HR: 0830h
AN: SP21A-04    [Abstracts]
TI: Center to Limb Variation of Hard X-ray Spectra from RHESSI
AU: * McTiernan, J M
EM: jimm@ssl.berkeley.edu
AF: Space Sciences Lab, University of California, 7 Gauss Way, Berkeley, CA 94720 United States
AB: In this work we use the massive RHESSI flare database to measure the center to limb variation of the hard X-ray spectral index in the 50 to 100 keV energy range and the 100 to 300 keV energy range. If Coulomb collisions are the dominant scattering mechanism for accelerated electrons in solar flares, then there should be some variation in the steepness of the spectrum, the spectral index, from the center of the sun to the solar limb. The issue is complicated by the presence of backscatter of the radiation and the large spread in observed spectral index with respect to the expected center to limb variation. Previous work (Vestrand, et al, 1987, Apj 322, 1010) has shown that such a variation exists at high energies (300 to 1000 keV), but not necessarily at lower energies (Li, 1994, Apj 421, 381). It is also true that direct comparisons of energy spectra using multiple instruments have never found any noticeable anisotropy in solar flare X-rays (e.g., Kane, et al, 1988, Apj 326, 1017). The large number of flares and excellent spectral resolution of RHESSI should enable us to detect any center to limb variation of the spectra if it is present. This research is supported by NASA contract NAS5-98033.
DE: 7519 Flares
DE: 7544 Stellar interiors and dynamo theory
SC: Solar Physics Division - AAS [SP]
MN: 2005 Joint Assembly