Radio Jet Properties of the Flaring Gamma-Ray Blazar PKS 0346-27

The blazar PKS 0346-27 at redshift z=0.991 is among the most distant extragalactic sources detected in very high energy γ-rays. It underwent a major flare reaching TeV energies in November 2021. Recent modelling of its spectral energy distribution favoured a single-zone proton–synchrotron-dominated hadronic model with bulk Lorentz factor Γ=10 over a single-zone leptonic jet model with much higher Γ. Here we analyse archival radio data to give independent estimates of the jet bulk Lorentz factor. We present high-resolution radio imaging and brightness distribution modelling, as well as flare detection in long-term radio flux density monitoring data, and obtain Γ≲10 values. This lends support to the hadronic model proposed for the PKS 0346-27 jet. Our results highlight the importance of long-term, very long baseline interferometry and total flux density monitoring in studying blazar jets.