[vsnet-grb-info 4868] GRB 070704: Swift-XRT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6598
SUBJECT: GRB 070704: Swift-XRT refined analysis
DATE:    07/07/05 11:43:49 GMT
FROM:    Olivier Godet at U.of Leicester  <og19 at star.le.ac.uk>

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) 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).

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). 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.