GCN Circular 14614

P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

GCN 14126
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  was sent in error, with several pieces of information missing, 
as new data were being processed as the circular was sent.

The corrected refined XRT analysis is as follows:


We have analysed 10 ks of XRT data for GRB 130508A (Holland  et al. GCN 
Circ. 14607
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 ),  from 134 s to 45.8 ks after the  BAT trigger. The data 
comprise 53 s in Windowed Timing (WT) mode with the remainder 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).

The light curve can be modelled with  a power-law decay with a decay 
index of alpha=1.98 (+0.39, -0.28).

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)

If the light curve continues to decay with a power-law decay index of 
1.98, the count rate at T+24 hours will be 6.0 x 10^-6 count s^-1, 
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.1 x 
10^-16 (7.8 x 10^-16) erg cm^-2 s^-1.

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.