Seimei User’s Meeting 2023 (Sep. 12-13)

SN2020uem:
A Possible Thermonuclear Explosion
within A Dense Circumstellar Medium
Kohki Uno (Kyoto Univ.)
collaborator: K., Maeda, T., Nagao, T., Nakaoka, K., Motohara, A., Tajitsu, M., Konishi, S., Koyama, H., Takahashi, M., Tanaka,H., Kuncarayakti, M., Kawabata, M., Yamanaka., K., Aoki, K, Isogai, M., Ogawa, K., Kawabata, Y., Yoshii, T., Miyata, R., Imazawa

KU, Keiichi Maeda, Takashi Nagao et al. 2023a (https://ui.adsabs.harvard.edu/abs/2023ApJ...944..203U/abstract)
KU, Takashi Nagao, Keiichi Maeda et al. 2023b (https://ui.adsabs.harvard.edu/abs/2023ApJ...944..204U/abstract)1

Introduction
highDiversity of Type Ia Supernovae

Taubenberger 17

Type Ia Supernova: Standard Candles, but…

Peak mag

New Generation Surveys• different progenitor & explosion Mechanisms• new insights for Stellar Evolution• more robust cosmology

lowMuch more diversity than expected !

SN 2020uem is one of the peculiar SN Ia.
slow

Decline rate

fast

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Introduction

Type Ia-CSM Supernovae
Type Ia-CSM Supernovae• Spectrum: high temperature Ia + narrow H emission lines• Light cueve: high and long-lasting luminosity
HαHβType Ia-CSM SNe = Interaction between energetic Ia and dense circumstellar matter (CSM)
What is the origin of the dense CSM？
Seimei User’s Meeting 20233

Observation

Type Ia-CSM SN 2020uem• Discovery: 16.5 mag on 2020-09-22 by ATLAS• Coordinate: RA = 08h24m23.85s, Dec=-3°29′19.1″• Distance: dL = 173.3 Mpc (z = 0.041)• Follow-up observation- Photometry: Kanata 19/21 nignts (HOWpol/HONIR)
Subaru 1 nights (SWIMS)
Seimei 3 nights (TriCCS)- Spectroscopy: Seimei 8 nights (VPH-blue & VPH-683)
Subaru 3 nights (FOCAS, HDS & SWIMS)- Polarimetry: Subaru 1 nights (FOCAS)

20uem

Tohoku T60 1 nights (Dipol-2)

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Results

Spectral Evolution
SN 2005gj+7HDS spectrum+22+34+47+62+69+74+91+97+103+110• Prominent narrow H lines• Narrow P-Cygni Profile with 100 km/s
• intermediate mass elements (Fe)→ Typecal spectral features of SNe Ia-CSM
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Results

Multi-band Light Curves
JHKs
Kanata(HONIR)

JKs
Subaru(SWIMS)End of theCSM interaction?
griSeimei(TriCCS)
BVRI
Kanata(HOWPol)

Constraint on the CSM mass ?? (later slides)
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Results

Polarimetry: Polarization Degree & Angle
Interstellar Polarization (ISP)

PISP(λ) = Pmax exp [−K ln2 (λmax /λ)]PISP ∼ 0.8 %SN Polarization:• PSN ∼ 1.0 − 1.5 %• constant angle of ~85 degree• without wavelength dependencegeometry: aspherical CSM
polarization source: electron scattering
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Modeling

CSM Geometry
PSN ∼ 1.0 − 1.5 % → asymmetric CSM geometry

sphere• ’Elliptical’ CSM (c.f., Ho ich 91)
requires extremely- at CSMbθ

observerphotona
innerboundary• ’Disk/Torus’ CSM ?

face onedge on

flfl

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Modeling

Lighr Curve Modeling
CSM interaction model (modified Nagao+ 20)• disk-like CSM• ρ∝ r-2• CSM velocity: 100 km/s ← constrained by Subaru/HDS• kinetic energy: 1×1051 erg• ejecta mass: 1.4 M⊙

assuming Ia explosion

Seimei User’s Meeting 2023

9Modeling

Fitting Free Parameter: ε(ε: radiation-kinetic conversion efficiency)
best-fit ε

ε=1best tε=0.1

t − data
RMS ≡∑ ( data )best tfi

2fifi

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Modeling

Light Curve & CSM Mass

• Mass-loss rate: 0.02-0.03 M⊙/yr with v = 100 km/s
• Opening angle: 30-60 degree• CSM mass: 0.5-3 M⊙
Seimei User’s Meeting 2023

11Discussion

Possible Progenitor System of SN 2020uem• Mass-loss rate: 0.02-0.03 M⊙/yr w/ 100 km/s
• Opening angle: 30-60 degree• CSM mass: 0.5-3 M⊙(c) K. Maeda & R. Iaconi

Progenitor: WD + AGB/RG common envelope？
Scenario: Core-Degenerate scenario？
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SummeryTake Away
• We performed follow-up observation for 2020uem with Seimei/Subaru.
• Photometric & Spectroscopic properties suggest that 2020uem is an SN Ia-CSM.
• 2020uem shows polarization of ~1% without wavelength dependence.
- geometry: disk-like CSM- polarization source: electron scattering• We compute light curves and constrain the CSM mass.
- CSM mass: 0.5 - 4 M⊙

• We propose the following scenario for 2020uem.
- progenitor: common envelope of WD + AGB/RG star
- explosion scenario: core-degenerate scenario
Seimei User’s Meeting 202313