The ‘Dark Side’‘Dark Side’ of Gamma-Ray Burstsand Implications for Nucleosynthesis

neutron capture elements (‘n-process’)light elements (spallation?)

ApJ (2003) 595, 294

Susumu Inoue

Nucleosynthesis in Baryon-RichOutflows Associated with GRBs

in collaboration with

Nobuyuki Iwamoto (U. Tokyo)Manabu Orito (Tokyo Inst. Tech.)Mariko Terasawa (CNS)

‘‘Dark Side’Dark Side’

outflows in GRBs

ultrarelativistic (>100) , baryon-poor (M<10-4M◎ ) outflow E=c2

Meszaros ‘01

massive star core collapse, compact binary, etc… →

hot T0>~MeV, thick ~e≫1,n-rich initial conditions→ expansion→ nucleosynthesis?

GRB jet → limited nucleosynthesis (small amounts of D,4He)Lemoine 02, Pruet, et al 02, Beloborodov 03

entropy/baryon s/kb=4mpc2/3T0~1250T0/1MeV

dimensionless entropy 〜 final Lorentz factor=L/Mc2

.

baryon-rich outflow(BRO)

≪ → much more interesting! (n-capture elements, up to Pt, Au, U?)

evidence for the dark sidedark side of GRBs (baryon-rich outflows)numerical simulations of jet propagation in collapsars Zhang, Woosley & Heger ‘03

significant energy in peripheral, low outflow → X-ray flashes, statistics of afterglow light curve breaks

evidence for the dark sidedark side of GRBs (baryon-rich outflows)observations! of low outflow in GRB030329/SN2003dh Berger et al. ‘03, Nature, 426, 154

dominant energy in peripheral, low (~a few) outflow → dark energy rules (at least in some GRBs) !

evidence for the dark sidedark side of GRBs (baryon-rich outflows)numerical simulations of jet propagation in collapsars Zhang, Woosley & Heger ‘03

example of failed GRB → GRB-less hypernovae?

parametersL=1052 erg/s luminosityr0=107 cm central engine radius

=L/Mc2 dimensionless entropyYe=(nn/np+1)-1

initial electron fraction

.

log t’ [s] (comoving time)

log

T [M

eV]

=2

=102

=10

=103

T

0

2

4

6

-2

-4

-6

-6 -5 -4 -3 -2 -1

log

[g

cm

-3]

fireball &T profile(comoving frame trajectory)

exponential

power-law

start from the simplest dynamical model:spherical, adiabatic, freely expandingthermally-driven steady flow

choose 2 (M~10-2M◎)relativistic limit,validity of fireball model

parametersL=1052 erg/s luminosityr0=107 cm central engine radius

=L/Mc2 dimensionless entropyYe=(nn/np+1)-1

initial electron fraction

.

log t’ [s] (comoving time)

log

T [M

eV]

=2

=102

=10

=103

T

0

2

4

6

-2

-4

-6

-6 -5 -4 -3 -2 -1

log

[g

cm

-3]

fireball &T profile(comoving frame trajectory)

exponential

power-law

start from the simplest dynamical model:spherical, adiabatic, freely expandingthermally-driven steady flow

choose 2 (M~10-2M◎)relativistic limit,validity of fireball modelnuclear reaction network

>3000 n-rich speciesinclusion of light n-rich nuclei(Terasawa et al. ‘01)crucial for n-rich, rapid expansion

=100, Ye=0.4

T9

D2

He4

np

B11Be9

T3

He3

Li7

s/kb~105, 0~ 3 103 g/cm3

• some D, 4He production• freezeout t’>~1ms not very exciting…

D2

He4

n

p

B11

Be9

T3

He3

Li7

• reactions continue, t’>~100s, A>16 and beyond• late D production by n decay → p(n,)d a lot more interesting!

=2, Ye=0.4 s/kb~2500, 0~ 2 105 g/cm3

Ye=0.1, =2

• near r-process (n-dripline) path• flow > 3rd peak → fission cycling?• abundance at peaks Y1<<Y2~Y3~10-6, neutrons remaining

s/kb~20000~ 2 105 g/cm3

NS mergers? high M, low disks?.

Ye=0.4, =2

• intermediate path > 2nd peak• small flow > 3rd peak• abundance at peaks Y1~10-7,Y2~10-6,Y3~10-8, neutrons remaining

low M, high disks?.

final heavy element abundances =2, Ye=0.1-0.498

----- Ye=0.1----- Ye=0.3----- Ye=0.4----- Ye=0.48----- Ye=0.498

----- solar total arbitrary norm.

• production up to actinides for Ye<~0.4 → fission cycling?• peaks intermediate between r & s (n-process)• abundances at peaks Yp~10-6 for Ye<~0.4; small flow to high A for Ye~0.5• neutrons always remaining → external n-capture process?

heavy element abundances vs. observations

GRB-BRO (=2)peak abundance YF~10-

6

ejected mass MF~10-2

M◎

SN -driven windpeak abundance YSN~10-

4

ejected mass MSN~10-4M◎

Galactic abundances?assume:event rate RF~10-4-10-3/yr/gal ~1-10 RGRB(f=10-3) ~0.01-0.1 RSN

MGal=1011M◎, tGal=1010yrYGal=YF MF RF tGal/MGal

~10-13 ~ 10-2-10-1×solarpattern different from SN → contribution to some Galactic elements?

comparableper event!

kinetic energy EF =4 1052 erg

heavy element abundances vs. observations

GRB-BRO (=2)peak abundance YF~10-

6

ejected mass MF~10-2

M◎

SN -driven windpeak abundance YSN~10-

4

ejected mass MSN~10-4M◎

metal poor stars?assume:fMPS=MF/Msh~10-7.5 1 event dilution factor(Msh=3 105M◎ mass of mixing shell)YMPS=fMPSYF~10-13.5 ~ 10-2.5×solar

association with most massive stars → prominent contribution at low Fe/H?

comparableper event!

kinetic energy EF =4 1052 erg

assume:fbin=fcapMF/Mmix~10-3-10-1

binary dilution factor(Mmix=10-4-10-2M◎ mass of mixing zone)

BH binary companion surface

Ybin=fbinYF~10-9-10-7≫ solar! (Y◎~10-11) sensitivity to Ye → probe of GRB central engine conditions?

c.f. GRO J1655-60Israelian et al. (1999)

BH

companion

heavy element abundances vs. observations

GRB-BRO (=2)peak abundance YF~10-

6

ejected mass MF~10-2

M◎

SN -driven windpeak abundance YSN~10-

4

ejected mass MSN~10-4M◎

comparableper event!

kinetic energy EF =4 1052 erg

next directions

need good understanding of central engine… but we don’t

more realistic dynamical conditions, microphysics(→ more nucleosynthesis? r-process pattern?) non-relativistic, collimation, … -interactions, fission, p-rich heavy nuclei, , …

Pruet, Woosley & Hoffman 03, Pruet, Surman & McLaughlin 03…

BH accretion disk models? modeling of ‘wind’ difficult…

interaction with external matter (spallation, external n-capture, etc)…

crude estimateMCO~10M◎ r~1010cmXL~nBRO (p+CO->L) rp(GeV) f~10-7-10-6

CO

e.g. p+CO->Li, Be, B

contact discont.forward shock

p

CO

C+O->L?

Si, Fe layers?streaming neutrons?

after shock established:

Summary low baryon-rich outflows (the dark side) of GRBs

• synthesize heavy n-capture elements up to the actinides induce ‘n-process’ (intermediate between r & s)• synthesize some light elements D, Li, Be, B much more by spallation?

baryon-poor, ultrarelativistic outflows (successful GRBs): not much happens…

heavy n-capture elements possibly observable in:Galactic abundances, metal poor starsBH binary companions → probe of GRB central engine conditions?

baryon-rich, mildly relativistic outflows (circum-jet winds or failed GRBs) can:

observational implications

Something interesting may be going on in places not readily seen!

• energetically important (often dominant)• interesting for nucleosynthesis