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GCN Circular 14260

Subject
GRB 130305A: Fermi LAT Detection
Date
2013-03-05T22:54:38Z (11 years ago)
From
Sylvain Guiriec at UAH <sylvain.guiriec@lpta.in2p3.fr>
S. Guiriec (NASA/GSFC/NPP), J. L. Racusin (NASA/GSFC),
G. Vianello (Stanford) and D. Kocevski (NASA/GSFC/NPP)
report on behalf of the Fermi-LAT team:

The Fermi Large Area Telescope (LAT) detected emission from GRB 130305A at
 approximately 11:39:11 UT on March 5th, 2013, while in Target Of
Opportunity
(i.e., pointing) mode observing the Crab (ATEL #4855). GRB 130305A was
detected
by Fermi-GBM (GBM trigger 130305486/384176354)
and Swift-BAT (Cummings et al., GCN #14257).

The burst location was within the LAT field of view at an angle of ~41
degrees to
the LAT boresight, and ~100 degrees from the zenith, placing it very close
to
the Earth's limb, which is a very bright source of gamma rays. No
significant excess is
seen using standard analysis procedures (>100 MeV) neither in the prompt
phase nor
in a search for extended emission when the burst position was no longer
occulted
from ~1500 to 5000 s.

Using the non-standard LAT Low Energy (LLE) data selection,
>550 counts above background were detected in a single FRED like pulse,
peaking
between 5 and 10 s after the GBM trigger and coinciding with the time of
the GBM emission, with a significance of ~10.7 sigma. This detection is due
to
low energy gamma-rays, below 75 MeV, and therefore has insufficient spatial
resolution
to provide a reliable LAT localization.

A GBM circular on GRB 130305A is forthcoming.

The Fermi LAT point of contact for this burst is Sylvain Guiriec
(sylvain.guiriec@nasa.gov)
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