[vsnet-grb-info 10719] GRB 110709B: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  12142
SUBJECT: GRB 110709B: Swift-XRT refined Analysis
DATE:    11/07/10 22:13:25 GMT
FROM:    Valerio D'Elia at ASDC  <delia at asdc.asi.it>

V. D'Elia, G. Stratta and J. R. Cummings (NASA/UMBC) report on behalf
of the Swift-XRT team:

We have analysed 16 ks of XRT data for GRB 110709B (Cummings  et al.
GCN Circ. 12122), from 70 s to 36.8 ks after the  BAT trigger. The data
comprise 2.3 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 12136).

The light curve shows a prolonged and powerful flaring activity up to
T0+2 ks. The late-time light curve (from T0+5.4 ks) can be modelled
with  a power-law decay with a decay index of alpha=1.08 (+/-0.04).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.550 (+/-0.020). The
best-fitting absorption column is  1.79 (+/-0.07) x 10^21 cm^-2, in
excess of the Galactic value of 5.6 x 10^20 cm^-2 (Kalberla et al.
2005). We stress that this fit averages over strong spectral
variations. In fact, the hard-to-soft band ratio during this time
period varies from about 0.5 to about 3. The PC mode spectrum has a
photon index of 2.19 (+/-0.08) and a best-fitting absorption column of
2.14 (+0.22, -0.21) x 10^21 cm^-2. The counts to observed (unabsorbed)
0.3-10 keV flux conversion factor deduced from this spectrum  is 3.7 x
10^-11 (6.0 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.14 (+0.22, -0.21) x 10^21 cm^-2
Galactic foreground: 5.6 x 10^20 cm^-2
Excess significance: 16.8 sigma
Photon index:	     2.19 (+/-0.08)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00456967.

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