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GCN Circular 12484

GRB 111022B: Swift-XRT refined Analysis
2011-10-23T15:38:04Z (13 years ago)
Valerio D'Elia at ASDC <>
V. D'Elia, G. Stratta (ASDC), S. T. Holland (CRESST/USRA/GSFC) report
on behalf of the Swift-XRT team:

We have analysed 8.5 ks of XRT data for GRB 111022B (Holland  et al.
GCN Circ. 12472), from 127 s to 18.5 ks after the  BAT trigger. The
data comprise 134 s in Windowed Timing (WT) mode (the first 8 s were
taken while Swift was slewing) with the remainder in Photon Counting
(PC) mode. The enhanced XRT position for this burst was given by
Beardmore et al. (GCN. Circ 12478).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=1.7 (+/-0.9). At T+176 s  the decay
steepens to an alpha of 3.64 (+0.26, -0.22) before breaking again at
T+404 s to a final decay with index alpha=2.05 (+0.26, -0.21).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.41 (+0.14, -0.13). The
best-fitting absorption column is  1.46 (+0.27, -0.26) x 10^21 cm^-2,
in excess of the Galactic value of 7.3 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 1.59 (+0.15, -0.12)
and a best-fitting absorption column consistent with the Galactic
value. The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 4.5 x 10^-11 (5.0 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     0 (+2.7, -0) x 10^20 cm^-2
Galactic foreground: 7.3 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.59 (+0.15, -0.12)

The results of the XRT-team automatic analysis are available at

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