[vsnet-grb-info 6982] GRB 081127: Swift-XRT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8566
SUBJECT: GRB 081127: Swift-XRT refined analysis
DATE:    08/11/27 17:42:56 GMT
FROM:    Jirong Mao at INAF-OAB  <jirong.mao at brera.inaf.it>

J. Mao, C. Guidorzi (INAF-OAB) and R. Margutti (Univ. Bicocca & 
INAF-OAB) report on behalf of the Swift XRT team:

We have analysed the first 4 orbits of Swift-XRT data obtained for GRB 
081127 (Mao et al., GCN Circ. 8560), covering from 128 to 219 s in 
Windowed Timing (WT) and from 220 s to 19.5 ks in Photon Counting (PC) 
mode data, respectively. The net exposures are 90 s and 9.4 ks for the 
WT and PC modes data, respectively.  The UVOT-enhanced XRT position was 
given by Beardmore et al. in GCN Circ. 8565.

The light curve shows an inital steep decay of index 5.6 until 420 s, 
then it shows a shallow decay with index of 0.6. After 13.3 ks the 
lightcurve shows a decay with an index of about 2.0. The WT spectrum can 
be fit with an absorbed power-law model with a photon index of 4.2 +- 
0.2 and an absorbing
equivalent hydrogen column density is (2.8 +- 0.3)e21 cm^-2, which is 
larger than the Galactic one, 6.7e20 cm^-2 (Kalberla et al.  2005). The 
observed (unabsorbed) 0.3-10 keV flux is 3.7(4.5)e-10 erg cm^-2  s^-1. 
The PC spectrum can be fit with an absorbed power-law model with a 
photon index of 2.3 +- 0.3 with an absorbing equivalent hydrogen column 
density compatible with the Galactic value.

If the light curve continues to decay with an index of 2.0, the count 
rate 24 hours after the burst will be 2.9e-4 c/s, corresponding to an 
absorbed flux of 9.9e-15 erg cm^-2 s^-1.

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