TITLE: GCN CIRCULAR NUMBER: 8968 SUBJECT: GRB 090306B: INTEGRAL SPI-ACS light curve DATE: 09/03/10 14:23:05 GMT FROM: Volker Beckmann at ISDC V. Beckmann, M. Beck, C. Ferrigno, N. Produit, V. Savchenko (ISDC), J. Borkowski (CAMK/Torun), D. Gotz (CEA/Saclay), S. Mereghetti (INAF/IASF-Milano), A. von Kienlin (MPE) report on behalf of the INTEGRAL SPI-ACS GRB team: GRB 090306B, detected in Swift/BAT slew data (Copete et al. GCN 8944), has been independently detected by the SPI Anti-Coincidence System (ACS) on-board INTEGRAL. The SPI-ACS light curve shows the peak of the burst at 2009-03-06T23:07:21.9 with a maximum count-rate of ~390 counts/50msec. The duration of the GRB is about 14 seconds. The SPI-ACS light curves are available (both as images and data files) at http://isdc.unige.ch/Soft/ibas/ibas_acs_web.cgi The light curves, binned at 50 ms, are derived from 91 independent detectors with different lower energy thresholds (mainly between 50 keV and 150 keV) and an upper threshold at about 100 MeV. The ACS response varies as a function of the GRB incident angle. For these reasons we caution that the count rates cannot be easily translated into physical flux units.