Date of Award

Winter 12-15-2014

Author's School

Graduate School of Arts and Sciences

Author's Department


Degree Name

Doctor of Philosophy (PhD)

Degree Type




X-Ray Polarimetry with X-Calibur


Qingzhen Guo

Doctor of Philosophy in Physics, Washington University in St. Louis,

September, 2014. Professor Henric Krawczynski, Chair

X-ray polarimetry is a prime tool to investigate the unexplored compact sources and to provide crucial information that other techniques can not produce. By measuring the degree and orientation of the polarization of radiation from a cosmic source, unique inferences about the morphology and the magnetic field structure can be made.

Krawczysnki's group at Washington University is working on a uniquely sensitive scattering polarimeter, X-Calibur, to be used in the focal plane of a focusing X-ray telescope. The design of X-Calibur is based on Thomson/Compton/Rayleigh scattering effects. All these scattering processes share the property that the photons scatter preferentially to the direction perpendicular to the electric field vector. X-Calibur consists mainly of a low-Z scintillator stick as Compton scatterer and high-Z semiconductor CdZnTe detectors surrounding the Compton scatterer to absorb the scattered photons. It performs X-ray polarimetry measurements in the energy range 2-75 keV when it is carried on a satellite, and in the 20-75 keV range when it is carried on a balloon. X-Calibur achieves a high detection efficiency of > 80% and an averaged energy resolution (FWHM) of 3 to 5 keV over the energy band at a very low background level.

First, I report on the optimization of the scattering X-ray polarimeter X-Calibur on board InFOCuS X-ray telescope balloon flight at Fort Sumner (NM) in Fall 2014. The optimization is based on Monte Carlo simulations of polarized and unpolarized X-ray beams and the most important background components. I calculated the sensitivity of the polarimeter for the upcoming balloon flight in Fort Sumner and for additional longer balloon flights.

Additionally, I describe the optimization of the design to extend the energy range of the polarimeter towards lower energies. Such a broadband polarimeter would use LiH as the scatterer as it combines a high efficiency for scattering interactions even at < 10 keV energies (as opposed to photoelectric effect absorption interactions) with a relatively high density.

Lastly, I describe the scientific potential of space borne observations of blazars with a first generation X-ray polarimeter mission like X-Calibur, GEMS and XIPE. I present a proposed observation program including observations strategies, sources of interest, recommended accompanying multiwavelength observations, and the observations results. The analysis uses the daily flux values of all monitored sources by the RXTE All-Sky Monitor (2-12 keV) and Swift BAT 70-month hard X-ray survey (15-50 keV). Based on the analysis, fifteen sources are selected as target candidates for the science investigations.


English (en)

Chair and Committee

Henric Krawczynski

Committee Members

Martin Israel, Ramanath Cowsik, Thomas Bernatowicz, Mark Anastasio, Richard Laforest


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