TITLE:   GCN CIRCULAR
NUMBER:  41753
SUBJECT: GRB 250909A: Fermi GBM Final Real-time Localization
DATE:    25/09/09 02:43:59 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 02:33:28 UT on 9 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250909A (trigger 779078013.882702 / 250909107).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 78.8, Dec = 39.5 (J2000 degrees, equivalent to J2000 05h 15m, 39d 30'), with a statistical uncertainty of 3.3 degrees.

The angle from the Fermi LAT boresight is 85.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250909107/quicklook/glg_skymap_all_bn250909107.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/bn250909107/quicklook/glg_healpix_all_bn250909107.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250909107/quicklook/glg_lc_medres34_bn250909107.gif