Combining MinXSS and RHESSI X-ray Spectra for a Comprehensive View of the Temperature Distribution in Solar Flares
Abstract
Solar flares explosively release large amounts of magnetic energy, a significant fraction of which goes into transient heating of coronal plasma to temperatures up to tens of MK. Decades of observations have shown that flares are multi-thermal, exhibiting broad temperature distributions or "differential emission measures" (DEMs). Recent studies suggest that the hottest parts of the DEM evolve differently from, and are heated by a different physical mechanism than, the DEM bulk. For example, the peak temperature of the hot, likely in-situ-heated plasma observed by RHESSI correlates significantly differently with flare intensity (GOES class) than does the cooler, likely chromospherically evaporated plasma observed by GOES XRS and/or Yohkoh BCS. These studies, however, used discrete (iso-/bi-) thermal approximations, in part because temperature determinations by the ratio of 2-channel GOES photometer data or selected BCS lines necessitated such methods. Consequently, the exact DEM profile, its evolution, and how these correlate with other flare parameters, remain poorly known. The MinXSS CubeSat deployed from the ISS in May 2016, and since June has observed (at least) 7 M-class and over 40 C-class flares. MinXSS's X123 spectrometer measures solar soft X-rays (SXRs) from 0.5 to 30 keV with 0.15 keV FWHM resolution; this energy range entirely covers both GOES XRS passbands, and overlaps with and extends the RHESSI observing range with 5x better resolution. It includes the thermal continuum emission from plasmas with temperatures down to 2 MK, as well as a number of mid- and high-temperature spectral lines from various low- and high-FIP ion species, providing critical temperature diagnostics for studying flare DEMs with far greater fidelity than is possible with GOES, or using RHESSI alone. We present spectral analyses of several flares observed simultaneously by MinXSS and RHESSI. We compare and contrast the observations of each instrument separately, and present the results of a joint-instrument DEM analysis that forward-fits a parametrized DEM model - including variable elemental abundances - to the combined spectra of both instruments simultaneously. We discuss the DEM evolution and its correlation with other flare parameters, and discuss the implications for plasma heating in solar flares.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMSH13A2288C
- Keywords:
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- 2479 Solar radiation and cosmic ray effects;
- IONOSPHEREDE: 7509 Corona;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMYDE: 7538 Solar irradiance;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMYDE: 7554 X-rays;
- gamma rays;
- and neutrinos;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY