GHIRLANDA, GiancarloGiancarloGHIRLANDA2020-04-062020-04-0620151824-8039http://hdl.handle.net/20.500.12386/23885GRBs detected in the γ–ray band are those “seen" within their jets (which have typical opening angles θjet ∼ 2 − 10 degrees). When seen off–axis, the high relativistic beaming (due to bulk Lorentz factors Γ > 100) prevents the detection of the high energy γ–ray emission. However, the slow down of the outflow (due to the interaction with the interstellar matter) makes the afterglow potentially observable a few days after the GRB itself. Deep wide field radio surveys have the. potential to detect the off-axis population of Gamma Ray Bursts (dubbed Orphan Afterglows - OA) as relatively slow (days to months timescales) transients (at a flux density level of 10-100 µJy at GHz frequencies) with a detection rate of few events per year. The detection rate of OA should increase from the the VLASS (∼16 yr−1) through the VAST-Wide (∼25–45 yr−1) to the SKA1 (∼220 yr−1) survey. On the other hand, low frequency (MHz) surveys have less chances to detect these transients. Spectroscopy and multi wavelength follow up will be necessary to distinguish OA from extragalactic transients (SN, TDE and AGN flares) with similar temporal properties and brightness. Detection and study of the OA population in the radio band is of primary importance for the potential support in the identification of the counterparts of gravitational wave events.ELETTRONICOenConference paper10.22323/1.267.00182-s2.0-84988815053https://pos.sissa.it/267/018/2015fers.confE..18GFIS/05 - ASTRONOMIA E ASTROFISICA