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arXiv:astro-ph/9606159 (astro-ph)
[Submitted on 26 Jun 1996 (v1), last revised 27 Jun 1996 (this version, v2)]

Title:Detection of VHE Gamma-rays from Mkn 421 with the HEGRA Cherenkov Telescopes

Authors:D. Petry (1), S.M. Bradbury (1), A. Konopelko (2), J. Fernandez (1) (3), et al. (The HEGRA Collaboration) (1) (2) (3) (4) (5) (6) (7) ((1) Max-Planck-Institut fuer Physik, Munich, Germany, (2) Max-Planck-Institut fuer Kernphysik, (3) Universidad Complutense, Madrid, Spain, (4) Yerevan Physics Institute, Yerevan, Armenia, (5) Universitaet Kiel, Inst. fuer Kernphysik, Germany, (6) BUGH Wuppertal, Fachbereich Physik, Wuppertal, Germany, (7) Universitaet Hamburg, II. Inst. fuer Experimentalphysik, Germany)
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Abstract: A detection of Gamma-rays from Mkn 421 at energies above 1 TeV is reported, based on observations made in December 1994 - May 1995 with the first two HEGRA Cherenkov telescopes. >From the image analysis, 111 excess gamma candidates are obtained from the 26 h Telescope #1 (CT1) dataset (significance 4.0 sigma) and 218 from the 41 h Telescope #2 (CT2) dataset (significance 4.2 sigma) at zenith angles theta < 25 degrees. The combined significance is approx. 5.8 sigma. 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 5.4 +- 1.3 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 differential spectral index of 3.6 +- 1.0 and an integral flux above 1 TeV of 8 (+-2)_(Stat) (+6-3)_(Syst) x 10^-12 cm^-2 s^-1 from a comparison with Monte Carlo data. This flux is smaller than the Crab Nebula flux by a factor of 2.0 +- 0.8.
Comments: 4 pages, single ps-file, accepted as Letter to A&A on 11 June 96
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:astro-ph/9606159
  (or arXiv:astro-ph/9606159v2 for this version)
  https://doi.org/10.48550/arXiv.astro-ph/9606159
Journal reference: Astron.Astrophys. 311 (1996) L13-L16

Submission history

From: Dirk Petry [view email]
[v1] Wed, 26 Jun 1996 17:25:31 UTC (92 KB)
[v2] Thu, 27 Jun 1996 19:20:59 UTC (92 KB)
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