GRB 241209D: CALET Gamma-Ray Burst Monitor detection

The long GRB 241209D (Fermi GBM Final Real-time Localization: Fermi GBM team, GCN Circ 38488; Swift detection of a burst: Parsotan et al., GCN Circ 38489; Fermi GBM Observation: Malacaria et al., GCN Circ 38507; AstroSat CZTI detection: Tembhurnikar et al., GCN Circ 38518; Konus-Wind detection: Ridnaia et al., GCN Circ 38526) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 10:59:46.760 UTC on 9 December 2024 (https://cgbm.calet.jp/cgbm_trigger/flight/1417777157/index.html). The burst signal was seen by only the SGM detector. Because of a problem with the ground alert processing script, the GCN notice was not distributed automatically for this event. The burst light curve shows a single pulse that starts at T-4.0 sec, peaks at T+0.6 sec, and ends at T+6.7 sec. The T90 and T50 durations measured by the SGM data are 9.2 +/- 0.7 sec and 4.6 +/- 0.4 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1417777157/ The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University.