GCN Circular 7951

R.L.C. Starling (U. Leicester) and P. Schady (MSSL-UCL) report, on behalf 
of the Swift XRT team:

We have analysed the first 4 orbits of Swift XRT data (from T0+64s to 
T0+17.8 ks) for GRB 080707 (trigger=316204, Schady et al., GCN Circ. 
7947
Not found
 
 
).

Using 1482 seconds of overlapping XRT Photon Counting (PC) mode and UVOT 
data, we find an updated astrometrically corrected X-ray position (using 
the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 
catalogue): RA, Dec = 32.61860, 33.10983 deg which is equivalent to:
 
RA(J2000) = 02 10 28.46 
Dec(J2000)= +33 06 35.4 

with an uncertainty of 1.5 arcseconds (radius, 90% confidence). This 
position lies 1.35 arcseconds from the optical counterpart reported in 
Clemens et al. (GCN Circ. 7948
Not found
 
 
).

The light curve can be fit by an initial steep decay followed by a shallow 
plateau phase. The final orbit of data so far collected may indicate a 
further break to a steeper slope, but this is not required by the fit. 
A  singly broken power law gives alpha1=5.6+1/-0.8, Tbk=145+17/-13 and 
alpha2=0.35+0.06/-0.07. 
A doubly broken power law model gives the following parameters: 
alpha1=5.5+0.9/-0.8, Tbk1=151+6/-15s, alpha2=0.2+0.1/-0.5, 
Tbk2=5300+5400/-4200s and alpha3=0.7+0.6/-0.3.

The PC mode spectrum comprising 1.64 ks of data from the latter part of 
orbit 1 and from orbit 2 (T0+96s - T0+6384s) is well fit with a power law 
of photon index Gamma=2.1+0.4/-0.5 (90%) absorbed by the Galactic column 
of 6.99E+20 cm^-2 (Kalberla et al. 2005) and by a column at the inferred 
redshift of the host galaxy (z=1.23, Fynbo et al. GCN Circ. 7949
Not found
 
 
) which 
can only be constrained to be nH<1.23e22 cm^-2. The 0.3-10 keV observed 
(unabsorbed) flux is 5.4e-12 (6.73-12) erg/cm^2/s, corresponding to a 
count rate of 0.12 count/s, hence the observed count rate to flux 
conversion is 1 count/s = 4.5e-11 erg/cm^2/s.

The predicted count rate at T0+24h is 0.011 counts/s, assuming a decay 
rate of alpha=0.7 from the doubly broken power law model.

This is an official product of the Swift XRT team.