TITLE:   GCN CIRCULAR
NUMBER:  33703
SUBJECT: GRB 230427A: Swift-XRT refined Analysis
DATE:    23/04/28 12:54:32 GMT
FROM:    Phil Evans at U of Leicester <pae9@star.le.ac.uk>

A. Tohuvavohu (U. Toronto), D.N. Burrows (PSU), J.P. Osborne (U.
Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M.
Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti
(INAF-OAB), J. D. Gropp (PSU) report on behalf of the Swift-XRT team:

We have analysed 4.5 ks of XRT data for GRB 230427A, from 80 s to 75.0
ks after the  BAT trigger. The data comprise 7 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=1.21 (+0.12, -0.11).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.94 (+0.30, -0.26). The
best-fitting absorption column is  4.0 (+6.6, -3.2) x 10^20 cm^-2,
consistent with the Galactic value of 8.4 x 10^19 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 (3.6 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.0 (+6.6, -3.2) x 10^20 cm^-2
Galactic foreground: 8.4 x 10^19 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.94 (+0.30, -0.26)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01165948.

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