THE ULTRAVIOLET PROPERTIES OF SUPERNOVAE

Open Access
Author:
Brown, Peter Johnson
Graduate Program:
Astronomy and Astrophysics
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 08, 2009
Committee Members:
  • Peter W A Roming, Dissertation Advisor
  • Peter W A Roming, Committee Chair
  • David Nelson Burrows, Committee Member
  • Robin Bruce Ciardullo, Committee Member
  • Lee S Finn, Committee Member
  • Eric D Feigelson, Committee Member
  • Ruth Daly, Committee Member
Keywords:
  • supernovae
  • ultraviolet
  • distance scale
  • Swift
Abstract:
Ultraviolet (UV) observations of supernovae (SNe) probe an important wavelength region where hot temperatures, extinction, and metallicity have strong effects. In addition, they provide a comparison set against which to compare and better understand rest frame UV observations of high redshift SNe observed in the optical. UV observations, however, are rare due to the need for telescopes above the atmosphere and the difficulty in observing transient objects with space based observatories. Limited observations with space based observatories, primarily the International Ultraviolet Explorer and the Hubble Space Telescope, are reviewed, after which the Ultra-Violet/Optical Telescope (UVOT) on the Swift spacecraft is introduced. With Swift we have observed more SNe than all previous UV missions combined. Case studies of two individual SNe are first presented: SNe 2005am and 2005cs. SN 2005am is the first young SN observed with Swift, and the near-UV (uvw1: central wavelength ~2600 Angstroms) light curve is consistent with the previous template derived from IUE and HST observations of SNe 1990N and 1992A. SN 2005cs is the first plateau-type II (IIP) with a well observed UV light curve. UVOT observations show a dramatic drop in the UV brightness and shift in the spectral energy distribution from blue to red caused by the dropping temperature and resulting line blanketing in the UV. These case studies demonstrate the information available from the UV data for individual SNe. A photometry method for proper accounting of coincidence loss, aperture corrections, and subtraction of the underlying galaxy is detailed. This method is then applied to a large sample of SNe observed with UVOT. We present 25 light curves and compare SNe by type and across types. The SNe Ia, with a few exceptions, are shown to have very similar light curves in the near UV, whereas, the three SNe Ib/c we have observed are very different. The SNe IIP all have rapidly fading UV light curves, though with different decay rates. The usefulness of UV-optical colors in differentiating the different SN types, particularly young SNe II which are blue and the redder SNe I, is then demonstrated. In a study of the absolute magnitudes of SNe Ia, we find that normal SNe Ia are standard candles in the near UV (u and uvw1 bands: central wavelengths 3500 and 2600 Angstroms), but the scatter increases dramatically at shorter wavelengths (uvm2 filter: central wavelength 2200 Angstroms). The utility of this UV database of light curves for better understanding local SN events and for the discovery, classification, and understanding of high redshift SNe is discussed.