A data-driven method was applied to measurements of Au+Au collisions at $sqrt{s_{_{rm NN}}} =$ 200 GeV made with the STAR detector at RHIC to isolate pseudorapidity distance $Deltaeta$-dependent and $Deltaeta$-independent correlations by using two- and four-particle azimuthal cumulant measurements. We identified a component of the correlation that is $Deltaeta$-independent, which is likely dominated by anisotropic flow and flow fluctuations. It was also found to be independent of $eta$ within the measured range of pseudorapidity $|eta|<1$. The relative flow fluctuation was found to be $34% pm 2% (stat.) pm 3% (sys.)$ for particles of transverse momentum $p_{T}$ less than $2$ GeV/$c$. The $Deltaeta$-dependent part may be attributed to nonflow correlations, and is found to be $5% pm 2% (sys.)$ relative to the flow of the measured second harmonic cumulant at $|Deltaeta| > 0.7$.
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