GCN Circular 19836

M. Arimoto (Waseda U./Tokyo Tech), M. Axelsson (KTH Stockholm), F.
Dirirsa (U. Johannesburg) and F. Longo (INFN/Trieste)
report on behalf of the Fermi-LAT team:
We report the on-ground localization and analysis of GRB 160821A,
which triggered
an onboard LAT detection (McEnery et al., GCN 19831
Not found
 
 
).  All times are
relative to the initial GBM
trigger (Stanbro et al., GCN 19835
Not found
 
 
).
The best LAT on-ground location is found to be:
RA, Dec = 171.3, 42.3 deg (J2000)
with an error radius of 0.08 deg (90 % containment, statistical error
only). This is fully
compatible with the position of the prompt emission detected by
Swift/BAT (Siegel et al., GCN 19830
Not found
 
 
).
This was 17 deg from the LAT boresight at the time of the GBM trigger
and triggered
an autonomous repoint of the spacecraft.

More than 50 photons above 100 MeV and 4 photons above 1 GeV were
detected within 245s,
before the spacecraft entered the SAA. The GRB did not come back into
the Fermi-LAT FoV until T0 + 1380s.

 The LAT emission was coincident with the bright pulse observed by GBM
at ~T0+135 s.
The highest-energy photon is a 4.7 GeV event which is observed ~212
seconds after the GBM trigger.


The Fermi-LAT point of contact for this burst is Francesco Longo
(francesco.longo@trieste.infn.it).


The Fermi-LAT is a pair conversion telescope designed to cover the
energy band from
20 MeV to greater than 300 GeV. It is the product of an international
collaboration
between NASA and DOE in the U.S. and many scientific institutions across France,
Italy, Japan and Sweden.