  Directed and elliptic flows of neutrons and light charged particles were
measured for the reaction 197Au+197Au at 400 MeV/nucleon incident energy within
the ASY-EOS experimental campaign at the GSI laboratory. The detection system
consisted of the Large Area Neutron Detector LAND, combined with parts of the
CHIMERA multidetector, of the ALADIN Time-of-flight Wall, and of the
Washington-University Microball detector. The latter three arrays were used for
the event characterization and reaction-plane reconstruction. In addition, an
array of triple telescopes, KRATTA, was used for complementary measurements of
the isotopic composition and flows of light charged particles. From the
comparison of the elliptic flow ratio of neutrons with respect to charged
particles with UrQMD predictions, a value \gamma = 0.72 \pm 0.19 is obtained
for the power-law coefficient describing the density dependence of the
potential part in the parametrization of the symmetry energy. It represents a
new and more stringent constraint for the regime of supra-saturation density
and confirms, with a considerably smaller uncertainty, the moderately soft to
linear density dependence deduced from the earlier FOPI-LAND data. The
densities probed are shown to reach beyond twice saturation.
