Possible Proton Synchrotron Origin of X-Ray & Gamma Ray Emission in Large Scale Jet of 3C 273

TL;DR

This paper proposes a proton synchrotron model to explain the X-ray and gamma-ray emission from the large-scale jet of quasar 3C 273, addressing limitations of previous inverse Compton models and exploring different jet conditions.

Contribution

It introduces a proton synchrotron emission model for the jet's high-energy radiation, considering two scenarios based on proton energy loss and escape times, and evaluates their feasibility.

Findings

Proton synchrotron emission can fit observed spectra with moderate Doppler factors.

The second scenario requires lower jet luminosity, making it more plausible.

The model addresses gamma-ray overproduction issues in earlier inverse Compton explanations.

Abstract

The large scale jet of quasar 3C 273 has been observed in radio to $\gamma$ ray frequencies. Earlier the X-ray emission from knot A of this jet has been explained with inverse Compton scattering of the cosmic microwave background radiations by the shock accelerated relativistic electrons in the jet. More recently it has been shown that this mechanism overproduces the gamma ray flux at GeV energy and violates the observational results from Fermi LAT. We have considered the synchrotron emission from a broken power law spectrum of accelerated protons in the jet to explain the observed X-ray to $\gamma$ ray flux from knot A. The two scenarios discussed in our work are (i) magnetic field is high, synchrotron energy loss time of the protons is shorter than their escape time from the knot region and the age of the jet (ii) their escape time is shorter than their synchrotron energy loss time and the age of the jet. These scenarios can explain the observed photon spectrum well for moderate values of Doppler factor. The required jet luminosity is high $\sim 10^{46}$ erg/sec in the first scenario and moderate $\sim 10^{45}$ erg/sec in the second, which makes the second scenario more favorable.