  X-ray bright knots of kpc-scale jets of several radio loud quasars have been
an actively discussed issue. Among various models to explain observations,
synchrotron radiation from the electron population different from radio to IR
emitting electrons is promising. However, the origin of this electron
population has been debated. Recently, we proposed that this electron
population is produced by proton-photon collisions (mainly, Bethe-Heitler
process), and we applied this model to PKS 0637-752. We found that this model
works if the proton power is by an order of magnitude larger than the Eddington
power. In this paper we apply this model to the X-ray emission in the knots of
3C 273 and PKS 1136-135. The target photons for electron-positron pair
production are supplied by synchrotron radiation at radio-IR by primary
electrons and by the active galactic nucleus (AGN) core as well as cosmic
microwave background (CMB) radiation. The effects of the AGN photons are
included for the first time in the hadronic model. Though the observed X-ray
flux is obtained with the contribution of the AGN photons, the required proton
power turns out to be highly super-Eddington. However, we find that our model
works for a nearly Eddington proton power, if the photon density of the AGN is
enhanced. This can occur if the AGN photons are more beamed toward the X-ray
knots than toward our line of sight and the AGN photon frequency is shifted by
the Doppler effect.
