TITLE: GCN CIRCULAR NUMBER: 39618 SUBJECT: GRB 250307A: Fermi GBM Final Real-time Localization DATE: 25/03/07 20:08:14 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 19:57:53 UT on 7 Mar 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250307A (trigger 763070278.733804 / 250307832).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 265.6, Dec = 2.2 (J2000 degrees, equivalent to J2000 17h 42m, 2d 12'), with a statistical uncertainty of 2.7 degrees.

The angle from the Fermi LAT boresight is 82.0 degrees.

The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250307832/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/bn250307832/q...

The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250307832/q...

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