GCN Circular 19586

F. Dirirsa (U. Johannesburg), G. Vianello (Stanford), J. Racusin (NASA/GSFC), and
M. Axelsson (KTH Stockholm) report on behalf of the Fermi-LAT team:
We report the on-ground localization and analysis of GRB 160625B, which triggered 
the LAT onboard (Dirisa et al., GCN 19580
Not found
 
 
).  All times are relative to the initial GBM 
trigger (Burns et al, GCN 19581
Not found
 
 
).
The best LAT on-ground location is found to be:
RA, Dec = 308.56, 6.93 deg (J2000)
with an error radius of 0.06 deg (90 % containment, statistical error only). This is fully 
compatible with the position of the afterglow detected by Swift/XRT (Melandri et al., 
GCN 19585
Not found
 
 
).
This was 42 deg from the LAT boresight at the time of the GBM trigger and triggered 
an autonomous repoint of the spacecraft.

More than 300 photons were detected above 100 MeV.  The LAT emission became 
detectable during the second bright pulse observed by GBM at ~T0+181 s.  The 
highest-energy photon is a 15 GeV event which is observed ~345 seconds after 
the GBM trigger.  The GRB was detectable by the LAT up to ~1 ks after the 
trigger.  Data are still being collected, and pointed mode observations are continuing 
to maximize exposure to the GRB location. 
The Fermi-LAT point of contact for this burst is Feraol Dirirsa (fdirirsa@uj.ac.za <mailto:fdirirsa@uj.ac.za>).
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.