TITLE: GCN CIRCULAR NUMBER: 30758 SUBJECT: GRB 210903C: Fermi GBM Final Real-time Localization DATE: 21/09/03 17:37:06 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 17:26:58 UT on 3 Sep 2021, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 210903C (trigger 652382823.653196 / 210903727).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 155.0, Dec = 22.0 (J2000 degrees, equivalent to J2000 10h 20m, 22d 00'), with a statistical uncertainty of 4.2 degrees.

The angle from the Fermi LAT boresight is 72.0 degrees.

The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210903727/q...

The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210903727/q...

The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210903727/q...