1998A&A...332L..13B

The γ-ray burst source GRB 970508 has been detected as a continuum point source at 86.2 GHz with the IRAM Plateau de Bure Interferometer (PdBI). By combining the UV tables of May 17th, 19th, 21st and 22nd, one obtains a point source flux of 1.62±0.25mJy, which amounts to a 6.5σ detection. Three individual tentative detections were made on May 19-22, and the source was only non-detected later with 3σ upper limits between 0.87 and 1.83mJy. Observations at 232GHz gave only upper limits. The lowest one from combined May 19 and 21 data is 4.5mJy (3σ). No significant variation of the source during individual observing dates was seen in either frequency band. Comparing the May 17-22 detection with the later non-detections, we see a significant fading which is not well fitted with the F∝t^–1.1±0.1 law found at higher frequencies. We exclude that the 86.2GHz fluxes have been modulated significantly by interstellar scintillation. This indicates that the millimetre characteristics of GRB 970508 provide a new aspect of the intrinsic development of the source.