  This paper describes the measurement of the energy dependence of elliptic
flow for charged particles in Au+Au collisions using the PHOBOS detector at the
Relativistic Heavy Ion Collider (RHIC). Data taken at collision energies of
$\sqrt{s_{_{NN}}} =$ 19.6, 62.4, 130 and 200 GeV are shown over a wide range in
pseudorapidity. These results, when plotted as a function of
$\eta'=|\eta|-y_{beam}$, scale with approximate linearity throughout $\eta'$,
implying no sharp changes in the dynamics of particle production as a function
of pseudorapidity or increasing beam energy.

Nuclear Experiment