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Oct 30, 2003 SN Survey - SSII 1
A SALT Spectropolarimetric Survey
of Supernovae (“S4”)K. Nordsieck
Univ 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 II’s 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 γ ray bursts
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Classification• Currently classified by 2 criteria
– Spectra (I, II; a,b,c..)– Light Curves (P = plateau , L = linear)
Class Criterion Early (P-Cyg) Late (em)
Ia Si, no H,He SiII, CaII (abs) FeII (P-Cyg)
Ic No H,He OI, FeII, CaII, NaI [OI], CaII
Ib No H HeI MgI], [OI]
IIb H, II->Ib H, CaII [OI], [CaII]
IIn Narrow H ? H, He
IIL H H, CaII H, [CaII]
IIP H H, CaII H
Progenitor?
WD at C Limit
Massive core collapse
H, He stripped; γ bursts?
H stripped
Tiny H envelope
Circumstellar H
Some H
Much H
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Past Polarization of Supernovae
Type Period # SN Result CommentBroadband 1968 –
199513 Some II’s polarized Unknown
interstellar pol (ISP)
Low S/N Spectro- Polarimetry
1983 – 1999
10? Ia: < 0.3%
Ib-II: all pol, up to 4%; decr w/ H mass
Usually peak only
Med S/N Spectro- Polarimetry
1987 – 2003
7 Line pol => modeling
Multiple PA’s; jets?
Time dependence:
I decreases; II increases
Bright, or 8m class telescopes
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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
SN Type Pk V Epochs Group Comment
1987A II-P pec 2.9 -84 – 176 AAT et al Incr to 1%, axisym
1993J IIb 10.8 -1 – 40 PBO, Steward, Lick
Incr to 1%, diff PA lines & cont
1998S IIn 12 -10 – 40 Lick, Keck 2%? Uncertain ISP
1999by Ia pec (lo lum)
13.1 -1 MacDonald 0.5%, axisym
1999em II-P 13.5 7 - 163 Lick, Keck 0.7%, axisym
2001el Ia 12.7 5 VLT 0.7% Ca jet?
2002ap Ic pec 12.5 -6 – 3 VLT, Suburu 2%, 3 PA’s
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Oct 30, 2003 SN Survey - SSII 7
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 < 1000), very high S/N
– can be done in poor seeing and bright/ grey moon
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Oct 30, 2003 SN Survey - SSII 8
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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Oct 30, 2003 SN Survey - SSII 9
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 < 16
• 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!
Mag Pol err R
19 Faintest useful
0.1% 40
16 Faintest peak
0.1% 650
12 Brightest peak
0.02% 1000
Type <15 <16
Ia 5.7 10.1
Ib,c 1.2 2.0
II 2.8 6.3
Tot 9.6 18.3
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Astrophysical questions - Ia
• Ia’s 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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Oct 30, 2003 SN Survey - SSII 11
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 II’s 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)
Continuum axis
Ca jet axis
Model
Kasen et al 2003 ApJ 593, 788
Flux
% Pol
Vector
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SN 1999em (II-P)
Leonard et al 2001 ApJ 553, 861
Spectral symmetry
Time variability
Flux