宇宙線研究所小研究会 高エネルギー現象で探る宇宙の多様性

キロノバのスペクトルで探る
r-process元素合成の痕跡
土本菜々恵 (東北大学)
田中雅臣 (東北大学), 川口恭平 (宇宙線研), 加藤太治 (核融合研), 和南城伸也 (MPI)

2021/10/18 (Mon.)

元素の起源
ビッグバン

星の中、超新星爆発?

連星中性子星合体: r-process site
neutronradioactive decaye−γ-> Thermal radiation (kilonova)

Sekiguchi et al. 2015

元素組成
合成される元素の電子割合 (Ye) 依存

Ye =npnn + np- low Ye: heavy elements- high Ye: lighter elements

Shibata et al. 2017

Tanaka et al. 2017

GW170817/ Kilonova
Which and how much elements?
Sr II Watson et al. 2019

Utsumi et al. 2017(broad) r-process!

Kawaguchi et al. 2018

Pian et al. 2017

観測スペクトル
恒星

キロノバ:(鉄より重い) 重元素ばかり
膨張速度が速い
赤外線で長時間光る
Sneden et al. 2008

超新星爆発v ~ 0.2 cv ~ 10,000 km/s

Filippenko et al. 1997

Pian et al. 2017

Motivation
元素組成→ 元素の起源、中性子星合体の物理
スペクトルにおける元素の同定に向けて:どの元素が強い吸収を作れるのか？

輻射輸送計算
Tanaka & Hotokezaka 2013, Tanaka et al. 2014, 2017, Kawaguchi et al. 2018

- 質量: Mej = 0.03 Msun
- 速度: v = 0.05-0.3 c- 密度構造: 1D simple power law (ρ ∝ r −3)- 元素組成 : a multi-components free expansion model Wanajo 2018

- Line strength of bound-bound transitions
2πeτl =flni,jtλlmec- Line list : VALD (the Vienna Atomic Line Database)*based on atomic experiments

輻射輸送計算- 元素組成 : a multi-component free expansion model
0LightSolar
Heavyr-residuals-1Log mass fraction

Wanajo 2018

-2-3-4-5-6Lanthanides-7050

100150
Atomic mass number

200250Results: synthetic spectrum
Light

Sr II

Sobolev optical depth

103

10−14

Ca II
Sr IICe IIITb III
Th III

10−15

X(Ca)~2E-2X(Sr)~1E-2102

10−1610110−17100

1.5 d10−110−205000

10000
15000
20000
Wavelength (Å)

25000

10−1810−1930000

Flux (erg s−1 cm−2 Å−1)

Ca II104ρ ∼ 6 × 10−15 g cm−3, T ∼ 5200 K at v ∼ 0.2c

Sr II/Ca II triplet
They have a similar atomic structure and transitions.
2[Ar]3dD5,3
Ca II triplet
22 2

Sr II triplet [Kr]4d D 52 , 32

[Ar]4p 2Po3 , 1
2 2

2 o[Kr]5p P 3 , 12 2https://www.nist.gov/pml/
periodic-table-elements

10410

3Ca II
Light, T=5000 K

Sr IICa
SrCeTbTh102

10−16101

100

10−1
10−2

10−17

1.5 d05000

10000
15000
20000
Wavelength (Å)

25000

30000

GW170817 → X(Ca)/X(Sr) < 0.002

Flux (erg s−1 cm−2 Å−1)

Sobolev optical depth

For GW170817

Physical conditions
color: v=0.2c & different entropies0

s=10 (kB/nuc)s=15 (kB/nuc)s=20 (kB/nuc)s=25 (kB/nuc)s=30 (kB/nuc)s=35 (kB/nuc)

Mass fraction X(Ca)

10-1

10100-2

10-3

10-2

10-3

10-4

10-4

10-510-500.1

s=10 (kB/nuc)s=15 (kB/nuc)s=20 (kB/nuc)s=25 (kB/nuc)s=30 (kB/nuc)s=35 (kB/nuc)10-1

Mass fraction X(Sr)

100.2

0.3
Ye0.4

0.5

00.1

0.2

0.3

0.4

Ye

X(Ca)/X(Sr) < 0.002→Velocity and entropy of high-Ye component is relatively highfor GW170817.

0.5近赤外線における吸収線
In the λ < 10000 A:- Sr IIとCa IIが強い吸収線を作りうる(high-Ye tracer)→ GW1701817へ制限

赤外線の吸収線を同定できるか？
*Problem:lack of accurate atomic data
- Spectral features must be affectedby accurate atomic data
Pian et al. 2017

Summary• The origin of elements, physics of NS mergers• Identification in spectra is
direct way to find synthesized elements.

• Which elements can produce absorption features?
- Not only Sr II but also Ca II lines also appear in the spectra
if including less heavy elements (high-Ye tracer).
- We can directly obtain the evidence ofsynthesized heavy elements like lanthanides.
- NIR lines are important for understanding of NSM.

• Observational properties of high energy explosion
is determined by (micro) atomic physics.