GCN Circular 12058

P. D'Avanzo (INAF-OAB) reports on behalf of the Swift-XRT team:

We have analysed 12 ks of XRT data for GRB 110530A (D'Avanzo  et al.
GCN Circ. 12046
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 ), from 446 s to 43.1 ks after the  BAT trigger. The
data comprise 29 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Evans et al. (GCN. Circ 12055).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=0.81 (+0.05, -0.04).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.30 (+0.09, -0.17). The
best-fitting absorption column is  2.8 (+/-0.5) x 10^21 cm^-2, in
excess of the Galactic value of 5.6 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 3.7 x 10^-11 (7.0 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.8 (+/-0.5) x 10^21 cm^-2
Galactic foreground: 5.6 x 10^20 cm^-2
Excess significance: 9.2 sigma
Photon index:	     2.30 (+0.09, -0.17)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00454473.

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