HST observations of the quasar PKS 0637-752: equipartition electron-proton jet from the most complete spectral coverage to date

TL;DR

This study uses comprehensive multiwavelength observations of quasar PKS 0637-752 to analyze jet composition, finding that an equipartition electron-proton jet best explains the data, challenging magnetic dominance models.

Contribution

It provides the most complete spectral coverage to date and demonstrates that a proton-electron jet under equipartition best fits the observations, excluding magnetic dominance.

Findings

Magnetic field dominated jets are excluded by observations.

Protons are necessary for all jet configurations analyzed.

Equipartition with one proton per lepton best reproduces the data.

Abstract

We present new NICMOS and ACS observations of the quasar jet PKS 0637-752, and we use them, together with existing multiwavelength observations, to produce the most complete spectral coverage of the source to date. We explore the implications of these observations in the context of models for the jet X-ray emission. By relaxing the assumption of equipartition, we undertake an exhaustive study of the parameter space for external Compton off the CMB (EC/CMB) model. We find that the multiwavelength observations exclude a magnetic field dominated jet. Using the method proposed by Georganopoulos et al. (2005) for probing the jet matter content we show that protons are needed for practically all jet configurations, extending a previous application of the method by Uchiyama et al. (2005) that was based on exploring three particular jet configurations. We also show that equipartition is the only configuration that can reproduce the observations and have one proton per radiating lepton. We finally present a rather model - independent argument that the jet has a spine-sheath flow pattern, with the spine being faster and emitting most of the IR-optical-X-ray emission.