First Results of Joint OVSA and HESSI Observations

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First Results of Joint OVSA and HESSI Observations
Dale E. Gary1, Edward J. Schmahl2 1New Jersey
Institute of Technology 2University of Maryland
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Joint Observations of Five Solar Bursts

• We present 5 solar bursts observed jointly in
  microwaves with Owens Valley Solar Array (OVSA)
  and in hard X-rays with the Ramaty Hi-Energy
  Solar Spectroscopic Imager (RHESSI).
• A spectral comparison of the 5 bursts in both
  microwaves and hard X-rays is presented in the
  accompanying figures.
• We examine one event, 2002 Mar 18, in more
  detail, both spectrally and spatially.

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2002 Feb 20
4
2002 Feb 23
5
2002 Feb 25
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2002 Mar 18
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2002 Mar 29
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• Ask to see this animation of the RHESSI spectrum
  for the 2002 Mar 18 burst on a laptop computer!

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OVSA Radio Spectra (2002 Mar 18)
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Spectral Results (2002 Mar 18)

• Thermal part of X-ray emission rises and falls
  relatively smoothly.
• gt 25 keV X-rays vary in several acceleration
  episodes, apparently independently of the thermal
  emission.
• In first acceleration episode, gt 25 keV X-rays
  progressively harden (from d 7.5-4.7) .
• At the same time, the OVSA spectral peak
  increases monotonically.
• Spectral peak can increase due to three effects
  increase in NL, increase in B, or decrease in d
  (Dulk 1985).

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RHESSI Images (2002 Mar 18)
12-25 keV
25-50 keV
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BBSO Context (2002 Mar 18)
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Spatial Results (2002 Mar 18)

• Thermal part of X-ray emission fills a small
  loop, about 20 long.
• gt 25 keV X-rays come from a smaller source at one
  end of the loop.
• OVSA source is compact, and all frequencies
  appear to be nearly cospatial.

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Conclusions

• After only four months OVSA and RHESSI have
  jointly observed at least a dozen events.
• We have presented some preliminary comparisons of
  5 events.
• The outstanding spectral resolution of RHESSI
  allows detailed comparison with OVSA microwave
  spectra.
• The thermal components seen by RHESSI are only
  weakly detected with OVSA.
• Comparisons of spatial source structure have not
  yet been done, but will be done as soon as
  possible.