D. N. Burrows and J. Racusin report on behalf of the Swift XRT team:
Garnavich et al. (GCN Circ. 6165) have suggested that the X-ray light
curve of GRB 070125 has a late break to a steep slope, in agreement
with the optical break reported by Mirabel, Halpern & Thorstensen
(GCN 6096) and confirmed by their observations.
We have re-examined the XRT light curve, which extends from ~44 ks to
~1.5 Ms post-burst, and reconfirm our original conclusions. Full
details, including a plot of the X-ray light curve showing several
possible fits of single and broken power laws, are given in GCN
Report 28.3 (http://gcn.gsfc.nasa.gov/reports/report_28_3.pdf). We find:
1) the X-ray light curve is best fit by a broken power law, but with
a break time at 1.35 +/- 0.35 days (90% confidence), not > 4 days as
required by the optical data (Mirabel, Halpern & Thorstensen, GCN
6096). However, this fit, with reduced chi**2=1.6 for 15 degrees of
freedom, is rather poor (P=0.065), due primarily to large residuals
between 100 and 200 ks.
2) a better fit can be obtained under the assumption that there is a
small X-ray flare at about 110 ks. If these data points are
excluded, the remaining X-ray data can be fit by a single power law
of slope 1.57 +/- 0.07 (90% confidence) with reduced chi**2 of 0.82
for 14 degrees of freedom. A broken power law fit to this data set
is slightly worse and has very poor constraints on the fit parameters.
We conclude that we cannot distinguish between a single power law fit
with a small flare at 110 ks, and a broken power law fit with
additional flaring (to account for the poor residuals). Therefore
the X-ray data do not show evidence for a jet break: they are
consistent with a jet break coincident with the optical break, but
are equally consistent with no break at all.