TITLE:   GCN CIRCULAR
NUMBER:  44451
SUBJECT: GRB 260503A: Fermi GBM Final Real-time Localization
DATE:    26/05/03 20:50:53 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 20:40:17 UT on 3 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260503A (trigger 799533622.581348 / 260503861).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 287.1, Dec = -2.0 (J2000 degrees, equivalent to J2000 19h 08m, -2d 00'), with a statistical uncertainty of 2.6 degrees.

The angle from the Fermi LAT boresight is 30.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260503861/quicklook/glg_skymap_all_bn260503861.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/bn260503861/quicklook/glg_healpix_all_bn260503861.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260503861/quicklook/glg_lc_medres34_bn260503861.gif