Global energetics of solar flares. III. Nonthermal energies

Journal Article · Sun Nov 20 04:00:00 EST 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/832/1/27· OSTI ID:22868462

Aschwanden, Markus J. ^[1]; Holman, Gordon ^[2]; O’Flannagain, Aidan ^[3]; Caspi, Amir ^[4]; McTiernan, James M. ^[5]

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1. Lockheed Martin, Solar and Astrophysics Laboratory, Org. A021S, Bldg. 252, 3251 Hanover Street, Palo Alto, CA 94304 (United States)
2. Code 671, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
3. Astrophysics Research Group, School of Physics, Trinity College Dublin, Dublin 2 (Ireland)
4. Planetary Science Directorate, Southwest Research Institute, Boulder, CO 80302 (United States)
5. Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States)

This study entails the third part of a global flare energetics project, in which Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) data of 191 M and X-class flare events from the first 3.5 years of the Solar Dynamics Observatory mission are analyzed. We fit a thermal and a nonthermal component to RHESSI spectra, yielding the temperature of the differential emission measure (DEM) tail, the nonthermal power-law slope and flux, and the thermal/nonthermal cross-over energy e {sub co}. From these parameters, we calculate the total nonthermal energy E {sub nt} in electrons with two different methods: (1) using the observed cross-over energy e {sub co} as low-energy cutoff, and (2) using the low-energy cutoff e {sub wt} predicted by the warm thick-target bremsstrahlung model of Kontar et al. Based on a mean temperature of T {sub e} = 8.6 MK in active regions, we find low-energy cutoff energies of e{sub wt}=6.2±1.6 keV for the warm-target model, which is significantly lower than the cross-over energies e{sub co}=21±6 keV. Comparing with the statistics of magnetically dissipated energies E {sub mag} and thermal energies E {sub th} from the two previous studies, we find the following mean (logarithmic) energy ratios with the warm-target model: E{sub nt}=0.41 E{sub mag}, E{sub th}=0.08 E{sub mag}, and E{sub th}=0.15 E{sub nt}. The total dissipated magnetic energy exceeds the thermal energy in 95% and the nonthermal energy in 71% of the flare events, which confirms that magnetic reconnection processes are sufficient to explain flare energies. The nonthermal energy exceeds the thermal energy in 85% of the events, which largely confirms the warm thick-target model.

• OSTI ID: 22868462
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 832; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BREMSSTRAHLUNG
COMPARATIVE EVALUATIONS
ELECTRONS
EMISSION
GAMMA RADIATION
KEV RANGE
MAGNETIC RECONNECTION
SOLAR FLARES
SPECTRA
STATISTICS
SUN
X RADIATION