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Millimetre detection of GRB 970508

M. Bremer tex2html_wrap_inline1968 , T.P. Krichbaum tex2html_wrap_inline1978 , T.J. Galama tex2html_wrap_inline1974 , A.J. Castro-Tirado tex2html_wrap_inline2320 , F. Frontera tex2html_wrap_inline2322 , J. Van Paradijs tex2html_wrap_inline1974 , I.F. Mirabel tex2html_wrap_inline2326 , E. Costa tex2html_wrap_inline2328
tex2html_wrap_inline1968 Institut de RadioAstronomie Millimétrique, 300 rue de la Piscine, F-38406 Saint Martin d'Hères, France
tex2html_wrap_inline1978 Max Planck Institut für Radioastronomie, Auf dem Hügel 69, D-53121,Bonn, Germany
tex2html_wrap_inline1974 University of Amsterdam, Kruislaan 403, NL-1098 SJ Amsterdam, The Netherlands
tex2html_wrap_inline2320 LAEFF-INTA, Villafranca del Castillo, PO Box 50.727, E-28080 Madrid, Spain
tex2html_wrap_inline2338 Dipartimento di Fisica, Università di Ferrara, Via Paradiso, 11, I-44100 Ferrara, Italy
tex2html_wrap_inline2340 CEA/DSM/DAPNIA Service d'Astrophysique, F-91191 Gif-sur-Yvette, France
tex2html_wrap_inline2328 Istituto di Astrofisica Spaziale, CNR., Via E. Fermi, 21, I-00044 Frascati, Italy
tex2html_wrap_inline2344 Instituto de Astronomia y Fisica del Espacio, CC 67, Suc 28, 1428 Buenos Aires, Argentina
tex2html_wrap_inline2346 Istituto TESRE, CNR, Via P. Gobetti, 101, I-40129 Bologna, Italy
Abstract: The tex2html_wrap_inline2348 -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 tex2html_wrap_inline2350  mJy, which amounts to a tex2html_wrap_inline2352 detection. Three individual tentative detections were made on May 19-22, and the source was only non-detected later with tex2html_wrap_inline2354 upper limits between 0.87 and 1.83 mJy. Observations at 232 GHz gave only upper limits. The lowest one from combined May 19 and 21 data is 4.5 mJy ( tex2html_wrap_inline2354 ). 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 tex2html_wrap_inline2358 law found at higher frequencies.

We exclude that the 86.2 GHz 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.