HR: 0830h
AN: SP21A-12    [Abstracts]
TI: Measurement and Interpretation of X-ray Visibilities with RHESSI
AU: * Hurford, G J
EM: ghurford@ssl.berkeley.edu
AF: Space Sciences Lab University of California, Berkeley, CA 94720 United States
AU: Schmahl, E J
EM: ed@astro.umd.edu
AF: NASA/GSFC, Greenbelt, MD 20771 United States
AU: Schmahl, E J
EM: ed@astro.umd.edu
AF: University of Maryland, College Park, MD United States
AU: Schwartz, R A
EM: richard.schwartz@gsfc.nasa.gov
AF: NASA/GSFC, Greenbelt, MD 20771 United States
AB: The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) uses a set of 9 rotating modulation collimators to image solar flares at x-ray and gamma-ray energies. RHESSI's imaging information is encoded in the rapid time modulation (~2 to ~500 Hz) of the detected flux. This poster discusses two new approaches to converting this modulated time profile into images. Currently telemetered time-tagged photon data are presented to imaging algorithms as counts in a series of very short time bins. For long integrations, this approach has the disadvantage that the number of time bins can become very large ((>10⁶)) and unwieldy. A new adaptation of folded epoch analysis is described that permits the "stacking" of data over multiple rotations. This can be done despite the distortion of the observed modulated time profile caused by variations in spacecraft pointing. For long integrations, stacking can dramatically compress the observational input to the imaging algorithms with little or no loss of imaging information. A second new development is the conversion of the stacked data into complex visibilities. Visibilities (which represent Fourier components of the source distribution) are determined from the amplitude and phase of short segments of the modulated x-ray waveform. They represent a compact, background-subtracted and fully-calibrated data product that is intermediate between the observed photon stream and images. Visibilities can be converted to images using reconstruction algorithms developed for radio interferometry. This poster also illustrates how RHESSI visibilities can be directly and quantitatively interpreted in terms of x-ray source size, shape and morphology.
DE: 7519 Flares
DE: 7554 X rays, gamma rays, and neutrinos
DE: 7594 Instruments and techniques
SC: Solar Physics Division - AAS [SP]
MN: 2005 Joint Assembly