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/q...

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/q...

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

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