The Use of Gamma-Ray Bursts as Direction and Time Markers in SETI Strategies

Abstract

When transmitting a signal over a large distance, it is more efficient to send a brief beamed signal than a continuous omnidirectional transmission, but this requires that the receiver knows where and when to look for the transmission. For SETI, the use of various natural phenomena has previously been suggested to achieve the desired synchronization. Here it is proposed that gamma-ray bursts may well be the best ``synchronizers'' of all currently known phenomena because of their large intrinsic luminosities, high occurrence rate, isotropic sky distribution, large distance from the Galaxy, short duration, and easy detectability. For targeted searches, precise positions for gamma-ray bursts are required together with precise distance measurements to a target star. The required burst position determinations are now starting to be obtained, aided in large part by the discovery of optical afterglows. Good distance measurements are currently available from Hipparcos, and even better measurements should be provided by spacecraft now being developed. For nontargeted searches, positional accuracies simply better than a detector's field of view may suffice, but the time delay between the detection of a gamma-ray burst and the reception of the transmitted signal cannot be predicted in an obvious way.