TITLE:   GCN CIRCULAR
NUMBER:  44415
SUBJECT: GRB 260428A: Fermi GBM Final Real-time Localization
DATE:    26/04/28 14:31:09 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 14:20:35 UT on 28 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260428A (trigger 799078840.683444 / 260428598).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 277.0, Dec = 1.9 (J2000 degrees, equivalent to J2000 18h 27m, 1d 53'), with a statistical uncertainty of 2.1 degrees.

The angle from the Fermi LAT boresight is 88.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260428598/quicklook/glg_skymap_all_bn260428598.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/bn260428598/quicklook/glg_healpix_all_bn260428598.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260428598/quicklook/glg_lc_medres34_bn260428598.gif