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The BL Lac Object 1ES 1426+428, at a red-shift of z=0.129, has been monitoredby the CAT telescope from February 1998 to June 2000. The accumulation of 26hours of observations shows a gamma-ray signal of 321 events above 250 GeV at5.2 standard deviations, determined using data analysis cuts adapted to a weak,steep-spectrum source. The source emission has an average flux of Phi_diff(400GeV) = 6.73 +/- 1.27stat +/- 1.45syst x 10^-11 /cm^-2/s/TeV, and a very steepspectrum, with a differential spectral index of gamma = -3.60 +/- 0.57 whichcan be refined to gamma = -3.66 +/- 0.41 using a higher flux data subset. If,as expected from its broad-band properties, the Very High Energy emission ishard at the source, these observations support a strong absorption effect ofgamma-rays by the Intergalactic Infrared field.Comment: 4 pages, 3 figures, accepted for publication in A&A Letter

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