[vsnet-grb-info 26900] GRB 201208A: Fermi-LAT detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29003
SUBJECT: GRB 201208A: Fermi-LAT detection
DATE:    20/12/09 03:07:46 GMT
FROM:    Magnus Axelsson at Stockholm U.  <magaxe at kth.se>

F. Dirirsa (LAPP), N. Omodei (Stanford University),  F. Longo (University and INFN Trieste), D. Kocevski (NASA/MSFC), M. Ohno (Hiroshima Univ. & Eotvos Univ.) and M. Axelsson (KTH and Stockholm Univ.) report on behalf of the Fermi-LAT Collaboration:

On December 08, 2020, Fermi-LAT detected high-energy emission from GRB 201208A, which was also detected by Fermi-GBM (trigger 201208252, GCN 28998) and AstroSat CZTI (GCN 29001).

The best LAT on-ground location is found to be

RA, Dec 158.3, -28.8 (degrees, J2000)

with an error radius of 0.16 deg (90% containment, statistical error only).
This was 11 deg from the LAT boresight at the time of the GBM trigger:

T0 = 06:03:23 UT.

The data from the Fermi-LAT show a significant increase in the event rate after the GBM trigger that is spatially correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0-3000 s after the GBM trigger is (9.7+/-5.8)e-07 ph/cm2/s.

The estimated photon index above 100 MeV is -1.6 +/- 0.3.

The highest-energy photon is a 6.2 GeV event which is observed 1320 seconds after the GBM trigger.

A Swift ToO has been approved for this burst.

The Fermi-LAT point of contact for this burst is Feraol Fana Dirirsa (ffdirirsa at gmail.com).

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.