Measurement of the Crab Flux above 60 GeV with the CELESTE Cerenkov Telescope
- 10 February 2002
- journal article
- research article
- Published by American Astronomical Society in The Astrophysical Journal
- Vol. 566 (1), 343-357
- https://doi.org/10.1086/337991
Abstract
We have converted the former solar electrical plant THEMIS (French Pyrenees) into an atmospheric Cerenkov detector called CELESTE, which records gamma rays above 30 GeV (7 × 1024 Hz). Here we present the first sub-100 GeV detection by a ground-based telescope of a gamma-ray source, the Crab Nebula, in the energy region between satellite measurements and imaging atmospheric Cerenkov telescopes. At our analysis threshold energy of 60 ± 20 GeV we measure a gamma-ray rate of 6.1 ± 0.8 minute-1. Allowing for 30% systematic uncertainties and a 30% error on the energy scale yields an integral gamma-ray flux of I(E > 60GeV) = 6.2 × 10-6 photons m-2 s-1. The analysis methods used to obtain the gamma-ray signal from the raw data are detailed. In addition, we determine the upper limit for pulsed emission to be less than 12% of the Crab flux at the 99% confidence level, in the same energy range. Our result indicates that if the power law observed by EGRET is attenuated by a cutoff of form e, then E0 < 26 GeV. This is the lowest energy probed by a Cerenkov detector and leaves only a narrow range unexplored beyond the energy range studied by EGRET.Keywords
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