V. La Parola, T. Mineo, B. Sbarufatti, V. Mangano, G. Cusumano
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), with a total exposure of 427 s
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
RA (J2000) = 03h 13m 56.9s
Dec(J2000) = -42d 56m 43.6s
with an estimated error radius of 3.5 arcseconds (90% confidence).
position is 16.8 arcseconds from the BAT refined position (Cummings,
et al., GCN 6212), 6.2 arcseconds from the initial XRT position, and
arcseconds from the UVOT optical candidate (Cummings, et al., GCN
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
the bright flare is well fit by an absorbed power-law with a photon
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
The unabsorbed 0.3-10 keV flux of the bright flare is 8.2E-10
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.