Detection of the BL Lac object 1ES 1426+428 in the Very High Energy gamma-ray band by the CAT Telescope from 1998–2000

The BL Lac Object 1ES 1426+428, at a red-shift of , has been monitored by the Cat telescope from February 1998 to June 2000. The accumulation of 26 h of observations shows a γ-ray signal of 321 events above at 5.2 standard deviations, determined using data analysis cuts adapted to a weak, steep-spectrum source. The source emission has an average flux of , and a very steep spectrum, with a differential spectral index of which can be refined to using a higher flux data subset. If, as expected from its broad-band properties, the Very High Energy emission is hard at the source, these observations support a strong absorption effect of γ-rays by the Intergalactic Infrared field.