GCN Circular 43164
Subject
GRB 251221A: Fermi GBM Final Real-time Localization
Event
Date
2025-12-21T05:35:02Z (2 days ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
Via
email
The Fermi GBM team reports the detection of a likely LONG GRB
At 05:24:28 UT on 21 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251221A (trigger 787987473.613216 / 251221225).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 96.6, Dec = 1.6 (J2000 degrees, equivalent to J2000 06h 26m, 1d 36'), with a statistical uncertainty of 5.1 degrees.
The angle from the Fermi LAT boresight is 100.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251221225/quicklook/glg_skymap_all_bn251221225.png
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251221225/quicklook/glg_healpix_all_bn251221225.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251221225/quicklook/glg_lc_medres34_bn251221225.gif