TITLE:   GCN CIRCULAR
NUMBER:  43274
SUBJECT: GRB 251231A: Fermi GBM Final Real-time Localization
DATE:    25/12/31 00:36:41 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 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