GCN Circular 6167

C. Pagani, J. L. Racusin, L. Vetere, D. Grupe, D. N. Burrows (PSU), report on 
behalf of the Swift XRT team:

We have analysed the Swift-XRT Photon Counting data of GRB 070227 (GCN Circ. 
6156
Not found
 
 
) from T+56ks to T+386ks (where T is the BAT trigger time). The candidate 
X-ray afterglow reported in GCN Circ. 6157
Not found
 
 
 has faded from the initial count 
rate of ~ 0.01 counts/s to a count rate of 0.002 counts/s. 
Using 39ks of PC data the refined XRT position is RA,Dec= 120.5805, -46.3135 
which is:

RA(J2000): 08h 02m 19.33s
Dec(J2000): -46d 18' 48.7"

with an uncertainty of 4 arcseconds (90% containment).  This position is 47 
arcseconds from the refined BAT position given in GCN Circ. 6158
Not found
 
 
 and 0
Not found
 
 
.7 
arcseconds from the XRT position given in GCN Circ. 6157
Not found
 
 
. 

The light-curve shows an initial flat phase during the first 20ks of XRT 
obervations ending at about 80ks after the burst, followed by a decay that can 
be fitted with a power law with index 0.9+/-0.2.

The spectral fit to the PC data is not very well constrained due to the low 
number of afterglow events.  The fit with an absorbed power law, applying 
C-statistics, gives a photon index of 2.9 (+0.8/-0.5) in the [0.3-10] keV 
band, and a column density of (0.57 +0.26/-0.18)e22 cm^-2 (compared with the 
Galactic value in this direction of 0.31e22 cm^-2).  
The average estimated unabsorbed 0.3-10 keV flux from T+56ks to T+386ks of XRT 
Photon Counting observations was 3.6e-13 erg cm^-2 s^-1.

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