Details

Autor(en) / Beteiligte

• Konopelko, A.

Titel

The TeV spectrum of Mkn 501 as measured during the high state in 1997 by the HEGRA stereoscopic system of imaging air Čerenkov telescopes

Ist Teil von

• Astroparticle physics, 1999-06, Vol.11 (1), p.135-139

Ort / Verlag

Elsevier B.V

Erscheinungsjahr

1999

Link zum Volltext

Quelle

Elsevier Journal Backfiles on ScienceDirect (DFG Nationallizenzen)

Beschreibungen/Notizen

• The BL Lac object Mkn 501 has shown very high emission in TeV γ-rays from March to October, 1997. During this period the source was continuously monitored with the HEGRA stereoscopic system of 4 imaging air Čerenkov telescopes for a total exposure time of 110 hours. The unprecedented statistics of about 38 000 TeV photons, combined with the good energy resolution of ∼ 20% over the entire energy range and with detailed simulations of the detector response, allowed a determination of the average energy spectrum from 500 GeV to 24 TeV. Although the γ-ray flux varied strongly with time, the daily energy spectra remained rather constant in their shape. Therefore, it is justified to derive a time averaged spectrum and thus to extend, for the first time, the spectral measurement well beyond 10 TeV. The energy resolution restricts the maximum true energy of the detected γ-rays at ∼ 18 TeV. The TeV spectrum of Mkn 501 shows a gradual steepening which could be caused by a number of physical processes, such as a limited energy range of the radiating particles, intrinsic γ-ray absorption inside the source, the Klein-Nishina effect (in the case of an inverse Compton origin of the radiation) and finally, absorption of the TeV γ-rays propagating in the intergalactic medium.