TITLE:   GCN CIRCULAR
NUMBER:  44818
SUBJECT: GRB 260604B: Fermi GBM Final Real-time Localization
DATE:    26/06/04 08:58:18 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 SHORT GRB

At 08:45:55 UT on 4 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260604B (trigger 802255560.356374 / 260604365).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 173.4, Dec = -19.9 (J2000 degrees, equivalent to J2000 11h 33m, -19d 53'), with a statistical uncertainty of 10.8 degrees.

The angle from the Fermi LAT boresight is 60.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260604365/quicklook/glg_skymap_all_bn260604365.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/bn260604365/quicklook/glg_healpix_all_bn260604365.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260604365/quicklook/glg_lc_medres34_bn260604365.gif