TITLE:   GCN CIRCULAR
NUMBER:  46007
SUBJECT: GRB 261021A: Fermi GBM Final Real-time Localization
DATE:    26/10/21 19:03:40 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 18:53:09 UT on 21 Oct 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 261021A (trigger 814301594.113176 / 261021787).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 245.7, Dec = 42.9 (J2000 degrees, equivalent to J2000 16h 22m, 42d 53'), with a statistical uncertainty of 6.1 degrees.

The angle from the Fermi LAT boresight is 119.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn261021787/quicklook/glg_skymap_all_bn261021787.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/bn261021787/quicklook/glg_healpix_all_bn261021787.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn261021787/quicklook/glg_lc_medres34_bn261021787.gif