[vsnet-grb-info 19984] GRB 171022A: Fermi-LAT detection retraction

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22071
SUBJECT: GRB 171022A: Fermi-LAT detection retraction
DATE:    17/10/30 20:24:53 GMT
FROM:    Elisabetta Bissaldi at U.Innsbruk/IAPP  <Elisabetta.Bissaldi at uibk.ac.at>

M. Palatiello (Univ & INFN Trieste), E. Bissaldi (Poiltecnico & INFN Bari),
and E. Moretti (MPI Munich) report on behalf of the Fermi-LAT team:


On October 22nd, 2017, the Fermi-LAT collaboration reported
the detection of GRB 171022A (Palatiello et al., GCN #22045).

Following the publication of the GRB IPN triangulation
(Hurley et al., GCN #22051), we performed further analysis to
investigate the discrepancy of the Fermi-LAT localization
with respect to the region defined by the Konus Wind,
Fermi-GBM and INTEGRAL annuli.

The LAT excess reported in Palatiello et al. has a
significance which is only slightly
above the 5 sigma threshold. Moreover, the Fermi-LAT
Point Source Catalog (3FGL, Acero et al. 2015) contains
the source 3FGL J1339.0+1153 in the proximity of the position
of the LAT excess. A likelihood analysis where the normalization
for 3FGL J1339.0+1153 is set as a free parameter of the fit
returns a marginal increase (20 +/- 15 %) in the flux
of that source, tentatively associated with
SDSS J133859.05+115316.7, and results in a non-detection of the
excess which we previously associated with GRB 171022A.
Therefore, we cannot confirm at this stage that
the LAT excess is associated with GRB 171022A.


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.