, such as supernova remnants and pulsar wind nebulae, and emission from isolated compact source populations. The diffuse emission and emission from the extended sources provide the dominant contribution to the flux almost everywhere in the inner Galaxy, preventing the detection of isolated compact sources. In spite of this difficulty, compact sources in the Galactic plane can be singled out based on the variability properties of their gamma-ray emission. Our aim is to find sources in the Fermi data that show long-term variability. We performed a systematic study of the emission variability from the Galactic plane, by constructing the variability maps. We find that emission from several directions along the Galactic plane is significantly variable on a time scale of months. These directions include, in addition to known variable Galactic sources and background blazars, the Galactic ridge region at positive Galactic longitudes and several regions containing young pulsars. We argue that variability on the time scale of months may be common to pulsars, originating from the inner parts of pulsar wind nebulae, similarly to what is observed in the Crab pulsar.