TITLE:   GCN CIRCULAR
NUMBER:  45674
SUBJECT: GRB 260921A: Fermi GBM Final Real-time Localization
DATE:    26/09/21 09:39:40 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 09:29:08 UT on 21 Sep 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260921A (trigger 811675753.423246 / 260921395).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 148.9, Dec = 0.6 (J2000 degrees, equivalent to J2000 09h 55m, 0d 36'), with a statistical uncertainty of 1.4 degrees.

The angle from the Fermi LAT boresight is 91.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260921395/quicklook/glg_skymap_all_bn260921395.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/bn260921395/quicklook/glg_healpix_all_bn260921395.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260921395/quicklook/glg_lc_medres34_bn260921395.gif