[vsnet-grb-info 24499] GRB 191227A: Marginal detection by Fermi-LAT

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  26598
SUBJECT: GRB 191227A: Marginal detection by Fermi-LAT
DATE:    19/12/27 17:15:42 GMT
FROM:    Francesco Longo at U of Trieste,INFN Trieste  <franzlongo1969 at gmail.com>

F. Fana Dirirsa (Univ. of Johannesburg), F. Longo (University & INFN,
Trieste), M. Axelsson (KTH & Stockholm Univ.),
D. Kocevski (NASA/MSFC) and J. Racusin (NASA/GSFC) report on behalf of
the Fermi-LAT team:

On December 27, 2019, Fermi-LAT marginally detected high-energy emission from
GRB 191227A, which was also detected by Fermi-GBM (GCN 26593) and
Swift/BAT (Melandri et al, GCN 26595).
The best LAT on-ground location is found to be

RA, Dec 318.0, -16.9 (degrees, J2000)

with an error radius of 0.33 deg (90% containment, statistical error only).

This was 96 deg from the LAT boresight at the time of the GBM trigger
and entered in the LAT field of view around
1 ks later. The localisation is consistent with the Swift/BAT position.

The detection significance lies just below the 5-sigma threshold, but
more than 3 photons with >90% probability to
be associated with the GRB are found in the time interval up to 10ks
after the GBM trigger. The photon flux above
100 MeV in this time interval is (9 +/- 4) e-7 ph/cm2/s.

The estimated photon index above 100 MeV is -2.0 +/- 0.3.

Further analysis is ongoing.

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