Off-Axis Afterglow Emission from Jetted Gamma-Ray Bursts
  We calculate Gamma-Ray Burst afterglow light-curves from a relativistic jet of initial opening angle theta_0, as seen by observers at a wide range of viewing angles, theta_obs, from the jet axis. We describe three increasingly more realistic models and compare the resulting light-curves. An observer at theta_obs < theta_0 should see a light curve very similar to that for an on-axis observer. An observer at theta_obs > theta_0 should see a rising light curve at early times, the flux peaking when the jet Lorentz factor sim 1/theta_obs. After this time the flux is not very different from that seen by an on-axis observer. A strong linear polarization (<40%) may occur near the peak in the light curve, and slowly decay with time. We show that if GRB jets have a universal energy, then orphan afterglows associated with off-axis jets should be seen up to a constant theta_obs, therefore the detection rate of orphan afterglows would be proportional to the true GRB rate. We also discuss the proposed connection between supernova 1998bw and GRB 980425. 
J. Granot, A. Panaitescu, P. Kumar, S.E. Woosley