[vsnet-grb-info 12359] GRB 120909A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13734
SUBJECT: GRB 120909A: Swift-XRT refined Analysis
DATE:    12/09/09 15:55:07 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at star.le.ac.uk>

V. Mangano (INAF-IASFPA), A. Melandri (INAF-OAB), M.C. Stroh (PSU),
D.N. Burrows (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), C.
Pagani (U. Leicester), A.P. Beardmore (U. Leicester), B. Sbarufatti
(INAF-OAB/PSU) and S. Immler report on behalf of the Swift-XRT team:

We have analysed 9.3 ks of XRT data for GRB 120909A (Immler  et al. GCN
Circ. 13727), from 3.3 ks to 33.3 ks after the	BAT trigger. The data
comprise 173 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Osborne et al. (GCN. Circ 13732).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.19 (+/-0.06).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.04 (+/-0.09). The
best-fitting absorption column is  1.9 (+0.8, -0.7) x 10^22 cm^-2, at a
redshift of 3.93, in addition to the Galactic value of 6.5 x 10^20
cm^-2 (Kalberla et al. 2005). The counts to observed (unabsorbed)
0.3-10 keV flux conversion factor deduced from this spectrum  is 3.5 x
10^-11 (4.7 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 6.5 x 10^20 cm^-2
Intrinsic column:    1.9 (+0.8, -0.7) x 10^22 cm^-2 at z=3.93
Photon index:	     2.04 (+/-0.09)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00533060.

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