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Energy Release and Particle Acceleration in Flares: Summary and Future Prospects View all abstracts by submitter

Amir Caspi   Submitted: 2011-10-28 12:23

RHESSI measurements relevant to the fundamental processes of energy releaseand particle acceleration in flares are summarized. RHESSI's precisemeasurements of hard X-ray continuum spectra enable model-independentdeconvolution to obtain the parent electron spectrum. Taking into account theeffects of albedo, these show that the low energy cut-off to the electronpower-law spectrum is typically below tens of keV, confirming that theaccelerated electrons contain a large fraction of the energy released inflares. RHESSI has detected a high coronal hard X-ray source that is filledwith accelerated electrons whose energy density is comparable to themagnetic-field energy density. This suggests an efficient conversion of energy,previously stored in the magnetic field, into the bulk acceleration ofelectrons. A new, collisionless (Hall) magnetic reconnection process has beenidentified through theory and simulations, and directly observed in space andin the laboratory; it should occur in the solar corona as well, with areconnection rate fast enough for the energy release in flares. Thereconnection process could result in the formation of multiple elongatedmagnetic islands, that then collapse to bulk-accelerate the electrons, rapidlyenough to produce the observed hard X-ray emissions. RHESSI's pioneering{gamma}-ray line imaging of energetic ions, revealing footpoints straddling aflare loop arcade, has provided strong evidence that ion acceleration is alsorelated to magnetic reconnection. Flare particle acceleration is shown to havea close relationship to impulsive Solar Energetic Particle (SEP) eventsobserved in the interplanetary medium, and also to both fast coronal massejections and gradual SEP events.

Authors: R.P. Lin
Projects: GONG,Hinode/EIS,Hinode/SOT,Hinode/XRT,Nobeyama Radioheliograph,Owens Valley Solar Array,RHESSI,SDO-AIA,SDO-HMI,SDO-EVE,SoHO-EIT,SoHO-MDI,SoHO-CDS,SoHO-LASCO,SoHO-SUMER,STEREO,TRACE

Publication Status: Published -- Lin, R. P. 2011, Space Sci. Rev., 159, 421; DOI 10.1007/s11214-011-9801-0
Last Modified: 2011-11-17 14:21
Go to main E-Print page  Frequency drifts of 3-min oscillations in microwave and EUV emission above sunspots  Deducing Electron Properties From Hard X-Ray Observations  Edit Entry  Download Preprint  Delete Entry 

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