TITLE:   GCN CIRCULAR
NUMBER:  41482
SUBJECT: GRB 250821C: Fermi GBM Final Real-time Localization
DATE:    25/08/21 23:52:36 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 23:42:00 UT on 21 Aug 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250821C (trigger 777512525.658232 / 250821988).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 104.3, Dec = -1.1 (J2000 degrees, equivalent to J2000 06h 57m, -1d 06'), with a statistical uncertainty of 15.0 degrees.

The angle from the Fermi LAT boresight is 90.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250821988/quicklook/glg_skymap_all_bn250821988.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250821988/quicklook/glg_healpix_all_bn250821988.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250821988/quicklook/glg_lc_medres34_bn250821988.gif