Peter J. Brown
Mitchell Institute -- Texas A&M
FOE – North Carolina State University May 13, 2013

Ultraviolet observations are hard must be obtained from space
SNe are transient
Sample size is historically small

A Swift Explosion in the number of SNe observed in the UV

Swift UVOT Light Curves

Launched November 20, 2004
Low earth orbit with ~90 min orbit
Three co-aligned instruments
BAT – Burst Alert Tel. (15-150 keV)
XRT – X-Ray Telescope (0.2-10 keV)
UVOT - UltraViolet/Optical Telescope

Gamma Ray Burst and Supernova
Hunter
Rapid response capability – Targets of Opportunity can be uploaded to the spacecraft for immediate observation
Short term scheduling, required by the different behavior of burst afterglows, requires observations to be planned the day before rather than weeks in advance
SN observations can be analyzed in near real time (hours delay from observation to analysis) to assist in planning the future observations
Unique UV and X-ray observations unobtainable from the ground

Swift UVOT
30 cm modified Ritchey-Chretien Telescope
Wavelength Range 1600-6000 Angstroms
Photon Counting detector centroiding into 0.5 arcsec virtual pixels
2 arcsec point spread function
17x17 arcminute field of view

Swift UVOT Filter Curves

SNe Ia – behind the iron curtain

Metallicity effects in nature and modeling of Type Ia Supernovae

Original progenitor composition
 stellar evolution/winds
 white dwarf composition
 explosion/flame propagation

Density structure

Heavy element abundance in outer layers

Ratios of particular elements

Effect of heavy element abundances on
UV Spectra of SNe Ia
Based on Walker et al. 2012

Effect of 56 Ni abundances on UV
Spectra of SNe Ia
Based on Sauer et al. 2008

Effect of heavy element abundances on
UV Spectra of SNe Ia
Based on Lentz et al. 2000

Effect of heavy element abundances on
UV Spectra of SNe Ia
Based on Lentz et al. 2000

Determining Metallicity from flux ratios
Foley & Kirshner 2013 determine the relative metallicity between
SNe 2011by and
2011fe using flux ratios from the models of Lentz et al. 2000

Model Color differences
The same change in spectral shape can be measured using
Swift/UVOT photometry
Brown et al. in prep

Model Color differences
The same change in spectral shape can be measured using
Swift/UVOT photometry
Foley & Kirshner 2013 determine a difference of > 1.5 dex from HST
UV spectroscopy

Model Color differences
The same change in spectral shape can be measured using
Swift/UVOT photometry
Foley & Kirshner 2013 determine a difference of > 1.5 dex from HST
UV spectroscopy
< UVOT photometry gives the same result

Model Color differences
Different “metallicity” models have different effects on the observed colors
Brown et al. in prep

Effect of Extinction on UV colors
Scatter in observed colors is not consistent with reddening of the models

Observed v. Model Color Evolution
Large sample of well sampled UV light curves are an excellent data set upon which to build future models
More data, including photometry and spectroscopy, needed to explore the diversity of
SNe Ia

High Quality HST UV Spectral
Series also now available
Mazzali et al. 2013 arXiv:1305.2356

The need to synthesize UV observations and theory

Effects of metallicity strong in UV, particularly shortward of 2500 Angstroms

The many ways that metallicity could effect the progenitor/evolution/explosion/radiation and the many ways that those differences could be modeled make it difficult to uniquely determine parameters based on UV photometry

However, UV photometry can narrow down the allowed parameter space for better modeling

There is now plenty of UV data!!

NASA ADAP funded project underway to create a more user friendly database of the Swift/UVOT data of the 200+
Supernovae observed, including organized image sets, analysis subproducts, light curves, and spectral dependent products (flux converstion factors, extinction coefficients, bolometric contributions, etc.
For more info please e-mail uv.supernova@gmail.com