# Properties of the Umbral Filament Observed in Active Region NOAA 12529

## TL;DR

This study characterizes an umbral filament in active region NOAA 12529, revealing it as a flux rope structure with strong horizontal fields and penumbral-like filaments, distinct from light bridges, based on high-resolution solar observations.

## Contribution

The paper provides detailed observational evidence that umbral filaments are flux ropes with specific magnetic properties, differentiating them from light bridges and supporting a flux rope formation scenario.

## Key findings

- Umbral filament is a flux rope with strong horizontal magnetic fields.
- No evidence of low-field or field-free regions in the UF.
- UF exhibits penumbral-like filaments in the upper atmosphere.

## Abstract

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.