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The injection of ten electron/3He-rich SEP events  

Linghua Wang   Submitted: 2016-05-28 05:58

We have derived the particle injections at the Sun for ten good electron/3He-rich solar energetic particle (SEP) events, using a 1.2 AU particle path length (suggested by analysis of the velocity dispersion). The inferred solar injections of high-energy (∼10 to 300 keV) electrons and of ∼MeV/nucleon ions (carbon and heavier) start with a delay of 17±3 minutes and 75±14 minutes, respectively, after the injection of low-energy (∼0.4 to 9 keV) electrons. The injection duration (averaged over energy) ranges from ∼200 to 550 minutes for ions, from ∼90 to 160 minutes for low-energy electrons, and from ∼10 to 30 minutes for high-energy electrons. Most of the selected events have no reported Hα flares or GOES SXR bursts, but all have type III radio bursts that typically start after the onset of a low-energy electron injection. All nine events with SOHO/LASCO coverage have a relatively fast (>570km s-1), mostly narrow (≲30°), west-limb coronal mass ejection (CME) that launches near the start of the low-energy electron injection, and reaches an average altitude of ∼1.0 and 4.7 R, respectively, at the start of the high-energy electron injection and of the ion injection. The electron energy spectra show a continuous power law extending across the transition from low to high energies, suggesting that the low-energy electron injection may provide seed electrons for the delayed high-energy electron acceleration. The delayed ion injections and high ionization states may suggest an ion acceleration along the lower altitude flanks, rather than at the nose of the CMEs.

Authors: Linghua Wang, Säm Krucker, Glenn M. Mason, Robert P. Lin, Gang Li
Projects: ACE,SoHO-LASCO,Wind

Publication Status: Astronomy & Astrophysics, Volume 585, 119, 2016
Last Modified: 2016-06-01 10:15
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Simulation of Quiet-Sun Hard X-rays Related to Solar Wind Superhalo Electrons  

Linghua Wang   Submitted: 2016-05-20 07:14

In this paper, we propose that the accelerated electrons in the quiet Sun could collide with the solar atmosphere to emit Hard X-rays (HXRs) via non-thermal bremsstrahlung, while some of these electrons would move upwards and escape into the interplanetary medium, to form a superhalo electron population measured in the solar wind. After considering the electron energy loss due to Coulomb collisions and the ambipolar electrostatic potential, we find that the sources of the superhalo could only occur high in the corona (at a heliocentric altitude ≳ 1.9 R⊙ (the mean radius of the Sun), to remain a power-law shape of electron spectrum as observed by STEREO at 1AU near solar minimum (Wang et al., 2012). The modeled quiet-Sun HXRs related to the superhalo electrons fit well to a power-law spectrum, f ~ ε, with an index γ ≈ 2.0-2.3 (3.3-3.7) at 10-100 keV, for the warm/cold thick-target (thin-target) emissions produced by the downward-traveling (upward-traveling) accelerated electrons. These simulated quiet-Sun spectra are significantly harder than the observed spectra of most solar HXR flares. Assuming that the quiet-Sun sources cover 5% of the solar surface, the modeled thin-target HXRs are more than six orders of magnitude weaker than the RHESSI upper limit for quiet-Sun HXRs (Hannah et al., 2010). Using the thick-target model for the downward-traveling electrons, the RHESSI upper limit restricts the number of downward-traveling electrons to at most ≈3 times the number of escaping electrons. This ratio is fundamentally different from what is observed during solar flares associated with escaping electrons where the fraction of downward-traveling electrons dominates by a factor of 100 to 1000 over the escaping population.

Authors: Wen Wang, Linghua Wang, Säm Krucker, and Iain Hannah
Projects: STEREO

Publication Status: Solar Physics (accepted)
Last Modified: 2016-05-25 12:28
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The injection of ten electron/3He-rich SEP events
Simulation of Quiet-Sun Hard X-rays Related to Solar Wind Superhalo Electrons

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