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Astron. Astrophys. Suppl. Ser. 138, 599-600

Search for GeV GRBs with the INCA experiment

R. Cabrera1 - A. Castellina2,3 - P.L. Ghia2,3 - F. Kakimoto5 - T. Kaneko6 - C. Morello2,3 - G. Navarra3,4 - K. Nishi7 - O. Saavedra3,4 - G. Trinchero2,3 - D. Urzagasti1 - P. Vallania2,3 - A. Velarde1 - S. Vernetto2,3 - H. Yoshii8

Send offprint request: S. Vernetto

1 - Instituto de Investigaciones Fisicas, Universidad Mayor de San Andres, La Paz, Bolivia
2 - Istituto di Cosmo-Geofisica del CNR, Torino, Italy
3 - Istituto Nazionale di Fisica Nucleare, Torino, Italy
4 - Dipartimento di Fisica Generale dell' Università, Torino, Italy
5 - Department of Physics, Tokyo Institute of Technology, Meguro, Tokyo 152, Japan
6 - Department of Physics, Okayama University, Okayama 700, Japan
7 - The Institute of Physical and Chemical Research, Wako, Saitama 351-01, Japan
8 - Department of Physics, Ehime University, Ehime 790, Japan

Received December 18, 1998; accepted March 10, 1999


INCA is an air shower array located at Mount Chacaltaya in Bolivia, at 5200 m a.s.l., searching for Gamma Ray Bursts of energy E>1 GeV. The results presented here concern a GRB search made in correlation with 70 events recorded by BATSE since December 1996 to August 1998. For every burst, the INCA counting rate has been studied both during the BATSE detection time and in 2 hours around. No significant excess has been found in any of the trials. Assuming for the burst a power low energy spectrum extending up to 1 TeV with a slope $\alpha = -2$ and a time duration of 10 s, the obtained $1~{\rm GeV}\div 1~{\rm TeV}$ energy fluence upper limits range from $5.3 \ 10^{-5}~{\rm erg}~{\rm cm}^{-2}$ to $2.9 \ 10^{-2}~{\rm erg}~{\rm cm}^{-2}$depending on the event zenith angle.

Key words: gamma-ray bursts

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