Study of High-temperature Emission in Solar Active Regions

The high-temperature (T > 4 MK) emissions of nonflaring active regions are investigated in the context of the coronal heating problem. We study the role of emerging flux, nonpotential magnetic fields, and sunspots in the heating of active-region loops. Using extreme ultraviolet images from the Atmospheric Imaging Assembly on the Solar Dynamic Observatory (SDO), we construct intensity maps in Fe XVIII 94 Å for 48 active regions. We also use the corresponding magnetograms from the Helioseismic and Magnetic Imager on SDO to measure the total magnetic flux. The Fe XVIII 94 Å emission intensity of the brightest loops is found to be correlated with the presence of sunspots and emerging or canceling magnetic flux in the photosphere below. We conclude that sunspots and emerging flux play an important role in the process of coronal heating and the production of high-temperature plasmas. We suggest that energy may be injected into the corona as a result of the dynamics of magnetic fields associated with sunspots and/or emerging flux. These processes may cause the large magnetic disturbances (δB _⊥ ∼ 10 G) needed to produce strong nanoflare-heating events.