Radio detections towards unidentified variable EGRET sources

Abstract

Context. A considerable fraction of theγ-ray sources discovered with the Energetic Gamma-Ray Experiment Telescope (EGRET) remain unidentified. The EGRET sources that have been proper ly identified are either pulsars or variable sources at both r adio and gamma-ray wavelengths. Most of the variable sources are strong radio blazars. However, some low galactic-latitude EGRET sources, with highly variableγ-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 γ-ray sources in the galactic plane through mapping the radio surroundings of the EGRET confidence contours and determining th e variable radio sources in the field whenever possible. Methods. We have carried out a radio exploration of the fields of the sel ected 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 counte rparts of highly variable, unidentified gamma-ray sources.