Heating Mechanisms for Intermittent Loops in Active Region Cores from AIA/SDO EUV Observations

TL;DR

This study analyzes intensity variations in active region coronal loops, revealing impulsive heating consistent with nanoflare storms and turbulent energy dissipation, supported by observations and a magneto-turbulence model.

Contribution

It demonstrates that impulsive nanoflare-like heating and turbulence-driven energy dissipation explain observed coronal loop variability.

Findings

Loops are impulsively heated with a nanoflare storm signature.

Hot 131 Å signals lead the cooling sequence, indicating impulsive heating.

Energy dissipation aligns with nanoflare statistics and turbulence models.

Abstract

We investigate intensity variations and energy deposition in five coronal loops in active region cores. These were selected for their strong variability in the AIA/SDO 94 {\AA} intensity channel. We isolate the hot Fe XVIII and Fe XXI components of the 94 {\AA} and 131 {\AA} by modeling and subtracting the "warm" contributions to the emission. HMI/SDO data allow us to concentrate on "inter-moss" regions in the loops. The detailed evolution of the inter-moss intensity time series reveals loops that are impulsively heated in a mode compatible with a nanoflare storm, with a spike in the hot 131 {\AA} signals leading and the other five EUV emission channels following in progressive cooling order. A sharp increase in electron temperature tends to follow closely after the hot 131 {\AA} signal confirming the impulsive nature of the process. A cooler process of growing emission measure follows more slowly. The Fourier power spectra of the hot 131 {\AA} signals, when averaged over the five loops, present three scaling regimes with break frequencies at (0.1/min) and (0.7/min). The low frequency regime corresponds to 1/f noise; the intermediate indicates a persistent scaling process and the high frequencies show white noise. Very similar results are found for the energy dissipation in a 2-D "hybrid" shell model of loop magneto-turbulence, based on reduced magnetohydrodynamics, which is compatible with nanoflare statistics. We suggest that such turbulent dissipation is the energy source for our loops.