TITLE: GCN CIRCULAR NUMBER: 35288 SUBJECT: GRB 231129C: ASIM MXGS observation and localization DATE: 23/12/06 12:42:06 GMT FROM: Martino Marisaldi at U of Bergen, Norway <martino.marisaldi@uib.no> M. Marisaldi (University of Bergen), A. Mezentsev (University of Bergen), P.Connell, Javier Navarro-Gonzalez (University of Valencia), N. Østgaard (University of Bergen), V. Reglero (University of Valencia) and T. Neubert (DTU Space) report on behalf of the ASIM Team: At 19:10:18 UT on 29 November 2023, the Atmosphere-Space Interactions Monitor (ASIM) mission triggered on the long bright GRB 231129C. The burst was also detected by Fermi-GBM (Sharma et al., GCN Circ. 35221, and Sharma et al., GCN Circ. 227), MAXI/GSC (Kawakubo et al., GCN Circ. 35223), CALET (Shimizu et al., GCN Circ. 35228), AstroSat CZTI (Waratkar et al., GCN Circ. 35230), GECAM-B (Zheng et al., GCN Circ. 35231), Swift-XRT (Gropp et al., GCN Circ. 35234), Glowbug (Cheung et al., GCN Circ. 35235), GRBAlpha (Dafcikova et al., GCN Circ. 35236), Fermi-LAT (Arimoto et al., GCN Circ. 35238, AGILE (Panebianco et al., GCN Circ. 35244), and Konus-Wind (Lysenko et al., GCN Circ. 35256). Photon by photon data with <1 microsecond time resolution have been collected for a time interval of 19 seconds. The emission is detected in the MXGS High Energy Detector (HED), sensitive in the range 0.3 to >30 MeV, and in the MXGS Low Energy Detector (LED), sensitive in the range 0.05 to 0.4 MeV. In January 2022 ASIM was relocated so that the MXGS coded mask imaging system is pointing towards the Earth’s limb, observing a large fraction of unocculted sky, therefore enabling localization of the GRB prompt emission. This GRB was observed within the MXGS Field of View resulting in a very high significant localization (>100 sigma) at R.A.,Dec(2000) = 00:51:12.56 -81:45:35.5 consistent within a 25 arcmin error (radius, 99% confidence level) with the Swift-XRT X-ray afterglow (Gropp et al., GCN Circ. 35251) and the MASTER OT detection (Antipov et al., GCN Circ.35240). ASIM is an ESA mission onboard the International Space Station dedicated to the observation of Terrestrial Gamma-ray Flashes (TGFs) and Transient Luminous Events (TLEs) operative since June 2018 (Neubert et al., Space Sci Rev (2019) 215:26 https://doi.org/10.1007/s11214-019-0592-z ). The payload includes the Modular X- and Gamma-Ray Sensor (MXGS) (Østgaard et al., Space Sci Rev (2019) 215:23 https://doi.org/10.1007/s11214-018-0573-7 ), and the the Modular Multispectral Imaging Array (MMIA) (Chanrion et al., Space Sci Rev (2019) 215:28 https://doi.org/10.1007/s11214-019-0593-y ). The ASIM Science Data Centre (ASDC) website is https://asdc.space.dtu.dk/ View this GCN Circular online at https://gcn.nasa.gov/circulars/35288. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...