GCN Circular 6214

V. La Parola, T. Mineo, B. Sbarufatti, V. Mangano, G. Cusumano
(INAF-IASF Pa)
report on behalf of the Swift XRT team:

We have analysed the first two orbits of Swift-XRT data on GRB 070318
(Cummings, et al., GCN Circ. 6210
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 ), with a total exposure of 427 s
seconds
in Window Timing (WT) mode and 33.4 ks seconds in Photon Counting (PC)
mode. This provides a refined XRT position at RA,Dec=48.4870,-42.9454
which is:

RA (J2000) = 03h 13m 56.9s
Dec(J2000) = -42d 56m 43.6s

with an estimated error radius of 3.5 arcseconds (90% confidence).
This
position is 16.8 arcseconds from the BAT refined position (Cummings,
et al., GCN 6212
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 ), 6.2 arcseconds from the initial XRT position, and
2.9
arcseconds from the UVOT optical candidate (Cummings, et al., GCN
Circ.
6210
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 ).

The 0.3-10 keV X-ray light curve presents a bright flare peaking at
about 280 s from the trigger and a second fainter peak
at 200 s. The underlying light curve between 70 s and 7.5 ks
can be fit with a simple power-law with a decay slope of 1.11 � 0.02.

The X-ray spectrum from the XRT/WT data covering up to the beginning
of
the bright flare is well fit by an absorbed power-law with a photon
index
of 1.4�0.1 and column density of (1.5�0.7)E21 cm**-2, higher
than the Galactic column density in the direction of the source
(2.5E20 cm**-2). The unabsorbed 0.3-10 keV flux for this spectrum is
1.3E-9 erg/cm**2/s. The XRT/WT spectrum of the bright flare and the
XRT/PC spectrum are modelled by an absorbed power law
with photon index of 1.9�0.1 and column density of (1.3�0.3)E21
cm**-2.
The unabsorbed 0.3-10 keV flux of the bright flare is 8.2E-10
erg/cm**2/s
and the one relative to the PC spectrum is 1.0E-10 erg/cm**2/s.

Assuming the X-ray emission continues to decline at the same rate, we
predict a 0.3-10 keV XRT count rate of 5E-3 count/s at T+48hr, which
corresponds to an observed 0.3-10 keV flux of 2.5e-13 erg/cm**2/s.

This circular is an official product of the Swift XRT Team.