Radio detections towards unidentified variable EGRET sources

TL;DR

This study used the GMRT to explore radio counterparts of four highly variable gamma-ray sources from EGRET, identifying potential variable radio sources that could be linked to the gamma-ray variability.

Contribution

First radio mapping of the fields of specific variable EGRET sources, identifying candidate variable radio counterparts for further multiwavelength investigation.

Findings

Detected 151 radio sources in the fields

Identified radio sources with apparent flux variability over months

Prioritized candidate sources for follow-up studies

Abstract

Context. A considerable fraction of the gamma-ray sources discovered with the Energetic Gamma-Ray Experiment Telescope (EGRET) remain unidentified. The EGRET sources that have been properly identified are either pulsars or variable sources at both radio and gamma-ray wavelengths. Most of the variable sources are strong radio blazars.However, some low galactic-latitude EGRET sources, with highly variable gamma-ray emission, lack any evident counterpart according to the radio data available until now. Aims. The primary goal of this paper is to identify and characterise the potential radio counterparts of four highly variable gamma-ray sources in the galactic plane through mapping the radio surroundings of the EGRET confidence contours and determining the variable radio sources in the field whenever possible. Methods. We have carried out a radio exploration of the fields of the selected EGRET sources using the Giant Metrewave Radio Telescope (GMRT) interferometer at 21 cm wavelength, with pointings being separated by months. Results. We detected a total of 151 radio sources. Among them, we identified a few radio sources whose flux density has apparently changed on timescales of months. Despite the limitations of our search, their possible variability makes these objects a top-priority target for multiwavelength studies of the potential counterparts of highly variable, unidentified gamma-ray sources.