Constraining X-ray emission in HBL blazars using multiwavelength observations

Abstract

The X-ray spectrum of extreme HBL type blazars is located in the synchrotron branch of the broadband spectral energy distribution (SED), at energies below the peak. A joint fit of the extrapolated X-ray spectra together with a host galaxy template allows characterizing the synchrotron branch in the SED. The X-ray spectrum is usually characterized either with a pure or a curved power-law model. In the latter case, however, it is hard to distinguish an intrinsic curvature from excess absorption. In this paper, we focus on five well-observed blazars: 1ES 0229+200, PKS 0548-322, RX J1136+6737, 1ES 1741+196, 1ES 2344+514. We constrain the infrared-to-X-ray emission of these five blazars using a model that is characterized by the host galaxy, spectral curvature, absorption, and ultraviolet excess to separate these spectral features. In the case of four sources: 1ES 0229+200, PKS 0548-322, 1ES 1741+196, 1ES 2344+514 the spectral fit with the atomic neutral hydrogen from the Leiden Argentina Bonn Survey result in a significant UV excess present in the broadband spectral energy distribution. Such excess can be interpreted as an additional component, for example, a blue bump. However, in order to describe spectra of these blazars without such excess, additional absorption to the atomic neutral hydrogen from the Leiden Argentina Bonn Survey is needed.

12 pages, 6 figures, accepted for publication in MNRAS

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