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GCN Circular 12442

Subject
GRB 111016A: Swift-XRT refined Analysis
Date
2011-10-17T09:25:16Z (13 years ago)
From
Vanessa Mangano at INAF-IASFPA <vanessa@ifc.inaf.it>
V. Mangano (INAF-IASFPA) reports on behalf of the Swift-XRT team:

We have analysed 10 ks of XRT data for GRB 111016A (Mangano  et al. GCN
Circ. 12439), from 185 s to 23.8 ks after the  BAT trigger. The data
comprise 693 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 12441).

The late-time light curve (from T0+4.1 ks) can be modelled with an
initial power-law decay with an index of alpha=3.62 (+0.24, -0.98),
followed by a break at T+5533 s to an alpha of 1.06 (+0.15, -0.23).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.800 (+/-0.024). The
best-fitting absorption column is  1.85 (+/-0.07) x 10^21 cm^-2, in
excess of the Galactic value of 2.5 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 2.23 (+0.09, -0.14)
and a best-fitting absorption column of 7.3 (+2.2, -3.3) x 10^20 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.2 x 10^-11 (4.1 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.3 (+2.2, -3.3) x 10^20 cm^-2
Galactic foreground: 2.5 x 10^20 cm^-2
Excess significance: 3.6 sigma
Photon index:	     2.23 (+0.09, -0.14)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00505646.

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