Detection of Vhe -rays from Mkn 421 with the Hegra Cherenkov Telescopes
نویسندگان
چکیده
A detection of-rays from Mkn 421 at energies above 1 TeV is reported, based on observations made in December 1994-May 1995 with the rst two HEGRA Cherenkov telescopes. From the image analysis, 111 excess gamma candidates are obtained from the 26 h Telescope #1 (CT1) dataset (signiicance 4.0) and 218 from the 41 h Telescope #2 (CT2) dataset (signiicance 4.2) at zenith angles < 25. The combined signiicance is approx. 5.8. This is the second detection of Mkn 421 at TeV energies. The average excess rate is 4:3 1:0 h ?1 for CT1 and 5:41:3 h ?1 for CT2. Comparison with our contemporary observations of the Crab Nebula indicates that Mkn 421 has a steeper spectrum than the Crab Nebula above 1 TeV. Under the assumption that the spectrum of Mkn 421 follows a power law, we obtain a diierential spectral index of 3.61:0 and an integral ux above 1 TeV of 8(2) Stat (+6?3) Syst 10 ?12 cm ?2 s ?1 from a comparison with Monte Carlo data. This ux is smaller than the Crab Nebula ux by a factor of 2.00:8.
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تاریخ انتشار 2007