TITLE:   GCN CIRCULAR
NUMBER:  40516
SUBJECT: GRB 250521D: Fermi GBM Final Real-time Localization
DATE:    25/05/21 22:32:26 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 22:21:56 UT on 21 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250521D (trigger 769558921.008874 / 250521932).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 281.6, Dec = 21.3 (J2000 degrees, equivalent to J2000 18h 46m, 21d 18'), with a statistical uncertainty of 2.6 degrees.

The angle from the Fermi LAT boresight is 65.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250521932/quicklook/glg_skymap_all_bn250521932.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/bn250521932/quicklook/glg_healpix_all_bn250521932.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250521932/quicklook/glg_lc_medres34_bn250521932.gif