TeV gamma rays from the blazar H 1426+428 and the diffuse extragalactic background radiation

The detection of TeV -rays from the blazar H 1426+428 at an integral flux level of (4 2stat 1syst) 10 12 erg cm 2 s 1 above 1 TeV with the HEGRA imaging atmospheric Cherenkov telescope system is reported. H 1426+428 is located at a redshift of z = 0.129, which makes it the most distant source detected in TeV -rays so far. The TeV radiation is expected to be strongly absorbed by the diuse extragalactic background radiation (DEBRA). The observed energy spectrum of TeV photons is in good agreement with an intrinsic power law spectrum of the source/ E 1:9 corrected for DEBRA absorption. Statistical errors as well as uncertainties about the intrinsic source spectrum, however, do not permit strong statements about the density of the DEBRA infrared photon eld.