[vsnet-grb-info 18700] GRB 161108A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20148
SUBJECT: GRB 161108A: Swift-XRT refined Analysis
DATE:    16/11/08 14:19:15 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

L.M. McCauley (PSU), P.A. Evans (U. Leicester), S.L. Gibson (U.
Leicester), J.P. Osborne (U. Leicester), V. D'Elia (ASDC), A. D'Ai
(INAF-IASFPA), A. Melandri (INAF-OAB), J.A. Kennea (PSU), B. Sbarufatti
(INAF-OAB/PSU) and A.P. Beardmore report on behalf of the Swift-XRT
team:

We have analysed 6.5 ks of XRT data for GRB 161108A (Beardmore et al.
GCN Circ. 20145), from 73 s to 27.1 ks after the  BAT trigger. The data
comprise 263 s in Windowed Timing (WT) mode (the first 6 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. 20147).Considering only the late-time light curve
(from T0+4.5 ks), the source is fading with alpha >1.2.

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.20 (+/-0.04). The
best-fitting absorption column is  2.20 (+0.15, -0.14) x 10^21 cm^-2,
in excess of the Galactic value of 1.8 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.09 (+0.24, -0.22)
and a best-fitting absorption column of 1.5 (+0.7, -0.6) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.3 x 10^-11 (4.4 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.5 (+0.7, -0.6) x 10^21 cm^-2
Galactic foreground: 1.8 x 10^20 cm^-2
Excess significance: 3.7 sigma
Photon index:	     2.09 (+0.24, -0.22)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00721234.

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