We have recently shown that in nonequilibrium spin systems at criticality the limit $X^{\infty }$ of the fluctuation-dissipation ratio $X(t,t_w)$ for $t⪢t_w⪢1$ can be measured using observables such as magnetization or energy [Phys. Rev. E 68, 016116 (2003)]. Pleimling argues in a Comment [preceding paper, Phys. Rev. 70, 018101 (2004)] on our paper that for such observables correlation and response functions are dominated by one-time quantities dependent only on $t$, and are therefore not suitable for a determination of $X^{\infty }$. Using standard scaling forms of correlation and response functions, as used by Pleimling, we show that our data do have a genuine two-time dependence and allow $X(t,t_w)$ and $X^{\infty }$ to be measured, so that Pleimling’s criticisms are easily refuted. We also compare with predictions from renormalization-group calculations, which are consistent with our numerical observation of a fluctuation-dissipation plot for the magnetization that is very close to a straight line. A key point remains that coherent observables make measurements of $X^{\infty }$ easier than the traditionally used incoherent ones, producing fluctuation-dissipation plots whose slope is close to $X^{\infty }$ over a much larger range.

• Received 12 March 2004

DOI:https://doi.org/10.1103/PhysRevE.70.018102