GCN Circular 7153

A.P. Beardmore, K.L. Page (U. Leicester) and T. Sakamoto (NASA/UMBC)
report on behalf of the Swift-XRT team:

The Swift-XRT began observing GRB 071227 (trigger #299787) at
20:15:04UT, 79.5 seconds after the BAT trigger (Sakamoto et al., GCN
Circ. 7147
Not found
 
 
). Using 382 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) of RA, Dec = 58.13002, -55.98419, which is equivalent 
to:

  RA (J2000):  03h 52m 31.21s
Dec (J2000): -55d 59' 03.1"

with an uncertainty of 2.0 arcsec (radius, 90% confidence). This is
4.5 arcsec away from the position derived from the promptly downlinked
XRT data reported in Sakamoto et al. (GCN Circ. 7147
Not found
 
 
), 91 arcsec from
the refined BAT position of Sato et al. (GCN Circ. 7148
Not found
 
 
) and 2.6 arcsec
from the possible UVOT optical transient reported by Cucchiara and 
Sakamoto (GCN Circ. 7150
Not found
 
 
).

The XRT light curve from 210s to 34.8ks after the BAT trigger can be
modelled by a doubly broken power-law, with parameters alpha1 = 1.1
+/- 0.2, tbreak1 = 183 +/- 7s, alpha2 = 5.3 +1.2 -0.6, tbreak2 = 389
+/- 65s, alpha3 = 1.1 +/- 0.2.

The XRT spectrum from a time interval spanning 104s to 208s after the
BAT trigger is well fit by an absorbed power-law, with a photon index
of 1.62+/-0.14 and a column density (9.3+/-4.3)e20 cm^-2, in addition
to the Galactic column of 2.6e20 cm^-2 in this direction. The observed
(unabsorbed) 0.3-10.0 keV flux from this period is 3.9e-10 (4.6e-10)
ergs cm^-2 s^-1.

The predicted XRT count rate 24 hours after the trigger is 4.0e-4 
count s^-1, which corresponds to an observed 0.3-10.0 keV flux of 
2.0e-14 ergs cm^-2 s^-1.

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