Hard Xrays associated with CMEs

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Hard X-rays associated with CMEs

• H.S. Hudson, UCB SPRC

Y10, Jan. 24, 2001
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Yohkoh observational goals, as of 1991

• White-light flares correlated with hard X-rays
  (Mathews poster)
• Direct coronal observations of Type II bursts
  (Shibata presentation)
• Coronal non-thermal sources (this talk)

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Hard X-rays associated with CMEs

• Prototype event of March 30, 1969 (Frost and
  Dennis, 1971 Enome et al., 1971)
• Metric-decimetric radio observations from an
  X-ray point of view
• The Masuda event
• The event of April 18, 2001

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Background

• Hard X-rays come from bremsstrahlung in the
  non-thermal tail of the electron distribution
  function
• Limb occultation allows us to see hard X-rays
  from the middle corona
• With hard X-ray imaging, it is sometimes possible
  to see disk events

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A very few other related events

• The Hinotori event of May 13, 1981, notable
  because seen on disk via hard X-ray imaging
• See Cliver et al., ApJ 305, 920 (1986) for a
  general review

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Masudas event

• Masuda et al. found a non-thermal source located
  above the soft X-ray loop tops in a limb flare
• This source suggests electron trapping in an
  unusual mirror geometry favoring magnetic
  reconnection
• Occurrence in the impulsive phase

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Event of April 18, 2001

• Distinguished by non-Neupert behavior
• Highly occulted source (100-200 Mm altitude)
• Overlay with microwave source
• Motion at about 1,000 km/s outward
• Movies

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How many electrons?

• Thin-target peak 1036 electrons gt 20 keV
• Source density 4 x 109 cm-3
• Tail fraction gt 0.2 gt 20 keV
• Electrons dominate gas pressure and energy

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Conclusions

• Coronal hard X-ray sources occur within the
  volumes forming CMEs
• Non-thermal electrons may be dynamically
  important in some cases
• The observational situation is far from
  satisfactory, but HESSI should help