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GCN Circular 17307

Subject
GRB 150118B: Fermi-LAT detection
Date
2015-01-18T23:05:42Z (9 years ago)
From
Daniel Kocevski at GSFC <daniel.kocevski@nasa.gov>
D. Kocevski (NASA/GSFC), J. Racusin (NASA/GSFC), S. Zhu (UMD) and M. Arimoto (Tokyo Tech) report on behalf of the Fermi-LAT team:

At 09:48:17 UT on Jan 18th, 2015, Fermi-LAT detected high-energy emission from GRB 150118B, which was also detected by Fermi-GBM (trigger 443267300/150118409).

The best LAT on-ground location is found to be

RA, Dec = 240.24, -35.75 (J2000)

with an error radius of 0.5 deg (90% containment, statistical error only). This was ~60 deg from the LAT boresight at the time of the trigger and triggered an autonomous repoint of the spacecraft, although the source was occulted by the Earth within 150s of the GBM trigger and didn't re-enter the LAT field of view until T0+2500s

The data from the Fermi-LAT show an increase in the event rate after the GBM trigger that is temporally correlated with the GBM emission.  The detection above 100 MeV is primarily driven by a single 2 GeV event which is observed within 5 degrees of the GBM position and ~50 seconds after the GBM trigger. Using the LAT Low Energy (LLE) data selection, which is sensitive to > 30 MeV, an increase in the event rate at > 8 sigma significance above background was observed approximately coincident with the time of the GBM emission.

The Fermi-LAT point of contact for this burst is

Makoto Arimoto (arimoto@hp.phys.titech.ac.jp<mailto:arimoto@hp.phys.titech.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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