[vsnet-grb-info 27678] GRB 210410A: Fermi-LAT detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29781
SUBJECT: GRB 210410A: Fermi-LAT detection
DATE:    21/04/10 08:25:22 GMT
FROM:    Makoto Arimoto at Tokyo Inst of Tech  <arimoto at hp.phys.titech.ac.jp>

M. Arimoto (Kanazawa Univ.), M. Ohno (Hiroshima Univ. & Eotvos Univ.),
F. Longo (University and INFN, Trieste) and M. Axelsson (KTH &
Stockholm Univ.) report on behalf of the Fermi-LAT team:

On April 10, 2021, Fermi-LAT detected high-energy emission from GRB
210410A, which was also detected by Fermi-GBM (trigger 639708801 /
210410037, Fermi GBM team, GCN 29777) and Swift/BAT&XRT (Kennea et al.
2021, GCN 29778).

The best LAT on-ground location is found to be
RA, Dec = 268.9, 45.2 (J2000)
with an error radius of 0.5 deg (90 % containment, statistical error
only). This position is consistent with the Swift/XRT localization.
This was 51 deg from the LAT boresight at the time of the GBM trigger:
T0 = 00:53:16.5 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 (2 degrees from the GBM location) with high
significance.

The photon flux above 100 MeV in the time interval 0-300s after the
GBM trigger is (4.0 +/- 0.7)e-05 ph/cm2/s, while the flux above 1 GeV
is (1.3 +/- 0.7)e-06 ph/cm2/s.

The estimated photon index above 100 MeV is -2.5 +/- 0.2.

The highest-energy photon is a 4.2 GeV event which is observed 30
seconds after the GBM trigger.

The Fermi-LAT point of contact for this burst is Masanori Ohno
(ohno at astro.hiroshima-u.ac.jp).

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.