Markus Böttcher, Charles D. Dermer, and Justin D. Finke
Astrophysical Journal Letters, 679, L9 (2008)
Observations of very-high-energy (VHE, E > 250 GeV) gamma-ray emission from blazars at z > 0.1 have placed stringent constraints on the elusive spectrum and intensity of the intergalactic infrared background radiation (IIBR). In the case of the high-frequency-peaked BL Lac object 1ES 1101-232 (z = 0.186), correcting the observed VHE spectrum for gamma-gamma absorption by the IIBR provided evidence for a very hard (photon index ~ 1.5) intrinsic source spectrum. Such a hard VHE gamma-ray spectrum poses a serious challenge to the conventional synchrotron-self-Compton interpretation of the VHE emission of TeV blazars and suggests the emergence of a separate emission component beyond a few hundred GeV. Here we propose that such a very hard, slowly variable VHE emission component in TeV blazars may be produced via Compton upscattering of Cosmic Microwave Background (CMB) photons by shock-accelerated electrons in an extended jet. For the case of 1ES 1101-232, this component could dominate the bolometric luminosity of the extended jet if the magnetic fields are of the order of typical intergalactic magnetic fields (B ~ 10-5 G) and electrons are still being accelerated out to TeV energies, with very hard injection power-law spectral indices of q ~ 1.5, on length scales of ~ 100 pc along the jet.