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GCN Circular 34392

Subject
GRB 230812B: Fermi-LAT detection
Date
2023-08-13T02:50:20Z (4 months ago)
From
Lorenzo Scotton at UAH <lscottongcn@outlook.com>
Via
Web form
L. Scotton (UAH), D. Kocevski (NASA/MSFC), J. Racusin (NASA/GSFC), and N. Omodei (Stanford University)
report on behalf of the Fermi-LAT Collaboration:

On August 12, 2023, Fermi-LAT detected high-energy emission from
GRB 230812B, which was also detected by Fermi-GBM (trigger 713559497/230812790, S. Lesage GCN 34387, O. Roberts GCN 34391).

The best LAT on-ground location is found to be

RA, Dec = 249.10, 47.75 (degrees, J2000)

with an error radius of 0.13 deg (90% containment, statistical error only).
This was 29 deg from the LAT boresight at the time of the GBM trigger:

T0 = 18:58:12.05 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 (1.69 degrees from the GBM location) with high significance.
The photon flux above 100 MeV in the time interval 0-50 s after the
GBM trigger is (1.96 +/- 0.27)E-4 ph/cm2/s.

The estimated photon index above 100 MeV is -2.16 +/- 0.14.

The highest-energy photon is a 72 GeV event which is observed 32.2 seconds
after the GBM trigger.

The Fermi-LAT point of contact for this burst is
Lorenzo Scotton (lorenzo.scotton AT uah.edu).

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.
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