1. Nucleosynthesis in jets from Collapsars
Shin-ichiro Fujimoto
(KNCT, Japan),
Collaboration with
Nobuya Nishimura, & Masa-aki Hashimoto
(Kyusyu Univ., Japan)
Japan

2. Collapsar model of gamma-ray bursts
Collapsar = Rapidly rotating massive star collapsing to BH
(Woosley 1993)
During gravitational collapse of a massive star ( > about 20Msun)
The central core collapses to a black hole (BH)
Outer layers form an accretion disk around BH due to high angular momentum.
Jets from an inner part of the disk.
The jets are accelerated to relativistic velocities.
We can observe a GRB if we locate on directions to jet propagation.
Scenario plausible for GRB
because of the discovery of GRB with a core collapse supernova (SN)
(GRB980425/SN1998bw, GRB030329/SN2003dh)

3. Motivations R (rapid neutron capture)-process in collapsar jets
Neutron-rich disk in a collapsar from 1D study
Collapsar = New r-process site ?
Variety of masses of 56Ni in SN with nearby GRBs
GRB with hypernova (HN): GRB030329: M(56Ni) > 0.3 Msun
GRB with normal SN: GRB060219: M(56Ni) < 0.1 Msun
GRB without SN: GRB060505: M(56Ni) < 0.01 Msun
 Can such the diversity be explained in light of collapsar model ?
Based on 2D MHD simulations of collapsars
with various distributions of rotation and B fields
 Nucleosynthesis in jets from the collapsars
R-process & masses of 56Ni
No parameters other than initial conditions of a collapsar before core collapse

4. Numerical setup in MHD simulations
40Msun collapsar
before the core collapse
(Hashimoto 1995)
Rapid, Moderate, or Slow core
Vertical and uniform magnetic fields
Angular velocity: R (rapid), M (moderate), S (slow)
Magnetic field B0: 108G, 1010G, 1012G
9 collapsars: R8, R10, R12, no ejection of jets
M8, M10, M12, ejection of jets
S8, S10, S12
rapid
moderate
slow

5. Lagrangian evolution of the jets
Distribution of jet particles: M12
3000km x 3000km
Tracer particle method
ρ,T↑
t=0.20s
Lagrangian evolution from Eulerian evolution (M12).
2,000 tracer particles are initially placed from Fe core to O-rich layers.
We can follow time evolution of position of all tracer particles.
One can select particles (jet particles) that are ejected through the jets jet particles
ρ,T↓
t=0.25s
ρ,T↓
t=0.31s
the onset of collapse: t = 0 s

6. Maximum densities and temperatures of jet particles
Higher density & T states
High density jet particles
are expected
to be neutron-rich
due to p+e n
1e+11
1e+9g/cc
56Ni produced
Similar to Type II SNe
Incomplete Si burning
Complete
Si burning
1e+06
3e+9
3e+10
1e+9 g/cc
B0=1010G
Incomplete Si burning
Complete
Si Burning
3e+9
3e+10
B0=1012G

7. Ye vs maximum density of jet particles
Ye = electron fraction (=electron par baryon) at T = 9e+9 K
Ye = 0.4
more n-rich for Ye↓
1e+9g/cc
1e+06
1e+11
B0=1010G
Ye = 0.4
Many n-rich particles
for M10, M12, & R12
1e+9g/cc
R-process is expected to operate
1e+06
1e+11
B0=1012G

8. Composition of collapsar jets and Eu-scaled solar r-elements
□: Eu-scaled solar r-nuclei
Abundance profiles of
collapsar jets are similar to
those of the solar r-elements
for A >
U,Th
M12
R12
U,Th
U,Th
A=80
A=80

9. Ejected masses of 56Ni & r-elements
Bright SNe (HNe)
Enegetic jet with r-elements
0.12 & 0.3 Msun/s
Normal SNe
Weak or no SNe
M(56Ni)ej↑ for Eej↑
Bright-ness of SNe
Eej [1051 ergs]

10. Summary R-process in the jets Masses of 56Ni in the jets
We have investigated nucleosynthesis inside the jets from collapsars, based on 2D MHD simulations of the collapsars in light of the collapsar model of GRBs
R-process in the jets
R-process in the energetic jets (Eej > 1051ergs) from three collapsars (M10, M12, R12)
Even for a collapsar (M10) with moderate rotation (2.5Hz) and 1010G
Large amounts of r-nuclei (> 0.01Msun)
Masses of 56Ni in the jets
Jets with Eej ↑, Mass of 56Ni ↑
The diversity of Ni56 mass in GRBs is likely to be explained in light of the collapsar model
ApJ644, 1040, 2006 (MHD), ApJ656, 382, 2007 (r-proc.)