TITLE: GCN CIRCULAR NUMBER: 43072 SUBJECT: GRB 251211B: Fermi GBM Final Real-time Localization DATE: 25/12/11 20:42:26 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 20:32:04 UT on 11 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251211B (trigger 787177929.268096 / 251211856).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 176.2, Dec = -11.6 (J2000 degrees, equivalent to J2000 11h 44m, -11d 35'), with a statistical uncertainty of 4.5 degrees.

The angle from the Fermi LAT boresight is 56.0 degrees.

The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251211856/q...

The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251211856/q...

The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251211856/q...

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