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@star.le.ac.uk>

O. M. Littlejohns (U. Leicester) and S. R. Oates (UCL-MSSL) report on
behalf of the
Swift-XRT team:
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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).
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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.
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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.
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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.
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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.