The Acceleration and Release of Near-Relativistic Electrons by CMEs

Details The Acceleration and Release of Near-Relativistic Electrons by CMEs The Acceleration and Release of Near-Relativistic Electrons by CMEs

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsh31c..07s&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #SH31C-07

Physics

7513 Coronal Mass Ejections, 7514 Energetic Particles (2114)

Scientific paper

We have examined transient coronal activity observed by SOHO/LASCO around the solar release time of beams of near-relativistic electrons ( ~40-300 keV) observed by ACE/EPAM at 1 AU. The majority of west hemisphere CMEs seen by LASCO are not associated with near-relativistic electron beams seen by ACE/EPAM. However, when they are present, strong antisunward beams of electrons may be used to infer reliably the actual solar release time of impulsive events as the intensity is not distorted by the effects of scattering. 52 electron beams were observed between the launch of ACE in 1997 through September 2000 at times when there were LASCO observations. Of these, there were 47 observations of an associated coronal transient, of which 33 were ``classical'' CMEs, as distinct from blobs and jets; it was possible with all events to extrapolate the radius-time plot back to a nominal 1 solar radius to obtain a CME launch time. All but two of the CMEs were seen in projection off the west solar limb. For 37 events there was an associated GOES soft X-ray event, mainly from western active regions. The electron injection time was typically delayed by around 20 minutes from the CME launch. Half the CMEs had projected speeds >600 km/s. There was some anticorrelation between the electron delay time and the CME speed because the altitude of the majority of the CMEs at the electron release time was between 1.5 and 3.5 solar radii. All events had decametric type III emission observed by WIND/WAVES, which were consistent with coronal electron beams having exciter energies of ~3 keV. We suggest that the bulk of the near-relativistic electrons seen by ACE/EPAM are accelerated by the shock driven by the coronal transient and are released at an altitude around 2-3 solar radii. Prompt near-relativistic electrons associated with the chromospheric emissions are not seen by ACE, so we presume that most do not escape into the high corona.

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