Polarimetry and the High‐Energy Emission Mechanisms in Quasar Jets

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 (FRII 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.