‘Dark Side’ The ‘Dark Side’ of Gamma-Ray Bursts and Implications for Nucleosynthesis neutron capture elements (‘n-process’) light elements (spallation?) ApJ (2003) 595, 294 Susumu Inoue Nucleosynthesis in Baryon-Rich Outflows Associated with GRBs in collaboration with Nobuyuki Iwamoto (U. Tokyo) Manabu Orito (Tokyo Inst. Tech.) Mariko Terasawa (CNS) ‘Dark Side’

outflows in GRBs ultrarelativistic (  >100), baryon-poor (M<10 -4 M ◎ ) outflow E=  c 2 Meszaros ‘01 massive star core collapse, compact binary, etc… → hot T 0 >~MeV, thick   ~  e ≫ 1, n-rich initial conditions → expansion → nucleosynthesis?  GRB jet → limited nucleosynthesis (small amounts of D, 4 He) Lemoine 02, Pruet, et al 02, Beloborodov 03 entropy/baryon s/k b =4  m p c 2 /3T 0 ~1250  T 0 /1MeV   dimensionless entropy 〜 final Lorentz factor  =L/Mc 2. baryon-rich outflow (BRO)    → much more interesting! (n-capture elements, up to Pt, Au, U?)

dark side evidence for the dark side of GRBs (baryon-rich outflows) generic initial conditions for central engine → nucleosynthesis likely! optically thick   ~  e ≫ 1 high temperature T>~MeV → expansion high neutron fraction in most models Pruet, Woosley, Hoffman ‘02 L=  c 2. 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

dark side evidence for the dark side of GRBs (baryon-rich outflows) generic initial conditions for central engine → nucleosynthesis likely! optically thick   ~  e ≫ 1 high temperature T>~MeV → expansion high neutron fraction in most models Pruet, Woosley, Hoffman ‘02 L=  c 2. 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) !

dark side evidence for the dark side of GRBs (baryon-rich outflows) generic initial conditions for central engine → nucleosynthesis likely! optically thick   ~  e ≫ 1 high temperature T>~MeV → expansion high neutron fraction in most models Pruet, Woosley, Hoffman ‘02 L=  c 2. numerical simulations of jet propagation in collapsars Zhang, Woosley & Heger ‘03 example of failed GRB → GRB-less hypernovae?

parameters L =10 52 erg/s luminosity r 0 =10 7 cm central engine radius  =L/Mc 2 dimensionless entropy Y e =(n n /n p +1) -1 initial electron fraction. log t’ [s] (comoving time) log T [MeV]  =2  =10 2  =10  =10 3  T log  [g cm -3 ] fireball  &T profile (comoving frame trajectory) exponential power-law start from the simplest dynamical model: spherical, adiabatic, freely expanding thermally-driven steady flow choose  2 (M~10 -2 M ◎ ) relativistic limit, validity of fireball model

parameters L =10 52 erg/s luminosity r 0 =10 7 cm central engine radius  =L/Mc 2 dimensionless entropy Y e =(n n /n p +1) -1 initial electron fraction. log t’ [s] (comoving time) log T [MeV]  =2  =10 2  =10  =10 3  T log  [g cm -3 ] fireball  &T profile (comoving frame trajectory) exponential power-law start from the simplest dynamical model: spherical, adiabatic, freely expanding thermally-driven steady flow choose  2 (M~10 -2 M ◎ ) relativistic limit, validity of fireball model nuclear reaction network >3000 n-rich species inclusion of light n-rich nuclei (Terasawa et al. ‘01) crucial for n-rich, rapid expansion

 =100, Y e =0.4  T9 D2 He4 n p B11 Be9 T3 He3 Li7 s/k b ~10 5,  0 ~ g/cm 3 some D, 4 He production freezeout t’>~1ms not very exciting…  T9 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, Y e =0.4 s/k b ~2500,  0 ~ g/cm 3

Y e =0.1,  =2 near r-process (n-dripline) path flow > 3rd peak → fission cycling? abundance at peaks Y 1 <<Y 2 ~Y 3 ~10 -6, neutrons remaining s/k b ~2000  0 ~ g/cm 3 NS mergers? high M, low  disks?.

Y e =0.4,  =2 intermediate path > 2nd peak small flow > 3rd peak abundance at peaks Y 1 ~10 -7,Y 2 ~10 -6,Y 3 ~10 -8, neutrons remaining low M, high  disks?.

final heavy element abundances  =2, Y e = Ye= Ye= Ye= Ye= Ye= solar total arbitrary norm. production up to actinides for Y e <~0.4 → fission cycling? peaks intermediate between r & s (n-process) abundances at peaks Y p ~10 -6 for Y e <~0.4; small flow to high A for Y e ~0.5 neutrons always remaining → external n-capture process?

heavy element abundances vs. observations GRB-BRO (  =2) peak abundance Y F ~10 -6 ejected mass M F ~10 -2 M ◎ SN -driven wind peak abundance Y SN ~10 -4 ejected mass M SN ~10 -4 M ◎ Galactic abundances? assume: event rate R F ~ /yr/gal ~1-10 R GRB (f  =10 -3 ) ~ R SN M Gal =10 11 M ◎, t Gal =10 10 yr Y Gal =Y F M F R F t Gal /M Gal ~ ~ × solar pattern different from SN → contribution to some Galactic elements? comparable per event! kinetic energy E F = erg

heavy element abundances vs. observations GRB-BRO (  =2) peak abundance Y F ~10 -6 ejected mass M F ~10 -2 M ◎ SN -driven wind peak abundance Y SN ~10 -4 ejected mass M SN ~10 -4 M ◎ metal poor stars? assume: f MPS =M F /M sh ~ event dilution factor (M sh = M ◎ mass of mixing shell) Y MPS =f MPS Y F ~ ~ × solar association with most massive stars → prominent contribution at low Fe/H? comparable per event! kinetic energy E F = erg

assume: f bin =f cap M F /M mix ~ binary dilution factor (M mix = M ◎ mass of mixing zone) BH binary companion surface Y bin =f bin Y F ~ ≫ solar! (Y ◎ ~ ) sensitivity to Y e → probe of GRB central engine conditions? c.f. GRO J Israelian et al. (1999) BH companion heavy element abundances vs. observations GRB-BRO (  =2) peak abundance Y F ~10 -6 ejected mass M F ~10 -2 M ◎ SN -driven wind peak abundance Y SN ~10 -4 ejected mass M SN ~10 -4 M ◎ comparable per event! kinetic energy E F = 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 estimate M CO ~10M ◎ r~10 10 cm X L ~n BRO  (p+CO->L) r p (GeV) f   ~ 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 stars BH 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