TITLE:   GCN CIRCULAR
NUMBER:  43160
SUBJECT: GRB 251220B: Fermi GBM Final Real-time Localization
DATE:    25/12/20 23:48:38 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 23:38:04 UT on 20 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251220B (trigger 787966689.62881 / 251220985).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 251.4, Dec = 47.9 (J2000 degrees, equivalent to J2000 16h 45m, 47d 53'), with a statistical uncertainty of 6.4 degrees.

The angle from the Fermi LAT boresight is 40.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251220985/quicklook/glg_skymap_all_bn251220985.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/bn251220985/quicklook/glg_healpix_all_bn251220985.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251220985/quicklook/glg_lc_medres34_bn251220985.gif