[vsnet-grb-info 13275] GRB 130508A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  14612
SUBJECT: GRB 130508A: Swift-XRT refined Analysis
DATE:    13/05/09 10:34:06 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), B.P. Gompertz
(U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. Maselli 
(INAF-IASFPA), J.A. Kennea (PSU), M.C. Stroh (PSU), D.N. Burrows (PSU)
and S.T. Holland report on behalf of the Swift-XRT team:

We have analysed xx ks of XRT data for GRB 130508A (Holland  et al. GCN
Circ. 14607),  from 0 s to 0 s after the  BAT trigger. The data are
entirely in Photon Counting (PC) mode. The best available XRT position 
(using the promptly downlinked event data, the XRT-UVOT alignment and
matching UVOT field sources to the USNO-B1 catalogue) is RA, Dec =
305.3218, 34.9583 which is equivalent to:

RA (J2000): 20 21 17.22
Dec(J2000): +34 57 29.9

with an uncertainty of 2.5 arcsec (radius, 90% confidence). We cannot
determine at the present time whether the source is fading.

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.0 (+0.6, -0.5). The
best-fitting absorption column is  1.6 (+1.0, -0.8) x 10^22 cm^-2, in
excess of the Galactic value of 7.7 x 10^21 cm^-2 (Kalberla et al.
2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 1.0 x 10^-10 (1.3 x 10^-10) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.6 (+1.0, -0.8) x 10^22 cm^-2
Galactic foreground: 7.7 x 10^21 cm^-2
Excess significance: 1.7 sigma
Photon index:	     1.0 (+0.6, -0.5)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00555413.

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