One of the most striking results is the large elliptic flow (\(v_2\)) at RHIC. Detailed mass and transverse momentum dependence of elliptic flow are well described by ideal hydrodynamic calculations for \(p_{\mathrm{T}} < \) 1 GeV/c, and by parton coalescence/recombination picture for \(p_{\mathrm{T}} = 2 - 6\) GeV/c. The systematic error on \(v_2\) is dominated by so-called "non-flow effects", which is the correlation not originated from reaction plane. It is crucial to understand and reduce the systematic error from non-flow effects in order to understand the underlying collision dynamics. In this paper, we present the centrality dependence of \(v_2\) with respect to the first harmonic event plane at ZDC-SMD (\(v_2\)\{ZDC-SMD\}) in Au + Au collisions at \(\sqrt{s_{NN}}\) = 200 GeV. Large rapidity gap (\(|\Delta\eta| > 6\)) between midrapidity and the ZDC could enable us to minimize possible non-flow contributions. We compare the results of \(v_2\)\{ZDC-SMD\} with \(v_2\)\{BBC\}, which is measured by event plane determined at \(|\eta| = 3.1 - 3.9\). Possible non-flow contributions in those results will be discussed.
