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We have observed 1ES 1426+428 with INTEGRAL detecting it up to $\sim$150 keV.The spectrum is hard, confirming that this source is an extreme BL Lac object,with a synchrotron component peaking, in a $\nu F_\nu$ plot, at or above 100keV, resembling the hard states of Mkn 501 and 1ES 2344+514. All these threesources are TeV emitters, with 1ES 1426+428 lying at a larger redshift(z=0.129): for this source the absorption of high energy photons by the IRcosmic background is particularly relevant. The observed hard synchrotron tailhelps the modeling of its spectral energy distribution, giving information onthe expected intrinsic shape and flux in the TeV band. This in turn constrainsthe amount of the poorly known IR background.

The hard synchrotron X-ray spectrum of the TeV BL Lac 1ES 1426+428