GCN Circular 5369

GRB 060729: Swift-XRT refined analysis

D. Grupe (PSU) reports on behalf of the Swift/XRT team



We have analyzed the first 5 orbits with a total observing time of 10.9 ks
of Swift XRT data (2.3 ks in Windowed Timing and 8.6 in photon counting 
mode)
of GRB 060729 (Grupe et al., GCN 5365
Not found
 
 
). The Photon Counting mode image
provides a refined XRT position:

RA(J2000) = 06h 21m 31.29s,
Dec(J2000) = -62d 22' 13.4"

with an error of 3.5" (90% confidence). This position is 3.2"
away from the preliminary XRT position reported in GCN 5365
Not found
 
 
.

The X-ray light curve displays the end of a giant flare (at the 
beginning of the
XRT observation this flare had a count rate of 1000 counts/s) followed by a
second flare at 174s after the burst. The afterglow shows a long 
late-time flare
between 1 ks to 10 ks after the burst. We do not see a break in the 
light curve
yet that allows us to give a reliable prediction of the flux for the 
next 24h.
Right now the count rate is at a level of 0.3 counts s**-1 or a flux of 
about
1.5e-11 ergs s**-1 cm**-2.

Spectral fits to the Windowed Timing mode data during the flare phase
suggest a significant absorption column density in excess of the 
Galactic value
(4.82e20 cm**-2). The later photon counting mode data after the flares
can be fitted by a single power law model with a photon index Gamma =
2.14+0.15-0.14 and an absorption column density NH=1.0+/-0.3 e21 cm**-2.


We also want to point out that this burst is also an optically bright burst
(Immler 2006, GCN 5267
Not found
 
 
).  Even
though it is only 2h away from the sun in RA, it is circumpolar for most
southern observatories. We would like to encourage all southern observers to
obtain a spectrum of this burst in order to determine its redshift.


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