Temporal - Spectral Analysis of Hard X-ray Flares

Solar hard X-ray (HXR) spectra can reveal key aspects of flare energization, since this part of the electromagnetic spectrum is dominated by emission from flare-heated plasma and flare-accelerated electrons. HXR spectra are typically modeled with thermal and nonthermal bremsstrahlung components, which dominate the spectrum at low and high HXR energies, respectively. This type of spectral fitting often provides a good fit, but it can sometimes be degenerate in terms of how many thermal components are present, the details of the nonthermal emission, and in particular, at which energy the nonthermal component begins to become dominant. It is well established that thermal and nonthermal components usually have different temporal characteristics, with nonthermal components changing more rapidly, and peaking earlier, than thermal components do. Those different temporal characteristics could be used to distinguish thermal and nonthermal components.

This poster presents an analysis that uses the observed temporal characteristics of thermal and nonthermal HXR emission to perform spectroscopy separately on each component. HXR time evolution in many energy bins is compared to template time evolution from thermal and nonthermal flaring plasma (which can be determined empirically from a given flare) to produce HXR count spectra separately for thermal and nonthermal components. Spectroscopy is then performed separately on these different components, reducing the degeneracy in the spectral fits.

While the poster concentrates on demonstrating the feasibility of the method, future application of the method is expected to augment what can be learned from HXR spectroscopy. For example, the method could result in more thorough HXR thermal diagnostics, a clear indicator of whether nonthermal emission is present at all, and, when nonthermal emission is present, a better determination of the low energy cutoff of the emitting electron distribution.