AAS 204th Meeting, June 2004
Session 54 Solar Flares
SPD Poster, Wednesday, June 2, 2004, 10:00am-7:00pm, Ballroom

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[54.09] RHESSI Observations of Flare Albedo

E. J. Schmahl (University of Maryland and NASA/GSFC), G. J. Hurford (Space Science Lab, UC Berkeley), RHESSI Team

Previous studies have shown that hard X-ray flares often have both small scale (~3-10'') and large-scale (~ 20-5'') components. The large-scale sources have low surface brightness, but total flux on the order of 1/4 to 1/2 of the small-scale sources, so they cannot be directly imaged by the standard methods (Back-projection, Clean, MEM, or Pixons). The earlier studies assumed that the sources were circularly symmetric, which may have been true for the compact sources, but is not generally true for large-scale sources, such as those produced by albedo. However, by using in-phase superposition of RHESSI's rotational modulation profiles over many rotations ("STACKING"), we can obtain high S/N Fourier amplitudes and phases as functions of wavenumber and energy. The amplitudes, plotted as a function of roll angle, can provide evidence for modulation caused by large-scale, asymmetric sources. We can invert the Fourier amplitudes back to the image plane to determine the 2-D spatial scales as functions of time (~1 min) and energy (10-50 keV). We will show these results and discuss their implications regarding the fluxes and shapes of albedo patches.

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