  Among ongoing reactor-based experiments, Double Chooz is unique in obtaining
data when the reactor cores are brought down for maintenance. These reactor-off
data allow for a clean measurement of the backgrounds of the experiment, thus
being of uppermost importance for the theta13 oscillation analysis. While the
oscillation results published by the collaboration in 2011 and 2012 rely on
background models derived from reactor-on data, in this talk we present an
independent study based on the handle provided by 7.53 days of reactor-off
data. A global fit to both theta13 and the total background is performed by
analyzing the observed neutrino rate as a function of the non-oscillated
expected rate for different reactor power conditions. The result presented in
this talk is fully consistent with the one already published by Double Chooz.
As they both yield almost the same precision, this work stands as a prove of
the reliability of the background estimates and the oscillation analysis of the
experiment.
