Spectropolarimetry ofInteracting Supernovae
Kaew Samaporn Tinyanont
National Astronomical Research Institute of Thailand

Interacting Supernovae Workshop, MIAPbP
samaporn@narit.or.thChiang Mai
เชียงใหม่

Wikipedia

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0.7m

2.4-m Thai National Observatory

0.7m

PROMPT 0.6m

0.7m

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High-speed photometer
Low-res spectrograph planned3Goals for this talk
• Polarization and geometry• How do we measure it, actually?
• What have we learned from spectropolarimetry of interacting SNe?
• Future prospects

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4Supernovae are NOT SphericallySymmetric
3D Hydrodynamical Model ofCore Collapse

SN 1987A
HSTPI Kirshner

Burrows+ 2019
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5Interacting SNe are especially asymmetric
Eta Car: LBV, potential IInprogenitor

VY CMa: eruptive eRSG

Keck NIRC2, unpublished
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HST NASA/ESA ; N. Smith, J. Morse6

Scattering Polarizes LightObserver

Top view

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Polarization records light scattering history

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If the scattering region is symmetric, polarization cancels out

Unpolarizedthermalemission

Electron scattering
ionized ejectaKaew Tinyanont

9Asymmetry à Net Polarization

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CSM could have more extreme geometry
SN 2013ej

Polarization could be
especially strong

Mauerhan+ 2017
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11Translating polarimetry to geometry

Höflich 1991

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12Optical depth also affects polarization

Höflich 1991

Unpolarized
thermalemission

Multiplescattering
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Test case: SN1987A
Polarimetry inferred b/a ~ 0.6-0.7 if prolate at 14° position angle and inclination angle of ~40°
Höflich 1991, Jeffery 1991

Schematic from Tinyanont+2021
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Geometry info without
spatially-resolved observations

SN 2018hna(1987A-like)Tinyanont+ 2021
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15Direct evidence for asymmetric core collapse
SN 2004dj--- decline predicted byfalling e- density

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Leonard+ 2006

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Stokes Parameters

++I

––

QU
q = Q/I u = U/I𝒑=

𝒒𝟐 + 𝒖𝟐

𝜽 = 𝟎. 𝟓 𝐚𝐫𝐜𝐭𝐚𝐧
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Specpol probes geometry at a given wavelength.
Fluxp

Line forming at lowe- scattering opacity

e- scattering

Photospheree- scattering
Photosphere

Multiple scattering inline core
P-Cyg absorption
from hydrogen absorb
less-polarized flux
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McCall 198418

A (spectro)polarimeter
Incoming light
Mixed polarization

Light with known
polarization basis

Modulator (Half-wave plate):
Rotates polarization axes

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Beam splitting Analyzer
e.g. Wollaston prisms
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𝐼&%

𝐼"!

𝐼#$%

𝐼!

WIRC+PolTinyanont+2019

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Previous Specpol Observations of SNe IIn
SN NameNumber of Epochs

Ref1997eg

3

Leonard+2000a1998S

3

Leonard+2000b; Wang+2001

2003ee1Wang & Wheeler 20082003hy1

Wang & Wheeler 2008

2009ip14

Mauerhan+14; Reilly+17

2010jl3

Patat+11; Quirola-Vásquez+19(more to come from the SNSPOL group)

2012ab

2

Bilinski+18

2014ab

5

Bilinski+20

2017hcc>1

Mauerhan+17 (ATel)

2018evt

4

Yang+23
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Typical observation: 2012ab

Bilinski+18

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Evidence for CSM asymmetry• SNe IIn are much more polarized (~few %) in the continuum compared to normal
core-collapse (~0.5 %).
• The continuum is from the shocked CSM; the observed polarization infers strong
asymmetry.
• A ring geometry has been proposed for SN 2009ip.

SN 2009ip

Reilly+17
Reilly+17

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Mauerhan+14
23Modeling asymmetry in SN 2010jl
1+A1 = pole-to-eq density ratio

Dessart+2015
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Caveats• Can be done on very few events (brighter than ~17 mag with 8-m)
• Unknown InterStellar Polarization (ISP) in the host & MW ISM• somewhat mitigated in the IR• Need proper modeling to interprete the results

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Future Prospects• Spectropolarimetry of flash ionization, probably need FORS2 ToO or
LRISp upgrade• More observations. More model grids.
• Spectropolarimetry needs lots of photons (106 to get to 0.1%);
ELTs could revolutionize SN spectropolarimetry

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Summary• Polarization records the history of scattering of photons.
• For SNe we can’t resolve, spectropolarimetry is the only way to gain
geometric information.
• A few interacting SNe have spectropolarimetric observations; they
are typically highly polarized, pointing at asymmetric CSM.
• More measurements needed, but they are hard to do.
samaporn@narit.or.th

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