Search for gamma ray burst counterparts

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Abstract
The confident detection of a Gamma Ray Burst counterpart would likely provide the much needed breakthrough in our understanding of the cause and site of bursts. As such, a lot of work has been expended since the early 1970’s in attempts to find bursts at energies below 2 keV. These searches can be divided based on the wavelength and the time (since the burst) of observation. Searches have been made in the soft x‐ray, ultraviolet, optical, infrared, and radio bands. The counterpart might be detected while flaring (during the burst), while fading (soon after the burst), or in quiescence (long after the burst). This review gives an extensive bibliography and summary of these results. This review also highlights five recent results: First, in the last several years the speed of burst position measures has greatly increased, and this has allowed for deep, fading counterpart searches within roughly a day of the burst, although no counterparts have been identified. Second, the lack of galaxies and active galactic nuclei in small error boxes puts severe constraints on any extragalactic model. Third, a consensus has developed that the optical transient images inside small burst error regions on archival photographs are of real astrophysical flares, however the relationship of these events to the burst phenomenon is unclear. Fourth, a study of the ROSAT all‐sky survey data has been unable to reproduce the detection of ‘ultrasoft transients.’ Fifth, the recent discovery of counterparts for Soft Gamma Repeaters has identified the type of system (a young and magnetized neutron star in a supernova remnant) out of the many possibilities, and this advance should provide strong encouragement in the search for classical burst counterparts. Several ideas for future instrumentation offers good hope that the burst distance scale will be resolved with counterparts. One such idea is that a cosmological distance could be confirmed by observing a delay of the radio burst caused by dispersion. Another idea is to detect counterparts by hooking sensitive telescopes up to the BATSE and HETE data steams so that they can look in the right direction during the burst. A third idea is that if the soft x‐ray burst spectra can be measured, then the derived column density of the intervening neutral gas will uniquely identify the burst distance scale.

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