Description of Atypical Bursts Seen Slightly Off-axis

The detection of gravitational waves together with their electromagnetic counterpart, in the gamma-ray burst GRB 170817A, marked a new era o multi-messenger astronomy. Several theoretical models have been propose to explain the atypical behaviour of this event. Recently, it was show that the multi-wavelength afterglow of GRB 170817A was consistent with synchrotron forward-shock model when the outflow was viewed off-axis decelerated in a uniform medium and parametrized through a power-la energy emission, and the stratified medium in the close vicinity of binary neutron star merger proposed to explain the gamma-ray flux in th short GRB 150101B, we extend the mechanism proposed to explain GR 170817A to a more general scenario deriving the synchrotron self-Compto (SSC) and synchrotron forward-shock model when the off-axis outflow i decelerated in a uniform and stratified circumburst density. A particular cases, we show that the delayed and long-lasting afterglo emission observed in GRB 080503, GRB140903A, GRB 150101B and GRB 160821 could be interpreted by a similar scenario to the one used to describ GRB 170817A. In addition, we show that the proposed scenario agrees wit the MAGIC, Fermi-LAT and H.E.S.S upper limits on gamma-ray emission fro GRB 160821B and GRB 170817A.