2025A&A...704L..10T

The VERITAS Collaboration recently reported the detection of very high-energy (VHE) gamma-ray emission from the prototypical radio quasar 3C273. The temporal and spectral properties of this component do not appear compatible with the extrapolation of the beamed blazar-like emission of the inner, parsec-scale jet. We explore the possibility that the VHE component is produced in the jet at kiloparsec scales through the inverse Compton emission of a population of ultra-high-energy electrons (with Lorentz factor γ ∼ 10⁸). In the model these electrons are accelerated through the shear acceleration mechanism, and they account for the still puzzling X-ray emission of knots detected by Chandra in the large-scale jets of several powerful quasars (including 3C273). In our scenario, the VHE component can be interpreted as the integrated emission from the two brightest knots of the 3C273 jet. We speculate that the decay of the emission on a timescale of ∼3 years could be accounted for by the scenario if the VHE radiation is produced in some compact regions in the downstream flow of a recollimation shock.