GCN Circular 22457

M. Axelsson (KTH and Stockholm Univ.) and E. Bissaldi (Politecnico and INFN Bari), report on behalf of the Fermi-LAT team:

At 09:26:08.66 UT on March 05, 2018, Fermi-LAT detected high-energy emission from GRB 180305A, which was also detected by Fermi-GBM (trigger 541934773 / 180305393).

The best LAT on-ground location is found to be

RA, Dec = 49.7, 32.1 (J2000)

with an error radius of 0.12 deg (90 % containment, statistical error only).

This location was a few degrees outside the LAT field of view at the time of the trigger. It entered the FoV approximately 200s later, and remained visible until around 2600s after the trigger time.

The data from the Fermi-LAT show a significant increase in the event rate that is spatially correlated with the trigger with high significance. More than 10 events above 100 MeV are detected. The highest-energy photon is a 9 GeV event which is observed ~1630 seconds after the GBM trigger.

A Swift ToO has been approved for this burst.

The Fermi-LAT point of contact for this burst is Magnus Axelsson (magaxe@kth.se<mailto:magaxe@kth.se>).

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.