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Abstract:
The blazar H1426+428 (z=0.129) has been observed with the HEGRA stereoscopic system of imaging air Cherenkov telescopes for 270 h in the years 1999, 2000, and 2002. The object is detected with a significance of 7.5. The energy spectrum measured by HEGRA extends up to 8 TeV with indications for a change in the spectral slope at energies above 2 TeV. The integral flux above 1 TeV in 1999 and 2000 amounts to 8% of the flux of the Crab Nebula. In 2002, the flux drops to a level of 3% of the Crab Nebula. The extragalactic background light at wavelengths between 1 and 10 m causes substantial (=1,...,9) absorption of photons in the measured energy spectrum. The intrinsic spectra after correction for absorption are discussed. Contemporaneous observations with the X-ray observatory RXTE in 2000 and 2002 indicate flux and spectral variability in the X-ray band between 2 and 20 keV.
