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Constraints on Particle Acceleration in Interplanetary Space: Insights from Energetic Particle Events

This study investigates particle acceleration mechanisms in interplanetary space using interplanetary observations. Key findings reveal that 3He-rich solar energetic particle (SEP) events, occurring thousands of times per year, are primarily composed of electrons and heavy nuclei accelerated during large solar flares and coronal mass ejections. With energies reaching tens of MeV for ions and hundreds of MeV for electrons, the research explores the energetic particle spectra and their correlation with solar phenomena, such as Type III radio bursts and impulsive soft X-ray bursts, providing new insights into solar particle acceleration.

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Constraints on Particle Acceleration in Interplanetary Space: Insights from Energetic Particle Events

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  1. Constraints on Particle Acceleration from Interplanetary ObservationsR. P. Lin together with L. Wang, S. Krucker at UC Berkeley, G Mason at U. Maryland, and R. Mewaldt at Caltech

  2. Krucker and Lin 2002

  3. Electron -3He-rich SEP events • - ~1000s/year at solar maximum • - dominated by: • - electrons of ~0.1 (!) to ~100 keV energy • - 3He ~10s keV/nuc to ~MeV/nuc • x10-x104 (!) enhancements • - heavy nuclei: Fe, Mg, Si, S enhancements • - high charge states • - associated with: • - small flares/coronal microflares • - Type III radio bursts • - Impulsive soft X-ray bursts (so also called Impulsive SEP events)

  4. L=v(t-to) or L/v=t-to ~0.05 MeV/nuc - 1/vof3He (Mason & Mazur) ~1.5 MeV/nuc - 1/v for Electrons / Electrons 0.14–13 keV Electrons 20 – 350 keV Ions ~ 0.5 – 1 MeV

  5. Electron spectrum at 1AU Typical electron spectrum can be fitted with broken power law: Break around: 30-100 keV Steeper at higher energies Oakley, Krucker, & Lin 2004

  6. Comparing spectra PHOTON SPECTRA: Power law fit to HXR spectra averaged over peak ELECTRON SPECTRA: Power law fit to peak flux • Assuming power spectra: • THIN: d = g – 1 • THICK: d = g + 1 • RESULTS: • correlation seen • values are between

  7. Wang, Krucker, Lin, & Gosling, 2005

  8. Wang, Krucker, Lin, & Gosling 2005

  9. Wang, Krucker, Lin, & Gosling 2005

  10. Wang, Krucker, Lin, & Gosling 2005

  11. The Sun is the most energetic particle accelerator in the solar system:- Ions up to ~ 10s of GeV - Electrons up to ~100s of MeVAcceleration to these energies occurs in transient energy releases, in two (!) processes:- Large Solar Flares, in the lower corona - Fast Coronal Mass Ejections (CMEs), in the inner heliosphere, ~2-40 solar radii

  12. X-Class Flare of 2002 July 23 • 00:27:20–00:43:20 UT • GOES X4.8 • Location: S13E72 (Lin et al. 2003)

  13. RHESSIGamma-Ray Flares Ramaty High Energy Solar Spectroscopic Imager (RHESSI)

  14. Mewaldt et al 2005

  15. (Mewaldt et al. 2005)

  16. e+ - e- n-capture bremsstrahlung narrow lines broad lines Oct. 28, 2003, RHESSI solar count spectrum from 11:06:20 – 11:10:04 (Smith et al. 2004, Share et al. 2004)

  17. Murphy 2004

  18. Energetic Proton Power-law Exponents28 Oct 03 2 Nov 03S16E08 S15W56γ-ray lines Energy range γ-ray (SEP) γ-ray (SEP)Ne/C+O2-20 MeV 2.0-3.2 (1.3)1.6-3.2 (1.7) e+/C+O 10-50 MeV2.2-3.3 (2.0)2.3-3.3 (2.8)n-capt/C+O10-100 MeV2.8-3.8 (2.5) 2.8-3.8 (3.0)

  19. GOES soft X-rays RHESSI 2.2 MeV line RHESSI 100-200 keV RHESSI hard X-rays WIND/WAVES radio WIND/3DP electrons

  20. 20 Jan 05 Flare RHESSI Gamma-ray Spectrum - 20 Jan 05 Flare

  21. In the Jan 20 Event the high energy particle-intensities reach Earth just minutes after the x-rays from the flare

  22. X-ray imaging RHESSI X-ray imaging during HXR peak: Two ribbon flare with HXR footpoints (contours) with thermal loop (image)

  23. Timing Red line (06:48UT): Solar release time derived from onsets at 1 AU assuming first arriving particles travel with the speed of light along L=1.2 AU LASCO (06:54UT): Around ~3 solar radii; lines show height assuming a constant velocity. For v=2500km/s, CME could be at ~1.5 solar radius at particle release time. Red crosses: Rising SXR loops (top of SXI emission) 2.2 MeV peaks at 06:47:30UT HXRs peak at 06:45:00UT

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