TITLE:   GCN CIRCULAR
NUMBER:  39988
SUBJECT: GRB 250331E: Fermi GBM Final Real-time Localization
DATE:    25/03/31 22:57:04 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 22:46:32 UT on 31 Mar 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250331E (trigger 765153997.78765 / 250331949).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 196.6, Dec = -27.7 (J2000 degrees, equivalent to J2000 13h 06m, -27d 41'), with a statistical uncertainty of 14.0 degrees.

The angle from the Fermi LAT boresight is 73.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250331949/quicklook/glg_skymap_all_bn250331949.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250331949/quicklook/glg_healpix_all_bn250331949.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250331949/quicklook/glg_lc_medres34_bn250331949.gif