TITLE: GCN CIRCULAR NUMBER: 43173 SUBJECT: GRB 251221B: Fermi GBM Final Real-time Localization DATE: 25/12/21 18:56:51 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 18:46:21 UT on 21 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251221B (trigger 788035586.997792 / 251221782). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 274.7, Dec = -21.4 (J2000 degrees, equivalent to J2000 18h 18m, -21d 23'), with a statistical uncertainty of 7.2 degrees. The angle from the Fermi LAT boresight is 86.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251221782/q... The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251221782/q... The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251221782/q... View this GCN Circular online at https://gcn.nasa.gov/circulars/43173. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...