Radio detections towards unidentified variable EGRET sources

J.M. PAREDES, J. MARTÍ, C.H. ISHWARA-CHANDRA, D.F. TORRES, G.E. ROMERO, J.A. COMBI, V. BOSCH-RAMON, A.J. MUÑOZ-ARJONILLA, J.R. SÁNCHEZ-SUTIL.

ASTRONOMY AND ASTROPHYSICS

EDP Science

Lugar: Francia; Año: 2008 vol. 482 p. 247 - 253

0004-6361

Context: A considerable fraction of the ã-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 ã-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 ã-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.