TITLE:   GCN CIRCULAR
NUMBER:  8384
SUBJECT: GRB 081016B: Swift-XRT Team refined Analysis 
DATE:    08/10/17 05:10:42 GMT
FROM:    Kim Page at U.of Leicester  <kpa@star.le.ac.uk>

K.L. Page (U. Leicester) reports on behalf of the Swift-XRT team:

We have analysed the first six orbits of the XRT data obtained for GRB 
081016B (Page et al., GCN Circ. 8381). After an initial 18 seconds in 
Windowed Timing mode, the remaining 3.5 ks were collected in Photon 
Counting (PC) mode. The UVOT-enhanced position was given by Osborne et al. 
in GCN Circ. 8383.

The first orbit of data shows a decay of alpha = 1.1 +/- 0.3. However, 
after the end of this orbit (~265 s after the trigger), the source is no 
longer detected, indicating a break to a significantly steeper decay 
occurred.

The spectrum of the first orbit of PC data can be modelled with a 
power-law (Gamma = 1.20 +/- 0.18) absorbed at the Galactic value of NH = 
1.96x10^20 cm^-2. The upper limit on the total absorbing column is 
2.2x10^21 cm^-2. The observed (unabsorbed) flux over this time is 
2.43x10^-10 (2.48x10^-10) erg cm^-2 s^-1, corresponding to a counts to 
observed flux conversion of 6.8x10^-11 erg cm^-2 count^-1.

Because of the lack of detection after the first orbit, we cannot 
predict the future count rate.

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