TITLE: GCN CIRCULAR NUMBER: 40580 SUBJECT: GRB 250530B: Fermi GBM Final Real-time Localization DATE: 25/05/30 11:27:57 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 11:17:18 UT on 30 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250530B (trigger 770296643.008128 / 250530470).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 324.9, Dec = 11.3 (J2000 degrees, equivalent to J2000 21h 39m, 11d 18'), with a statistical uncertainty of 1.0 degrees.

The angle from the Fermi LAT boresight is 0.0 degrees.

The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250530470/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/bn250530470/q...

The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250530470/q...

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