Synchrotron vs Compton Interpretations for Extended X-ray Jets

Abstract

A widely discussed explanation for the origin of the X-ray emission observed from knots in extended quasar jets with the Chandra X-ray Obseratory is Compton-scattered CMBR by electrons with Lorentz factors $\gamma^\prime \sim 10^2$. This model faces difficulties in terms of total energy requirements, and in explaining the spatial profiles of the radio, optical, and X-ray knots in sources such as PKS 0637-752, 3C 273, or PKS 1127-145. These difficulties can be resolved in the framework of one- and two-component synchrotron models. We propose a model where the broad band radio to X-ray synchrotron emission in quasar jets is powered by collimated beams of ultra-high energy neutrons and gamma-rays formed in the sub-parsec scale jets. The decay of the neutral beam in the intergalactic medium drives relativistic shocks to accelerate nonthermal electrons out of the ambient medium. A second synchrotron component arises from the injection of leptons with Lorentz factors $\gg 10^7$ that appear in the extended jet in the process of decay of ultra-high energy gamma rays. This approach could account for qualitative differences in the extended X-ray jets of FR1 and FR2 galaxies. Detection of high-energy neutrinos from blazars and core-dominated quasars will provide strong evidence for this model.