[vsnet-grb-info 3818] GRB 060729: An update on the late-time Swift observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  5652
SUBJECT: GRB 060729: An update on the late-time Swift observations
DATE:    06/09/29 12:56:18 GMT
FROM:    Dirk Grupe at PSU/Swift-XRT  <grupe at astro.psu.edu>

D. Grupe (PSU) and Caryl Gronwall (PSU) report on behalf of the Swift team

We report on an update of the Swift XRT and UVOT observations
of GRB 060729 (Grupe et al., GCN 5365). The afterglow is still
detectable in X-rays at a level of 1e-3 counts/s in the Swift
XRT (5e-14 ergs/s/cm2). The late-time decay slope is 1.29+/-0.03.
Assuming this decay slope continues, we expect the afterglow to
be still detectable in the XRT until the end of December 2006.
We plan to follow the afterglow as long as possible.
Currently we are at day 61 after the burst, which is the
longest period Swift has ever followed and detected an
afterglow in X-rays.

In the UVOT the afterglow was still visible in all 6 filters
until 9 days after the burst. In UV W1 the afterglow was
detectable until 2006-August-29 (31 days after the burst).
we still obtain a 3.9 sigma detection at a level of 22.8+/-0.3
mag. We calculated the following late-time flux decay slopes in
the 6 UVOT filters:

V:    1.11+/-0.14
B:    0.98+/-0.07
U:    1.40+/-0.08
UVW1: 1.29+/-0.03
UVM2: 1.45+/-0.07
UVW2: 1.38+/-0.04

These values are slightly different than what has been reported
earlier by Grupe (2006, GCN Circ. 5432). However, our new
light curves contain more data than what was available earlier.

Assuming the power law decay continues without a break in the
optical, our extrapolation of the light curves show that the
afterglow will be visible at the beginning of October with
V=24.0 mag, B=23.4 mag, U=24.0 mag. At this level a detection
of the afterglow is still feasible for a large southern telescope.
We, therefore, encourage everybody again who has access to one
of the large southern telescopes to follow this afterglow in V,
B, and U in order to search for a break in the light curves.


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