TITLE: GCN CIRCULAR NUMBER: 40501 SUBJECT: GRB 250520B: Fermi GBM Final Real-time Localization DATE: 25/05/20 10:46:39 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 10:36:02 UT on 20 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250520B (trigger 769430167.408886 / 250520442).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 100.6, Dec = 68.7 (J2000 degrees, equivalent to J2000 06h 42m, 68d 42'), with a statistical uncertainty of 4.3 degrees.

The angle from the Fermi LAT boresight is 21.0 degrees.

The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250520442/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/bn250520442/q...

The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250520442/q...

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