Authors: Sherry Chhabra (George Mason University, Fairfax, VA), Jeffrey Reep (Naval Research Laboratory, Washington DC), Harry Warren (Naval Research Laboratory, Washington DC), N.P.S. Mithun (Physical Research Laboratory, Ahmedabad, India)

A majority of radiative losses from the million-degree hot solar corona are in the form of X-rays and EUV radiation which plays a vital role in driving our space weather. The solar soft X-ray (SXR) emission has been used to obtain unique diagnostics of hot plasma, primarily during flares. However, attempts to characterize the SXR non-flaring (background) emission from the Sun have been sparsely performed in the past. The problem is rooted in the lack of spectrally resolved observations over the energy range of 0.5-10 keV, limited sensitivity for low solar flux levels, and limited imaging capabilities. Recently, missions such as MinXSS CubeSat and CORONAS/SPhinX have provided such observations, exhibiting much higher sensitivity for quiescent emission, but they are limited by their short mission-lengths.

The Solar X-ray Monitor (XSM) onboard Chandrayaan-2 observes the solar spectra between 1-15 keV at a spectral resolution of 0.18 keV (at 5.9 keV) with a cadence of 1 s. The mission began in Sept. 2019 and continues to collect solar spectra to date, making it the only high-resolution instrument that has observed an absolute solar minimum and the rise of the solar cycle, thus providing ideal measurements to characterize the background emission. In this study, we use XSM data to constrain active region and quiet Sun temperatures by performing 2-Temperature (2T) fits to the spectra. We examine their variability with time and correlation with proxies for magnetic activity on the Sun, such as F10.7 index and the Mg II index. We also use this method to constrain the evolution of elemental abundances of trace elements as an active region emerges on a quiescent disk. The results are then used to validate the findings from MinXSS, and SPhinX studies mentioned above. This work significantly aids in quantifying the temperature and emission measure variations with solar activity and will be used to improve a solar spectral irradiance model.