  Recent observations of the solar photosphere revealed the presence of
elongated filamentary bright structures inside sunspot umbrae, called umbral
filaments (UFs). These features differ in morphology, magnetic configuration,
and evolution from light bridges that are usually observed to intrude in
sunspots. To characterize an UF observed in the umbra of the giant leading
sunspot of active region NOAA 12529, we analyze high-resolution observations
taken in the photosphere with the spectropolarimeter aboard the Hinode
satellite and in the upper chromosphere and transition region with the IRIS
telescope. The results of this analysis definitely rule out the hypothesis that
the UF might be a kind of light bridge. In fact, we find no field-free or
low-field strength region cospatial to the UF. Conversely, we recognize the
presence of a strong horizontal field larger than 2500 G, a significant portion
of the UF with opposite polarity with respect to the surroundings, and
filaments in the upper atmospheric layers corresponding to the UF in the
photosphere. These findings suggest that this structure is the photospheric
manifestation of a flux rope hanging above the sunspot and forming
penumbral-like filaments within the umbra via magneto-convection. This
reinforces a previously proposed scenario.
