TITLE: GCN CIRCULAR NUMBER: 21925 SUBJECT: Correction to GCN Circular 21919: GRB 170921C: Insight-HXMT detection DATE: 17/09/25 06:25:32 GMT FROM: Yifei Zhang at IHEP Y. F. Zhang and the Insight-HXMT collaboration We just find that the GRB name (GRB 170921A) used in our pervious GCN circular (Zhang et al. GCN 21919) is wrong. The correct GRB name is GRB 170921C since GRB 170921A and GRB 170921B were already named for the GRBs detected respectively by Swift/BAT on 14:28:48 UT (D'Ai et al. GCN 21901) and Fermi/GBM on 04:02:11.51 UT (Bissaldi et al. GCN 21902). Apologies for any confusion caused.