High Energy Radiation Properties Of Large-scale Jet Knots In 3C 273

Active galactic nuclei(AGNs)are the centers of galaxies with violent activities.They are characterized by the violent activities and variabilities at multiwavelength.The radiations of AGNs almost cover the whole electromagnetic spectrum from radio to ?-ray bands.About 10%?15% of AGNs are radio loud,which have the powerful jets.The jets of some AGNs can extend to the kpc-Mpc scale and form some substructures,such as knots,hotspots and radio lobes.The detection of polarization in the radio and optical emission indicates that they are from synchrotron radiation of relativistic electrons,but the X-ray radiation mechanisms of these extended regions are highly debated.A comprehensively theoretical analysis on the broadband spectral energy distributions(SEDs)of nine large-scale jet knots in 3C 273 is presented to reveal their X-ray radiation mechanism.We found that the SEDs of these knots cannot be represented with the leptonic model of a single-electron population.By adding a more energetic electron or proton(the hadronic model)population,the SEDs of all knots are well represented.In the leptonic model of two-electron populations,the electron population that contributes the X-ray emission is more energetic than the one responsible for the radio-optical emission by almost two orders of magnitude;the derived equipartition magnetic field is ?0.1 m G.In thehadronic model,protons with energy ?20 Pe V are required to interpret theobserved X-rays,and the derived equipartition magnetic field is several m G,higher than that in the leptonic model.But there is no observational evidence to support the two-electron population model.And the fast cooling time of the high-energy electrons does not easily explain the observed X-ray morphologies.We thus suggested that the X-ray radiation of these knots is produced by the synchrotron emission of high-energy protons in the same region as the electron population.Considering the Doppler boosting effect,the super-Eddington issue of the hadronic model can also be avoided.