TITLE:   GCN CIRCULAR
NUMBER:  42316
SUBJECT: GRB 251016B: Fermi GBM Final Real-time Localization
DATE:    25/10/17 00:10:30 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 23:59:00 UT on 16 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251016B (trigger 782351945.722452 / 251016999).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 183.6, Dec = 59.6 (J2000 degrees, equivalent to J2000 12h 14m, 59d 36'), with a statistical uncertainty of 1.0 degrees.

The angle from the Fermi LAT boresight is 46.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251016999/quicklook/glg_skymap_all_bn251016999.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/bn251016999/quicklook/glg_healpix_all_bn251016999.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251016999/quicklook/glg_lc_medres34_bn251016999.gif