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GCN Circular 20987

Subject
GRB 170405A: Fermi-LAT detection
Date
2017-04-06T00:24:15Z (7 years ago)
From
Giacomo Vianello at SLAC <giacomov@slac.stanford.edu>
G.Vianello (Stanford), D.Kocevski (NASA/MSFC)

report on behalf of the Fermi-LAT team:

At 18:39:22.89 on April, 05, 2017 Fermi-LAT detected high-energy
emission from GRB 170405A, which was also detected by Swift (Troja et
al., GCN 20984) and Fermi/GBM (trigger 513110367/170405777).

The best LAT on-ground location is found to be:

RA, Dec = 219.37, -25.23 (J2000)

with an error radius of 0.51 deg (90 % containment, statistical error
only). This was 53 deg from the LAT boresight at the time of the
trigger and triggered an autonomous repoint of the spacecraft.  This
position is compatible with the XRT position reported by Evans et al.
(GCN 20985).

The data from the Fermi-LAT show a significant increase in the event
rate that is spatially and temporally correlated with the trigger with
high significance. More than 13 events have been observed above 100
MeV which are spatially and temporally correlated with the GRB. The
highest-energy photon is a 900 MeV event which is observed 445 seconds
after the GBM trigger.

We note that roughly 5 ks of data are currently available.  We will
provide an update, if necessary, as more data become available.

The Fermi-LAT point of contact for this burst is Giacomo Vianello
(giacomov@stanford.edu)

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.
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