TITLE: GCN CIRCULAR NUMBER: 41420 SUBJECT: GRB 250818C: Fermi GBM Final Real-time Localization DATE: 25/08/18 23:26:54 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 23:16:23 UT on 18 Aug 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250818C (trigger 777251788.512804 / 250818970).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 203.8, Dec = 74.7 (J2000 degrees, equivalent to J2000 13h 35m, 74d 42'), with a statistical uncertainty of 1.0 degrees.
The angle from the Fermi LAT boresight is 0.0 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250818970/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/bn250818970/q...
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250818970/q...
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