A shocking outcome: Jet dynamics and polarimetric signatures of the multi-band flare in blazar OJ 248

The connection between γ -ray flares and blazars is a topic of active research. Few sources exhibit outbursts distinct enough to be conclusively connected with features in their jet morphology. Here we present an investigation of the sole γ -ray flare of the blazar OJ 248 to date and how it is associated with its jet structure, as revealed by very long baseline interferometry (VLBI). We find that throughout the course of the γ -ray flare, the fractional linear polarisation increases in the jet of OJ 248, and the VLBI electric vector position angles (EVPAs) rotate to become perpendicular to the bulk jet flow. We interpret this behaviour as a moving shock, travelling through a recollimation shock, up-scattering photons via the inverse Compton scattering process, and producing a γ -ray flare. Our hypothesised shock-shock interaction scenario is a viable mechanism for inducing such EVPA rotations in both optical and radio bands.