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GCN Circular 34943

GRB 231104A: Fermi-LAT detection
2023-11-04T16:29:52Z (7 months ago)
N. Di Lalla at Stanford University <>
G. Principe (University of Trieste), F. Longo (University of Trieste), N. Di Lalla (Stanford University), D. Tak (Seoul National University) report on behalf of the Fermi-LAT Collaboration:

At 01:47:28 on November 04, 2023 Fermi-LAT detected high-energy emission from GRB 231104A, which was also detected by Fermi-GBM (trigger 720755253.13875 / 231104075, GCN 34937) and Swift (GCN 34938).

The best LAT on-ground location is found to be

RA, Dec = 24.1, 84.0 (degrees, J2000)

with an error radius of 0.7 deg (90 % containment, statistical error only). This was 29 deg from the LAT boresight at the time of the trigger.

The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the trigger with high significance. The 100 MeV - 1 GeV photon flux in the time interval 0-400 s after the GBM trigger is (6.6 ± 2.2) E-06 ph/cm2/s.

The estimated integrated photon index above 100 MeV is -2.7 +/- 0.5. The highest-energy photon is a 530 MeV event which is observed 120 seconds after the GBM trigger.

The Fermi-LAT point of contact for this burst is Giacomo Principe (

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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