TITLE:   GCN CIRCULAR
NUMBER:  40323
SUBJECT: GRB 250430A: Swift-XRT refined Analysis
DATE:    25/05/02 13:27:07 GMT
FROM:    Phil Evans at U of Leicester <pae9@star.le.ac.uk>

R. Brivio (INAF-OAB), M. A. Williams (PSU), S. Dichiara (PSU), J.A.
Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester),
A.P. Beardmore (U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri
(INAF-OAR) and P.A. Evans (U. Leicester) reports on behalf of the
Swift-XRT team:

We have analysed 1.4 ks of XRT data for GRB 250430A, from 166 s to 1.9
ks after the  BAT trigger. The data are entirely in Photon Counting
(PC) mode. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.37 (+0.13, -0.14).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.89 (+0.26, -0.24). The
best-fitting absorption column is  1.7 (+0.9, -0.8) x 10^21 cm^-2, in
excess of the Galactic value of 9.6 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 3.8 x 10^-11 (4.8 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.7 (+0.9, -0.8) x 10^21 cm^-2
Galactic foreground: 9.6 x 10^20 cm^-2
Excess significance: 1.7 sigma
Photon index:	     1.89 (+0.26, -0.24)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01308754.

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