GCN Circular 6598

O. Godet (U. Leicester) & T. Sakamoto (GSFC/ISAS) report on behalf the
Swift/XRT team

We have analysed the first 8.5ks of Swift XRT PC and WT data of GRB
070704 (Sakamoto et al., GCN Circ. 6594
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 ) taken from T0+153s to T0+3e4s. 
Using 129 s of overlapping XRT Photon Counting mode and UVOT V-band
data, we find an astrometrically corrected X-ray position (using the
XRT-UVOT alignment and matching UVOT field sources to the USNO-B1
catalogue): RA, Dec = 354.69915, +66.25328 which is equivalent to:

RA (J2000):  23 38 47.80
Dec (J2000): +66 15 11.8

with an uncertainty of 2.7 arcsec (90% confidence). This is 3.7 arcsec
from the initially reported XRT position and 39.4 arcsec from the BAT
position (GCN Circ. 6594
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 ).

The XRT light curve exhibits an initial decay on which is superposed a
large flare peaking around T0+300s. We note that between T0+250s and T0
+410s an emission was also detected in the BAT (Markwardt et al., GCN
Circ. 6596
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 ). The light-curve from T0+600s to T0+3e4s is fit well by a
power-law with a decay index of 0.87 +0.11/-0.12. 

The spectrum of the WT data from T0+153s to T0+527s is fit well by an
absorbed power-law with a photon index of 1.85 +/-0.06 and column
density of N_H = (1.08+/-0.06)e22 cm^-2 in excess of the Galactic value
(8.6E21 cm^-2; Dickey & Lockman, 1990). The absorbed (unabsorbed)
0.3-10.0keV flux for that spectrum is (1.57+/-0.05)E-9 (2.85E-9) ergs
cm^-2 s^-1. The spectrum of the PC data from T0+530s to T0+3e4s is fit
well by an absorbed power-law with a photon index of 1.97+/-0.27 with
N_H fixed at 1.08e22 cm^-2. The absorbed (unabsorbed) 0.3-10.0keV flux
for that spectrum is (3.3 +0.6/-0.8)E-12 (6.54E-12) ergs cm^-2 s^-1.

Assuming the source continues to decay at the same rate, we predict an
XRT count rate of 0.0044 counts/s at T0+24 hours, which corresponds to
an observed (unabsorbed) flux of 6.2E-13 (2.9E-12) ergs cm^-2 s^-1.

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