2 Observations

Due to strong constraints on the allowed pointing directions of the satellite, only 2 out of the 12 well-localised GRBs that were detected between the beginning of the TOO program (February 1997) and the end of the ISO mission (April 1998) were immediately visible with ISO. An ISO follow-up observation of one (GRB 970402) was made within 55 hours ([Castro-Tirado et al. 1998]). However the second candidate (GRB 970828) was not observed due to unavoidable scheduling delays and the absence of an optical transient (OT). A further 3 of the 12 GRB locations only became visible at later times. Limited viewing windows of the GRB 970508 and GRB 980329 locations opened after several days, but there was a delay of 7 months before the location of GRB 970228 could be observed. Further details of the observations and analysis methods are presented elsewhere ([Delaney et al. 1999]). Results on GRB 980329 and GRB 970228 are in preparation ([Groot et al. 1999]; [Metcalfe et al. 1999]).