TITLE:   GCN CIRCULAR
NUMBER:  39825
SUBJECT: GRB 250321C: Fermi GBM Final Real-time Localization
DATE:    25/03/21 21:57:57 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 21:47:36 UT on 21 Mar 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250321C (trigger 764286461.175894 / 250321908).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 89.3, Dec = -28.5 (J2000 degrees, equivalent to J2000 05h 57m, -28d 30'), with a statistical uncertainty of 5.0 degrees.

The angle from the Fermi LAT boresight is 53.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250321908/quicklook/glg_skymap_all_bn250321908.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/bn250321908/quicklook/glg_healpix_all_bn250321908.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250321908/quicklook/glg_lc_medres34_bn250321908.gif