1997A&A...321..229G

We report on the results of a search for a radio counterpart to the strong gamma-ray burst GRB 940301. Observations with the Westerbork Synthesis Radio Telescope of the Compton Telescope error box region of GRB 940301 began on March 4, 1994, at 21cm and April 2, 1994, at 92cm. No flux density variations were detected at 92cm above S=10mJy (5σ) within a period of 1 to 4 months after the burst. However, when we compared the field with Westerbork Northern Sky Survey data, taken two years prior to GRB 940301, we found two radio sources with significantly increased flux densities. These sources, only 17' apart, are located at the 2.3 and 2.6σ Compton Telescope confidence contours. Their separation from the Inter Planetary Network annulus virtually excludes association with GRB 940301. Further observations in January 1996 reveal that the sources continued to change in flux density. The relatively large flux density variations at 92cm, compared to those at higher frequencies, and the inverted spectra in the frequency range from 325-380MHz make the sources somewhat unusual. Because the sources were already detected at 5GHz in 1986 most, if not all, of the radio emission is probably associated with activity in Active Galactic Nuclei in distant galaxies.