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

TL;DR

This study reports the detection of a hard X-ray spectrum from the TeV BL Lac object 1ES 1426+428, revealing an extreme synchrotron component peaking above 100 keV, which aids in understanding its spectral energy distribution and the IR background.

Contribution

First detection of a hard X-ray spectrum up to 150 keV from 1ES 1426+428, confirming its extreme synchrotron emission and providing insights into its intrinsic TeV flux and IR background constraints.

Findings

Synchrotron component peaks at or above 100 keV.

Source is an extreme BL Lac with a hard X-ray spectrum.

Implications for TeV emission modeling and IR background constraints.

Abstract

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 100 keV, resembling the hard states of Mkn 501 and 1ES 2344+514. All these three sources 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 IR cosmic background is particularly relevant. The observed hard synchrotron tail helps the modeling of its spectral energy distribution, giving information on the expected intrinsic shape and flux in the TeV band. This in turn constrains the amount of the poorly known IR background.