A Modified Stratified Model for 3C 273 Jet

TL;DR

This paper introduces a modified stratified jet model for 3C 273, explaining spectral differences among knots via Doppler factor deviations and fitting the overall spectrum with synchrotron and inverse Compton components.

Contribution

It proposes a new stratified jet model assuming a single particle energy spectrum and identical emission processes, explaining spectral variations through Doppler factor deviations.

Findings

Spectral energy distribution of all knots fits two components: synchrotron and inverse Compton.

Derived a characteristic Doppler factor of 7.4 for the jet.

Discussed implications for physical properties and future gamma-ray observations.

Abstract

We present a modified stratified jet model to interpret the observed spectral energy distributions of knots in 3C 273 jet. Based on the hypothesis of the single index of the particle energy spectrum at injection and identical emission processes among all the knots, the observed difference of spectral shape among different 3C273 knots can be understood as a manifestation of deviation of the equivalent Doppler factor of stratified emission regions in individual knot from a characteristic one. The summed spectral energy distribution of all the ten knots in 3C 273 jet can be well fitted by two components, low-energy (radio to optical) component dominated by the synchrotron radiation and high-energy component (UV, X-ray and $\gamma$-ray) dominated by the inverse Compton scattering of the cosmic microwave background. This gives a consistent spectral index of $\alpha=0.88$ ($S_\nu \propto \nu^{-\alpha}$) and a characteristic Doppler factor of 7.4. Assuming the average of the summed spectrum as the characteristic spectrum of each knot in the 3C273 jet, we further get a distribution of Doppler factor. We discuss the possible implications of these results for the physical properties in 3C 273 jet. Future GeV observations with $\it GLAST$ could separate the $\gamma$-ray emission of 3C 273 from the large scale jet and the small scale jet (i.e. the core) through measuring the GeV spectrum.