GCN Circular 7608

E. Troja (U. Leicester/INAF-IASFPa) and M. Stamatikos (NASA/ORAU)
report on behalf of the Swift-XRT team:

We have analysed 9.9 ks of Swift XRT data for GRB 080413B (Stamatikos et
al. GCN Circ. 7598
Not found
 
 
), from T0+134 s to T0+20.1 ks. 
The data set consists of 376 s exposure in Windowed Timing (WT) mode 
followed by 9.5 ks exposure in Photon Counting (PC) mode.

By using orbits 2-4 of PC data [from T0+6.0 ks to T0+20.1 ks]
in order to avoid pile-up effects, we derive an XRT refined position 

     RA (2000) = 21h 44m 34.43s  = 326.1435 d
     Dec (2000) = -19d 58' 52.9" = -19.9814 d

with an uncertainty of 3.7 arcsec (90% containment). This position
is 3.6 arcsec from the UVOT candidate afterglow (GCN Circ. 7598
Not found
 
 
), 
and 3.4 arcsec from the source reported in Kruehler et al. (GCN Circ.
7599
Not found
 
 
).

The X-ray light curve is well fitted by a simple power-law, with a 
decay slope of 0.88 +/- 0.06.

A spectrum obtained from the WT mode data, from T0+135 s to T0+511 s,
can be modelled with an absorbed power-law with a photon index of 
2.05 +/- 0.10 , and a redshifted absorbing column of (0.32 +/- 0.13) 
x 10^22 cm^-2 at a redshift of z=1.1 (Vreeswijk et al. GCN Circ 7601) 
in addition to the Galactic column of 3.06 x 10^20 cm^-2 (Kalberla et 
al. 2005). The observed (unabsorbed) 0.3-10 keV flux in this spectrum is
1.79 x 10^-10 (2.13 x 10^-10) erg/cm^2/s. 
The PC spectrum of the first four orbits, from T0+512 s to T0+20.1 ks, 
can be fit by an absorbed power-law model with photon index 1.93 +/-
0.08 and a column density consistent with the WT spectrum. 
All the reported errors are at the 90% confidence level.

If the source continues to decay at the present rate, we predict a count
rate of 0.035 count/sec at T0+24 hours, which corresponds to a 0.3-10 keV 
observed (unabsorbed) flux of 1.6 x 10^-12 (1.8 x 10^-12) erg/cm^2/s.

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