TITLE:   GCN CIRCULAR
NUMBER:  41865
SUBJECT: GRB 250918A: Fermi GBM Final Real-time Localization
DATE:    25/09/18 12:42:57 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 12:32:18 UT on 18 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250918A (trigger 779891543.0931 / 250918522).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 221.8, Dec = -15.9 (J2000 degrees, equivalent to J2000 14h 47m, -15d 54'), with a statistical uncertainty of 3.4 degrees.

The angle from the Fermi LAT boresight is 93.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250918522/quicklook/glg_skymap_all_bn250918522.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/bn250918522/quicklook/glg_healpix_all_bn250918522.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250918522/quicklook/glg_lc_medres34_bn250918522.gif