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)

Oct 30, 2003 SN Survey - SSII 2

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, 2003 SN Survey - SSII 3

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

Oct 30, 2003 SN Survey - SSII 4

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

Oct 30, 2003 SN Survey - SSII 5

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 6

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

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

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

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

Oct 30, 2003 SN Survey - SSII 10

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, 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!

Oct 30, 2003 SN Survey - SSII 12

SN 1993J (IIb)

Tran et al 1997 PASP 109, 489

Oct 30, 2003 SN Survey - SSII 13

SN 2001el (Ia)

Continuum axis

Ca jet axis

Model

Kasen et al 2003 ApJ 593, 788

Flux

% Pol

Vector

Oct 30, 2003 SN Survey - SSII 14

SN 1999em (II-P)

Leonard et al 2001 ApJ 553, 861

Spectral symmetry

Time variability

Flux