Searches for prompt radio emission at 151 MHz from the gamma-ray bursts GRB 950430 and GRB 950706

Abstract

The Cambridge Low Frequency Synthesis Telescope (CLFST) has been used to search for prompt radio emission at 151 MHz from gamma-ray bursts (GRBs) detected by the Burst And Transient Source Experiment (BATSE) aboard the Compton Gamma-Ray Observatory. The CLFST was reconfigured so that it can reach ∼ 10 per cent of the sky in 1.5 min. The real-time follow-up observations of GRB 950430 and GRB 950706 presented here provide deep upper limits on the flux density of any radio pulse matching the GRB duration. For GRB 950430 the (3σ) limits are 73 Jy for the period from 280 min before to 6 min after the burst, and 35 Jy for the period 6 to 145 min after the burst. For GRB 950706 the limit is 16 Jy for the period 16 to 60 min after the burst. Assuming a thermal radio spectrum, our limits for the period 6 to 145 min following GRB 950430 yield an upper limit of ∼ 3 × 10−4 for the ratio of the radio to the γ-ray luminosity of this burst. In addition we have looked for variable sources in the field of GRB 950430 for the 3 h following the GRB: no new source with a flux density above 1 Jy was found.