TITLE: GCN CIRCULAR NUMBER: 38873 SUBJECT: GRB 250109A /EP250109a: Fermi GBM Final Localization DATE: 25/01/09 16:02:55 GMT FROM: Utkarsh Pathak at IIT Bombay utkarshpathak.07@gmail.com

The Fermi GBM team reports the detection of a likely LONG GRB

At 06:17:08.60 UT on 9 January 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250109A (trigger 758096233/250109262).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 84.43, Dec = 2.26 (J2000 degrees, equivalent to J2000 05h 37m, 02d 15'), with a statistical uncertainty of 13.52 degrees. This event is associated with EP250109a (Li et al. 2025, GCN 38864).

The angle from the Fermi LAT boresight is 69.0 degrees.

The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250109262/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/bn250109262/q...

The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250109262/q...

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