Solar Physics

, Volume 210, Issue 1–2, pp 125–142 | Cite as

RHESSI as a Hard X-Ray Polarimeter

  • Mark L. McConnell
  • James M. Ryan
  • David M. Smith
  • Robert P. Lin
  • A. Gordon Emslie


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.


Solar Phys Modulation Pattern Scattered Photon Polarization Signature Polarization Sensitivity 
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Copyright information

© Kluwer Academic Publishers 2002

Authors and Affiliations

  • Mark L. McConnell
    • 1
  • James M. Ryan
    • 1
  • David M. Smith
    • 2
  • Robert P. Lin
    • 3
  • A. Gordon Emslie
    • 4
  1. 1.Space Science CenterUniversity of New HampshireDurhamU.S.A
  2. 2.Space Sciences LaboratoryUniversity of CaliforniaBerkeleyU.S.A
  3. 3.Physics Department and Space Sciences LaboratoryUniversity of CaliforniaBerkeleyU.S.A
  4. 4.Physics DepartmentUniversity of AlabamaHuntsvileU.S.A

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