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P.S. Kortenkamp, S.R. Spangler, R.L. Mutel (Univ. of Iowa)
We report evidence of anisotropic angular broadening due to plasma turbulence in the inner solar wind at heliocentric distances of 19 R\odot and 32 R\odot. Such anisotropy indicates that the density irregularities themselves are anisotropic. The observations were made with the Very Long Baseline Array (VLBA) of the National Radio Astronomy Observatory at frequencies of 2.3, 5.0, and 8.4 GHz. The sources 3C273 and 3C279 were observed on September 30, 1999. Angular broadening was detected by comparing two maps for each source and observing frequency. The first incorporated no time averaging of the visibility data and employed self calibration techniques to remove the effect of the solar wind, thus revealing the intrinsic structure. This process is analogous to speckle interferometry in optical astronomy. The second type of map averaged the visibility data over timescales of 3 minutes and did not apply phase self calibration. The second set of maps displayed angular broadening or blurring relative to the first. The analysis involved a deconvolution of the intrinsic source structure from the broadened image to yield the ``point spread function'' of coronal radio scattering. A primary result of our study is that this scattering is anisotropic, and that the axial ratio of the anisotropic broadening is between 1.5 and 3.0 for 3C273 (19 R\odot), and 1.1 and 2.7 for 3C279 (32 R\odot). The position angle of the observed anisotropy is consistent with radial for both sources, indicating that the irregularities are extended along the solar wind magnetic field. This research was supported at the University of Iowa by grant ATM99-86887 from the National Science Foundation.
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.