A SALT Spectropolarimetric Survey of Supernovae S4 K. Nordsieck Univ of Wisconsin

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A SALT Spectropolarimetric Survey of Supernovae
(S4)K. NordsieckUniv of Wisconsin

• Supernova taxonomy
• Polarization of Supernovae
• Survey Structure
• Why SALT?
• Astrophysical questions
• SNIa
• Core Collapse SNe

1993J (IIb)
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Supernova Importance

• Need to understand explosion process to model
• return of heavy elements to ISM
• energetic input to ISM
• Need to clarify progenitors to couple to star
  formation/ galaxy models
  
• Both I and IIs used for cosmological distance
  indicators- are they really standard candles?
  
• Some really fun gas dynamics problems
• Non spherical explosions a hot theoretical topic-
  needs observational input!
  
• Possible relation to ? ray bursts

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Classification

• Currently classified by 2 criteria
• Spectra (I, II a,b,c..)
• Light Curves (P plateau , L linear)

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Past Polarization of Supernovae
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What Causes Polarization?

• Two possibilities
• Scattering of SN light off ambient dust No,
  time dependence is wrong
  
• Electron scattering in ejecta Yes
• Electron scattering pseudo-photosphere is
  asymmetric 10 40 ? 0.5 2 pol
  
• Explosion is homologous (Hubble flow). As it
  expands, see deeper into ejecta, to lower
  velocities and asymmetry of inner layers
  
• Eventually, becomes optically thin, polarization
  vanishes
  
• Line polarization
• competition of line opacity with e-scat in
  photosphere ? polarization reduction
  
• P-Cygni lines above photosphere polarization
  inverse P-Cygni

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Good Spectropolarimetry
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Survey

• We need more than one example in each bin!
• Adding asymmetry to spectra and light curve may
  clarify classification (eg Seyfert I-II
  unification)
  
• Need
• time coverage (3 -4 epochs) for classification
  and ISP estimation
  
• to get on as early as possible (I highest pol, II
  unpol)
  
• low resolution (R
• can be done in poor seeing and bright/ grey moon

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Why SALT?

• Spectroscopic survey distributed over sky the
  best kind for SALT/ HET telescopes
  
• Spectropolarimeter 2x more sensitive than Keck
  LRS, VLT FORS1
  
• Polarimeter always available
• 100 queue mode- can get on quickly, schedule
  epochs optimally

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Time estimation

• Want to go down 3 mag from peak
• Use 900 l/mm VPH (R 1000), binning to lower
  polarimetric resolution as required
  
• Faintest peak mag
• Using discovery rate/yr for last 12 yrs, will see
  10 20/year
  
• Run for 3 years to get statistics
• 20/ year x 4 epochs 80 tracks 8 nights 3
  of SALT
  
• Soliciting SALT collaborators!

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Astrophysical questions - Ia

• Ias claimed to be a one-parameter family pk
  luminosity vs decline rate
  
• Theoretical explanation as time of deflagration
  ? detonation gets earlier, get incomplete
  combustion, less Ni, lower lum, faster decline
  
• But there must be a variety of progenitors, from
  accretion disk to WD mergers how do these lead
  to one-parameter family
  
• Clue from asymmetry mergers should give more
• The one low-lum Ia is more polarized than the one
  hi-lum one!

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Astrophysical Questions Core Collapse

• There are a variety of ways to induce asymmetry
• asymmetric explosion (axisymmetric? jet?)
• ejecta running into asymmetrical environment
  (axisymmetric)
  
• burning nonuniformities that make Ni clumps
  (non-axisymmetric)
  
• Do IIs with different H envelope masses and
  environments all have the same asymmetry source?
  
• Some are axisymmetric and some are not!

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SN 1993J (IIb)
Tran et al 1997 PASP 109, 489
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SN 2001el (Ia)
Model
Flux
Pol
Ca jet axis
Vector
Continuum axis
Kasen et al 2003 ApJ 593, 788
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SN 1999em (II-P)
Flux
Spectral symmetry
Time variability
Leonard et al 2001 ApJ 553, 861