Hard X-Ray Imaging of Individual Spectral Components in Solar Flares

TL;DR

This paper introduces a new imaging technique that combines high-resolution X-ray imaging and spectroscopy to visualize individual spectral components in solar flares, enabling better understanding of thermal sources and their spatial relationships.

Contribution

The authors develop a computationally efficient method to isolate and image specific thermal sources in solar flares using combined spectral and imaging data from RHESSI.

Findings

Successfully isolated super-hot and cooler thermal sources in a major solar flare

Super-hot source is located farther from footpoints and is more elongated

Technique enhances understanding of thermal plasma heating mechanisms

Abstract

We present a new analytical technique, combining Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) high-resolution imaging and spectroscopic observations, to visualize solar flare emission as a function of spectral component (e.g., isothermal temperature) rather than energy. This computationally inexpensive technique is applicable to all spatially-invariant spectral forms and is useful for visualizing spectroscopically-determined individual sources and placing them in context, e.g., comparing multiple isothermal sources with nonthermal emission locations. For example, while extreme ultraviolet images can usually be closely identified with narrow temperature ranges, due to the emission being primarily from spectral lines of specific ion species, X-ray images are dominated by continuum emission and therefore have a broad temperature response, making it difficult to identify sources of specific temperatures regardless of the energy band of the image. We combine RHESSI calibrated X-ray visibilities with spatially-integrated spectral models including multiple isothermal components to effectively isolate the individual thermal sources from the combined emission and image them separately. We apply this technique to the 2002 July 23 X4.8 event studied in prior works, and image for the first time the super-hot and cooler thermal sources independently. The super-hot source is farther from the footpoints and more elongated throughout the impulsive phase, consistent with an in situ heating mechanism for the super-hot plasma.