TITLE: GCN CIRCULAR NUMBER: 30721 SUBJECT: GRB 210826A: Fermi-LAT detection DATE: 21/08/26 19:15:46 GMT FROM: Masanori Ohno at Hiroshima U ohno@astro.hiroshima-u.ac.jp
M. Ohno (Eotvos U./Hiroshima U.), M. Axelsson (KTH & Stockholm Univ.), F. Longo (University and INFN, Trieste), N. Omodei (Stanford Univ.) and F Dirirsa (LAPP, Annecy) report on behalf of the Fermi-LAT Collaboration:
On August 26th, 2021, Fermi-LAT detected high-energy emission from GRB 210826A, which was also detected by Fermi GBM (trigger 651654110.161386 / 210826293; GCN 30716).
The best LAT on-ground location is found to be
RA, Dec 45.3, -71.7 (degrees, J2000)
with an error radius of 0.2 deg (90% containment, statistical error only). This was 55 deg from the LAT boresight at the time of the GBM trigger:
T0 = 07:01:45 UT.
The data from the Fermi-LAT show a significant increase in the event rate after the trigger that is spatially correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0-4000 s after the trigger is 9.3 (-/+ 3.8) e-07 ph/cm2/s.
The estimated photon index above 100 MeV is -1.9 (-/+ 0.3).
The highest-energy photon is a 7.7 GeV event which is observed ~2.6 ks after the trigger.
A Swift ToO has been approved for this burst.
The Fermi-LAT point of contact for this burst is Feraol Fana Dirirsa (dirirsa@lapp.in2p3.fr).
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.