GCN Circular 8470

V. Mangano, B. Sbarufatti, V. La Parola (INAF-IASF Pa), T. Ukwatta  
(GSFC/GWU)
report on behalf of the Swift-XRT team:

Swift-XRT began observing the field of GRB 081102 (trigger 333427,  
Ukwatta et
al., GCN circ.8462
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 ) at 17:46:11.5 UT, 92.0 seconds after the BAT  
trigger.
We analysed data from the first 10 orbits, consisting of 151 s in  
Windowed
Timing mode, from T+98 s to T+251s and 14 ks in Photon Counting mode,  
from
T+251s to T+42.1 ks. The lightcurve is best fit by a broken powerlaw  
model
with slopes alpha_1 = -2.35 +/- 0.15 and alpha_2= -1.22 (-0.11 +0.22)  
and
break time T_break = T+560 (-160 +500)s. After the break, we observe  
a strong
flare at T+960 (-11+21) s with decay time 157 +/-15 s.

The WT spectrum is best fit by a simple absorbed powerlaw with photon  
index
2.7 +/- 0.1 and an absorbing column consistent with the Galactic  
value of
4.9E21 cm^-2 (Kalberla et al. 2005). The observed (unabsorbed) flux  
in the
0.3 - 10 keV band is 4.0E-10 (1.3E-9) erg cm^-2 s^-1. The PC spectrum  
is best
fit by a simple absorbed powerlaw with photon index 1.97 +/- 0.1 and an
absorbing column consistent with the Galactic value. The observed  
(unabsorbed)
flux in the 0.3 - 10 keV band is 1.1 (1.8)E-11 erg cm^-2 s^-1. The  
countrate to flux
conversion factor is 7.1E-11.

The predicted countrate for November 3, 17:45 UT (T+ 24h) is 1.3E-3  
counts/s
equivalent to a flux of 9.2E-14 erg cm^-2 s^-1.

All quoted errors are at 90% confidence level.

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