GCN Circular 4959

C. Pagani, D. Morris, J. Racusin, J. Kennea and D. N. Burrows (PSU)  
report on behalf of the Swift XRT team:

We have analysed the first orbit of Swift XRT data on the BAT GRB 060413 
(Pagani, et al., GCN 4957
Not found
 
 
) with a total exposure of 1700 seconds.

The refined XRT position is:

RA(J2000):   19 25 07.7
Dec(J2000): +13 45 27.3

This position is 192 arcseconds from the BAT position 
and 4 arcsec from the XRT position given in GCN 4957
Not found
 
 
. 
We estimate an uncertainty of 3.6 arcseconds radius (90% containment).

The 0.2-10 keV light curve starts in Windowed Timing (WT) mode
119 seconds after the BAT trigger (T0) and then switches into Photon Counting 
(PC) at T0+305. 
The XRT data show a steep power law decay with slope of -3.5 +/- 0.2
followed by a flare centered at T0+646 seconds with a peak count rate of 
6 counts/s.

The X-ray spectrum covering the time period from T+119s to T+1840s is
well fit by an absorbed power-law with a photon index of 1.9+/-0.1 and a
column density of 2.30e22 cm-2, which is higher than the Galactic value 
in the direction of the source (1.20e22 cm-2). However, the NH measurement of 
this galactic plane line of sight is likely to be underestimated.
The unabsorbed 0.3-10 keV flux is 4.8e-09 erg/cm**2/s.

Due to the flare in the light curve the predicted XRT count rate is uncertain.  
Extrapolating the late part of the lightcurve of the first orbit we estimate 
the XRT count rate to be about 0.0006 cps at T+24 hr, corresponding to an 
unabsorbed 0.3-10 keV flux of about 1.6E-13 erg/cm2/s

This circular is an official product of the Swift XRT Team.