GCN Circular 43160
Subject
GRB 251220B: Fermi GBM Final Real-time Localization
Event
Date
2025-12-20T23:48:38Z (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 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