TITLE: GCN CIRCULAR NUMBER: 16730 SUBJECT: Fermi GBM Trigger 140819576/ 430148973/ MASTER OT DATE: 14/08/20 23:24:47 GMT FROM: Valerie Connaughton at UAH/NSSTC Valerie Connaughton (UAH) reports for the GBM team: "At 13:49:30.04 UT on 19 August 2014, Fermi GBM triggered on an event that was classified by the Flight Software as having an unreliable location and that was determined by the automated Ground software to be inconsistent with an astrophysical source location. The preliminary classification of this event was an accidental trigger. The complete data set has since been analyzed and we find no reason to revise this classification. It is possible based on the count rates in two detectors (NaI 1 and 6) that there is a very weak, short GRB in the 64 ms before the trigger time, but there is no obvious signal in other detectors. Based on the geometry of the GBM detectors to the MASTER OT position (Lipunov et al., GCN 16720), we would expect to see significant signal in other NaI detectors. We conclude that the GBM trigger is unrelated to the OT detected by MASTER and is most likely an accidental trigger. There is a small possibility that the trigger is a very weak short GRB from an undetermined location, probably at very large angle to the spacecraft z-axis. Recommendations to observers: observations using GBM Flight Software positions from triggers with classifications other than GRB, particularly those very large reported errors, have low probabilities of success. Triggers classified as GRBs by the Flight Software will have an automated Ground position distributed in a socket connection or GCN notice within seconds. These ground localizations are more accurate, and are always distributed unless the ground software classifies the localization as unreliable."