TITLE:   GCN CIRCULAR
NUMBER:  40406
SUBJECT: GRB 250509A: Fermi GBM Final Real-time Localization
DATE:    25/05/09 22:43:58 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 22:33:29 UT on 9 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250509A (trigger 768522814.285632 / 250509940).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 46.0, Dec = -35.3 (J2000 degrees, equivalent to J2000 03h 04m, -35d 17'), with a statistical uncertainty of 3.0 degrees.

The angle from the Fermi LAT boresight is 89.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250509940/quicklook/glg_skymap_all_bn250509940.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/bn250509940/quicklook/glg_healpix_all_bn250509940.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250509940/quicklook/glg_lc_medres34_bn250509940.gif