GCN Circular 7605

P.A. Evans, K.L. Page, A.P. Beardmore, R.L.C. Starling (U. Leicester)
and F.E. Marshall (NASA/GSFC) report on behalf of the Swift-XRT team:

We have analysed 5.2 ks of Swift XRT data for GRB 080413A (Beardmore et
al. GCN Circ. 7594
Not found
 
 
), from T0+67 s to T0+21000 s. The first 186 s of data
were obtained in Windowed Timing (WT mode); the remainder in Photon
Counting mode. The best XRT position for this object is the
UVOT-enhanced position given in Osborne et al. (GCN Circ. 7596
Not found
 
 
).

The X-ray light curve is well fitted by a power-law decay, with an
initial decay slope of 2.87 (+/- 0.19) up to T0+175 (+23/-16) s, at
which point the decay shallows to a slope of 1.10 (+0.06/-0.07).

A spectrum obtained from all of the WT mode data can be modelled with an
absorbed power-law with a photon index gamma=3.12 (+0.16/-0.15). A
redshifted absorbing column of 1.53 (+0.43/-0.38) x 10^22 cm^-2, at a
redshift of z=2.433 (Thoene et al. GCN Circ 7602) is necessary in
addition to the Galactic column of 8.71 x 10^20 cm^-2 (Kalberla et al.
2005). The observed (unabsorbed) 0.3-10 keV flux in this spectrum is
4.1 x 10^-10 (1.71 x 10^-9) erg cm^-2 s^-1.

If the source continues to decay at the present rate, we predict a count
rate of 3.51 x 10^-3 count/sec at T0+24 hours, which correponds to a
0.3-10 keV observed (unabsorbed) flux of 9.54 x 10^-14 (2.72 x 10^-13)
erg cms^-2 s^-1.

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