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Detection of the BL Lac object 1ES1426+428 in the Very High Energy gamma-ray band by the CAT Telescope from 1998-2000

A. Djannati-Atai·B. Khelifi·S. Vorobiov·R. Bazer-Bachi·G. Debiais·B. Degrange·P. Espigat·B. Fabre·G. Fontaine·P. Goret·C. Gouiffes·C. Masterson·F. Piron·M. Punch·M. Rivoal·L. Rob·J. -P. Tavernet
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Abstract

The BL Lac Object 1ES 1426+428, at a red-shift of z=0.129, has been monitored by the CAT telescope from February 1998 to June 2000. The accumulation of 26 hours of observations shows a gamma-ray signal of 321 events above 250 GeV 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 Phi_diff(400 GeV) = 6.73 +/- 1.27stat +/- 1.45syst x 10^-11 /cm^-2/s/TeV, and a very steep spectrum, with a differential spectral index of gamma = -3.60 +/- 0.57 which can 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 is hard at the source, these observations support a strong absorption effect of gamma-rays by the Intergalactic Infrared field.

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A. Djannati-Atai, B. Khelifi, S. Vorobiov, R. Bazer-Bachi, G. Debiais, B. Degrange, P. Espigat, B. Fabre, G. Fontaine, P. Goret, C. Gouiffes, C. Masterson, F. Piron, M. Punch, M. Rivoal, L. Rob, J. -P. Tavernet. 2002-07-29. Detection of the BL Lac object 1ES1426+428 in the Very High Energy gamma-ray band by the CAT Telescope from 1998-2000. https://doi.org/10.1051/0004-6361%3A20021034

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