TITLE:   GCN CIRCULAR
NUMBER:  41402
SUBJECT: GRB 250818A: Fermi GBM Final Real-time Localization
DATE:    25/08/18 01:42:02 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 01:31:22 UT on 18 Aug 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250818A (trigger 777173487.99771 / 250818063).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 232.7, Dec = -62.9 (J2000 degrees, equivalent to J2000 15h 30m, -62d 53'), with a statistical uncertainty of 7.8 degrees.

The angle from the Fermi LAT boresight is 140.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250818063/quicklook/glg_skymap_all_bn250818063.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/bn250818063/quicklook/glg_healpix_all_bn250818063.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250818063/quicklook/glg_lc_medres34_bn250818063.gif