- Conference date: 26-30 July 2004
- Location: Heidelberg (Germany)
Mkn 421 was observed during a high flux state for nine nights in April and May 2004 with the fully operational High Energy Stereoscopic System (H.E.S.S.) in Namibia. The observations were carried out at zenith angle distances of 61–64°, which result in an increased average threshold of 1.5 TeV. Observations of the Crab nebula at similar zenith angles are used to check on the reliability of the large zenith angle observation technique. Roughly 7000 photons from Mkn421 were accumulated with an average gamma‐ray rate of 11 gammas/min. The overall significance of the detection exceeds 80 standard deviations. The light curve shows night‐by‐night variations by a factor of 2. The energy spectrum is curved and may be fit with a power law with an exponential cut‐off at 2.1 TeV.
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