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Home , Stellar nucleosynthesis

NEUCOS, DESY, May 29–June 2 2017

Nuclear composion of GRB jets: sources and survival

Shunsaku Horiuchi (Center for Physics, Virginia Tech)

Image credit: NASA/ESA Contents A. Heavy nuclei in massive B. The nuclei composion of jets – Stellar – Inial loading – Explosive nucleosynthesis – Entrainment – In-situ jet nucleosynthesis – Destrucon processes C. Acceleraon to UHECR D. Conclusion

NEUCOS Shunsaku Horiuchi (Virginia Tech) 2

Nucleosynthesis 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

Inial mass Woosley et al (2002)

NEUCOS Shunsaku Horiuchi (Virginia Tech) 3 Explosive Nucleosynthesis

Propagaon of Compression Explosive through the core & envelope and heang nucleosynthesis

Energy injecon Mass cut defines final remnant

Expansion

Shock compression The rest and heang is ejected

However, how much heavy nuclei is released is model dependent: 1. Some amount of injecon 2. At some locaon 3. With some mass cut

NEUCOS Shunsaku Horiuchi (Virginia Tech) 4 How much is possible?

A lot of 56Ni (potenally) With large CO core, large explosion , 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. Inial loading 2. Entrainment 3. In-situ nucleosynthesis 4. Destrucon processes COMPOSITION OF JETS

NEUCOS Shunsaku Horiuchi (Virginia Tech) 6 1. Inial loading

External composion Depends on jet model and launch ming, e.g., • Original stellar nuclei if launched prior to shock revival • More nuclei if aer (20Msun) explosive nucleosynthesis Can nuclei survive?

NEUCOS Shunsaku Horiuchi (Virginia Tech) 7 Survival in inial loading

Photodisintegraon

Thermal photons with T0 as:

Spallaon Target ion/nucleons

thermalized to T0 Nuclei survival Opcal depths of destrucve processes must be small 8 à Needs large r0 > 10 cm or 49-50 low Lrad < 10 erg/s à Low-luminosity or magnec models beer for survival than fireball NEUCOS Shunsaku Horiuchi (Virginia Tech) Horiuchi, Murase, et al (2012) 8 Simulaons Loading simulaons 2D relavisc MHD simulaon of jet induced collapse, mass fall back, and jet bulk acceleraon. Fireball • Fireball: heavy nuclei dissociated • Magnec (parally): paral dissociaon of nuclei

à Magnec models (and low-Lrad) beer for nuclei composion

Magnec magnezaon

NEUCOS Shunsaku Horiuchi (Virginia Tech) Shibata & Tominaga (2015) 9 2. Entrainment

Entrainment of external nuclei into the jet medium: do nuclei survive?

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 maer ~ stellar and shocked jet material and has βh 0.1 (plenty of nuclei) expands non-relaviscally 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 instabilies) e.g., Aloy (2002) JET βc ~ 0.01 e±, γ,

some T cocoon jet h nuclei nuclei

cocoon

Stellar maer Can it safely do this?

NEUCOS Shunsaku Horiuchi (Virginia Tech) 11 Survival in entrainment

Survival Demand the nuclei velocity is always below the spallaon 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 thermalizaon 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 spallaon is slower spallaon 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: • Inial radiaon temperatures of a few MeV à nuclei are dissociated (NSE) 5 • Large entropy (nγ/np ~ 10 ) • needed for saturaon Lorentz factor η > 100 • Rapid expansion me scales (~0.1 ms) • fracon probably close to 0.5 • but uncertain

NEUCOS Shunsaku Horiuchi (Virginia Tech) 13 In-situ jet nucleosynthesis: fireball

Nucleosynthesis Boleneck to heavy nuclei synthesis due to easily destroyed .

He

d

When T is low enough for the

boleneck to be broken, the Mass fracon jet is too dilute for tripe- alpha to be fast enough. Freeze-out composion à Very few heavy nuclei are Radius [cm] made Pruet et al (2002), Lemoine (2002), Beloborodov (2003)

NEUCOS Shunsaku Horiuchi (Virginia Tech) 14 Alternaves

Importance of entropy and expansion mescale Lower entropy and larger mescale are conducive to nucleosynthesis à Deuterium producon is more efficient and deuterium boleneck is broken earlier while densies are sll high.

1. Magnec scenario

Lrad can be low if the GRB can be powered magnecally, e.g., for rapidly rotang - 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., magnezed disk winds or BH powered Znajek (1977)

2. Low- GRB and dirty (baryon) jets

With lower Lrad by default (but enough for inial dissociaon). 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 magnec driven oulow pair-wind as the neutrino-driven wind subsides χ=0: aligned χ=π/2: oblique

Pre-jet break phase Jet properes

GRB phase Pair wind phase “magnezaon” E˙

0 = Time since core bounce Mc˙ 2 Metzger et al (2011) (=η if fully converted to KE) NEUCOS Shunsaku Horiuchi (Virginia Tech) 16 Nucleosynthesis yields

Freezeout yield v Esmate the mass

fracon of A≥56 (Xh) with analyc wind v nucleosynthesis

• τexp: mescale v • s: entropy Roberts et al (2010) • Ye: electron fracon

For an oblique* rotator: Pre-jet • Expansion me-scale [ms] break phase • Entropy [kB/baryon] • Electron fracon?

*Obliquity reduces ν-heang GRB phase Pair wind phase by centrifugal force Time since core bounce NEUCOS Shunsaku Horiuchi (Virginia Tech) Metzger, Giannios, Horiuchi (2011) 17 Nucleosynthesis yields

Electron fracon: evolves by neutrino irradiaon to 0.4 – 0.6, but may be different due to B field alignment ˙ e + n e + p n N⌫¯e ⌫¯e L⌫¯e E⌫¯e ! + è h i ¯e + p e + n p ! N˙ ⇠ L⌫ E⌫ ! ⌫e ⌫e e h e i

Nucleosynthesis n-rich

à Freezeout composion Pre-jet can be heavy-dominated p-rich, oblique during the GRB phase break phase GRB phase Especially for: • Inially n-rich maer Pair wind phase • Oblique rotators (receive less ν-heang and hence

have lower entropies) A ≥56 nuclei mass fracon

Time [s]

NEUCOS Shunsaku Horiuchi (Virginia Tech) Metzger, Giannios, Horiuchi (2011) 18 Simulaons Aligned rotator simulaons Force-free approximaon, aligned dipole field 1014-15 G, SkyNet nuclear reacon network. Shows r-process nucleosynthesis across a range of rotaon periods Approximately 40% He, trace n and p The rest: abundance-weighed mean A

alpha

NEUCOS Shunsaku Horiuchi (Virginia Tech) Vlasov et al (2017) 19 4. Collisions with

Neutrons are collisionally coupled to the accelerang plasma: EM coulomb strong e p n $ $ $ But they lag behind if τcollision > τacc • Make sure the relave velocity ⌧coll 1 3 ˜ L r ⌘ ⇠ ⌧acc / does not exceed the spallaon threshold Conical jet • Or, the neutrons decouple (easier for collimated jet) before the spallaon threshold is reached Horiuchi et al (2012) Horiuchi, Murase, et al (2012) à Nuclei survive unless η is very large

NEUCOS Shunsaku Horiuchi (Virginia Tech) 20 5. Recollimaon shocks

Jet collimaon by cocoon pressure à becomes a shock and the post-shocked jet moves at s 1/✓j 8 ⇠ ⇠ Bromberg et al (2011)

Ions obtain random moons with the pre- and post-shocked relave Lorentz factor /2 10 ⇠ j s ⇠ But the thermal temperature is relavely high (but not high enough for photodisintegraon) à conducive to pair-creaon à creates more target to thermalize with Conical jet à Check if thermalizaon is faster than spallaon Mizuta & Aloy (2009) à Will be a problem once shock grows Horiuchi, Murase et al (2012) NEUCOS Shunsaku Horiuchi (Virginia Tech) 21 Brief Summary

Fireball GRB Magnec GRB Low-luminosity GRB Source: stellar Y Y Y nucleosynthesis Survives: inial loading? N Y Y Survives: entrainment? gradient gradient gradient Source: jet nucleosynthesis N Y maybe Survives: n-collisions? Y Y Y Survives: oblique shocks? Only early If collimaon Only early magnec “Y” means possible for canonical parameters; “N” is not possible; è In Fireball GRB, nuclei must be entrained beyond recollimaon shock radii è In magnec GRB, mulple opons è In LL GRB, mulple opons

NEUCOS Shunsaku Horiuchi (Virginia Tech) 22 ACCELERATION & SURVIVAL

NEUCOS Shunsaku Horiuchi (Virginia Tech) 23 Proto-magnetar model

Acceleraon: ~ 15-16 Demand acceleraon is Collision case: Rd 10 cm faster than cooling & GRB phase expansion mescales: Cooling limit Expansion limited Survival: Calculate the opcal depth of photodisintegraon based on the Band funcon for the Nuclei UHECR photon spectrum phase Demanding this is = 1 (or a few, allowing for a few destrucons) defines the UHECR phase Metzger, Giannios, Horiuchi (2011) à There remains a window for UHECR nuclei generaon

NEUCOS Shunsaku Horiuchi (Virginia Tech) 24 Low-luminosity GRB

Nuclei UHECR in LL GRB Nuclei can reach UHECR energies and maintain their composion for large enough dissipaon radii Murase et al (2008) L~1046 erg/s, Γ=10

see also Wang et al (2008) Anchordoqu et al (2008)

NEUCOS Shunsaku Horiuchi (Virginia Tech) 25 Summary • GRBs are stores of heavy nuclei: – Through stellar nucleosynthesis, explosive nucleosynthesis, and in-situ jet nucleosynthesis

• Composion of jets: – Magnetar models for GRBs, low-luminosity GRBs, and baryon- rich jets are especially conducive to heavy nuclei composion

• Nuclei survival: – Neutron collisions and destrucon during acceleraon appear avoidable depending on parameters – Recollimaon shocks may be more problemac, but safe while its size is small (=early epochs)

• Want self-consistent composion predicons!

NEUCOS Shunsaku Horiuchi (Virginia Tech) 26 Example: proto-magnetar scenario

Need a remnant:

Having the right

angular momentum

distribuon is key: M-out Fast rotang core M-out > M-in à B-field generaon M-in à Rapid mass-loss à Evades BH Central mass formaon

NEUCOS Shunsaku Horiuchi (Virginia Tech) 27 Proto-magnetar model

Acceleraon: 12-13 Demand acceleraon is Magnec reconnecon case: Rd ~ 10 cm faster than cooling & GRB phase expansion mescales: Nuclei UHECR Cooling limit phase Expansion limited Survival: Calculate the opcal depth of photodisintegraon based on the Band funcon for the photon spectrum Demanding this is = 1 (or a few, allowing for a few destrucons) defines the UHECR phase Metzger, Giannios, Horiuchi (2011) à There remains a window for UHECR nuclei generaon

NEUCOS Shunsaku Horiuchi (Virginia Tech) 28