We compile the radio-optical-X-ray spectral energy distributions (SEDs) of 65 knots and 29 hotspots in 41 active galactic nucleus jets to examine their high energy radiation mechanisms. Their SEDs can be fitted with the single-zone leptonic models, except for the hotspot of Pictor A and six knots of 3C 273. The X-ray emission of one hotspot and 22 knots is well explained as synchrotron radiations under the equipartition condition; they usually have lower X-ray and radio luminosities than the others, which may be due to a lower beaming factor. An inverse Compton (IC) process is involved for explaining the X-ray emission of the other SEDs. Without considering the equipartition condition, their X-ray emission can be attributed to the synchrotron-self-Compton (SSC) process, but the derived jet power (P jet ) are not correlated with L k and most of them are larger than L k with more than three orders of magnitude, where L k is the jet kinetic power estimated with their radio emission. Under the equipartition condition, the X-ray emission is well interpreted with the IC process to the cosmic microwave background photons (IC/CMB). In this scenario, the derived P jet of knots and hotspots are correlated with and comparable to L k . These results suggest that the IC/CMB model may be the promising interpretation of their X-ray emission. In addition, a tentative knot-hotspot sequence in the synchrotron peak-energypeak-luminosity plane is observed, similar to the blazar sequence, which may be attributed to their different cooling mechanisms of electrons.

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). Analyzing its Fermi /LAT data in the past 8 years, a long-term steady γ-ray emission component is found 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 γ-ray flux decays, likely indicating that a large part of the magnetic energy is converted to the kinetic energy of particles in pc-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 ∼ 10 24 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 along the distance to the core, illustrating as deceleration of jet in large-scale. The powers of the core and knots are roughly in the same order, but the jet changes from highly magnetized at the core region into particle-dominated at the large-scale knots.

3C 207 is a lobe-dominant radio galaxy with one sided jet and the bright knots in kpc-Mpc scale were resolved in the radio, optical and X-ray bands. It was confirmed as a γ-ray emitter with Fermi/LAT, but it is uncertain whether the γ-ray emission region is the core or knots due to the low spatial resolution of Fermi/LAT. We present an analysis of its Fermi/LAT data in the past 9 years. Different from the radio and optical emission from the core, it is found that the γ-ray emission is steady without detection of flux variation over 2σ confidence level. This likely implies that the γ-ray emission is from its knots. We collect the radio, optical, and X-ray data of knot-A, the closest knot from the core at 1. ′′ 4, and compile its spectral energy distribution (SED). Although the single-zone synchrotron+SSC+IC/CMB model by assuming knot-A at rest can reproduce the SED in the radio-optical-X-ray band, the predicted γ-ray flux is lower than the LAT observations and the derived magnetic field strength deviates the equipartition condition with 3 orders of magnitude. Assuming that knot-A is relativistically moving, its SED from radio to γ-ray bands would be well represented with the single-zone synchrotron+SSC+IC/CMB model under the equipartition condition.These results likely suggest that the γ-ray emission may be from knot-A via the IC/CMB process and the knot should have relativistical motion. The jet power derived from our model parameters is also roughly consistent with the kinetic power estimated with the radio data.