Date of Award

8-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Physics

Committee Member

Dr. Mark Leising, Committee Chair

Committee Member

Dr. Marco Ajello

Committee Member

Dr. Dieter Hartmann

Committee Member

Dr. Joan Marler

Abstract

Defining the progenitor system and explaining how the explosion proceeds through the star are two difficult, and as of yet unexplained, matters regarding Type Ia supernovae (SNe Ia). Explor-ing the intricacies left behind by the explosion is one means of finding answers to these questions. The most sensitive method of collecting this information is through spectropolarimetry, measuring the polarization as a function of wavelength, as it reveals the geometry of the last scattering surface of the supernova for each epoch of observation. We present well-sampled spectropolarimetric observations of three normal SNe Ia that were obtained with the CCD Imaging/Spectropolarimeter instrument mounted on the 1.5-m Kuiper, 2.3-m Bok, and 6.5-m MMT telescopes in Arizona. We find that the geometry of each supernova is unique. We begin with the analysis of SN 2014J which displayed a strong continuum polarization with a wavelength dependence unlike that produced by linear dichroism in Milky Way dust. How-ever, the continuum’s constancy with time and its polarization angle that aligns with the magnetic field structure of the host galaxy argue for an interstellar origin. After removing the interstellar polarization (ISP) signal, we find that the supernova is nearly spherically symmetric overall, but moderate levels of polarization across the Si II λ6355 ˚A line is indicative of clumpy material in the supernova’s atmosphere. We also discuss the creation of a simple polarization model that calculates the integrated line polarization resulting from the asymmetric shadowing of a polarized source by clumps of enhanced opacity. When applied to the line polarization of SN 2014J at its +0 and +7 day epochs, we determine that a combination of four clumps spanning a range of velocities offer a good fit to the observed degree of polarization. The intrinsic polarization of SN 2011fe between -12 and +5 days shows four distinct line polarization features which we label as Features A-D. Features B and D are generally associated with Si II λ6355 ˚A and the S II “W” feature, respectively. However, Features A and C form over wavelength regions where several elements are blended in the absorption spectrum due to the large velocities at which the ejecta is expanding. We use the individual spectra of elements in the flux spectrum, generated with the spectral fitting codes SYNAPPS/SYN++, to compare with the line polarization features. We find that Feature A may be formed by Si II, S II, Fe II, or a combination of those ions and Feature C may be due to Mg II or Fe II. From a literature review and additional analysis of published polarization spectra, we demonstrate that Features A-D are common in a number of SNe Ia. We present nine epochs of observed continuum polarization of ASASSN-14lp. The degree of polarization at the longer optical wavelengths changes rapidly between -9 and +150 days and the polarization angle also shows a wavelength dependence at particular epochs. These two deductions indicate that the supernova is intrinsically polarized or it may be interacting with a dust cloud nearby.

Share

COinS