TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1703 SUBJECT: GRB021113, SPI ACS observation DATE: 02/11/21 08:52:38 GMT FROM: Arne Rau at MPI A. Rau, V. Schoenfelder, A.v. Kienlin, G. Lichti G., N. Arend, on behalf of the MPE INTEGRAL SPI-team; J.-P. Roques on behalf of the Toulouse INTEGRAL SPI-team; J. Borkowski, R. Walter, N. Produit on behalf of the INTEGRAL Science Data Center (ISDC) Geneve; K. Hurley on behalf of the IPN team report: The Anticoincidence Shield (ACS) of the Spectrometer onboard the INTEGRAL satellite (SPI) was switched on on the 26th of October 2002. Since then, besides the major calibration and verification activities, the ACS rates have already been monitored for GRBs. The ACS has registered approximately 1 GRB per day, among them also the following IPN-localized GRBs 021027 (GCN#1658), 021102 (GCN#1667) and 021108 (GCN#1679). The first HETE-localized GRB detected by SPI ACS was GRB 021113 (=H2449; GCN #1686). The ACS lower energy threshold during this burst was set to ~100 keV, but this threshold is broad; there exists no high-energy threshold. GRB 021113 was seen in the total ACS rate (all 91 BGO crystals) with 4 sigma on a 1s time scale. The ACS lightcurve of GRB 021113 (http://www.mpe.mpg.de/gamma/instruments/integral/spi/acs/grb/021113_acs.html) shows a single, smooth peak (similar to the HETE light curve), with a maximum occuring at 6:38:58 UT. The absolute timing of the ACS is known int the moment with an accuracy of ~100ms. Continued "tuning" of the energy threshold and burst verification algorithm is anticipated over the coming weeks, before the ACS will be fully implemented into the INTEGRAL Burst Alert System (IBAS). Acknowledgement is given to INTEGRAL Science Working Team for making these burst data public. This message is citable.