NEUCOS, DESY, May 29–June 2 2017
Nuclear composi on of GRB jets: sources and survival
Shunsaku Horiuchi (Center for Neutrino Physics, Virginia Tech)
Image credit: NASA/ESA Contents A. Heavy nuclei in massive stars B. The nuclei composi on of jets – Stellar nucleosynthesis – Ini al loading – Explosive nucleosynthesis – Entrainment – In-situ jet nucleosynthesis – Destruc on processes C. Accelera on to UHECR D. Conclusion
NEUCOS Shunsaku Horiuchi (Virginia Tech) 2 Stellar Nucleosynthesis
Nucleosynthesis Iron nuclei abundance Massive stellar nucleosynthesis The final Fe core mass is typically some 1.5 results in the famous onion-shell Msun with radius of 108 cm or so structure:
+ : Fe core mass Core mass
Ini al mass Woosley et al (2002)
NEUCOS Shunsaku Horiuchi (Virginia Tech) 3 Explosive Nucleosynthesis
Propaga on of shock wave Compression Explosive through the core & envelope and hea ng nucleosynthesis
Energy injec on Mass cut defines final remnant
Expansion
Shock compression The rest and hea ng is ejected
However, how much heavy nuclei is released is model dependent: 1. Some amount of energy injec on 2. At some loca on 3. With some mass cut
NEUCOS Shunsaku Horiuchi (Virginia Tech) 4 How much is possible?
A lot of 56Ni (poten ally) With large CO core, large explosion energies, and small mass cut, up to ~10 Msun
~109 cm
Core collapses typically observed ~0.1 Msun of 56Ni. Umeda & Nomoto (2008) (some may have more, e.g., hypernovae, superluminous supernovae; x100 needed if 56Ni) NEUCOS Shunsaku Horiuchi (Virginia Tech) 5 1. Ini al loading 2. Entrainment 3. In-situ nucleosynthesis 4. Destruc on processes COMPOSITION OF JETS
NEUCOS Shunsaku Horiuchi (Virginia Tech) 6 1. Ini al loading
External composi on Depends on jet model and launch ming, e.g., • Original stellar nuclei if launched prior to supernova shock revival • More nuclei if a er (20Msun) explosive nucleosynthesis Can nuclei survive?
NEUCOS Shunsaku Horiuchi (Virginia Tech) 7 Survival in ini al loading
Photodisintegra on
Thermal photons with T0 as:
Spalla on Target ion/nucleons
thermalized to T0 Nuclei survival Op cal depths of destruc ve processes must be small 8 à Needs large r0 > 10 cm or 49-50 low Lrad < 10 erg/s à Low-luminosity or magne c models be er for survival than fireball NEUCOS Shunsaku Horiuchi (Virginia Tech) Horiuchi, Murase, et al (2012) 8 Simula ons Loading simula ons 2D rela vis c MHD simula on of jet induced collapse, mass fall back, and jet bulk accelera on. Fireball • Fireball: heavy nuclei dissociated • Magne c (par ally): par al dissocia on of nuclei
à Magne c models (and low-Lrad) be er for nuclei composi on
Magne c magne za on
NEUCOS Shunsaku Horiuchi (Virginia Tech) Shibata & Tominaga (2015) 9 2. Entrainment
Entrainment of external nuclei into the jet medium: do nuclei survive?
star jet nuclei
Can it safely do this?
NEUCOS Shunsaku Horiuchi (Virginia Tech) Zhang et al. (2003) 10 Survival in entrainment Cocoon The cocoon is made up of shocked Jet head Stellar ma er ~ stellar and shocked jet material and has βh 0.1 (plenty of nuclei) expands non-rela vis cally into the stellar material. Jet has Γ >> 1 (1) 0.01L3/8 r1/2 c ⇠ ke,50 9 (1) 3/16 1/2 nuclei-rich Tc 100L r9 keV ⇠ ke,50 à Cocoon can be nuclei rich (mixing Cocoon aided by instabili es) e.g., Aloy (2002) JET βc ~ 0.01 e±, γ,
some T cocoon jet h nuclei nuclei
cocoon
Stellar ma er Can it safely do this?
NEUCOS Shunsaku Horiuchi (Virginia Tech) 11 Survival in entrainment
Survival Demand the nuclei velocity is always below the spalla on threshold à requires the nuclei to be thermalized FASTER than it takes to move up the velocity gradient and its speed becomes too fast
Rapid thermaliza on for Survival KEFe < 20 GeV Energy loss on electrons are fast (can à If velocity gradient is small, nuclei be further helped by pair thermalize before reaching the e+e- when T is high) and spalla on is slower spalla on threshold
(Collimated jets can tolerate a higher gradient due to higher e- density)
cocoon jet nuclei Conical jet (easier for collimated jet)
Can it safely do this?
NEUCOS Shunsaku Horiuchi (Virginia Tech) Horiuchi et al (2012) 12 3. In-situ jet nucleosynthesis
GRB fireball: • Ini al radia on temperatures of a few MeV à nuclei are dissociated (NSE) 5 • Large entropy (nγ/np ~ 10 ) • needed for satura on Lorentz factor η > 100 • Rapid expansion me scales (~0.1 ms) • Electron frac on probably close to 0.5 • but uncertain
NEUCOS Shunsaku Horiuchi (Virginia Tech) 13 In-situ jet nucleosynthesis: fireball
Nucleosynthesis Bo leneck to heavy nuclei synthesis due to easily destroyed deuterium.
He
d
When T is low enough for the
bo leneck to be broken, the Mass frac on jet is too dilute for tripe- alpha to be fast enough. Freeze-out composi on à Very few heavy nuclei are Radius [cm] made Pruet et al (2002), Lemoine (2002), Beloborodov (2003)
NEUCOS Shunsaku Horiuchi (Virginia Tech) 14 Alterna ves
Importance of entropy and expansion mescale Lower entropy and larger mescale are conducive to nucleosynthesis à Deuterium produc on is more efficient and deuterium bo leneck is broken earlier while densi es are s ll high.
1. Magne c scenario
Lrad can be low if the GRB can be powered magne cally, e.g., for rapidly rota ng proto-magnetar model e.g., Usov (1992) ˙ 49 4 2 6 1 Thompson (1994) E 10 Pms B15R6 erg s ⇠ e.g., Blandford & Other models, e.g., magne zed disk winds or BH powered Znajek (1977)
2. Low-luminosity GRB and dirty (baryon) jets
With lower Lrad by default (but enough for ini al dissocia on). With large baryon loading by default
NEUCOS Shunsaku Horiuchi (Virginia Tech) 15 Example: proto-magnetar scenario
Proto-magnetar model: Neutrino-driven wind + The GRB jet fills a sweet spot; later, it becomes a magne c driven ou low pair-wind as the neutrino-driven wind subsides χ=0: aligned χ=π/2: oblique
Pre-jet break phase Jet proper es
GRB phase Pair wind phase “magne za on” E˙