TITLE: GCN CIRCULAR NUMBER: 40593 SUBJECT: GRB 250531A: Fermi GBM Final Real-time Localization DATE: 25/05/31 18:12:52 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 18:02:24 UT on 31 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250531A (trigger 770407349.523472 / 250531752).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 170.8, Dec = 5.4 (J2000 degrees, equivalent to J2000 11h 23m, 5d 24'), with a statistical uncertainty of 6.4 degrees.

The angle from the Fermi LAT boresight is 37.0 degrees.

The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250531752/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/bn250531752/q...

The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250531752/q...

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