TITLE: GCN CIRCULAR NUMBER: 29870 SUBJECT: GRB 210421B: Fermi GBM Final Localization DATE: 21/04/21 20:03:10 GMT FROM: Joe Mangan at UCD The Fermi GBM team reports the detection of a likely short GRB At 10:54:44.812 UT on 21 Apr 2021, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 210421B (trigger 640695289 / 210421455). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 272.1, Dec = 57.2(J2000 degrees, equivalent to J2000 18h 08m, 57d 09'), with a statistical uncertainty of 2.1 degrees. The angle from the Fermi LAT boresight is 20.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210421455/quicklook/glg_skymap_all_bn210421455.png The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210421455/quicklook/glg_healpix_all_bn210421455.fit The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210421455/quicklook/glg_lc_medres34_bn210421455.gif