TITLE:   GCN CIRCULAR
NUMBER:  29880
SUBJECT: Fermi Gamma-ray Burst Monitor trigger 210421C is not a GRB
DATE:    21/04/22 02:18:40 GMT
FROM:    Oliver J Roberts at USRA/NASA  <oliver.roberts@nasa.gov>

 O.J. Roberts (USRA/MSFC) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:

“The Fermi Gamma-ray Burst Monitor (GBM) trigger 640728778/210421842 (210421C) 
at 20:12:53.03 UT on 21 April 2021 (Fermi-GBM Team 2021, GCN 29871), tentatively classified 
as a GRB, is in fact not due to a GRB. This trigger is likely due to a Terrestrial Electron Beam."