  We study the asymptotic behavior of the emptiness formation probability for
large spin strings in a translation invariant quasifree nonequilibrium steady
state of the isotropic XY chain. Besides the overall exponential decay, we
prove that, out of equilibrium, the exponent of the subleading power law
contribution to the asymptotics is nonvanishing and strictly positive due to
the singularities in the density of the steady state.
