A hard X - ray view on two distant VHE blazars : 1 ES 1101 - 232 and 1 ES 1553 + 113

TeV-blazars are known as prominent non-thermal emitters across the entire electromagnetic spectrum with their photon power peaking in the X-ray and TeVband. If distant, absorption of γ-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 May and July 2006, respectively, including a quasi-simultaneous coverage with the state of the art Cherenkov telescope facilities. We report on the resulting data sets with emphasis on the X-ray band, and set into context to their historical behaviour. During our campaign, we did not detect any significant X-ray or γ–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 W.W. Hansen Experimental Physics Laboratory & Kavli Institute for Particle Astrophysics & Cosmology, Stanford University, 452 Lomita Mall, Stanford, CA 94305, USA; [email protected], [email protected], [email protected] Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA 94305, and Stanford Linear Accelerator Center, 2575 Sand Hill Road, Menlo Park, CA 94025, USA; [email protected] Universität Würzburg, D-97074 Würzburg, Germany; [email protected] SLAC-PUB-13227 May 2008 Submitted to Astrophysical Journal