Detection of VHE γ-rays from MKN 421 with the HEGRA Cherenkov Telescopes.
Abstract
A detection of γ-rays from Mkn 421 at energies above 1TeV 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 26h Telescope #1 (CT1) dataset (significance 4.0σ) and 218 from the 41h Telescope #2 (CT2) dataset (significance 4.2σ) at zenith angles θ<25deg. The combined significance is approx. 5.8σ. This is the second detection of Mkn 421 at TeV energies. The average excess rate is 4.3+/-1.0h^-1^ for CT1 and 5.4+/-1.3h^-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 1TeV. 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 1TeV of 8(+/-2)_Stat_(+6-3)_Syst_x10-12cm-2/s from a comparison with Monte Carlo data. This flux is smaller than the Crab Nebula flux by a factor of 2.0+/-0.8.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- July 1996
- DOI:
- 10.48550/arXiv.astro-ph/9606159
- arXiv:
- arXiv:astro-ph/9606159
- Bibcode:
- 1996A&A...311L..13P
- Keywords:
-
- GAMMA RAYS: OBSERVATIONS;
- BL LACERTAE OBJECTS: INDIVIDUAL: MKN 421;
- Astrophysics
- E-Print:
- 4 pages, single ps-file, accepted as Letter to A&