[vsnet-grb-info 26616] GRB 201020B: Fermi-LAT detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  28716
SUBJECT: GRB 201020B: Fermi-LAT detection 
DATE:    20/10/21 09:28:52 GMT
FROM:    Magnus Axelsson at Stockholm U.  <magaxe at kth.se>

M. Arimoto (Kanazawa Univ.), M. Axelsson (KTH and Stockholm Univ.), F. Longo (University and INFN, Trieste) and E. Bissaldi (INFN and Politecnico Bari) report on behalf of the Fermi-LAT Collaboration:

On October 20, 2020, Fermi-LAT detected high-energy emission from GRB 201020B, which was also detected by Fermi-GBM (trigger 624908039.329288 / 201020732; GCN 28702). The best LAT on-ground location is found to be

RA, Dec = 74.9, 77.0 (degrees, J2000)

with an error radius of 0.21 deg (90% containment, statistical error only). This was 67 deg from the LAT boresight at the time of the GBM trigger:

T0 = 17:33:54.33 UT.

At the time of the trigger, the source was outside the field of view of the LAT. Observations began at T0+2300s and the data from the Fermi-LAT show a significant increase in the event rate in the interval T0+2300 to T0+4600s that is spatially correlated with the GBM emission with high significance. The photon flux above 100 MeV in this time interval is 6.5e-7 +/- 3.3e-7 ph/cm2/s. The estimated photon index above 100 MeV is -1.6+/-0.3.

The highest-energy photon is a 6 GeV event which is observed ~2700 seconds after the GBM trigger.

The Fermi-LAT point of contact for this burst is

Elisabetta Bissaldi (Elisabetta.Bissaldi at ba.infn.it<http://ba.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.