Homologous flaring activity over a sunspot light bridge in an emerging active region

TL;DR

This study reports on long-lasting, homologous flaring activity over a sunspot light bridge, driven by magnetic reconnection involving a low-lying flux rope, with detailed observations of jet dynamics and magnetic field evolution.

Contribution

It provides the first detailed analysis of persistent, homologous flaring over a sunspot light bridge linked to flux rope reconnection in an emerging flux region.

Findings

Flares produced broad, collimated jets reaching 98 Mm height.

Jets rose at approximately 200 km/s and lasted nearly 14 hours.

Flaring activity ceased after the flux rope lost sufficient twist.

Abstract

Sunspot light bridges are known to exhibit a variety of dynamic and persistent phenomena such as surges, small-scale jets etc. in the chromosphere and transition region. While it has generally been proposed that magnetic reconnection is responsible for this small-scale dynamism, persistent flaring activity lasting several hours from the same spatial location on a sunspot light bridge, has rarely been reported. We combine observations from the Atmospheric Imaging Assembly and the Helioseismic Magnetic Imager on board the Solar Dynamics Observatory to investigate homologous flaring activity over a small sunspot light bridge in an emerging flux region. The homologous flares all produced broad, collimated jets, including a B6.4 class flare. The jets rise at a speed of about 200 km/s, reach projected heights of about 98 Mm, and emerge from the same spatial location for nearly 14 hrs, after which they cease completely. A non-linear force free extrapolation of the photospheric magnetic field shows a low-lying flux rope connecting the light bridge to a remote opposite-polarity network. The persistent flares occur as a result of the rapid horizontal motion of the leading sunspot that causes the relatively vertical magnetic fields in the adjacent umbra to reconnect with the low-lying flux rope in the light bridge. Our results indicate that the flaring ceases once the flux rope has lost sufficient twist through repeated reconnections.