The Polarization Behavior of Relativistic Synchrotron Self-Compton Jets

Abstract: We describe a geometric model for synchrotron and synchrotron self-Compton (SSC) radiation from blazar jets, involving multiple emission zones with turbulent magnetic fields and fully self-consistent seed photon mixing for SSC. Including the effects of jet divergence, particle cooling and the Relativistic PA rotation (RPAR) to the observer frame, we find that the multi-zone model recovers simple predictions for SSC polarization, but describes new dependencies on jet viewing geometry and zone multiplicity. Increasing the zone number decreases both synchrotron and SSC polarization, but with different scaling. A rise in synchrotron polarization fraction $\Pi_{\rm Sync}$ at high energies is guaranteed by basic relativity considerations, and strengthened by jet non-uniformity. Finite light travel time effects can suppress the synchrotron polarization at energies well below the $\nu_{\rm Sync}$ peak. In general $\Pi_{\rm Sync}$ and $\Pi_{\rm SSC}$ are correlated with $\Pi_{\rm SSC}/\Pi_{\rm Sync}\approx 0.3$, but individual realizations can lie far from this trend. This study lets us estimate $\Pi$ across the SED, leading to predictions in the X-ray band helpful for planning observations with {\it IXPE} and other upcoming X-ray polarization missions.