TITLE:   GCN CIRCULAR
NUMBER:  34626
SUBJECT: GRB 230903A: Swift-XRT refined Analysis
DATE:    23/09/05 14:09:08 GMT
FROM:    Phil Evans at U of Leicester <pae9@star.le.ac.uk>

K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), V. D'Elia
(SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), A. D'Ai (INAF-IASFPA),
D.N. Burrows (PSU), J. D. Gropp (PSU), S. Dichiara (PSU) and P.A. Evans
report on behalf of the Swift-XRT team:

We have analysed 2.3 ks of XRT data for GRB 230903A, from 97 s to 29.3
ks after the  BAT trigger. The data comprise 8 s in Windowed Timing
(WT) mode (taken while Swift was slewing), with the remainder in Photon
Counting (PC) mode. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.17 (+/-0.09).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.00 (+0.24, -0.22). The
best-fitting absorption column is  8.2 (+5.9, -5.0) x 10^20 cm^-2, in
excess of the Galactic value of 2.7 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 3.3 x 10^-11 (3.9 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     8.2 (+5.9, -5.0) x 10^20 cm^-2
Galactic foreground: 2.7 x 10^20 cm^-2
Excess significance: 1.8 sigma
Photon index:	     2.00 (+0.24, -0.22)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01189514.

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