High Energy Radiation Mechanism Of Large-scale Jet Substructures In AGNs

Active galactic nuclei(AGNs)are the centers of galaxies with violent activities,which can produce the radiations from radio to gamma-ray bands.So far,most of the confirmed extragalactic gamma-ray emission sources are AGNs,and their broadband spectral energy distributions(SEDs)are dominated by the jet radiations.With great improvements in both the space resolution and detection sensitivity,the substructures of large-scale jets in AGNs,including knots,hot spots,and lobes were observed in the radio,infrared,optical,and X-ray bands.However,except for the two radio galaxies Fornax A and Cen A,the low space resolution of Fermi/LAT makes that it is difficult to conceivably judge the location of the y-ray emission for most of sources.Comparing with the core radiation,the gamma-ray emission from large-scale jets does not have significant variation with a harder spectrum.The observations and confirmations of gamma-ray emission from large-scale jets are very important to constrain the radiation mechanisms and particle acceleration mechanisms of large-scale jets.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.3C 207 had been confirmed as a gamma-ray emission source,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 presented an analysis of its Fermi/LAT data in the past 9 years and found that its y-ray emission is steady without detection of flux variation over 2σ confidence level.There is a bright knot(knot-A)close to the core,which was detected in the radio,optical and X-ray bands.The SEDs of knot-A can be explained well with the one-zone leptonic model,and the gamma-ray emission would be well represented by the inverse Compton scattering of cosmic microwave background photon(IC/CMB)process 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 relativistic motion.4C +49.22 is a gamma-ray flat spectrum radio quasar with a bright and knotty jet.We also presented an analysis for its Fermi/LAT observational data in the past 9 years and found that this source has a long-term,steady gamma-ray emission component besides a bright outburst.The gamma-ray outburst is companied by the flux variations in the radio,optical,and X-ray bands from the core region,suggesting that the outburst happened at the core region.We checked whether the steady gamma-ray emission observed with Fermi/LAT is contributed by the large-scale jet.We collected the radio-optical-X-ray data of its five large-scale knots and fit their SEDs with the leptonic model by considering the IC/CMB process.However,the predicted flux at the gamma-ray band by the model is lower than the observations of Fermi/LAT with a flux ratio of 0.16.These results likely imply that the steady gamma-ray emission of 4C+49.22 is partially contributed by the large-scale knots,which may conceal the low-level flux variation of the gamma-ray emission from the core region.Our works indicate that the gamma-ray emission of the confirmed gamma-ray sources should be dominated by the core region,but we cannot exclude the contributions from large-scale jets.The further research needs the detectors with better space resolution and detection sensitivity in the future.