Oct 30, 2003SN Survey - SSII1 A SALT Spectropolarimetric Survey of Supernovae (“S 4 ”) K. Nordsieck Univ of Wisconsin Supernova taxonomy Polarization of Supernovae Survey Structure Why SALT? Astrophysical questions –SNIa –Core Collapse SNe 1993J (IIb)

Oct 30, 2003SN Survey - SSII2 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

Oct 30, 2003SN Survey - SSII3 Classification Currently classified by 2 criteria –Spectra (I, II; a,b,c..) –Light Curves (P = plateau, L = linear) ClassCriterionEarly (P-Cyg)Late (em) IaSi, no H,He SiII, CaII (abs)FeII (P-Cyg) IcNo H,He OI, FeII, CaII, NaI[OI], CaII IbNo H HeIMgI], [OI] IIbH, II->Ib H, CaII[OI], [CaII] IInNarrow H ?H, He IILH H, CaIIH, [CaII] IIPH H, CaIIH Progenitor? WD at C Limit Massive core collapse H, He stripped; γ bursts? H stripped Tiny H envelope Circumstellar H Some H Much H

Oct 30, 2003SN Survey - SSII4 Past Polarization of Supernovae TypePeriod# SNResultComment Broadband1968 – Some II’s polarizedUnknown interstellar pol (ISP) Low S/N Spectro- Polarimetry 1983 – ?Ia: < 0.3% Ib-II: all pol, up to 4%; decr w/ H mass Usually peak only Med S/N Spectro- Polarimetry 1987 – Line pol => modeling Multiple PA’s; jets? Time dependence: I decreases; II increases Bright, or 8m class telescopes

Oct 30, 2003SN Survey - SSII5 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

Oct 30, 2003SN Survey - SSII6 Good Spectropolarimetry SNTypePk VEpochsGroupComment 1987AII-P pec – 176AAT et alIncr to 1%, axisym 1993JIIb – 40PBO, Steward, Lick Incr to 1%, diff PA lines & cont 1998SIIn12-10 – 40Lick, Keck2%? Uncertain ISP 1999byIa pec (lo lum) 13.1MacDonald0.5%, axisym 1999emII-P Lick, Keck0.7%, axisym 2001elIa12.75VLT0.7% Ca jet? 2002apIc pec – 3VLT, Suburu2%, 3 PA’s

Oct 30, 2003SN Survey - SSII7 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

Oct 30, 2003SN Survey - SSII8 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

Oct 30, 2003SN Survey - SSII9 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! MagPol errR 19Faintest useful 0.1%40 16Faintest peak 0.1%650 12Brightest peak 0.02%1000 Type<15<16 Ia Ib,c II Tot

Oct 30, 2003SN Survey - SSII10 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!

Oct 30, 2003SN Survey - SSII11 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!

Oct 30, 2003SN Survey - SSII12 SN 1993J (IIb) Tran et al 1997 PASP 109, 489

Oct 30, 2003SN Survey - SSII13 SN 2001el (Ia) Continuum axis Ca jet axis Model Kasen et al 2003 ApJ 593, 788 Flux % Pol Vector

Oct 30, 2003SN Survey - SSII14 SN 1999em (II-P) Leonard et al 2001 ApJ 553, 861 Spectral symmetry Time variability Flux