Energetic-Particle Abundances in Impulsive Solar Flare Events

Abstract

We report on the abundances of energetic particles from impulsive solar flares, including those from a survey of 228 3 He-rich events, with 3 He/ 4 He > 0.1, observed by the ISEE 3 spacecraft from 1978 August through 1991 April. The rate of occurrence of these events corresponds to ~1000 events yr -1 on the solar disk at solar maximum. Thus the resonant plasma processes that enhance 3 He and heavy elements are a common occurrence in impulsive solar flares. To supply the observed fluence of 3 He in large events, the acceleration must be highly efficient and the source region must be relatively deep in the atmosphere at a density of more than 10 10 atoms cm" 3 . 3 He/ 4 He may decrease in very large impulsive events because of depletion of 3 He in the source region.The event-to-event variations in 3 He/ 4 He, H/ 4 He, e/p, and Fe/C are uncorrected in our event sample. Abundances of the elements show a pattern in which, relative to coronal composition, 4 He, C, N, and O have normal abundance ratios, while Ne, Mg, and Si are enhanced by a factor ~2.5 and Fe by a factor ~7 . This pattern suggests that elements are accelerated from a region of the corona with an electron temperature of ~3 -5 MK, where elements in the first group are fully ionized (Q/A = 0.5), those in the second group have two orbital electrons (Q/A ~ 0.43), and Fe has Q/A ~ 0.28. Ions with the same gyrofrequency absorb waves of that frequency and are similarly accelerated and enhanced. Further stripping may occur after acceleration as the ions begin to interact with the streaming electrons that generated the plasma waves.

New observations of heavy‐ion‐rich solar particle events from ACE

“…Heavy elements (Ne -Fe) and 3He are significantly enhanced over coronal values in impulsive events but not in gradual events (Reames et al• 1994), and the mean charge states of the heavy ions are higher in impulsive events than in gradual events (Luhn et al 1987). …”

High Energy Astroparticle Physics at Ooty and the GRAPES-3 Experiment

“…The composition of the energetic ions in the impulsive events displays a very significant enhancement of the heavier nuclei as compared to the coronal abundances by an order of magnitude or more. In the case of helium, the ratio 3 He/ 4 He, is observed to be ~ 1 as compared to the coronal value of ~ 10 -3 [35][36][37][38].…”

Terrestrial aurora: astrophysical laboratory for anomalous abundances in stellar systems

“…Primordial nucleo-synthesis and galactic evolution confines the coronal ratio of the He isotopes 3 He/ 4 He to several times 10 −4 ; this ratio is enhanced in impulsive flares by a factor of 10 3 -10 5 (Hsieh and Simpson, 1970;Mason et al, 2000), while heavier ions (mainly Fe with higher charge state of 18-22 vs. 10-14 in solar wind) are enhanced by a factor up to 10 with respect to O (Mason et al, 1986;Reames et al, 1994). ACE satellite also observed impulsive events with 3 He and Fe of similar energy distributions, which differ from other ion spectra, indicating a commonality in their acceleration mechanisms.…”