Astron. Astrophys. 337, 43-50 (1998)

Search for gamma-ray bursts above 20 TeV with the HEGRA AIROBICC Cherenkov array

L. Padilla ¹, B. Funk ², H. Krawczynski ^{3, 4}, J.L. Contreras ¹, A. Moralejo ¹, F. Aharonian ³, A.G. Akhperjanian ⁵, J.A. Barrio ^{1, 6}, J.G. Beteta ¹, J. Cortina ¹, T. Deckers ⁷, V. Fonseca ¹, H.-J. Gebauer ⁶, J.C. González ^{1, 6}, G. Heinzelmann ⁴, D. Horns ⁴, H. Kornmayer ⁶, A. Lindner ⁴, E. Lorenz ⁶, N. Magnussen ², H. Meyer ², R. Mirzoyan ^{5, 6}, D. Petry ^{2, 6}, R. Plaga ⁶, J. Prahl ⁴, C. Prosch ⁶, G. Rauterberg ⁷, W. Rhode ², A. Röhring ⁴, V. Sahakian ⁵, M. Samorski ⁷, D. Schmele ⁴, W. Stamm ⁷, B. Wiebel-Sooth ², M. Willmer ⁷ and W. Wittek <sup>6

1</sup> Facultad de Ciencias Fí sicas, Universidad Complutense, E-28040 Madrid, Spain
² BUGH Wuppertal, Fachbereich Physik, Gaußstrasse 20, D-42119 Wuppertal, Germany
³ Max-Planck-Institut für Kernphysik, P.O. Box 103980, D-69029 Heidelberg, Germany
⁴ Universität Hamburg, II. Institut für Experimentalphysik, Luruper Chausee 149, D-22761 Hamburg, Germany
⁵ Yerevan Physics Institute, Yerevan, Armenia
⁶ Max-Planck-Institut für Physik, Föhringer Ring 6, D-80805 München, Germany
⁷ Universität Kiel, Institut für Experimentelle und Angewandte Physik, D-24098 Kiel, Germany

Received 6 April 1998 / Accepted 13 May 1998

Abstract

A search for gamma-ray bursts (GRBs) above 20 TeV within the field of view (1 sr) of the HEGRA AIROBICC Cherenkov array (29N, 18W, 2200 m a.s.l.) has been performed using data taken between March 1992 and March 1993. The search is based on an all-sky survey using four time scales, 10 seconds, 1 minute, 4 minutes and 1 hour. No evidence for TeV-emission has been found for the data sample. Flux upper limits are given. A special analysis has been performed for GRBs detected by BATSE and WATCH. Two partially and two fully contained GRBs in our field of view (FOV) were studied. For GRB 920925c which was fully contained in our FOV, the most significant excess has a probability of 7.7 (corresponding to 5.4) of being caused by a background fluctuation. Correcting this probability with the appropriate trial factor, yields a 99.7% confidence level (CL) for this excess to be related to the GRB (corresponding to 2.7). This result is discussed within the framework of the WATCH detection.

Key words: gamma rays: bursts ISM: cosmic rays

Send offprint requests to: padilla@gae.ucm.es

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Contents

• 1. Introduction
• 2. The AIROBICC array
• 3. Analysis
• 4. Results
• 5. Observational results for WATCH GRB 920925c
• 6. Discussion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: August 6, 1998
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