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

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 Ã intensity channel. We isolate the hot Fe XVIII and Fe XXI components of the 94 Ã and 131 Ã 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 Ã 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 Ã 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 Ã 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.

22 pages, 8 figures