[vsnet-grb-info 9646] GRB100816A Swift-XRT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  11114
SUBJECT: GRB100816A Swift-XRT refined analysis
DATE:    10/08/16 20:00:21 GMT
FROM:    Owen Littlejohns at U of Leicester  <oml2 at star.le.ac.uk>

O. M. Littlejohns (U. Leicester) and S. R. Oates (UCL-MSSL) report on
behalf of the
Swift-XRT team:
 
We have analysed 4.4 ks of XRT data for GRB 100816A (Oates et al. GCN
Circ. 11102), from 89 s to 12.2 ks after the BAT trigger. The data
comprise 144 s in Windowed Timing (WT) mode with the remainder in Photon
Counting (PC) mode. The enhanced XRT position for this burst was given
by Evans et al. (GCN. Circ 11110).
 
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.29 (+0.05, -0.04), with some flaring activity during
the first snapshot.
 
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.16 (+0.22, -0.21). The
best-fitting absorption column is 1.4 (+0.5, -0.4) x 10^21 cm^-2, in
excess of the Galactic value of 4.5 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 2.10 (+0.19, -0.16)
and a best-fitting absorption column of 1.5 (+0.5, -0.4) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 3.8 x 10^-11 (5.5 x 10^-11) erg cm^-2
count^-1.
 
If the light curve continues to decay with a power-law decay index of
1.29, the count rate at T+24 hours will be 1.6 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.9 x
10^-14 (8.6 x 10^-14) erg cm^-2 s^-1.
 
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00431764.

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