[vsnet-grb-info 10814] GRB 110801A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  12235
SUBJECT: GRB 110801A: Swift-XRT refined Analysis
DATE:    11/08/02 09:00:16 GMT
FROM:    Andy Beardmore at U Leicester  <apb at star.le.ac.uk>

A.P. Beardmore (U. Leicester) and M. De Pasquale (UCL-MSSL) report on
behalf of the Swift-XRT team:

We have analysed 9.9 ks of XRT data for GRB 110801A (De Pasquale  et
al. GCN Circ. 12228), from 89 s to 24.0 ks after the  BAT trigger. The
data comprise 566 s in Windowed Timing (WT) mode (the first 7 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 12232).

The light curve initially shows a number of flares, the largest peaking
at 500-600 count/s  between T+355 s and T+390 s after the trigger. Once
this flare has decayed, the light curve after T+800 s can be modelled
by a power-law with a slope of 1.12 +/- 0.06.

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.754 (+0.025, -0.026). The
best-fitting absorption column is  6.4 (+/-0.6) x 10^21 cm^-2, at a
redshift of 1.858, in addition to the Galactic value of 6.2 x 10^20
cm^-2 (Kalberla et al. 2005). We note this spectrum includes strong
spectral evolution through the flare. The PC mode spectrum has a photon
index of 2.04 (+/-0.09) and a best-fitting absorption column of 1.6
(+1.6, -1.4) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10
keV flux conversion factor deduced from this spectrum  is 3.6 x 10^-11
(4.5 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 6.2 x 10^20 cm^-2
Intrinsic column:    1.6 (+1.6, -1.4) x 10^21 cm^-2 at z=1.858
Photon index:	     2.04 (+/-0.09)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00458521.

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