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Gamma-ray burst (GRB) jets are narrow, and thus typically point away from us.They are initially ultra-relativistic, causing their prompt $\gamma$-ray andearly afterglow emission to be beamed away from us. However, as the jetgradually decelerates its beaming cone widens and eventually reaches our lineof sight and the afterglow emission may be detected. Such orphan afterglowswere not clearly detected so far. Nevertheless, they should be detected inupcoming optical or radio surveys, and it would be challenging to clearlydistinguish between them and other types of transients. Therefore, we performdetailed, realistic calculations of the expected afterglow emission from GRBjets viewed at different angles from the jet's symmetry axis. The dynamics arecalculated using 2D relativistic hydrodynamics simulations of jets propagatinginto different power-law external density profiles, $\rho_{\rmext}\propto{}R^{-k}$ for $k=0,\,1,\,1.5,\,2$, ranging from a uniform ISM-likemedium ($k=0$) to a stratified steady stellar-wind like profile ($k=2$). Wecalculate radio, optical and X-ray lightcurves, and the evolution of the radioafterglow image size, shape and flux centroid. This may help identifymisaligned relativistic jets, whether initially ultra-relativistic andproducing a GRB for observers within their beam, or (possibly intrinsicallymore common) moderately relativistic, in either (i) nearby supernovae Ib/c(some of which are associated with long duration GRBs), or (ii) in binaryneutron star mergers, which may produce short duration GRBs, and may also bedetected in gravitational waves (e.g. GW$\,$170827/GRB$\,$170817A with a weakprompt $\gamma$-ray emission may harbor an off-axis jet).

Off-axis afterglow light curves and images from 2D hydrodynamic simulations of double-sided GRB jets in a stratified external medium