Multimodal differential emission measure in the solar corona

Abstract

The Atmospheric Imaging Assembly (AIA) telescope on board the Solar Dynamics Observatory provides coronal extreme ultraviolet imaging over a broader temperature sensitivity range than the previous generations of instruments (Extreme Ultraviolet Imager; EUVI, EIT, and TRACE). Differential emission measure tomography (DEMT) of the solar corona based on AIA data is presented here for the first time. The main product of DEMT is the three-dimensional distribution of the local differential emission measure (LDEM). While in previous studies, based on EIT or EUVI data, there were three available EUV bands, the present study is based on the four cooler AIA bands (aimed at studying the quiet sun). The AIA filters allow exploration of new parametric LDEM models. Since DEMT is better suited for lower activity periods, we use data from Carrington Rotation 2099, when the Sun was in its most quiescent state during the AIA mission. Also, we validate the parametric LDEM models by using them to perform a bi-dimensional differential emission measure (DEM) analysis on sets of simultaneous AIA images, and comparing results with those obtained using other methods. Our study reveals a ubiquitous bimodal LDEM distribution in the quiet diffuse corona, characterized by two well-defined average centroid temperatures <T01> = ( 1.47 +- 0.05 ) MK and <T02> = ( 2.57 +- 0.05 ) MK. We argue that the nanoflare heating scenario is less likely to explain these results, and that alternative mechanisms, such as wave dissipation, appear better supported by our results.