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The X-ray to radio afterglow emission of GRB 170817A/GW 170817 so far scalesas $F_\nu\propto\nu^{-0.6}t^{0.8}$ with observed frequency and time, consistentwith a single power-law segment of the synchrotron spectrum from the externalshock going into the ambient medium. This requires the effective isotropicequivalent afterglow shock energy in the visible region to increase as $\simt^{1.7}$. The two main channels for such an energy increase are (i)\emph{radial}: more energy carried by slower material (in the visible region)gradually catches up with the afterglow shock and energizes it, and (ii)\emph{angular}: more energy in relativistic outflow moving at different anglesto our line of sight, whose radiation is initially beamed away from us but itsbeaming cone gradually reaches our line of sight as it decelerates. One cannotdistinguish between these explanations (or combinations of them) using only theX-ray to radio $F_\nu(t)$. Here we demonstrate that the most promising way tobreak this degeneracy is through afterglow imaging and polarization, bycalculating the predicted evolution of the afterglow image (its size, shape andflux centroid) and linear polarization $\Pi(t)$ for different angular and/orradial outflow structures that fit $F_\nu(t)$. We consider two angular profiles-- a Gaussian and a narrow core with power-law wings in energy per solid angle,as well as a (cocoon motivated) (quasi-) spherical flow with radial velocityprofile. For a jet viewed off-axis (and a magnetic field produced in theafterglow shock) $\Pi(t)$ peaks when the jet's core becomes visible, at$\approx2t_p$ where the lightcurve peaks at $t_p$, and the image can beelongated with aspect ratios$\;\gtrsim2$. A quasi-spherical flow has an almostcircular image and a much lower $\Pi(t)$ (peaking at $\approx t_p$) and fluxcentroid displacement.

Afterglow Imaging and Polarization of Misaligned Structured GRB Jets and Cocoons: Breaking the Degeneracy in GRB 170817A