Jet Radiation Properties of 4C +49.22: from the Core to Large-scale Knots

Abstract

Abstract 4C +49.22 is a γ-ray flat-spectrum radio quasar with a bright and knotty jet. We investigate the properties of the core and large-scale knots by using their spectral energy distributions (SEDs). Analysis of the Fermi/LAT data from 4C +49.22 over the past eight years reveals a long-term steady γ-ray emission component besides bright outbursts. For the core region, the γ-ray emission together with the simultaneous emission in the low-energy bands at different epochs is explained with the single-zone leptonic model. The derived magnetization parameters and radiation efficiencies of the radio-core jet decrease as the γ-ray flux decays, likely indicating that a large part of the magnetic energy is converted to the kinetic energy of particles on a parsec scale. For the large-scale knots, their radio–optical–X-ray SEDs can be reproduced with the leptonic model by considering the inverse Compton scattering of cosmic microwave background photons. The sum of the predicted γ-ray fluxes of these knots is comparable to that observed with LAT at ∼1024 Hz of the steady γ-ray component, indicating that the steady γ-ray emission may be partially contributed by these large-scale knots. This may conceal the flux variations of the low-level γ-ray emission from the radio core. The derived bulk Lorentz factors of the knots decrease with increasing distance from the core, illustrating the deceleration of the jet on a large scale. The powers of the core and knots are roughly of the same order, but the jet changes from highly magnetized in the core region to particle-dominated in the large-scale knots.