ν-driven wind in the Aftermath ofNeutron Star Merger
Albino Perego
in collaboration with A. Arcones, R. Cabezon, R. Käppeli, M. Liebendörfer, S. Rosswog
albino.perego@physik.tu-darmstadt.deTechnische Universität Darmstadt
Institute for Nuclear Physics, Theory

GRBs in Kyoto Conference, Kyoto, 11-15 November 2013
ν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 1/15

Outline of the presentation

Introduction: ejected matter from binary neutron starmerger
The model
initial conditions
ASL neutrino treatment
Preliminary results
Conclusion and outlookν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 2/15

Matter ejecta from BNS mergers
BNS mergers are among the most promising candidates toexplain short gamma-ray bursts (GRBs).
observations: good compatibility with observed rates,
redshifts and host galaxies
modelling: intense energy deposition in a relatively
baryon-free region as driving mechanism, due to matteraccretion on a stellar compact object (SMNS or BH)
Possible ejecta from BNS mergers
dynamical ejecta (e.g. Rosswog 13, Bauswein et al 13, Hotokezaka et al 13)
delayed disc evaporation (e.g. Fernandez & Metzger 2013)
neutrino-driven ejecta (e.g. Dessart et al. 2009)ν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 3/15

The model
Goal: extensive study the aftermath of BNSM
ν emission

disk dynamics and ν -driven wind formation
nucleosynthesis in the windbaryonic pollution and GRB engine
Model ingredients:
data from Newtonian SPH BNS merger simulations(Price & Rosswog (2006))

FISH 3D (M)HD Cartesian code

(Käppeli et al. (2011))

TM1 nuclear EoS(Hempel et al. (2012))

ν treatment: Advanced Spectral Leakage (ASL) scheme(Perego et al., in preparation)
ν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 4/15

Initial conditions
3D SPH data mapped on 3D FISH grid
1 km resolution: SMNS treated as stationary object
data relaxation: ∆t ≈ 10ms, hydro + ν emission

Matter density (2D avg)

Temperature (2D avg)

Electron fraction (2D avg)

ν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 5/15

Relevant timescales
disc lifetime:
tvisc ∼ α−1

HR

−2

 α −1  H/R −2  R 3/2  M −1/2Ω−
K 1 ∼ 0.31 s
0.05
1/3
100 km
2.5M⊙

α: viscosity coefficient
H: disc typical height
R: radial position in the disc
ΩK : Keplerian angular velocity
M : SMNS mass

ν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 6/15

Relevant timescalesdisc lifetime: tvisc ∼ 0.31 s
disc dynamical time:

−1
α0.05

2πtdyn disc ∼∼∼ 0.0109 s
ΩK



H/R
1/3

−2 

R100 km

R100 km3/2 

3/2 M
2.5M⊙

M2.5M⊙

−1/2

−1/2

ν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 6/15

Relevant timescales
disc lifetime: tvisc ∼ 0.31 s

−1
α0.05



H/R
1/3

−2 

disc dynamical time: tdyn disc ∼ 0.0109 s
disc cooling time:∆Edisc,t=0tcool ∼ P∼ 0.20 s
Lν ν



R100 km

R100 km

∆Edisc,t=02 × 1052 erg

3/2 

3/2  PM
2.5M⊙

M
2.5M⊙

ν Lν
1053 erg/s

−1/2

−1/2

−1

∆Edisc,t=0 = Eint,disc,t=0 + 12 Egrav,disc,t=0
Lν : neutrino luminosityν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 6/15

Relevant timescales
disc lifetime: tvisc ∼ 0.31 s−1α0.05



H/R
1/3

−2 

disc dynamical time: tdyn disc ∼ 0.0109 s
disc cooling time: tcool ∼ 0.20 s
wind time:
twind ∼egrav∼ 0.10 sėheat

M2.5M⊙

 ∆E

disc,t=02×1052 erg

R80 km

R100 km

R100 km

3/2 

3/2 Pν Lν
53
10 erg/s

Eν
13 MeV

−2M
2.5M⊙

M
2.5M⊙

−1

−1/2

−1/2

(Lν )iso,θ≈π/4
4 × 1052 erg/s!−1egrav = G M / R : specific gravitational energyėheat = Eν χabs nν / ρ : heating specific energy rate(Lν )iso : isotropized neutrino luminosity
χabs : neutrino absorptivitynν : neutrino density

ν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 6/15

Relevant timescales
disc lifetime: tvisc ∼ 0.31 s

−1
α0.05



H/R
1/3

−2 

disc dynamical time: tdyn disc ∼ 0.0109 s
disc cooling time: tcool ∼ 0.20 s
wind time: twind ∼ 0.10 s

M
2.5M⊙

 ∆E





disc,t=02×1052 erg

R80 kmR
100 km

R100 km

3/2 

3/2 Pν Lν5310 erg/sEν
13 MeVM
2.5M⊙M2.5M⊙

−1

−2  (L )

−1/2

−1/2

ν iso,θ≈π/4
4×1052 erg/s

−1tdyn disc < twind < tcool,disc < tvisc

but there is something missing . . .

ν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 6/15

Relevant timescales
disc lifetime: tvisc ∼ 0.31 s

−1
α0.05



H/R
1/3

−2 

disc dynamical time: tdyn disc ∼ 0.0109 s
disc cooling time: tcool ∼ 0.20 s
wind time: twind ∼ 0.10 s

M2.5M⊙ ∆Edisc,t=02×1052 erg

R80 km

R100 km

R100 km

3/2 

3/2 P

ν Lν
5310 erg/sEν
13 MeV

M
2.5M⊙

M
2.5M⊙

−1

−2  (L )

−1/2

−1/2

ν iso,θ≈π/4
4×1052 erg/s

−1tdyn disc < twind < tcool,disc < tvisc

but there is something missing . . .
SMNS → BH time (e.g. Bauswein’s and Metzger’s talk) :tBH ∼ 0.01 − 10 s
ν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 6/15The ASL scheme
based on previous grey leakage schemes(Ruffert et al. 1997, Rosswog & Liebendörfer 2003, Aloy’s talk)

spectral scheme (12 bins, 2 − 200 MeV)
3 flavors: νe ,ν̄e , νµ,τ (νµ,τ ≡ νµ , ντ , ν̄µ , ν̄τ )ν reactions: (ν ≡ νe , νµ , ντ , ν̄e , ν̄µ , ν̄τ )e − + p → n + νe

O,T,P(A, Z) + ν → (A, Z) + νOe+ + n → p + ν̄eO,T,Pe+ + e− → ν + ν̄T,Pe− + (A, Z) → νe + (A, Z − 1)

T,PN + N → N + N + ν + ν̄T,PN +ν →N +νO
major roles: O → opacity, T → thermalization, P → production
Bruenn 1985, Mezzacappa & Bruenn 1993, Hannestad & Raffelt 1998

treatment developed and tested in Core Collapse
Supernova context
ν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 7/15

Neutrino treatment
effective scheme: ASL mimics known solutions
cooling part:smooth interpolation between diffusion andproduction (spectral) rates
reproduction of the correct limits: diffusive (τν ≫ 1)
and free streaming (τν . 1)
(τν neutrino optical depth)

heating part (for τν . 1):
effective treatment of diffusion process in the opaqueregionnν (neutrino density) calculated with ray-tracing fromcooling rates, emitted at neutrino surfaces
rheat ∝ χab · nν(χab absorptivity)
ν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 8/15

Neutrino Surfacesτν = 2/3 ⇒ ν surfaces,νefor Eν = 4.6, 10.6, 16.2, 24.6, 57.0 MeV, at 40 ms
νµ,τν̄eτν,scatτν,effν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 9/15

Neutrino luminosities
ν rms energy
emerging from ν -surfaces

Isotropized ν luminosity
emerging from ν -surfaces
νe, 40 ms

Anti−ν , 0 ms

Anti−ν , 40 mse

ν

ν

µ,τ

70

Isotropized luminosity [10ν , 0 ms

ν , 40 ms

Anti−ν , 0 ms

Anti−ν , 40 msee

ee, 0 ms

, 40 ms

Neutrino rms energy [MeV]8022νe, 0 msµ,τ51erg/s]

9060
50
4030
2020ν, 0 ms

2040eµ,τν, 40 ms

140160µ,τ

18161412
10010022.5

4567.590112.5

Colatitude [deg]135157.5

18006080100120180

Colatitude [deg]θ angular dependence at t = 0 ms and t = 40 ms

luminosity hierarchy: Lν̄e > Lνe > Lνµ,τ
mean energy hierarchy: hEνµ,τ i > hEν̄e i > hEνe i
ν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 10/15

Neutrino net ratesėν @ 35 ms˙Ye ν @ 35 msv̇ν @ 35 ms

ν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 11/15

Disc dynamics

Movie I
left: matter density
right: projected velocity

Movie II
left: electron fraction
right: entropy
ν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 12/15

Wind properties
occurrence diagrams
large variation for Ye : 0.1 . Ye . 0.35
small variation in entropy: 15 . s [kB /bar] . 25

ν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 13/15

Conclusions & Outlook
FISH + ASL approximate, suitable tool to model theaftermath of BNS merger
obtained neutrino signature compatible with expectedone
relatively quick ν -driven wind development
wind properties:
low entropy: 15 . s[kB /baryon] . 25
mildly low Ye: 0.1 . Ye . 0.35
Outlook:ejecta properties? → nucleosynthesis, macro/kilo-novaν − ν̄ annihilation rate and baryonic pollution? → SGRBmechanism
ν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 14/15

ν -driven wind in the aftermath of NS merger, GRBs in Kyoto Conference - 11-15 November 2013 – p. 15/15