Temperature of the Source Plasma for Impulsive Solar Energetic Particles

Most cosmic ray particles observed derive from the explosions of massive stars. Massive stars from slightly above about 10 M explode as supernovae via a mechanism which we do not know yet: two not mutually exclusive main ideas are an explosion driven by neutrinos, or the magneto-rotational mechanism, in which the magnetic field acts like a conveyorbelt to transport energy outwards for an explosion. Massive stars above about 25 M , depending on their heavy element abundance, commonly produce stellar black holes in

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“…We note that this is quite different from the A, Q selection in Solar energetic ions (Reames et al 2015).…”

Section: Ionization Ratecontrasting

confidence: 55%

Supernova explosions of massive stars and cosmic rays

Biermann

Tjus

Caramete

et al. 2018

Advances in Space Research

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“…Note that event periods without significant enhancement or depression in abundances provide no information on A/Q or source temperature, and must be omitted. have included a 15% error, convolved with the statistical error, to obtain the weighting for each point in the fits (30% was the best value used for the impulsive SEP events as discussed by Reames, Cliver and Kahler 2015). These 15% errors are much smaller than the overall variations and might come from spatial variations in the source with better averaging in gradual SEP events that in impulsive.…”

Section: Discussionmentioning

confidence: 99%

Temperature of the Source Plasma in Gradual Solar Energetic Particle Events

Reames

2016

Sol Phys

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104

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Scattering, during interplanetary transport of particles during large, "gradual" solar energetic-particle (SEP) events, can cause element abundance enhancements or suppressions that depend upon the mass-to-charge ratio A/Q of the ions as an increasing function early in events and a decreasing function of the residual scattered ions later. Since the Q values for the ions depends upon the source plasma temperature T, best fits of the power-law dependence of enhancements vs.A/Q can determine T. These fits provide a fundamentally new method to determine the most probable value of T for these events in the energy region 3-10 MeV amu -1 . Complicated variations in the grouping of element enhancements or suppressions match similar variations in A/Q at the bestfit temperature. We find that fits to the times of increasing and decreasing powers give similar values of T, in the range of 0.8-1.6 MK for 69% of events, consistent with the acceleration of ambient coronal plasma by shock waves driven out from the Sun by coronal mass ejections (CMEs). However, 24% of the SEP events studied showed plasma of 2.5-3.2 MK, typical of that previously determined for the smaller impulsive SEP events; these particles may be reaccelerated preferentially by quasi-perpendicular shock waves that require a high injection threshold that the impulsive-event ions exceed or simply by high intensities of impulsive suprathermal ions at the shock. The source-temperature distribution of ten higher-energy ground-level events (GLEs) in the sample is similar to that of the other gradual events, at least for SEPs in the energy-range of 3-10 MeV amu -1 . Some events show evidence that a portion of the ions may have been further stripped of electrons prior to shock acceleration; such events are smaller and tend to cluster late in the solar cycle.

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“…The best fit at 3.2 MK (red circles), seen in the lower panel of Figure 6, is somewhat distorted by the high value of Ne/O. High Ne/O is common in impulsive SEP events, but these events may also have high non-thermal variations of ~30% in other species, as well (Reames, Cliver, and Kahler 2015;Reames 2016b). Decreasing the temperature from 3.2 to 1.6 MK (blue filled circles), increases A/Q for N, and O, but not for He, and C, and increases A/Q for Si through Fe but not for Ne and Mg; this causes severe distortion.…”

Section: Impulsive Sep Eventsmentioning

confidence: 97%

Abundances, Ionization States, Temperatures, and FIP in Solar Energetic Particles

Reames

2018

Space Sci Rev

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The relative abundances of chemical elements and isotopes have been our most effective tool in identifying and understanding the physical processes that control populations of energetic particles. The early surprise in solar energetic particles (SEPs) was 1000-fold enhancements in 3 He/ 4 He from resonant wave-particle interactions in the small "impulsive" SEP events that emit electron beams that produce type III radio bursts. Further studies found enhancements in Fe/O, then extreme enhancements in element abundances that increase with mass-to-charge ratio A/Q, rising by a factor of 1000 from He to Au or Pb arising in magnetic reconnection regions on open field lines in solar jets. In contrast, in the largest SEP events, the "gradual" events, acceleration occurs at shock waves driven out from the Sun by fast, wide coronal mass ejections (CMEs). Averaging many events provides a measure of solar coronal abundances, but A/Q-dependent scattering during transport causes variations with time; thus if Fe scatters less than O, Fe/O is enhanced early and depleted later. To complicate matters, shock waves often reaccelerate impulsive suprathermal ions left over or trapped above active regions that have spawned many impulsive events. Direct measurements of ionization states Q show coronal temperatures of 1-2 MK for most gradual events, but impulsive events often show stripping by matter traversal after acceleration. Direct measurements of Q are difficult and often unavailable. Since both impulsive and gradual SEP events have abundance enhancements that vary as powers of A/Q, we can use abundances to deduce the probable Q-values and the source plasma temperatures during acceleration, ≈3 MK for impulsive SEPs. This new technique also allows multiple spacecraft to measure temperature variations across the face of a shock wave, measurements otherwise unavailable and provides a new understanding of abundance variations in the element He. Comparing coronal abundances from SEPs and from the slow solar wind as a function of the first ionization potential (FIP) of the elements, remaining differences are for the elements C, P, and S. The theory of the fractionation of ions by Alfvén waves shows that C, P, and S are suppressed because of wave resonances during chromospheric transport on closed magnetic loops but not on open magnetic fields that supply the solar wind. Shock waves can accelerate ions B D.V. Reames

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Temperature of the Source Plasma for Impulsive Solar Energetic Particles

Cited by 30 publications

References 74 publications

Supernova explosions of massive stars and cosmic rays

Supernova explosions of massive stars and cosmic rays

Temperature of the Source Plasma in Gradual Solar Energetic Particle Events

Abundances, Ionization States, Temperatures, and FIP in Solar Energetic Particles

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