Modeling the Daily Variations of the Coronal X-ray Spectral Irradiance with Two Temperatures and Two Emission Measures

TL;DR

This paper presents a two-temperature, two-emission measure model for solar X-ray spectra based on MinXSS-1 data, enabling estimation of the spectrum from F10.7 measurements and validating it with GOES data.

Contribution

The paper introduces the SWM model linking solar X-ray spectral variations to F10.7 flux using a two-temperature approach, improving spectral predictions and understanding of solar activity effects.

Findings

The cooler component is independent of solar activity, with a stable temperature of 1.70 MK.

The warmer component varies between 5 MK and 6 MK, representing active regions.

The model's irradiance estimates closely match GOES XRS-B measurements.

Abstract

The Miniature X-ray Solar Spectrometer (MinXSS-1) CubeSat observed solar X-rays between 0.5 and 10 keV. A two-temperature, two-emission measure model is fit to each daily averaged spectrum. These daily average temperatures and emission measures are plotted against the corresponding daily solar 10.7 cm radio flux (F10.7) value and a linear correlation is found between each that we call the Schwab Woods Mason (SWM) model. The linear trends show that one can estimate the solar spectrum between 0.5 keV and 10 keV based on the F10.7 measurement alone. The cooler temperature component of this model represents the quiescent sun contribution to the spectra and is essentially independent of solar activity, meaning the daily average quiescent sun is accurately described by a single temperature (1.70 MK) regardless of solar intensity and only the emission measure corresponding to this temperature needs to be adjusted for higher or lower solar intensity. The warmer temperature component is shown to represent active region contributions to the spectra and varies between 5 MK to 6 MK. GOES XRS-B data between 1-8 Angstroms is used to validate this model and it is found that the ratio between the SWM model irradiance and the GOES XRS-B irradiance is close to unity on average. MinXSS-1 spectra during quiescent solar conditions have very low counts beyond around 3 keV. The SWM model can generate MinXSS-1 or DAXSS spectra at very high spectral resolution and with extended energy ranges to fill in gaps between measurements and extend predictions back to 1947.