GCN Circular 19553

G. Vianello (Stanford), F. Dirirsa (UJ), N. Omodei (Stanford), J. L.
Racusin (NASA/GSFC), M. Axelsson (KTH Stockholm), D.Kocevski
(NASA/GSFC)

report on behalf of the Fermi-LAT team:

At 05:00:34.23 UT on June, 23, 2016 Fermi-GBM triggered on GRB 160623A
(trigger 488350837 / 160623209).  This burst is also visible in the
Swift/BAT raw count rate light curve, during a slew with no event
capture (D. Palmer/Swift private communication).

As the source came into the field of view of Fermi-LAT 400 s later,
high-energy emission was detected at a position compatible with GRB
160623A.

The best LAT on-ground location is found to be

RA, Dec = 315.24, 42.27 deg (J2000)

with an error radius of 0.1 deg (90 % containment, statistical error only).

The source is very bright in the LAT, with a fading high-energy
emission detected up to approximately 12 ks after the trigger time. We
detect more than 15 photons above 1 GeV.

We note that the LAT position is close to the Galactic plane,
corresponding to (L,B) = (84.17, -2.69) deg. Given the large
uncertainty in the GBM localization, we cannot exclude at this stage
the possibility that the LAT transient is a Galactic transient
unrelated to the GBM GRB. However, as seen by the LAT, the transient
has spectral and temporal properties typical of a long GRB.

A Swift ToO has been requested for this burst.

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