A Hard X-Ray View of Two Distant VHE Blazars: 1ES 1101-232 and 1ES 1553+113

TL;DR

This study presents Suzaku X-ray observations of two distant TeV blazars, revealing spectral curvature and quiescent states, and discusses implications for their intrinsic properties and gamma-ray absorption by the EBL.

Contribution

First simultaneous X-ray and gamma-ray observations of these distant blazars, analyzing spectral shapes and variability to inform models of blazar emission and EBL absorption effects.

Findings

No significant X-ray or gamma-ray variability detected.

Spectral curvature observed up to 30 keV, indicating softening with energy.

No significant change in VHE spectrum compared to earlier observations.

Abstract

TeV blazars are known as prominent nonthermal emitters across the entire electromagnetic spectrum with their photon power peaking in the X-ray and TeV bands. If distant, absorption of gamma-ray photons by the extragalactic background light (EBL) alters the intrinsic TeV spectral shape, thereby affecting the overall interpretation. Suzaku observations for two of the more distant TeV blazars known to date, 1ES 1101-232 and 1ES 1553+113, were carried out in 2006 May and July, respectively, including a quasi-simultaneous coverage with the state-of-the-art Cerenkov telescope facilities. We report on the resulting data sets with emphasis on the X-ray band and set in context to their historical behavior. During our campaign, we did not detect any significant X-ray or gamma-ray variability. 1ES 1101-232 was found in a quiescent state with the lowest X-ray flux ever measured. The combined XIS and HXD PIN data for 1ES 1101-232 and 1ES 1553+113 clearly indicate spectral curvature up to the highest hard X-ray data point (~30 keV), manifesting as softening with increasing energy. We describe this spectral shape by either a broken power law or a log-parabolic fit with equal statistical goodness of fits. The combined 1ES 1553+113 very high energy spectrum (90-500 GeV) did not show any significant changes with respect to earlier observations. The resulting contemporaneous broadband spectral energy distributions of both TeV blazars are discussed in view of implications for intrinsic blazar parameter values, taking into account the gamma-ray absorption in the EBL.