[vsnet-grb-info 15028] GRB 140523A: Fermi-LAT detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16322
SUBJECT: GRB 140523A: Fermi-LAT detection
DATE:    14/05/23 18:39:14 GMT
FROM:    Giacomo Vianello at SLAC  <giacomov at slac.stanford.edu>

G. Vianello (Stanford University), J. Racusin (NASA/GSFC), M. Arimoto
(Tokyio Tech)

report on behalf of the Fermi-LAT team:

At UT 03:05:57.62  on May 23, 2014, Fermi-LAT detected high-energy
emission from GRB 140523A, which was also detected by Fermi-GBM
(trigger 422507160 / 140523129, von Kienlin et al., GCN 16321).

The best LAT on-ground location is found to be

(RA, Dec) = 133.3, 24.95 (deg, J2000)

with an approximate error radius of 0.4 deg (90% containment,
statistical error only).

This was 60 deg from the LAT boresight at the time of the trigger. At
this large off-axis angle, the LAT PSF is not symmetric, therefore the
error region is elongated on the direction pointing towards the center
of the instrument.

An image with the 68% and 90% containment regions have been posted at:

http://www-glast.stanford.edu/Software/GRB140523A_localization.jpg

The data from the Fermi-LAT show a significant increase in the event
rate that is spatially and temporally correlated with the GBM emission
with high significance.

More than 20 photons above 100 MeV and 6 photons above 1 GeV are
observed within 300 seconds. After that the GRB went out of the LAT
FoV. It entered again around 4500 s after the trigger, but no further
emission is detected at that point. The highest-energy photon is a 6.5
GeV event which is observed 43 seconds after the GBM trigger.

A Swift ToO has been requested for this burst.

The Fermi-LAT point of contact for this burst is Makoto Arimoto
(arimoto at hp.phys.titech.ac.jp).

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.