連星中性子星への進化における超新星の役割（Supernovae from the NS/WD formation boundary）

Keiichi Maeda
Kyoto University
第12回光赤外線天文学大学間連携ワークショップ(online) 2021.11.26

The Seimei SN/Transient Prog.
© Tanaka~ 5 / yr.
~ 50 / yr.

There are ~ 50 SNe / yr for which it can be observed
spectroscopically in the infant phase (~ 3-4 mag below the peak).
Telescope time and ToO flexibility can be practically more
important than the depth (no need to go deeper than the survey).
One key project: SNe leaving double NS systems.

Core-collapse Supernovae (CCSNe)
SN Ia

CCSNH-burning WS, 2009.2.19-20

Neutron stars formed behind CCSNe

Katsuda+ 2018

Holland-Ashford+
2017

NSs are formed at SNe (or SNe are triggered by NS formation).

NS diversities: Relation to properties of SNe?
Enoto+ 2019

What determines theproperties of a NS at birth?
Relation to the properties ofSNe (and then progenitor)?

Ib/c型
II型

The NS-SNR sample may
be biased.

Yasuda, Lee, KM 2021ab

The best we know: SN 1054=Crab
The best observed NS.
Progenitor and SN?

Electron-capture SN?
CSM Composition
SN Nucleosynthesis
Historical light curve(e.g., Tominaga+ 13)

Electron capture SNe
SN Ia

CCSN

H-burning WS, 2009.2.19-20

Electron capture SN
Theoretically
predicted since
1980’s

Wanajo+ 09

Nomoto 1984

Kitaura+ 06

RobustSN explosion
mechanismElectron capture SN
Mms ~ 8-10 M
Degenerate core
Nomoto 1984“Super-AGB star”
Huge mass loss
He/C/N-rich CSM

Kitaura+ 06

Wanajo+ 09

Low 56Ni production
High Ni/Fe, …
Low energy
Low ejecta mass

SN 2018zd

SN II @ 9.6 Mpc.
Very early discovery by K. Itagaki.
Intensive follow-up by LCO network.
Unfortunately, Seimei was not ready.
Hiramatsu+, 2021,
Nature Astronomy

LCO

Electron capture check list

Hiramatsu+, 2021,
Nature Astronomy

The “real-time” counterpart of the Crab.

HST SWIFT+ gound spectroscopy< a few days of < a few days.
the explosion.

Deep spectroscopy at~year (faint, Keck, etc).

Thanks to very-early discovery and intensive follow-up
observations, for a (rare) very nearby and faint SN.

What if it is in a binary
HFe

Type IIFeCaFeSiS SiII (but for IIn)
Red Supergiant
IIb/Ib/Ic(Stripped Envelope
SNe, SESNe)
Wolf-Rayet-like starType Ia

CaH-rich
H-richOHeFeType Ib

Na SiO

Type Ic@ maximum brightness (~ a few weeks):– Expanding optically thick medium → P-Cygni.

HeHeHeC+OC+OSiSiFeFe

Ultra-stripped envelope SNe (USSNe)
2nd SN toward the formationof compact binary NSs.
Close orbit: C+O or He star.
No binary disruption:
low mass ejecta (< 0.5M).
⇒ <~ 2 M He or C+O star.
⇒ corresponding to
MZAMS < 11 or 12 M.
⇒ Low-E + low M(56Ni)(e.g., Suwa+ 2015).

Tauris+ 17Prediction:“Faint” and “Fast” transients(e.g., Tauris+ 13, 15; Moriya+ 17).

Note: low mass SNe ⊃ USSNe, not =• A low-mas He/C+O SN can arise from thefollowing configurations:– A. a low-mass SN leaving short-period double NSs.
– B. a low-mass SN leaving long-period double NSs.
– C. a low-mass SN w/ a massive star companion.
• Genuine USSN (toward DCNS binary)= case A.

• It is still important to find low-mass SNe andtheir nature in general:– Includes USSNe anyway.
– The SN properties should be more like the same.
– Rate in the stellar evolution context.

Ultra-stripped envelope SNe (USSNe)

Electron capture or Fe CCSNe near the white dwarf – SN boundary(SN17properties are probably the same within this mass range).
Tauris+Expected Properties from the low-mass
He/C+O star explosion → rapid & faintDrout+ 10~ 16 mag~ 18 mag~ 10 days

Moriya+ 17~ 20 days

Low-mass CCSN Ib/c:
He 1.5 M (C+O 1.45M)← Mms ~ 10MThe “least” massive star toexplode as a CCSN.
Possible pathway to binary NSs.

“Normal” SNe Ib/c:
He 4 M (C+O 2.5 M)← Mms ~ 15M De+ 18, Science

Ultra-SESN candidate iPTF14gqr
LC+early spec:
Ultra SESN
model seem toworks.
Fast +(relatively) faintRapid light curve, with spectral
signature of a C+O star explosion(= The USSN expectation).

First peak in the LC:
Dense CSM
⇒massive star origin (=USSN).

Emerging link between USSN candidates(or a low-mass SNe) and Ca-rich transients

Ca-rich transient

iPTF14gqr

iPTF14qgr is avariant of enigmatic“Ca-rich transients”

Ca-rich Transients (rapid & faint)[O I][Ca II]“Ca-rich”
Kawabata, KM+ 10, NatureFirst reports:
2005cz (Kawabata+ 10) & 2005E (Perets+ 10)
SN Ib, but later strong [Ca II], not [O I].
Faint and rapid. First suggestions:
Low-mass He/C+O star CCSN, orWD explosion?

Ca-rich transients = old populations?

Kasliwal+ 12

Against the CC (core-collapse) SN origin.
However…
A small fraction are found in youngenvironment.
If they are CCSNe, it has several
implications.

Milisavljevic+17

Nakaoka, KM, Yamanaka+, 2021: One of the first results from Seimei

A new candidate of an Ultra-SESN?
iPTF14gqr

SN 2019ehk

Star formingenvironment

SN 2019ehk
iPTF16hgs

Maximum spectrum ~ a He star.
Rapid evolution & First peak.
⇒ USSN candidate.
Diversity between the USSNcandidates.

iPTF16hgs

iPTF14gqr
SN Ib

Emerging link between USSN candidates(or a low-mass SNe) and Ca-rich transients
The difference
disappears (orreduces) in the later
epochs.
They all evolved tothe (enigmatic) “Carich transients” (c.f.,

SN 2019ehk

iPTF16hgs
iPTF14gqr

Kawabata, KM+ 2010).

SN Ib

A need for morecandidates:
Consistent with theUSSN expectation?
(e.g., mass diversity)

Did SN 2019ehk leave NSs with close orbit?
• Optical observations would not discriminate thefollowing scenarios (genuine USSN = case A):– A. a low-mass SN leaving short-period double NSs.
– B. a low-mass SN leaving long-period double NSs.
– C. a low-mass SN w/ a massive star companion.

• Go for radio.
SN 2019ehk = either case B or C
(unfortunately not leading to theNS merger in the future).
Note: it is important to explore acensus of “low-mass SNe”.

Radioluminosity

NS merger within
Hubble time
Matsuoka+KM 20

VLA limit (Jacobson-Galan+ 20)

BinarySeparation

Search for USSNe: Requirements• High-cadence survey.
– They are rapid.

• Quick and intensive follow-up observations.
– They are faint.

• Multi-wavelength helps.
– The variant may look similar in the optical.

Search for USSNe with Seimei/Kanata

Survey capability already sufficient;
Follow-up key.

USSN rate ~ 1 / yr within 60 Mpc(otherwise ≠ DNS formation)
Seimei telescope for spectra with
Rapid & intensive SN follow-up program

Kools-IFU (present):
limit: 18 (cons)-19 (best) mag
TriCCS:
Imaging available, spec to come.

18 (19) mag @ 40 (60) Mpc

Next OISTER should help

Systematic transient
survey & follow-ups.
⇒ New transient sky.
New instruments
becoming available.
Tomo-e, TriCCS, …
e.g., TriCCS may help
establish the NS
population by the sub-sec
observations.
⇒ SN-NS synergy.
Multi-wavelength
NIR, radio, …
⇒ SN full characterization.
Identifying USSNe.

Summary• Core-collapse SNe (CCSNe) from the lowest mass boundary.
– A single star: Electron-capture SNe.
• A key in understanding stellar evolution and SN explosion mechanism.

• SN 2018zd as the strongest candidate.
– A “real-time” twin of the crab?
– In a binary system: Ultra-stripped SNe and calcium-rich transients.
• A possible pathway toward compact binary neutron star systems.

• SN 2019ehk as a new candidate; a companion is not a NS?
– The SN properties anyway shared with the USSNe.
– A new link to Ca-rich transients.

• Search for SNe leaving double NS systems.
– Doable and promising project for next OISTER.