TITLE:   GCN CIRCULAR
NUMBER:  44358
SUBJECT: GRB 260421A: Fermi GBM Final Real-time Localization
DATE:    26/04/21 02:23:18 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 02:12:44 UT on 21 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260421A (trigger 798430369.324586 / 260421092).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 198.8, Dec = 62.9 (J2000 degrees, equivalent to J2000 13h 15m, 62d 53'), with a statistical uncertainty of 8.2 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/bn260421092/quicklook/glg_skymap_all_bn260421092.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/bn260421092/quicklook/glg_healpix_all_bn260421092.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260421092/quicklook/glg_lc_medres34_bn260421092.gif