GCN Circular 7737

K.L. Page (U. Leicester) and S.T. Holland (CRESST/USRA/GSFC) report on 
behalf of the Swift-XRT team:

We have analysed the first five orbits of data obtained for GRB 080516 
(Holland et al., GCN Circ. 7733
Not found
 
 
), covering 11.5 ks of Photon Counting (PC) 
mode data. The UVOT-enhanced XRT position was given by Beardmore et al. in 
GCN Circ. 7735
Not found
 
 
.

The light-curve begins relatively flat, with a decay of alpha ~ 0.36 +/- 
0.17, until around 4800 seconds after the trigger, at which point the 
slope steepens to 1.04 +0.20/-0.18. 

The first five orbits of PC data can be modelled with an absorbed 
power-law, with Gamma = 2.7 +/- 0.4 and total NH = (1.3 +/- 0.3)x10^22 
cm^-2, considerably in excess of the Galactic value of 3.22x10^21 cm^-2. 
Using the relation in Grupe et al. (2007, ApJ, 133, 2216), this implies an 
estimated upper limit on the redshift of the burst of z<1.0. There is no 
evidence for spectral evolution across the temporal break. The observed 
(unabsorbed) flux over this time interval (90-2.5x10^4 s after the 
trigger) is 2.38x10^-12 (1.06x10^-11) erg cm^-2 s^-1. The counts to 
observed flux conversion is 5.8x10^-11 erg cm^-2 count^-1.

If the light-curve continues to decay at alpha ~ 1.04, the count rate at 
24 hours is predicted to be 3.7x10^-3 count s^-1, corresponding to an 
observed flux of 2.1x10^-13 erg cm^-2 s^-1.

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