GCN Circular 43274
Subject
GRB 251231A: Fermi GBM Final Real-time Localization
Event
Date
2025-12-31T00:36:41Z (20 hours 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 SHORT GRB
At 00:25:42 UT on 31 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251231A (trigger 788833547.728264 / 251231018).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 312.1, Dec = -46.0 (J2000 degrees, equivalent to J2000 20h 48m, -46d 00'), with a statistical uncertainty of 16.4 degrees.
The angle from the Fermi LAT boresight is 12.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251231018/quicklook/glg_skymap_all_bn251231018.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/bn251231018/quicklook/glg_healpix_all_bn251231018.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251231018/quicklook/glg_lc_medres34_bn251231018.gif