TITLE: GCN CIRCULAR NUMBER: 39711 SUBJECT: GRB 250313A: Fermi-LAT detection DATE: 25/03/14 00:13:09 GMT FROM: Rahul Gupta at NASA GSFC rahul.gupta@nasa.gov
N. Di Lalla (Stanford Univ.), R. Gupta (NASA GSFC), and M. Arimoto (Kanazawa Univ.) report on behalf of the Fermi-LAT Collaboration:
On March 13, 2025, Fermi-LAT detected high-energy emission from GRB 250313A, which was also detected by Fermi-GBM (trigger 763569278 / 250313607, GCN 39703).
The best LAT on-ground location is found to be:
RA, Dec = 278.53, 53.72 (J2000)
with an error radius of 0.23 deg (90 % containment, statistical error only). This was 1 deg from the LAT boresight at the time of the GBM trigger (T0 = 14:34:33.69 UT).
The data from the Fermi-LAT shows a significant increase in the event rate that is spatially and temporally correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0 - 1200 s after the GBM trigger is (4.0 ± 0.9) E-6 ph/cm2/s. The estimated photon index above 100 MeV is 2.0 ± 0.2.
The highest-energy photon is a 1.5 GeV event which is observed ~ 27 seconds after the GBM trigger.
A Swift ToO has been approved for this burst.
The Fermi-LAT point of contact for this burst is Makoto Arimoto (arimoto@se.kanazawa-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.
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