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GCN Circular 9934

GRB 090926: Fermi LAT detection
2009-09-26T19:39:23Z (15 years ago)
Takeshi Uehara at Hiroshima U <>
GRB 090926: Fermi LAT detection

Takeshi Uehara, Hiromitsu Takahashi (Hiroshima University) and
Julie McEnery (NASA/GSFC) report on behalf of the Fermi LAT team:

At 04:20:26.99 (UT) on 26 Sep 2009, the Fermi Large Area Telescope
(LAT) detected gamma rays from the long GRB 090926, which was
triggered and located by the Fermi Gamma-ray Burst Monitor (GBM)
(trigger 275631628 / 090926181, GCN9933). The angle of the GBM best
position (RA, Dec= 354.5, -64.2) with respect to the LAT boresight was
~52 degrees at the time of the trigger, which is close the edge of our
field of view.

The data from the Fermi LAT shows a significant increase in the event
rate within 2.5 degrees of the GBM location 7 s after the GBM trigger
that is spatially and temporally correlated with the GBM emission with
high significance. More than 150 photons above 100 MeV and more
than 20 photons above 1 GeV are observed up to more than 200 s after
the GBM trigger. The highest energy photon is a 19.6 GeV event which is
observed 26 seconds after the GBM trigger.

The best LAT on-ground localization is found to be (RA, Dec = 353.56,
-66.34) with a 90% containment radius of 0.07 deg (statistical; 68%
containment radius: 0.04 deg, preliminary systematic
error is less than 0.1 deg) which is consistent with the GBM localization.
A Swift TOO request has been issued.

Further analysis is ongoing.

The points of contact for this burst is

Takeshi Uehara :

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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