Unusual Filaments Inside the Umbra

TL;DR

This study investigates unusual filamentary structures in a sunspot umbra, revealing their unique morphology, dynamic behavior, and potential link to flare activity, using multi-instrument solar observations.

Contribution

It provides the first detailed analysis of these atypical umbral filaments, combining photospheric, chromospheric, and coronal data to understand their nature and evolution.

Findings

Horizontal inverse Evershed flow along filaments

Brightenings and energy dissipation in chromosphere

Coronal loops ending in umbral filaments

Abstract

We analyze several unusual filamentary structures, which appeared in the umbra of one of the sunspots in AR 11302. They do not resemble typical light bridges, neither in morphology, nor in evolution. We analyze data from SDO/HMI to investigate their temporal evolution, Hinode/SP for photospheric inversions, IBIS for chromospheric imaging, and SDO/AIA for the overlying corona. Photospheric inversions reveal a horizontal, inverse Evershed flow along these structures, which we call umbral filaments. Chromospheric images show brightenings and energy dissipation, while coronal images indicate that bright coronal loops seem to end in these umbral filaments. These rapidly evolving features do not seem to be common, and are possibly related to the high flare-productivity of the active region. Their analysis could help to understand the complex evolution of active regions.