GCN Circular 12692

A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), O.M.
Littlejohns (U. Leicester), A. Melandri (INAF-OAB), B. Sbarufatti
(INAF-OAB/PSU), G. Stratta (ASDC), J.A. Kennea (PSU), M.C. Stroh (PSU),
D.N. Burrows (PSU) and S.R. Oates report on behalf of the Swift-XRT
team:

We have analysed 7.1 ks of XRT data for GRB 111215A (Oates  et al. GCN
Circ. 12681
Not found
 
 
), from 407 s to 59.3 ks after the  BAT trigger. The data
comprise 2.2 ks in Windowed Timing (WT) mode (the first 9 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 12690).

The late-time light curve (from T0+5.9 ks) can be modelled with an
initial power-law decay with an index of alpha=2.13 (+0.13, -0.12),
followed by a break at T+14.6 ks to an alpha of 1.21 (+0.15, -0.16).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.847 (+/-0.027). The
best-fitting absorption column is  4.10 (+/-0.12) x 10^21 cm^-2, in
excess of the Galactic value of 5.6 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 2.14 (+/-0.12) and a
best-fitting absorption column of 3.2 (+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 3.9 x 10^-11 (6.8 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.2 (+0.5, -0.4) x 10^21 cm^-2
Galactic foreground: 5.6 x 10^20 cm^-2
Excess significance: 10.2 sigma
Photon index:	     2.14 (+/-0.12)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00509717.

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