TITLE:   GCN CIRCULAR
NUMBER:  43964
SUBJECT: GRB 260311B: Fermi GBM Final Real-time Localization
DATE:    26/03/11 19:08:31 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 18:57:55 UT on 11 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260311B (trigger 794948280.422386 / 260311790).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 278.5, Dec = 0.4 (J2000 degrees, equivalent to J2000 18h 33m, 0d 24'), with a statistical uncertainty of 11.7 degrees.

The angle from the Fermi LAT boresight is 54.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260311790/quicklook/glg_skymap_all_bn260311790.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/bn260311790/quicklook/glg_healpix_all_bn260311790.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260311790/quicklook/glg_lc_medres34_bn260311790.gif