[vsnet-grb-info 18132] GRB 160625B: Fermi-LAT detection of a bright burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19580
SUBJECT: GRB 160625B: Fermi-LAT detection of a bright burst 
DATE:    16/06/26 00:23:32 GMT
FROM:    Judith Racusin at GSFC  <judith.racusin at nasa.gov>

F. Dirirsa (U. Johannesburg), J. Racusin (NASA/GSFC), J. McEnery (NASA/GSFC), 
and R. Desiante (INFN Torino) report on behalf of the Fermi-LAT team:

At 22:43:24 on June 25, 2016, Fermi/LAT detected a sharp increase in the rate of 
high-energy photons, resulting in an onboard trigger on GRB 160625B.  Fermi/GBM 
triggered on this object two separate times (160625945/488587220, 
160625952/488587880), with emission evident between triggers, including the time 
at which LAT triggered.

Note that all of these triggers are distinct from the Swift/BAT trigger on GRB160625A 
(Maselli et al., GCN 19577) that occurred 15 seconds after the first GBM trigger, and 
was occulted by the Earth to Fermi at the time, and >100 degrees away on the sky.

The onboard location is:
RA, Dec = 308.3, +6.9  (J2000)

with an error radius of 0.5 deg (90% containment, systematic error only). 

This was 12.3 deg from the LAT boresight at the time of the LAT trigger. 

We anticipate providing a refined location within the next 8 hours when the LAT 
science data for this burst is downlinked and processed.

A Swift TOO request has been approved, and given the unusual nature of this trigger, 
a Fermi TOO will extended the pointed-mode observations to T0+24 hours beyond the 
initial autonomous repoint.

The Fermi-LAT point of contact for this burst is Feraol Dirirsa (fdirirsa at 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.