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Astron. Astrophys. 332, L13-L16 (1998)


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Letter to the Editor

Millimetre detection of GRB 970508

M. Bremer 1, T.P. Krichbaum 2, T.J. Galama 3, A.J. Castro-Tirado 4, F. Frontera 5, 9, J. Van Paradijs 3, I.F. Mirabel 6, 8, and E. Costa 7

1 Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, F-38406 Saint-Martin d'Hères, France
2 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
3 University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
4 LAEFF-INTA, Villafranca del Castillo, P.O. Box 50.727, E-28080 Madrid, Spain
5 Dipartimento di Fisica, Università di Ferrara, Via Paradiso, 11, I-44100 Ferrara, Italy
6 CEA/DSM/DAPNIA Service d'Astrophysique, F-91191 Gif-sur-Yvette, France
7 Istituto di Astrofisica Spaziale, CNR., Via E. Fermi, 21, I-00044 Frascati, Italy
8 Instituto de Astronomia y Fisica del Espacio, CC 67, Suc 28, 1428 Buenos Aires, Argentina
9 Istituto TESRE, CNR, Via P. Gobetti, 101, I-40129 Bologna, Italy

Received 23 December 1997 / Accepted 15 January 1998

Abstract

The [FORMULA] -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 [FORMULA]  mJy, which amounts to a [FORMULA] detection. Three individual tentative detections were made on May 19-22, and the source was only non-detected later with [FORMULA] 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 ([FORMULA]). 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 [FORMULA] 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.

Key words: Gamma-ray bursts – GRB 970508 – radio continuum observations

© European Southern Observatory (ESO) 1998

Online publication: March 10, 1998
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