First Results of Joint OVSA and HESSI Observations

Dale E. Gary1, Edward J. Schmahl2

1New Jersey Institute of Technology2University of Maryland

Joint Observations of Joint Observations of Five Solar BurstsFive Solar Bursts

• We present 5 solar bursts observed jointly in We present 5 solar bursts observed jointly in microwaves with Owens Valley Solar Array microwaves with Owens Valley Solar Array (OVSA) and in hard X-rays with the Ramaty (OVSA) and in hard X-rays with the Ramaty Hi-Energy Solar Spectroscopic Imager Hi-Energy Solar Spectroscopic Imager (RHESSI).(RHESSI).

• A spectral comparison of the 5 bursts in both A spectral comparison of the 5 bursts in both microwaves and hard X-rays is presented in the microwaves and hard X-rays is presented in the accompanying figures.accompanying figures.

• We examine one event, 2002 Mar 18, in more We examine one event, 2002 Mar 18, in more detail, both spectrally and spatially.detail, both spectrally and spatially.

2002 Feb 202002 Feb 20

2002 Feb 232002 Feb 23

2002 Feb 252002 Feb 25

2002 Mar 182002 Mar 18

2002 Mar 292002 Mar 29

•Ask to see this Ask to see this animation of the animation of the RHESSI spectrum RHESSI spectrum for the 2002 Mar 18 for the 2002 Mar 18 burst on a laptop burst on a laptop computer!computer!

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

Spectral Results (2002 Mar 18)Spectral Results (2002 Mar 18)

• Thermal part of X-ray emission rises and falls relatively Thermal part of X-ray emission rises and falls relatively smoothly.smoothly.

• > 25 keV X-rays vary in several acceleration episodes, > 25 keV X-rays vary in several acceleration episodes, apparently independently of the thermal emission.apparently independently of the thermal emission.

• In first acceleration episode, > 25 keV X-rays In first acceleration episode, > 25 keV X-rays progressively harden (from progressively harden (from ~ 7.5-4.7) . ~ 7.5-4.7) .

• At the same time, the OVSA spectral peak increases At the same time, the OVSA spectral peak increases monotonically.monotonically.

• Spectral peak can increase due to three effects: increase Spectral peak can increase due to three effects: increase in NL, increase in B, or decrease in in NL, increase in B, or decrease in (Dulk 1985).(Dulk 1985).

RHESSI Images (2002 Mar 18)RHESSI Images (2002 Mar 18)

12-25 keV12-25 keV 25-50 keV25-50 keV

BBSO Context (2002 Mar 18)BBSO Context (2002 Mar 18)

Spatial Results (2002 Mar 18)Spatial Results (2002 Mar 18)

• Thermal part of X-ray emission fills a small Thermal part of X-ray emission fills a small loop, about 20” long.loop, about 20” long.

• > 25 keV X-rays come from a smaller source at > 25 keV X-rays come from a smaller source at one end of the loop.one end of the loop.

• OVSA source is compact, and all frequencies OVSA source is compact, and all frequencies appear to be nearly cospatial.appear to be nearly cospatial.

ConclusionsConclusions

• After only four months OVSA and RHESSI have After only four months OVSA and RHESSI have jointly observed at least a dozen events.jointly observed at least a dozen events.

• We have presented some preliminary comparisons of 5 We have presented some preliminary comparisons of 5 events.events.

• The outstanding spectral resolution of RHESSI allows The outstanding spectral resolution of RHESSI allows detailed comparison with OVSA microwave spectra. detailed comparison with OVSA microwave spectra.

• The thermal components seen by RHESSI are only The thermal components seen by RHESSI are only weakly detected with OVSA.weakly detected with OVSA.

• Comparisons of spatial source structure have not yet Comparisons of spatial source structure have not yet been done, but will be done as soon as possible.been done, but will be done as soon as possible.