TITLE:   GCN CIRCULAR
NUMBER:  44452
SUBJECT: GRB 260504A: Fermi GBM Final Real-time Localization
DATE:    26/05/04 09:21:13 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 09:12:58 UT on 4 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260504A (trigger 799578783.057988 / 260504384).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 308.8, Dec = 48.4 (J2000 degrees, equivalent to J2000 20h 35m, 48d 23'), with a statistical uncertainty of 5.0 degrees.

The angle from the Fermi LAT boresight is 44.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260504384/quicklook/glg_skymap_all_bn260504384.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260504384/quicklook/glg_healpix_all_bn260504384.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260504384/quicklook/glg_lc_medres34_bn260504384.gif