Figure 6 shows a recent sky distribution of nearly 2300 GRBs observed with BATSE. The statistics are now such that the effect of earth-blockage is becoming apparent on the map. This shows as a slight deficiency along the celestial equator. Corrections for this blockage yield a map with a distribution consistent with isotropy.
Efforts have been made to both improve the location accuracy of bursts
observed with BATSE, and to quantify this accuracy. A recent paper by
Briggs et al. (1999), shows that the BATSE systematic error, as
determined by a comparison with the Interplanetary Network (IPN) GRB
locations, is best described by two near-Gaussian components. The larger
component has a standard deviation of 1.8 deg.
A number of recent studies have used BATSE untriggered data to search for weak events in order to extend analyses (e.g. the peak flux distribution) to weaker GRBs, to verify the BATSE on-board burst trigger, and to identify other types of transient phenomena (Kommers et al. 1997; Kommers 1999; Kommers et al. 1999; Schmidt 1999; Stern et al. 1999). These studies appear to be capable of extending the BATSE sensitivity beyond that of the triggered GRBs. However, it is expected that weak events found in these searches may be contaminated by non-GRB fluctuations of the background, hard X-ray transients, and systematic effects. It is difficult to quantify the number of the false GRBs thus found and to accurately locate them.
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