Magnetic Topology of quiet-Sun Ellerman bombs and associated Ultraviolet brightenings

TL;DR

This study investigates the magnetic topologies associated with quiet-Sun Ellerman bombs and UV brightenings, revealing how magnetic reconnection at null points facilitates energy transfer between the lower atmosphere and transition region.

Contribution

It identifies distinct magnetic configurations, including complex fan-spine topologies with null points, linking QSEBs and UV brightenings, and quantifies the energy released during these events.

Findings

Four magnetic configurations associated with QSEBs and UV brightenings.

UV brightenings occur near 3D null points in fan-spine topologies.

Energy released during QSEBs ranges from 10^23 to 10^24 ergs.

Abstract

Quiet-Sun Ellerman bombs (QSEBs) are small-scale magnetic reconnection events in the lower atmosphere of the quiet Sun. Recent work has shown that a small percentage of them can occur co-spatially and co-temporally to ultraviolet (UV) brightenings in the transition region. We aim to understand how the magnetic topologies associated with closely occurring QSEBs and UV brightenings can facilitate energy transport and connect these events. We used high-resolution H-beta observations from the Swedish 1-m Solar Telescope (SST) and detected QSEBs using k-means clustering. We obtained the magnetic field topology from potential field extrapolations using spectro-polarimetric data in the photospheric Fe I 6173 A line. To detect UV brightenings, we used coordinated and co-aligned data from the Interface Region Imaging Spectrograph (IRIS) and imposed a threshold of 5 sigma above the median background on the (IRIS) 1400 A slit-jaw image channel. We identify four distinct magnetic configurations that associate QSEBs with UV brightenings, including a simple dipole configuration and more complex fan-spine topologies with a three-dimensional (3D) magnetic null point. In the fan-spine topology, the UV brightenings occur near the 3D null point, while QSEBs can be found close to the footpoints of the outer spine, the inner spine, and the fan surface. We find that the height of the 3D null varies between 0.2 Mm to 2.6 Mm, depending on the magnetic field strength in the region. We note that some QSEBs and UV brightenings, though occurring close to each other, are not topologically connected with the same reconnection process. We find that the energy released during QSEBs falls in the range of 10^23 to 10^24 ergs. This study shows that magnetic connectivity and topological features, like 3D null points, are crucial in linking QSEBs in the lower atmosphere with UV brightenings in the transition region.