磁気駆動型超新星爆発に伴う元素合成 - ニュートリノ吸収の ... - 東京大学

1
磁気駆動型超新星爆発に伴う
元素合成 –
ニュートリノ吸収の影響
藤本信一郎
(熊本電波高専),
橋本正章, 西村信哉 (九州大学),
固武慶 (NAOJ)、山田章一(早稲田大学)
重力崩壊型超新星と高エネルギー天文学
2009年2月2日(月)-4日(水) 東京大学
1

2
講演内容
磁気駆動型超新星爆発
磁気駆動型超新星爆発における重元素合成
低金属星における中性子過剰核の観測
磁気駆動型超新星爆発における中性子過剰
核元素合成 (ニュートリノの影響を考慮)
Ni56合成

3
磁気駆動型超新星爆発
重力崩壊の際に増幅された磁場の
磁気圧(の勾配)による爆発
– 磁場
– 回転
– 非球対称爆発:Leblanc&Wilson 79,
Symbalisty 84 ….Kotake 03, Takiwaki 05
磁場増幅
– 圧縮
– 巻き込み:親星のpoloidal 磁場、回転
– 磁気回転不安定性(Akiyama+ 03, 05,
Obergaulinger 08)
降着円盤の粘性源
磁場増幅、角運動量輸送
指数関数的増幅、増幅率 1/Ω
親星の自転: 低金属量星、連星
重力崩壊の際の磁力線

4
neutron-rich ejecta from SNe
ニュートリノ駆動超新星爆発
– 中性子のニュートリノ吸収による
加熱
– 低い中性子/陽子比(n/p比)
磁気駆動超新星爆発
– ニュートリノ吸収は爆発に本質的
ではない
– 高いn/p比が期待
元素合成(Sato73,74)
– パラメータ:n/p比、放出ガス速度
– Dynamical r-process
– 高いn/p比の場合:速い中性子捕
獲反応R-processの可能性
Ejecta from nu-driven SN、Pruet05
9Msun
15Msun
Ejecta from nu-driven SN、Wanajo07
Ye>0.45

5
Nucleosynthesis in the n-rich ejecta
原始
中性子星
中性子過剰ジェット中
の元素合成の模式図
ベータ平衡
NSE
NSE
N-rich
5X10^9 K
光分解↓
1-2X10^9K
速い中性子捕獲
核分裂
ジェットの進行方向: 0.1c
ベータ崩壊
アルファ崩壊
核分裂
n/p比はDynamics
に敏感

磁気駆動超新星爆発における元素合成
6
2DMHD計算に基づく元素合成
13Msun球対称星
磁場、回転はパラメータ
高いn/p比
R-process元素合成
Nishimura06

7
超新星が付随するガンマ線バースト
回転大質量星(>30-40Msun)
の重力崩壊
Long GRB with SN
– GRB980425/SN1998bw
– GRB030229/SN2003dh
– GRB060218/SN2006aj
Hypernova
– 爆発エネルギー1e52erg
– 多量のNi56 > 0.3Msun
ニュートリノ駆動 < 1e51erg?
磁気駆動?
Collapsar model of GRB

磁気駆動超新星爆発における元素合成
8
2DMHD計算に基づく元素合成
40Msun大質量星
ブラックホール
高い中性子/陽子比
R-process元素合成
M(56Ni)ej↑
for Eej↑
Eej [10 51 ergs]
Fujimoto07, 08
M10
Mej = 0.24Msun
0 Ye 0.5

9
ニュートリノ吸収のn/p比への影響
r=10km, L=10^53 erg/s で全てのnはpに
(electron neutrino だけ放出されるなら)

n-rich elements in metal poor stars
r-rich
r-poor
10
太陽系組成に近い
Universality?
Data taken from SAGA@北大
rs-rich
a-rich
Binary、AGB

11
n-rich elements in metal poor stars
Data taken from SAGA@北大
r-rich r-poor
Eu↓Sr↑ 低金属量
LEPP(Lighter Elements Primary
Process)
Weak r-process

12
27 Sep. - 03 Aug. 2008
研究目的
MPSや太陽系における中性子過剰核の起源
Ni56放出量、Hypernova的な爆発(>0.1Msun)
LEPP?
P-elements?
1. MHD Simulation of core collapse of a collapsar before
the BH formation, using MHD code taking into account
neutrino cooling and change in electron fraction (Ye)
due to neutrino interactions
2. Nuclesynthesis, appropriately evaluating changes in Ye
due to electron and positron captures as well as
neutrino captures on nucleon

MHD Code
ZEUS 2D Code: 2.5D Axisymmetric, Newtonian
Realistic equation of state: Shen EOS (Kotake+03)
Neutrino reactions : Leakage Scheme (Ruffert+96)
four species
Cooling: e- e+ capture, e- e+ pair annihilation, plasmon
decay
Ye evolution: neutrino interactions in an optically thick
region, in addition to e- e+ capture
Self gravity with approximate GR effects (Marek+05)
Code test: reasonable agreement between our results and
those of more elaborate simulations (Sumiyoshi+05,07) for
spherical collapse of 15Msun and 40 Msun stars
13

Initial setup
Initial model = 35OC model (Woosley & Heger 06)
14
rotating, 35Msun star at presupernova
low metallicity: Z = 0.1 Zsun
low mass loss rate at WR phase: 0.1 x standard rate
candidate for progenitor of a gamma-ray bursts
Initial density, temperature, Ye(electron fraction), and
angular velocity of MHD calc. = those of 35OC model
Magnetic fields (Bz = 1e11 G, Bphi = 8e11 G)
same as in Dessart+08 model:
M0 (Bz = 2e10 G) & M1 (Bz 5*Bz = 1e11G)
Computational region: r

15
Log density
Ye
Jet-like explosion
0.46s 0.50s 0.53s
Dense
jets
0.46s 0.50s 0.53s
Note that neutrino
absorption is not
taken into account
in optically thin
regions
1000km
x1000km

16
Neutrino luminosity
rotating Non-rotating
t(bounce)=0.377sec
35OC
Luminosities
Luminosities
lower than those
for spherical case
t(final)=0.593sec
M(r): 35OC
Low
Mdot
Luminosities: u35
high
Mdot
t(bounce)=0.369sec
M(r): u35

17
質量放出率、エネルギー放出率
bounce
Time(s)
M1 M0
35OC-M1
@500km
dM/dt_ej ~ 0.5Msun/s
dEdt_ej ~ 5 x 10^52erg/s
dM/dt_ac ~ 0.5Msun/s
Dessart+08 with
VULCAN2D

18
Lagrangian evolution of the jets
Tracer particle method
To calculate Lagrangian evolution
from Eulerian evolution.
1. 3,000 tracer particles are initially
placed from iron core to silicate
layers.
2. We follow time evolution of
position of the tracer particles.
3. We can select particles (jet
particles) which are ejected
through the jets. We have 213
jet particles
Ye(NSE) = Electron fraction
(electron per baryon) at T9 = 9
3000km
x3000km
Trajectories of
3 jet particles
200km
x200km

19
Maximum density, T, & Vr of
the jet particles
Ejecta
from core
surface
Ejecta
from outer
layers
Max. density vs. Max. T
Tmax = Max. temperature
Vr,max = Max. radial velocity
Ejecta from
dense core
Ejecta from core and
core surface are
fast ( 0.2-0.3c)
Max. density vs. Max. Vr
Ejecta
from outer
layers
Ejecta from
dense core
Ejecta
from core
surface

20
Evolution of electron fraction (Ye) of
a jet particle
in high density (>= 1e11 g/cc) region
Ye = Ye(MHD) on the position of the
particle at the time
in low density (< 1e11 g/cc) region
DYe via e-,e+ captures and neutrino
absorptions
Note that neutrino absorption on nucleon is taken into
account in MHD simulations, only in an optically thick region.

21
Neutrino absorption
Neutrino absorption rates
per baryon for Yn = 0.5
0.53s
Y
10/sec
100
km
500km x 500km
1 neutrino/sec
L = 5.2e52ergs/s
200
km
neutrino
sphere
X
Log[ e- capture rate/
neutrino capture rate]
Ye↓
500km x 500km
Ye↑
e- capture
dominant
region in jets
Electron captures are dominate over neutrino
absorption in the dense jets near the polar axis
2
0
-2

22
Ye distribution of the jets
ニュートリノ無視
2 x e-neutrino flux
35OC-M1
0.042Msun
n-rich ejecta via
jets
Ni56-rich ejecta
from outer layers
0.028Msun
Ye(NSE)=Electron fraction (electron per baryon) at T9 = 9
0.014Msun
During 0.1sec

23
Evolution of electron fraction of jet
particles
Low Ye particle (Ye(NSE)=0.2) Middle Ye particle (Ye(NSE)=0.4)
Ye
Log r
R-process
In jets with small theta,
high rates of electron
capture due to high
densities
logT
Log rho
Ye
electron
capture
dominant
Log r
Log
rho
R-process
In jets with small theta,
low rates of electron
capture due to low
densities
Log r
logT
neutrino
capture
dominant
Ye(NSE)=Electron fraction (electron per baryon) at T9 = 9
Ye
logT
Ye

24
Abundances of the most neutronrich
jet particle: 35OC-M1
Abundances on the nuclear chart during neutron-capture
Ye(NSE) = 0.2
Z=42
(Mo)
Stability line
N=82
Z=100
alpha-decays
U,Th
N=126
Betadecays
neutron captures
+ beta decays
N=184

Abundances of jet particles after decay
25
Fe
poor
2 nd peak
r-process
in low
Ye(NSE)
particles
3 rd peak
small
amounts
of U & Th

Composition:Collapsar & Solar system
26
Abundances vs A
small amounts of
nuclei with A > 180
different from the
abundance profile of
solar r-elements
small amounts of
nuclei with Z > 80
Log Abundances vs Z

27
different from the
abundance profile of
MPS
Collapsar and MPSs
R-rich
Log eps vs Z
for collapsar & MPS
R-poor

28
中性子過剰核のYe依存性
Eu,Ba-rich
Ru,Pd,Ag-rich
2つのモデル(M12+35OC)

29
Mass of Ni56
•Ejecta from Core: Ni56 poor (Ye 0.1Msun
球対称?、~1秒間継続?
E=3x10^52erg
Maeda astro-ph0901.0410

30
Mass of Ni56:Ni56 winds
40Msun star
0.1 Msun nucleon
via winds
The winds are
driven via viscous
heating through
alpha-viscosity.
No winds in MHD
simulations
MacFadyen & Woosley 1999

31
まとめ
磁気駆動型超新星における中性子過剰核元素合成
– ニュートリノ駆動型超新星より中性子/陽子比が大きな
ガスを放出しやすい
– ガスの組成は中性子/陽子比に敏感
– 特にニュートリノのガスの組成への影響はダイナミクス
に敏感
Ni56質量
– コアから放出される量は非常に少ない
– 外層からの寄与 > 0.04Msun/sec
– 計算領域外のガスからの寄与はより大きい可能性あり
– Hypernova的な爆発?