Forward Modeling Transient Brightenings and Microflares around an Active Region Observed with Hi-C

TL;DR

This study uses high-resolution EUV observations from Hi-C to analyze small-scale brightenings around active regions, revealing frequent, strand-like microflares likely caused by bursty reconnection, advancing understanding of coronal heating.

Contribution

It demonstrates that microflares are more frequent and involve smaller strands than previously observed, supporting bursty reconnection as a key energy release mechanism.

Findings

Microflares occur much more frequently than expected.

Events are likely made from strands about 100 km wide.

Multiple heating events per strand suggest impulsive heating processes.

Abstract

Small scale flare-like brightenings around active regions are among the smallest and most fundamental of energetic transient events in the corona, providing a testbed for models of heating and active region dynamics. In a previous study, we modeled a large collection of these microflares observed with Hinode/XRT using EBTEL and found that they required multiple heating events, but could not distinguish between multiple heating events on a single strand, or multiple strands each experiencing a single heating event. We present here a similar study, but with EUV data of Active Region 11520 from the High Resolution Coronal Imager (Hi-C) sounding rocket. Hi- C provides an order of magnitude improvement to the spatial resolution of XRT, and a cooler temperature sensitivity, which combine to provide significant improvements to our ability to detect and model microflare activity around active regions. We have found that at the spatial resolution of Hi-C (approximately 0.3 arcseconds), the events occur much more frequently than expected (57 events detected, only 1 or 2 expected), and are most likely made from strands of order 100 km wide, each of which is impulsively heated with multiple heating events. These findings tend to support bursty reconnection as the cause of the energy release responsible for the brightenings.