X-ray and TeV emissions from High Frequency Peaked BL Lacs

Abstract

The majority of the extragalactic sources yet detected at TeV photon energies belong to the class of "high frequency peaked BL Lacs" (HBLs) that exhibit a spectral energy distribution with a lower peak in the X-ray band. Such spectra are well described in terms of a log-parabolic shape with a considerable curvature, and widely interpreted as synchrotron emission from ultrarelativistic electrons outflowing in a relativistic jet; these are expected to radiate also in gamma-rays by the inverse Compton process. Recently we have compared the X-ray spectral parameter distributions of TeV detected HBLs (TBLs) with those undetected (UBLs), and found that the distributions of the peak energies E_p are similarly symmetric around a value of a few keVs for both subclasses, while the X-ray spectra are broader for TBLs than for UBLs. Here we propose an acceleration scenario to interpret both the E_p and the spectral curvature distributions in terms of a coherent and a stochastic acceleration mechanisms, respectively. We show how the curvature parameter b< 0.3 - 0.7 of the synchrotron X rays, that depends only on the latter acceleration component, can be related to the inverse Compton luminosity in gamma-rays, so introducing a link between the X-ray and the TeV observations of HBLs.

4 pages, 2 figures, Astrophysical Journal published

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• The $\gamma$-ray sky seen at X-ray energies I. Searching for the connection between X-rays and $\gamma$-rays in Fermi BL Lac objects
• A New Multi-Wavelength Census of Blazars
• Te-REX: a sample of extragalactic TeV-emitting candidates
• A new look at the extragalactic Very High Energy sky: searching for TeV-emitting candidates among the X-ray bright, non-Fermi detected blazar population
• Disentangling the nature of the prototype radio weak BL Lac: Contemporaneous multifrequency observations of WISE J141046.00 + 740511.2
• SVOM discovery of a strong X-ray outburst of the blazar 1ES~1959+650 and multi-wavelength follow-up with the Neil Gehrels Swift observatory
• Constraining the synchrotron peak and estimating the VHE brightness of a sample of extreme high synchrotron peak blazars