Polarimetry and the High-Energy Emission Mechanisms in Quasar Jets

TL;DR

This paper explores how optical polarimetry can distinguish between different high-energy emission mechanisms in quasar jets, focusing on the debate between inverse-Compton and synchrotron processes at kpc scales.

Contribution

It demonstrates the use of optical polarimetry to diagnose high-energy emission mechanisms and reveals the jet's magnetic and energetic structure, with application to HST observations of PKS 1136-135.

Findings

Optical polarimetry can differentiate emission mechanisms in quasar jets.

HST polarimetry of PKS 1136-135 supports synchrotron emission at high energies.

The study provides insights into the magnetic field structure of jets.

Abstract

The emission mechanisms in extragalactic jets include synchrotron and various inverse-Compton processes. At low (radio through infrared) energies, it is widely agreed that synchrotron emission dominates in both low-power (FR I) and high-power (FR II and quasar) jets, because of the power-law nature of the spectra observed and high polarizations. However, at higher energies, the emission mechanism for high-power jets at kpc scales is hotly debated. Two mechanisms have been proposed: either inverse-Compton of cosmic microwave background photons or synchrotron emission from a second, high-energy population of electrons. Here we discuss optical polarimetry as a method for diagnosing the mechanism for the high-energy emission in quasar jets, as well as revealing the jet's three-dimensional energetic and magnetic field structure. We then discuss high-energy emission mechanisms for powerful jets in the light of the HST polarimetry of PKS 1136-135.