GCN Circular 10945

Veronique Pelassa (LPTA), Melissa Pesce-Rollins (INFN-Pisa) report on
behalf of the Fermi LAT collaboration:

The Fermi Large Area Telescope (LAT) detected emission from GRB
100707A (C. Wilson-Hodge et al, GCN 10944
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 ).

This burst was at an angle of 90 degrees to the LAT boresight, which
means that neither directional nor energy information can be obtained
with the standard analysis procedures.

Using a non-standard data selection, the LAT light curve shows a
single, sharply rising pulse that has a somewhat more gradual decay,
similar to the initial peak in the GBM light curve. The LAT T90
duration is <30 s. This is shorter than the GBM T90 (82+/-1 s), but
the LAT may be missing a long tail at later times owing to noisier
data. Over 300 counts above background were detected within a 5 s
interval in coincidence with the main GBM peak. The significance of
this excess was greater than 14 sigma. A preliminary study of the
instrument performance at such a large inclination suggests that these
events are likely to be low energy gamma-rays, with energies less than
200 MeV.

Further analysis is ongoing.

The Fermi LAT point of contact for this burst is Veronique Pelassa
(pelassa@lpta.in2p3.fr).

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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