34th Solar Physics Division Meeting, June 2003
Session 22 RHESSI Results III
Oral, Thursday, June 19, 2003, 9:00-10:30am, Auditorium

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[22.05] Evidence for Hard X-Ray Polarization from the Flare of 23 July 2002

M. L. McConnell (UNH), D. M. Smith (UCB), A. G. Emslie (UAH), G. J. Hurford, R. P. Lin (UCB), J. M. Ryan (UNH)

Although designed primarily as a hard X-ray imager and spectrometer, the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is also capable of measuring the polarization of hard X-rays (30-100 keV) from solar flares. This capability arises from the inclusion of a small unobstructed Be scattering element that is strategically located within the cryostat that houses the array of nine Germanium detectors. The Germanium detectors are segmented, with both a front and rear active volume. Low energy photons (below about 100 keV) can reach a rear segment of a Ge detector only indirectly, by scattering. Low energy photons from the Sun have a direct path to the Be and have a high probability of Compton scattering into a rear segment of a Ge detector. The azimuthal distribution of these scattered photons carries with it a signature of the linear polarization of the incident flux. Sensitivity estimates suggest that a 30-100 keV polarization sensitivity of less than a few percent could be achieved for X-class flares. Since its launch, RHESSI has observed a number of X-class solar flares. We have been analyzing polarimeter mode data from the X4.3 flare that took place on 23 July 2002. There is some evidence for linear polarization in the 20-40 keV energy band at a level of ~27 (+/-7) %, although contributions from systematic effects in the data cannot be completely ruled out. Here we shall review the RHESSI polarimetry capabilities and discuss the analysis of the 23 July 2002 event.

The author(s) of this abstract have provided an email address for comments about the abstract: Mark.McConnell@unh.edu

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.