1994A&A...287..824C

Two cylindrical interruptions of the SIGMA telescope passive shield act as collimators, projecting arc-shaped images on the detector. The field of view (FOV) of these collimators consists of significant sidelobes in the SIGMA sensitivity diagram. GRB localizations, provided by this imaging system, can be combined with the annulus derived from triangulation with other spacecraft, in order to provide a narrow window for the search for counterparts at other wavelengths. 4 cosmic gamma-ray bursts (GRBs) have been detected so far by the lower collimator. Localizations with an accuracy of a fraction of degree, as well as time structures and broad band spectroscopy in the 30-400keV energy range, of these 4 GRBs are presented.