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

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.

4 pages, 4 figures, accepted to Astronomy & Astrophysics

References in corpus (6)

• Fermi Large Area Telescope Second Source Catalog
• Gamma-ray flares from the Crab Nebula
• Gamma-Ray Emission Concurrent with the Nova in the Symbiotic Binary V407 Cygni
• Fermi LAT Observations of the Supernova Remnant W28 (G6.4-0.1)
• Periodic Emission from the Gamma-ray Binary 1FGL J1018.6-5856
• Fermi Large Area Telescope Observation of a Gamma-ray Source at the Position of Eta Carinae

Cited by in corpus (6)

• Gamma-ray binaries and related systems
• The Fermi All-sky Variability Analysis: A list of flaring gamma-ray sources and the search for transients in our Galaxy
• Gamma-ray observations of the microquasars Cygnus X-1, Cygnus X-3, GRS 1915+105, and GX 339-4 with the Fermi Large Area Telescope
• An update on Fermi-LAT transients in the Galactic plane, including strong activity of Cygnus X-3 in mid-2020
• Search for gamma rays from SNe with a variable-size sliding-time-window analysis of the Fermi-LAT data
• A blind search for intraday gamma-ray transients with Fermi-LAT: Detections of GRB and solar emissions