[vsnet-grb-info 10481] GRB 110407A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  11916
SUBJECT: GRB 110407A: Swift-XRT refined Analysis
DATE:    11/04/11 03:58:19 GMT
FROM:    Chris Wolf at PSU  <cwolf at astro.psu.edu>

C. W. Wolf (PSU) reports on behalf of the Swift-XRT team:

We have analysed 26 ks of XRT data for GRB 110407A (Wolf  et al. GCN
Circ. 11894), from 147 s to 272.1 ks after the	BAT trigger. The data
comprise 593 s in Windowed Timing (WT) mode (the first 10 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 Evans et
al. (GCN. Circ 11896).

After initial flaring (T>0.9 ks), the light curve can be modeled by a
broken power-law model, with an initial decay index of alpha1=2.19
(+0.12, -0.11). A break occurs at T+13.6 ks followed by a plateau phase
with a decay index of alpha2 = 0.4 (+0.5, -0.7).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.80 (+/-0.05). The
best-fitting absorption column is  1.00 (+/-0.13) x 10^21 cm^-2, in
excess of the Galactic value of 2.0 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 1.87 (+0.21, -0.11)
and a best-fitting absorption column of 8.4 (+5.1, -2.7) x 10^20 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 4.2 x 10^-11 (5.0 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     8.4 (+5.1, -2.7) x 10^20 cm^-2
Galactic foreground: 2.0 x 10^20 cm^-2
Excess significance: 5.2 sigma
Photon index:	     1.87 (+0.21, -0.11)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00450884.

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