TITLE:   GCN CIRCULAR
NUMBER:  43048
SUBJECT: GRB 251209A: Fermi GBM Final Real-time Localization
DATE:    25/12/09 13:34:44 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 LONG GRB

At 13:24:03 UT on 9 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251209A (trigger 786979448.987734 / 251209558).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 214.2, Dec = 43.1 (J2000 degrees, equivalent to J2000 14h 16m, 43d 06'), with a statistical uncertainty of 1.0 degrees.

The angle from the Fermi LAT boresight is 52.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251209558/quicklook/glg_skymap_all_bn251209558.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/bn251209558/quicklook/glg_healpix_all_bn251209558.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251209558/quicklook/glg_lc_medres34_bn251209558.gif