The method we follow for the localization of a GRB source is based on the comparison between the relative intensities registered by the four GRBM detectors and the expected values for the same ratios, as derived from the instrument's response functions. For a given GRB, we identify the two most illuminated detectors and consider the expected ratios between the registered intensities for each possible incoming direction (in this preliminary phase spectral characteristics are derived from BATSE data). These ratios are then compared with the observed ones, and only those directions whose expected and observed values are compatible are classified as possible locations for the source. This procedure determines a first error box whose shape and dimensions are strongly dependent on the GRB intensity and incoming direction. The same comparison is carried out with different couples and/or combinations of detectors and energy ranges to provide the maximum information. Finally the various error boxes are overlapped to obtain the best localization of the source.
|Figure: The GRBM confidence level error box of GRB 970517. The coordinate system is centered on the axis of detector GRBM3. Also the BATSE , and confidence radii (centered at , ) are shown, as derived from the double-Fisher error distribution in [Briggs et al. (1999)]|
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