GRBM Localization Capabilities

The GRBM localization technique has been tested by using the large sample of bursts detected in common with other experiments, that had already estimated the burst arrival directions. This has confirmed the $\sim 10\rm ^{\circ}$ systematic error; the typical total error radius (statistical plus systematic) ranges between $20\rm ^{\circ}$ and $40\rm ^{\circ}$. Due to the BeppoSAX payload symmetries, the possible solutions to the arrival direction of a burst are often more than one; among $\sim$ 500 bursts detected only with the GRBM, two hundreds have been positioned unambiguously. If the GRBM localization capabilities will be regularly exploited in combination with the automatic on-line quest via the Bacodine network, this could help the robotic search for optical transients. In any case, the possibility offered by this technique sometimes turned out very useful for resolving the IPN redundancy of solutions. The possibility of roughly estimating the arrival direction of a burst with this technique is fundamental also for another reason: actually, when no information about the direction is available from other experiments, in order to use the 240 channel 128 s GRBM spectra, some rough information about direction are required for the deconvolution by the GRBM spectral response, which does depend on the burst direction. This is, for instance, the case of the brightest GRB so far detected by the GRBM, occurred on May 16, 1998, for which it has been possible to extract a 240 channel spectrum in the 40-700 keV band, treated in appendix B; without the estimate of the burst direction, made possible only by the localization technique, the spectrum of the brightest GRBM burst could not be obtained.

Last but not least, the off-line scan has led to the identification of 26 bursts from three of the four known SGR sources: only for two out of these 26 bursts the association with an SGR source is uncertain, as no other experiment detected them. The 26 bursts are classified as follows: 14 from SGR1900+14 (2 giant flares, 11 certain bursts, 1 burst candidate); 10 bursts from SGR1627-41 (only one is a burst candidate, while the others have been detected by Konus/WIND as well), finally, two bursts from SGR1806-20, both detected by Konus.