On the Feasibility of Independent Detections of Optical Afterglows of GRBs

Abstract

The recent detection of optical afterglows (OAs, optical delayed emission) and optical transients (OTs, optical prompt emission) of gamma ray bursts (GRBs) allows to consider optical ground-based independent detection of these phenomena. It becomes evident that the optical surveys achieving lim mag better than 19 ... 23 for stars and/or 10 for 1 min exposures may detect OAs and OTs of GRBs. This opens the possibility of independent optical searches for GRBs. These searches must be of large field of view and high sensitivity i.e. CCD surveys and/or deep patrol plates are suitable. The prospects of optical surveys for GRBs may be summarized as follows. (1) The optical surveys may provide a larger sample (due to different beaming) and better localisation accuracy (1 arcmin or better) than provide gamma ray satellite detectors. (2) The larger sample of OAs and their host galaxies may be crucial for understanding the nature of GRBs. (3) The actual rate of OAs can place strong constraints on the afterglow appearance fraction and the initial beaming angle of GRB sources. (4) The UV flashes predicted by some theories such as Protheroe and Bednarek 1999 could be detected and studied. The corresponding delays regarding GRBs could serve to study the nature of the sources. This can be addressed only by surveys, not by follow-up devices since the flashes may precede the GRBs. (5) The optical surveys are cost-effective.