  New measurements of directed flow for charged hadrons, characterized by the
Fourier coefficient \vone, are presented for transverse momenta $\mathrm{p_T}$,
and centrality intervals in Au+Au collisions recorded by the STAR experiment
for the center-of-mass energy range $\mathrm{\sqrt{s_{_{NN}}}} = 7.7 - 200$
GeV. The measurements underscore the importance of momentum conservation and
the characteristic dependencies on $\mathrm{\sqrt{s_{_{NN}}}}$, centrality and
$\mathrm{p_T}$ are consistent with the expectations of geometric fluctuations
generated in the initial stages of the collision, acting in concert with a
hydrodynamic-like expansion. The centrality and $\mathrm{p_T}$ dependencies of
$\mathrm{v^{even}_{1}}$, as well as an observed similarity between its
excitation function and that for $\mathrm{v_3}$, could serve as constraints for
initial-state models. The $\mathrm{v^{even}_{1}}$ excitation function could
also provide an important supplement to the flow measurements employed for
precision extraction of the temperature dependence of the specific shear
viscosity.
