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RHESSI as a Hard X-Ray Polarimeter  

Mark McConnell   Submitted: 2002-09-19 19:59

Although designed primarily as a hard X-ray imager and spectrometer, the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is also capable of measuring the polarization of hard X-rays (20-100 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 Ge 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, based on Monte Carlo simulations and in-flight background measurements, indicate that a 20-100 keV polarization sensitivity of less than a few percent can be achieved for X-class flares.

Authors: M.L. McConnell, J.M. Ryan, D.M. Smith, R.P.Lin, and A.G. Emslie
Projects:

Publication Status: Solar Physics, in press.
Last Modified: 2002-10-07 09:33
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RHESSI as a Hard X-Ray Polarimeter  

Mark McConnell   Submitted: 2002-09-19 19:59

Although designed primarily as a hard X-ray imager and spectrometer, the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is also capable of measuring the polarization of hard X-rays (20-100 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 Ge 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, based on Monte Carlo simulations and in-flight background measurements, indicate that a 20-100 keV polarization sensitivity of less than a few percent can be achieved for X-class flares.

Authors: M.L. McConnell, J.M. Ryan, D.M. Smith, R.P.Lin, and A.G. Emslie
Projects:

Publication Status: Solar Physics, in press.
Last Modified: 2002-10-07 09:34
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 


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RHESSI as a Hard X-Ray Polarimeter
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