  Azimuthal distributions of $\eta$ and $\pi^{0}$ mesons emitted at midrapidity
in collisions of 1.9 AGeV $^{58}$Ni+$^{58}$Ni and 2 AGeV $^{40}$Ca+$^{nat}$Ca
are studied as a function of the number of projectile-like spectator nucleons.
The observed anisotropy corresponds to a negative elliptic flow signal for
$\eta$ mesons, indicating a preferred emission perpendicular to the reaction
plane. In contrast, only small azimuthal anisotropies are observed for
$\pi^{0}$ mesons. This may indicate that $\eta$ mesons freeze out earlier from
the fire ball than pions.
