TITLE: GCN CIRCULAR NUMBER: 39006 SUBJECT: GRB 250121A: Fermi GBM Final Real-time Localization DATE: 25/01/21 23:46:35 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 23:36:05 UT on 21 Jan 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250121A (trigger 759195370.779232 / 250121983).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 225.1, Dec = -36.9 (J2000 degrees, equivalent to J2000 15h 00m, -36d 53'), with a statistical uncertainty of 1.1 degrees.

The angle from the Fermi LAT boresight is 16.0 degrees.

The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250121983/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/bn250121983/q...

The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250121983/q...

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