[vsnet-grb-info 15441] Fermi GBM Trigger 140819576/ 430148973/ MASTER OT

[GCN Circulars]

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 at nasa.gov>

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."