Wiess School of Natural Sciences
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Biochemistry & Cell Biology
Earth Science
Ecology & Evolutionary Biology
Physics & Astronomy

Radiative Transfer of Polarized X-rays: Magnetized Thomson Scattering in Neutron Stars

Thesis Defense

Graduate and Postdoctoral Studies

By: Joseph Barchas
Doctoral Candidate
When: Thursday, May 25, 2017
1:00 PM - 4:00 PM
Where: Herman Brown Hall
Abstract: This thesis is a focused study of the polarization characteristics of radiative transfer in a strong magnetic field. The main process examined here is magnetized Compton scattering in a non-relativistic regime (i.e. magnetized Thomson scattering), and we focus on applying this study to predict polarization properties of the X-ray emission from magnetars. Magnetars are a highly magnetic sub-class of neutron stars, characterized by their extremely high surface magnetic fields, comparable to or exceeding the quantum critical field (B_{cr}~4.41*10^{13} Gauss) at which an electron's cyclotron energy and rest mass energy are equal. There are 29 known/candidate magnetars at this time, and they commonly exhibit persistent quasi-thermal surface emission in soft X-rays with flat tails extending into the hard X-rays up to around 150 keV, as well as transient bursting activity in hard X-rays attributed to magnetospheric flares. Magnetized Thomson scattering refers to electron-photon scattering in a background magnetic field. The field introduces anisotropy to the problem, giving it a more complicated angular dependence. It also produces a strong frequency dependence to the cross section: it is resonant at the cyclotron frequency w_B=eB/mc. Additionally, electron motion perpendicular to the field becomes increasingly suppressed at higher field strengths, leading to a reduction in the cross section for certain incoming photon angles when w<