TITLE: GCN CIRCULAR NUMBER: 39057 SUBJECT: GRB 250128B: Fermi GBM Final Real-time Localization DATE: 25/01/28 16:33:27 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 SHORT GRB

At 16:22:53 UT on 28 Jan 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250128B (trigger 759774178.772694 / 250128683).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 264.8, Dec = -46.6 (J2000 degrees, equivalent to J2000 17h 39m, -46d 36'), with a statistical uncertainty of 8.2 degrees.

The angle from the Fermi LAT boresight is 145.0 degrees.

The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250128683/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/bn250128683/q...

The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250128683/q...

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