[vsnet-grb-info 17965] GRB 160509A: Fermi-LAT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19413
SUBJECT: GRB 160509A: Fermi-LAT refined analysis
DATE:    16/05/09 18:09:47 GMT
FROM:    Elisabetta Bissaldi at U.Innsbruk/IAPP  <Elisabetta.Bissaldi at uibk.ac.at>

F. Longo (University and INFN, Trieste), E. Bissaldi (Politecnico and INFN, Bari),
G. Vianello (Stanford U.), E. Moretti (MPI, Munich), N. Omodei (Stanford U.),
J. Bregeon (CNRS/IN2P3/LUPM), F. Dirirsa (Johannesburg U.),  M. Yassine (LUPM, Montpellier),
D. Kocevski, J. Racusin, J. McEnery (all NASA/GSFC), M. Ohno (Hiroshima U.) and
S. Zhu (AEI Potsdam-Golm / AEI Hannover) report on behalf of the Fermi-LAT Team:


Using LAT source class events >100 MeV from 0 until 2660 seconds after the LAT trigger,
we find a LAT localization of

RA, Dec = 311.3, 76.1 (J2000 deg)

with a 90% containment radius of 0.12 degrees (statistical only).
The LAT executed an autonomous repoint 2 minutes after the trigger to follow
the burst for 2.5 hours. A Fermi ToO for the next 36 hours has been issued.

Following our detection, Swift followed the GRB and detected the X-ray afterglow
with the Swift/XRT (Kennea et al. GCN 19408).

The highest-energy photon is a 52 GeV event, which is observed
77 seconds after the GBM trigger.

The LAT Low Energy (LLE) emission consists of two bright structured
peaks (around T0+12 and T0+18 s), in coincidence with the main GBM emission episode.

The >100 MeV emission spectrum during the main GBM emission episode
(from T0 to T0+40 s, see Roberts et al. GCN 19411) is fit by a
soft power-law with index -3.4 +/- 0.2,
resulting in a flux of (0.56 +/- 0.06)E-4 ph cm^-2 s^-1.

The >100 MeV emission spectrum after 40 s and up to the currently
available data (up to 2660 s) is fit by a power-law with index -2.0 +/- 0.1.


The Fermi LAT point of contact for this burst is
Francesco Longo (francesco.longo at ts.infn.it).

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.