GCN Circular 5599

M.L. Conciatore, M. Capalbi, M. Perri, D.N. Burrows (PSU) and M.
Stamatikos (NASA/ORAU) report on behalf of the Swift XRT team:

We have analysed the first five orbits of Swift XRT data from GRB
060923A (Stamatikos et al., GCN 5583
Not found
 
 
). A ~2.5ks PC mode image provides
a refined X-ray position of:

RA(J2000)  =  16h 58m 28.2s
Dec(J2000) = +12d 21' 40.0"

with an uncertainty of 6.0 arcseconds radius (90% containment).This is
3.4 arcseconds from the XRT position given by Stamatikos et al.(GCN
5583
Not found
 
 
) and 74.8 arcsec from the refined (ground-calculated) BAT
position (Tueller et al., GCN 5589
Not found
 
 
). This position is 1.14 arcseconds
from the detected source reported by Tanvir et al. (GCN 5587
Not found
 
 
), and
1.32 arcseconds from the one reported by Fox et al. (GCN 5597
Not found
 
 
) as a
candidate counterpart afterglow.

X-ray light curve shows an initial power-law decay with a decay index
of 2.7+/-0.3. Then, after a slow rebrightening starting at ~650s, from
T+4200 the source decays with a slope of 1.23 +/-0.1.

An absorbed power-law fit to the X-ray spectrum from T+100s to T+960s
gave a photon index of 2.1+/-0.2 and a column density of (1.2+/0.1)e21
cm**-2. We note the galactic hydrogen column density in the direction
of the burst is 5.1e20 cm**-2. The 0.2-10.0 keV observed flux for this
spectrum is 4.1e-11 ergs cm**-2 s**-1, which corresponds to an unabsorbed
flux of 4.9e-11 ergs cm**-2 s**-1.

Assuming that the X-ray emission continues to decline at the same
rate, we predict a 0.2-10 keV XRT count rate of 0.006 count/s at
T+24hr, which corresponds to an observed 0.2-10 keV flux of 2.4e-13
erg/cm**2/s.

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

[GCN OPS NOTE(24sep06): Per author's request, the author list was added.]