  The nuclear region of Type 1 AGNs has only been partially resolved so far in
the near-infrared (IR) where we expect to see the dust sublimation region and
the nucleus directly without obscuration. Here we present the near-IR
interferometric observation of the brightest Type 1 AGN NGC4151 at long
baselines of ~250 m using the CHARA Array, reaching structures at hundred
micro-arcsecond scales. The squared visibilities decrease down to as low as
~0.25, definitely showing that the structure is resolved. Furthermore,
combining with the previous visibility measurements at shorter baselines but at
different position angles, we show that the structure is elongated
*perpendicular* to the polar axis of the nucleus, as defined by optical
polarization and a linear radio jet. A thin-ring fit gives a minor/major axis
ratio of ~0.7 at a radius ~0.5 mas (~0.03 pc). This is consistent with the case
where the sublimating dust grains are distributed preferentially in an
equatorial plane in a ring-like geometry, viewed at an inclination angle of ~40
deg. Recent mid-IR interferometric finding of polar-elongated geometry at a pc
scale, together with a larger-scale polar outflow as spectrally resolved by the
HST, would generally suggest a dusty, conical and hollow outflow being launched
presumably in the dust sublimation region. This might potentially lead to a
polar-elongated morphology in the near-IR, as opposed to the results here. We
discuss a possible scenario where an episodic, one-off anisotropic acceleration
formed a polar-fast and equatorially-slow velocity distribution, having lead to
an effectively flaring geometry as we observe.
