Soft X-Ray Spectral Diagnostics of Multithermal Plasma in Solar Flares with Chandrayaan-2 XSM

Abstract

Spectroscopic observations in X-ray wavelengths provide excellent diagnostics of the temperature distribution in solar flare plasma. The Solar X-ray Monitor (XSM) on board the Chandrayaan-2 mission provides broadband disk-integrated soft X-ray solar spectral measurements in the energy range of 1–15 keV with high spectral resolution and time cadence. In this study, we analyze the X-ray spectra of three representative GOES C-class flares obtained with the XSM to investigate the evolution of various plasma parameters during the course of the flares. Using the soft X-ray spectra consisting of the continuum and well-resolved line complexes of major elements like Mg, Si, and Fe, we investigate the validity of the isothermal and multithermal assumptions on the high-temperature components of the flaring plasma. We show that the soft X-ray spectra during the impulsive phase of the high-intensity flares are inconsistent with isothermal models and are best fitted with double-peaked differential emission measure distributions where the temperature of the hotter component rises faster than that of the cooler component. The two distinct temperature components observed in differential emission measure models during the impulsive phase of the flares suggest the presence of the directly heated plasma in the corona and evaporated plasma from the chromospheric footpoints. We also find that the abundances of low first ionization potential elements Mg, Si, and Fe reduce from near coronal to near photospheric values during the rising phase of the flare and recover back to coronal values during the decay phase, which is also consistent with the chromospheric evaporation scenario.

Multiwavelength Observations of a B-class Flare Using XSM, AIA, and XRT

“…We found that during the peak phase of the flare, the modeled spectrum (blue curve) was not able to explain the higher-energy Fe line complex (at 6-7 keV). Similar results were found for the bigger C-class flare as reported by Mithun et al (2022) and the 6.5 keV feature is not being fitted properly. This indicates that a single temperature component for the flaring plasma in the 2T model is insufficient to explain the observed spectrum at lower and higher energies.…”

“…XSM also observed multiple flaring in ARs and these data have been used to study the time evolution of the plasma parameters during A-class, B-class, and C-class flares (Mondal et al 2021;Mithun et al 2022;Nama et al 2023). These studies show that during the impulsive phase, the temperature of the flaring plasma reaches a few MK, whereas elemental abundances show a sharp transition from coronal to close to photospheric values.…”

Evolution of elemental abundances in hot active region cores from Chandrayaan-2 XSM observations

“…When ARs were present on-disk, XSM recorded hundreds of small flares of different classes. Elemental abundance variations during these small flares were found, for the first time, to initially drop to photospheric values, then rapidly return to coronal values, as described by Mondal et al (2021), Mithun et al (2022), andLakshitha et al (2022). In this paper, we analyze the temporal evolution of active regions outside of flaring activity and for this we have chosen to study three isolated active regions: AR12749, AR12758, and AR12759.…”

Evolution of Elemental Abundances in Hot Active Region Cores from Chandrayaan-2 XSM Observations

“…When ARs were present on-disk, XSM recorded hundreds of small flares of different classes. Elemental abundance variations during these small flares were found, for the first time, to initially drop toward photospheric values, then rapidly return to coronal values, as described by Mondal et al (2021), Mithun et al (2022), andNama et al (2023). In this paper, we analyze the temporal evolution of ARs outside of flaring activity, and for this, we have chosen to study three isolated ARs: AR 12749, AR 12758, and AR 12759.…”