Observations of H1426+428 with HEGRA

Observations in 2002 and reanalysis of 1999&2000 data

¹ Max-Planck-Institut für Kernphysik, Postfach 103980, 69029 Heidelberg, Germany
² Yerevan Physics Institute, Alikhanian Br. 2, 375036 Yerevan, Armenia
³ Universität Hamburg, Institut für Experimentalphysik, Luruper Chaussee 149, 22761 Hamburg, Germany
⁴ Universität Kiel, Institut für Experimentelle und Angewandte Physik, Leibnizstraße 15-19, 24118 Kiel, Germany
⁵ Universität Wuppertal, Fachbereich Physik, Gaußstr. 20, 42097 Wuppertal, Germany
⁶ Max-Planck-Institut für Physik, Föhringer Ring 6, 80805 München, Germany
⁷ Universidad Complutense, Facultad de Ciencias Físicas, Ciudad Universitaria, 28040 Madrid, Spain
⁸ Now at Institut de Física d'Altes Energies, UAB, Edifici Cn, 08193 Bellaterra (Barcelona), Spain
⁹ On leave from Altai State University, Dimitrov Street 66, 656099 Barnaul, Russia
¹⁰ Home institute: University Lodz, Poland

Corresponding author: D. Horns, Dieter.Horns@mpi-hd.mpg.de

Received: 22 January 2003
Accepted: 25 February 2003

Abstract

The HEGRA system of imaging air Cherenkov telescopes has been used to observe the BL Lac object H1426+428 () for 217.5 hours in 2002. In this data set alone, the source is detected at a confidence level of , confirming this object as a TeV source. The overall flux level during the observations in 2002 is found to be a factor of ≈2.5 lower than during the previous observations by HEGRA in 1999 and 2000. A new spectral analysis has been carried out, improving the signal-to-noise ratio at the expense of a slightly increased systematic uncertainty and reducing the relative energy resolution to over a wide range of energies. The new method has also been applied to the previously published data set taken in 1999 and 2000, confirming the earlier claim of a flattening of the energy spectrum between 1 and 5 TeV. The data set taken in 2002 shows again a signal at energies above 1 TeV. We combine the energy spectra as determined by the CAT and VERITAS groups with our reanalyzed result of the 1999 and 2000 data set and apply a correction to account for effects of absorption of high energy photons on extragalactic background light in the optical to mid infrared band. The shape of the inferred source spectrum is mostly sensitive to the characteristics of the extragalactic background light between wavelengths of 1 and 15 μm.