A SALT Spectropolarimetric Survey of Supernovae ( S 4 ) K. Nordsieck Univ of Wisconsin

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1 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, 2003 SN Survey - SSII 1 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 indicatorsare 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, 2003 SN Survey - SSII 2

2 Classification Currently classified by 2 criteria Spectra (I, II; a,b,c..) Light Curves (P = plateau, L = linear) Class Ia Ic Ib Criterion Si, no H,He No H,He No H Early (P-Cyg) SiII, CaII (abs) OI, FeII, CaII, NaI HeI Late (em) FeII (P-Cyg) [OI], CaII MgI], [OI] Progenitor? WD at C Limit Massive core collapse H, He stripped; γ bursts? H stripped IIb IIn IIL IIP H, II->Ib Narrow H H H H, CaII? H, CaII H, CaII [OI], [CaII] H, He H, [CaII] H Tiny H envelope Circumstellar H Some H Much H Oct 30, 2003 SN Survey - SSII 3 Past Polarization of Supernovae Type Period # SN Result Comment Broadband Low S/N Spectro- Polarimetry ? Some II s polarized Ia: < 0.3% Ib-II: all pol, up to 4%; decr w/ H mass Unknown interstellar pol (ISP) Usually peak only Med S/N Spectro- Polarimetry Line pol => modeling Multiple PA s; jets? Time dependence: I decreases; II increases Bright, or 8m class telescopes Oct 30, 2003 SN Survey - SSII 4

3 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, 2003 SN Survey - SSII 5 Good Spectropolarimetry SN Type Pk V Epochs Group Comment 1987A 1993J 1998S 1999by 1999em II-P pec IIb IIn Ia pec (lo lum) II-P AAT et al PBO, Steward, Lick Lick, Keck MacDonald Lick, Keck Incr to 1%, axisym Incr to 1%, diff PA lines & cont 2%? Uncertain ISP 0.5%, axisym 0.7%, axisym 2001el Ia VLT 0.7% Ca jet? 2002ap Ic pec VLT, Suburu 2%, 3 PA s Oct 30, 2003 SN Survey - SSII 6

4 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, 2003 SN Survey - SSII 7 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, 2003 SN Survey - SSII 8

5 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 Faintest useful Faintest peak Brightest peak Type Ia Ib,c II Pol err 0.1% 0.1% 0.02% < R < Tot Oct 30, 2003 SN Survey - SSII 9 Astrophysical questions - Ia Ia s claimed to be a oneparameter 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, 2003 SN Survey - SSII 10

6 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 (nonaxisymmetric) 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, 2003 SN Survey - SSII 11 SN 1993J (IIb) Tran et al 1997 PASP 109, 489 Oct 30, 2003 SN Survey - SSII 12

7 SN 2001el (Ia) Model Flux % Pol Vector Ca jet axis Continuum axis Kasen et al 2003 ApJ 593, 788 Oct 30, 2003 SN Survey - SSII 13 Flux SN 1999em (II-P) Spectral symmetry Time variability Leonard et al 2001 ApJ 553, 861 Oct 30, 2003 SN Survey - SSII 14