Measuring and modeling the rate of separator reconnection between an emerging and existing active region

TL;DR

This study quantifies magnetic reconnection between an emerging and existing active region using high-cadence solar data, revealing that observed brightening rates overestimate actual reconnection flux due to internal relaxation processes.

Contribution

It introduces a method to measure reconnection rates by analyzing brightening loops and accounts for internal magnetic relaxation effects, advancing understanding of solar magnetic reconnection.

Findings

Reconnection rate is overestimated by brightening flux.

Interconnecting region exhibits non-uniform alpha, indicating non-minimum energy state.

Taylor relaxation influences loop brightening after formation.

Abstract

Magnetic reconnection occurs when new flux emerges into the corona and becomes incorporated into the existing coronal field. A new active region (AR) emerging in the vicinity of an existing AR provides a convenient laboratory in which reconnection of this kind can be quantified. We use high time-cadence 171 $\AA$ data from SDO/AIA focused on new/old active region pair 11147/11149, to quantify reconnection. We identify new loops as brightenings within a strip of pixels between the regions. This strategy is premised on the assumption that the energy brightening a loop originates in magnetic reconnection. We catalog 301 loops observed in the 48-hour time period beginning with the emergence of AR 11149. The rate at which these loops appear between the two ARs is used to calculate the reconnection rate between them. We then fit these loops with magnetic field, solving for each loop's field strength, geometry, and twist (via its proxy, coronal $\alpha$). We find the rate of newly-brightened flux overestimates the flux which could be undergoing reconnection. This excess can be explained by our finding that the interconnecting region is not at its lowest energy (constant-$\alpha$) state; the extrapolations exhibit loop-to-loop variation in $\alpha$. This flux overestimate may result from the slow emergence of AR 11149, allowing time for Taylor relaxation internal to the domain of the reconnected flux to bring the $\alpha$ distribution towards a single value which provides another mechanism for brightening loops after they are first created.