[vsnet-grb-info 28486] GRB 210802A: Fermi-LAT detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30589
SUBJECT: GRB 210802A: Fermi-LAT detection
DATE:    21/08/03 13:12:38 GMT
FROM:    Magnus Axelsson at Stockholm U.  <magaxe at kth.se>

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

On 2 August 2021, Fermi-LAT detected high-energy emission from GRB 210802A which was also detected by Fermi-GBM (trigger 649627691/210802839). The best LAT on-ground location is found to be

RA, Dec = 230.9, 29.8 (degrees, J2000)

with an error radius of 0.35 deg (90% containment, statistical error only). This was 51 deg from the LAT boresight at the time of the GBM trigger:

T0 = 20:08:06.49 UT.

The data from the Fermi-LAT show a significant increase in the event rate after the GBM trigger that is spatially and temporally correlated with the GBM emission with high significance.

The photon flux above 100 MeV in the time interval 0-1000 s after the GBM trigger is (1.0 +/- 0.3) E-5 ph/cm2/s.
The estimated photon index above 100 MeV is -2.3 +/- 0.3.
The highest-energy photon is a 1.4 GeV event which is observed 3 seconds after the GBM trigger.

A Swift ToO has been approved for this burst.

The Fermi-LAT point of contact for this burst is Elisabetta Bissaldi (elisabetta.bissaldi at ba.infn.it<mailto:elisabetta.bissaldi at 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.