Electron Acceleration in Solar Flares and in Impulsive Solar Energetic Particle (SEP) Events

Details Electron Acceleration in Solar Flares and in Impulsive Solar Energetic Particle (SEP) Events Electron Acceleration in Solar Flares and in Impulsive Solar Energetic Particle (SEP) Events

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh44a..01l&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SH44A-01

Astronomy and Astrophysics

Astrophysics

[7514] Solar Physics, Astrophysics, And Astronomy / Energetic Particles, [7519] Solar Physics, Astrophysics, And Astronomy / Flares, [7554] Solar Physics, Astrophysics, And Astronomy / X-Rays, Gamma Rays, And Neutrinos

Scientific paper

We investigate the relationship between electron acceleration in solar flares [detected via the electron bremsstrahlung hard x-ray (HXR) emission], and in impulsive solar energetic particle (SEP) events where the escaping electrons are detected in situ near 1 AU. These are most common types of particle acceleration by the Sun, with of order ~104 events occurring per year over the whole Sun during solar maximum. Both types predominantly accelerate electrons (large electron/proton ratios) to ~1-10s of keV energies, typically with double power-law energy spectra with a downward break at a few tens of keV. Impulsive electron events are associated one-to-one with low frequency type III radio bursts, but only ~25% have reported chromospheric flares or detectable HXR emission. Wind 3DP observations show that the electrons often exhibit nearly scatter-free propagation in the interplanetary medium. Relative to the start of the type III burst at the Sun, the injection of the electrons above ~20 keV is found to be often (~80%) delayed by ~10-30 minutes. Where HXR emission is detected, RHESSI imaging often shows coronal sources that suggests magnetic reconnection between open field lines and an underlying loop (interchange reconnection), resulting in a jet. Comparison of the electron energy spectrum derived from the RHESSI hard X-ray measurements with the impulsive event electron spectrum observed by Wind for prompt (not delayed) events, suggests a model where electrons accelerated by this interchange magnetic reconnection on open field lines escape, while electrons on closed field lines are further accelerated as those fields collapse, to produce the spectrum and much larger (by a factor of >100) total number of HXR emitting electrons. Impulsive electron events also appear to be associated with fast (>~580 km/s) narrow CMEs as well as jets, suggesting that in delayed events the escaping >~20 keV electrons (and ions) might be accelerated by the jet/fast narrow CME as it travels outward through the corona.

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