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The Astrophysics of Supernova Cosmology

This preprint explores the contributions and limitations of Type Ia Supernovae to cosmology, including the observational evidence, systematics, and requirements for future surveys. It also discusses the diversity of Type Ia supernovae, ejecta masses, and the need to understand reddening and other factors affecting the light from these sources. Additionally, it proposes using supernova data to identify AGNs based on their variability.

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The Astrophysics of Supernova Cosmology

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  1. The Astrophysics of Supernova Cosmology Contributions (and Limitations) of Type Ia Supernovae to Cosmology Bruno Leibundgut European Southern Observatory

  2. If the observational evidence upon which these claims are based are reinforced by future experiments, the implications for cosmology will be incredible. Preprint August 1999

  3. Where are we? • Already in hand • about 1000 SNe Ia for cosmology • constant ω determined to 5% • accuracy dominated by systematic effects • reddening, correlations, local field, evolution • Test for variable ω • required accuracy ~2% in individual distances • can SNe Ia provide this? • can the systematics be reduced to this level? • homogeneous photometry? • handle 250000 SNe Ia per year?

  4. Where are we … SN Factory Carnegie SN Project SDSSII ESSENCE CFHT Legacy Survey Higher-z SN Search (GOODS) JDEM/LSST Plus the local searches: LOTOSS, CfA, ESC

  5. Wood-Vasey et al. 2007 Systematics table

  6. Astrophysics • To measure cosmological parameters (distances) you need to • understand your source • understand what can affect the light on its path to the observer (‘foregrounds’) • know your local environment

  7. Contamination Photometry K-corrections Malmquist bias Normalisation Evolution Absorption Local expansion field “[T]he length of the list indicates the maturity of the field, and is the result of more than a decade of careful study.” Systematics

  8. Requirements for future surveys • Overall error • has to be • reduced to 2%! Peacock & Schneider 2007; input from A. Ealet

  9. Phillips et al. 2007 Howell et al. 2006 Howell et al. 2006 Jha et al. 2006 Hamuy et al. 2003 What is a SN Ia? • Peculiar cases abound … • SN 1991T, SN 1991bg • SN 1999aa, SN 1999ac • SN 2000cx, SN 2002cx • SN 2002ic • SN 03D3bb • SN 2005hk • and more

  10. Benetti et al. 2005 Benetti et al. 2005 Diverse spectral evolution Branch et al. 2006

  11. also at higher redshifts … Blondin et al. 2006 also Garavini et al. 2007 Bronder et al. 2008

  12. Polarimetry Wang et al. 2006

  13. Polarimetry results • Very small continuum polarisation • overall shape appears fairly round Partially strong line polarisation • distribution of individual elements could be clumped • inhomogeneous explosion mechanism? • dependence on viewing angle? Possible correlation with light curve shape parameter (Wang et al. 2007)

  14. Ejecta masses • γ-ray escape depends on the total mass of the ejecta • v: expansionvelocity • κ: γ-ray opacity • q: distributionof nickel Stritzinger et al. 2006

  15. Ejecta masses • Large range in nickel and ejecta masses • no ejecta mass at 1.4M • factor of 2 in ejecta masses • some rather smalldifferences betweennickel and ejectamass Stritzinger et al. 2006

  16. Type Ia Supernovae • Individual explosions • differences in explosion mechanism • deflagration vs. delayed detonations • 3-dimensional structures • distribution of elements in the ejecta • high velocity material in the ejecta • explosion energies • different expansion velocities • fuel • amounts of nickel mass synthesised • progenitors • ejecta masses?

  17. Elias-Rosa et al. (2007) Know what happens on the way • Do we know the reddening law? • indications from many SNe Ia that RV<3.1 • e.g. Krisciunas et al., Elias-Rosa et al. • free fit to distant SNe Ia gives RV≈2 • Guy et al., Astier et al. • Hubble bubble disappears with RV≈2 • Conley et al., Wang • Need good physical understanding for this!

  18. Work to do • Collecting thousands of supernovae may be fun, but for future cosmology applications we • need to understand photometry • accuracy requirements strongly increased • need to understand their variations • simple correlations may work, but are ad hoc • need to solve the reddening problem • go to rest-frame IR?  JWST will show whether this works • understand another ‘dark’ component of the universe (dust)

  19. Boutsia 2008 A different use of the data • Find AGNs through their variability Based on the ESSENCE data Find point-like objects with a detection: • at least 10 epochs • S/N> 5 at each epoch • no other source within 2” The light curves cover 2-year time interval

  20. Effective selection method • Based on structure functions • 372 priority-1 AGN candidates (ascending SF) • 192 priority-2 AGN candidates (non-flat SF) • First spectroscopic confirmations • 18.5<R<20.5 • 53 out of 58 objects are broad-line AGN • 3 show only one broad line • 95% success rate Boutsia 2008

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