[PPT] - Neutrino-Driven Jets in Compact Object Mergers Oliver Just PowerPoint Presentation

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Neutrino-Driven Jets in Compact Object Mergers

Oliver Just

Max-Planck-Institut für Astrophysik, Garching

MICRA Workshop Stockholm, August 18th 2015

With: H.-Th. Janka, N. Schwarz, A. Bauswein, M. Obergaulinger

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August 18th, 2015 MICRA Workshop Stockholm

Mo t i v a t i

n

➔ central engine and launch mechanism of short GRBs not safely

identified yet

➔ two most likely systems: BH-tori and (H)MNS ➔ two most likely mechanisms: neutrino-annihilation and (several)

magneto-rotational processes

➔ most previous studies compute annihilation rate using 1D models

(Popham, DiMatteo, Liu, ...) or by post-processing individual snapshots (Ruffert, Dessart, Richers, …)

➔ other studies evolve jets without resolving the central engine (Aloy,

Nagataki, Duffel, Murguia-Berthier, …)

➔ 2 necessary conditions to obtain about ~1048 – 1050 erg in relativistic

utflow material:
sufficient energy provided by nu-annihilation
sufficiently small energy loss during expansion

➔ What is the impact of the dynamical ejecta on the jet?

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August 18th, 2015 MICRA Workshop Stockholm

“ A L C A R ” N e u t r i n

T

r a n s p

r

t C

d

e

Radiation-hydro with Boltzmann solver too expensive!

Our approach (see also: O'Connor '14, Kuroda '15):

➔ Two-moment scheme with algebraic Eddington factor (AEF or M1 scheme)

← e n e r g y d e n s i t y ← mo me n t u m d e n s i t y ← p r e s s u r e e v

l

u t i

n

e q u a t i

n

s a p p r

x

i ma t e a l g e b r a i c c l

s

u r e r e l a t i

n

s ( e . g . " M1 c l

s

u r e " )

Effective save up of the two angular degrees of freedom!

(OJ, Obergaulinger, Janka '15, ArXiv:1501.02999)

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August 18th, 2015 MICRA Workshop Stockholm

S e t u p

f

B H

T
r

u s Mo d e l s ( fj r s t w i t h

u

t d y n a mi c a l e j e c t a )

➔ initial configuration given by equilibrium tori with constant specific

angular moment

➔ simulations performed in 2D axisymmetry ➔ multi-group neutrino transport with 10 energy groups ➔ most dominant (electron) neutrino interactions included:

✔ emission/absorption by nucleons ✔ neutrino-nucleon scattering ✔ neutrino-antineutrino annihilation

➔ Newtonian hydrodynamics with pseudo-Newtonian gravitational

potential by Artemova → mimics the ISCO and BH spin

➔ angular momentum transport: Shakura & Sunyaev α-viscosity ➔ variation of mtorus, MBH, ABH, αvis ➔ similar models as used for nucleosynthesis study Just et al. '15

MNRAS 448, 541 and conceptually similar as in Fernandez '13, '14

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August 18th, 2015 MICRA Workshop Stockholm

Mo v i e : B H

t
r

u s w i t h

u

t p r

mp

t e j e c t a

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August 18th, 2015 MICRA Workshop Stockholm

N e u t r i n

e

mi s s i

n

p r

p

e r t i e s v s . t

r

u s ma s s

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August 18th, 2015 MICRA Workshop Stockholm

N e u t r i n

e

mi s s i

n

p r

p

e r t i e s v s . B H ma s s

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August 18th, 2015 MICRA Workshop Stockholm

N e u t r i n

e

mi s s i

n

p r

p

e r t i e s v s . B H s p i n

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August 18th, 2015 MICRA Workshop Stockholm

N e u t r i n

e

mi s s i

n

p r

p

e r t i e s v s . v i s c . p a r a me t e r

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August 18th, 2015 MICRA Workshop Stockholm

R e l a t i v i s t i c e j e c t a e x p a n s i

n

i n t

d

y n a mi c a l e j e c t a

➔ we now extend Newtonian to special relativistic hydro ➔ data for dynamical ejecta mapped from SPH

simulations onto 2D BH-torus grid

➔ extend EOS to low densities, include

electron recombination, radioactive heating

(Bauswein et. al. '13)

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August 18th, 2015 MICRA Workshop Stockholm

Mo d e l T M1 1 4 5 1 : N S

B

H r e mn a n t

➔ MOVIE ➔ dynamical ejecta are ignored since they are almost exclusively ejected

in equatorial plane

➔ thermal fireball is successfully launched ➔ annihilation energy is efficiently converted to relativistic kinetic energy ➔ jet can expand almost unimpeded ➔ amount of energy sufficient at least to explain low-luminosity sGRBs

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August 18th, 2015 MICRA Workshop Stockholm

Mo d e l T M1 1 3 5 2 : N S

N

S r e mn a n t

➔ MOVIE ➔ dynamical ejecta are slightly equatorially dominated

→ favorable for jet launch

➔ jet is successfully launched, but only after significant energy input by

annihilation

➔ in the jet beam, annihilation energy is efficiently converted to

relativistic kinetic energy

➔ however, during expansion the jet beam dissipates almost all kinetic

energy due to interaction with the cocoon and jet head

➔ amount of energy not sufficient to explain sGRBs

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August 18th, 2015 MICRA Workshop Stockholm

Mo d e l S F H O 1 4 5 1 4 5 : N S

N

S r e mn a n t

➔ MOVIE ➔ dynamical ejecta are almost spherical

→ not favorable for jet launch

➔ annihilation only deposits thermal energy into dynamical ejecta ➔ however, not powerful enough to launch a jet

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August 18th, 2015 MICRA Workshop Stockholm

S u mma r y

➔ using the M1 code ALCAR we examined neutrino emission +

annihilation in BH-torus systems as functions of mtorus, MBH, ABH, αvis

➔ typical annihilation energies are 1047 – 1049 erg and efficiencies are

10-5 – 10-4 , while high values favor high mtorus, low MBH, high ABH, high αvis

➔ for selected models we followed the relativistic jet expansion into the

dynamical ejecta

➔ NS-BH mergers: major fraction of anni. energy may end up in

relativistic ejecta → could explain at least low-luminosity sGRBs

➔ NS-NS mergers: either no jet is launched or the major fraction of anni.

energy is dissipated in the dynamical ejecta → annihilation too weak

➔ for a delayed collapse in NS-NS mergers, the situation is likely even

worse due to additional neutrino-driven winds

➔ results suggest that other mechanisms are needed to explain

sGRBs in NS-NS mergers and high-energy sGRBs in NS-BH mergers!

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August 18th, 2015 MICRA Workshop Stockholm

T h a n k y

u

f

r

y

u

r a t t e n t i

n

!

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August 18th, 2015 MICRA Workshop Stockholm

A p p e n d i x : T e s t

f

N e u t r i n

S

c h e me