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Binary neutron star mergers: observations and modelling in the - - PowerPoint PPT Presentation

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Binary neutron star mergers: observations and modelling in the multimessenger astronomy era Albino Perego INFN, Milano-Bicocca & Gruppo collegato di Parma On the behalf of the Virgo Scientific Collaboration 26 November 2018 DISCRETE

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SLIDE 1

Binary neutron star mergers: observations and modelling in the multimessenger astronomy era

Albino Perego

INFN, Milano-Bicocca & Gruppo collegato di Parma

On the behalf of the Virgo Scientific Collaboration 26 November 2018 DISCRETE Conference, Vienna

Albino Perego DISCRETE conference, 26/11/2018 1 / 34

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Multimessenger astrophysics

MM astrophysics: detection of different radiations from one sin- gle event or source

MM & Fundamental Questions

Gravity & Spacetime Dense and hot matter Origin of elements High Energy Burst Cosmology

MM astrophysics: answers to many fundamental questions

Albino Perego DISCRETE conference, 26/11/2018 2 / 34

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Detections from GW170817 and its EM counterparts

GW170817: first MM detection from a compact binary merger

◮ GWs from an event compatible with BNS merger reported by LVC

LVC PRL 119 2017

◮ ∼1.7 seconds after, γ-ray signal compatible with short GRB

LVC, Fermi, Integral ApJ 848 L13 2017

◮ 11 hrs after, kilonova emission from NGC 4993 (40 Mpc): AT2017gfo

e.g., LVC+ many other astronomy and astroparticle collaborations ApJ 848 L2 2017 Albino Perego DISCRETE conference, 26/11/2018 3 / 34

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SLIDE 4

Detections from GW170817 and its EM counterparts

GW170817: first MM detection from a compact binary merger

◮ GWs from an event compatible with BNS merger reported by LVC

LVC PRL 119 2017

◮ ∼1.7 seconds after, γ-ray signal compatible with short GRB

LVC, Fermi, Integral ApJ 848 L13 2017

◮ 11 hrs after, kilonova emission from NGC 4993 (40 Mpc): AT2017gfo

e.g., LVC+ many other astronomy and astroparticle collaborations ApJ 848 L2 2017 Albino Perego DISCRETE conference, 26/11/2018 4 / 34

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SLIDE 5

Detections from GW170817 and its EM counterparts

GW170817: first MM detection from a compact binary merger

◮ GWs from an event compatible with BNS merger reported by LVC

LVC PRL 119 2017

◮ ∼1.7 seconds after, γ-ray signal compatible with short GRB

LVC, Fermi, Integral ApJ 848 L13 2017

◮ 11 hrs after, kilonova emission from NGC 4993 (40 Mpc): AT2017gfo

e.g., LVC+ many other astronomy and astroparticle collaborations ApJ 848 L2 2017 Albino Perego DISCRETE conference, 26/11/2018 5 / 34

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SLIDE 6

Properties of GW170817 and its kilonova detection

◮ GW signal

◮ signal duration in GW detector network: 55 s ◮ largest to date network SNR: 32.4 ◮ inference of many source properties LVC PRL 2017. see LVC arXiv:1805.11579 for a refined analysis ◮ chirp mass: Mchirp = (m1m2)3/5 (m1 + m2)−1/5 ◮ upper limit on Erad only from BNS modelling:

Erad 0.126 M⊙c2

Zappa, Bernuzzi, Radice, Perego, Dietrich PRL 2018 Albino Perego DISCRETE conference, 26/11/2018 6 / 34

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SLIDE 7

Properties of GW170817 and its kilonova detection

◮ GW signal ◮ kilonova signal

◮ bright, UV/O component, with a peak @ ∼ 1day (blue component) ◮ rather bright, nIR component, with a peak @ ∼ 5day (red component) Light curves; Pian, D’Avanzo et al. Nature 2017 (left); Tanvir et al. Science 2017 (right). See also, e.g., Coulter et al. Science 358 2017; Troja et al. Nature 2017, Hallinan et al. Science 2017 Albino Perego DISCRETE conference, 26/11/2018 7 / 34

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Fundamental physics implications from GW170817 MM detection

Albino Perego DISCRETE conference, 26/11/2018 8 / 34

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SLIDE 9

Implications of joint GW+EM detection: vEM

Speed of gravity

◮ if vEM = vGW, delay in travel time ∆t:

vGW − vEM vEM ≈ vEM ∆t D

◮ arrival time difference between GW and photons from GRB

∆tGRB = (1.74 ± 0.05)s

◮ however, uncertainties on emission sequence

◮ if simultaneous emission (δt = 0), ∆t ≥ ∆tGRB and vGW > vEM ◮ if EM emitted δt ≤ 10s after GW, vEM > vGW

−3 × 10−15 ≤ ∆v vEM ≤ 7 × 10−16 D = 26Mpc

LVC PRL 119 2017 Albino Perego DISCRETE conference, 26/11/2018 9 / 34

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Implications of joint GW+EM detection: (γGW − γEM)

Test of equivalence principle

◮ are EM radiation and GWs affected by background potentials in the

same way?

◮ Shapiro delay: propagation time of massless particles larger in curved

spacetimes δtS ≈ −1 + γ c3 ro

re

U(r(l)) dl

◮ Einstein-Maxwell minimal coupling: γEM = γGW = 1 → (γGW − γEM) = 0 ◮ conservative limit obtained by assuming:

◮ 0 ≤ δt ≤ 10s ◮ measured arrival time delay ∆tGRB = (1.74 ± 0.05)s ◮ U(r) caused by Milky Way for distances > 100kpc,

−2.6 × 10−7 ≤ (γGW − γEM) ≤ 1.2 × 10−6

LVC PRL 119 2017 Albino Perego DISCRETE conference, 26/11/2018 10 / 34

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Implications of joint GW+EM detection: H0

GW as standard sirens for H0 measurement

LVC, 1M2H coll, Dark Energy Camera GW-EM coll and DES coll et al. Nature 551 2017

◮ Hubble law in the local Universe:

vH = H0 d + O (vH/c)

◮ analysis of GW signal (NGC

4993 sky location): d = 43.8+2.9

−6.9Mpc ◮ measurement of cosmological

redshift of NGC 4993 vH = 3017+166

−166km s−1

H0 = 70.0+12.0

−8.0 km s−1 Mpc−1

Albino Perego DISCRETE conference, 26/11/2018 11 / 34

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BNS merger modelling and the EOS of neutron star

Albino Perego DISCRETE conference, 26/11/2018 12 / 34

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BNS merger in a nutshell

Credit: D. Radice Rosswog 2015

◮ n-rich matter ejected

◮ r-process nucleosynthesis ◮ different mechanisms

◮ decay of freshly sinthetized r-process

element: release of nuclear energy

◮ kilonova: thermal photons diffuse and

are emitted at photosphere

Li & Paczynski ApJL 98, for a review: Metzger LRR 17 Albino Perego DISCRETE conference, 26/11/2018 13 / 34

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BNS modelling and NS equation of state (EOS)

BNS merger simulations in Numerical Relativity (NR): necessary to model highly non-linear, strong field (post-)merger phase

Volume rendering of matter density from BNS NR simulation. Courtesy of T. Dietrich & S. Bernuzzi

◮ NR: art of solving Einstein’s and

GR-HD equations on computer

◮ accurate GW waveforms,

energetics, final state properties, matter dynamics

◮ need of NS matter EOS to close the

system EOS of NS matter still affected by large uncertainties

e.g., Tsang et al 86 PRC 2012, Lattimer & Prakash Phys. Rep. 621 2016, ¨ Ortel et al. RMP 89 2017 for recent reviews

◮ nucleon Hamiltonian ◮ many-body treatment ◮ thermodynamical degrees of

freedom (hyperons, quarks?)

Mass-radius curves for several RMF NS EOS. Courtesy of M. Hempel Albino Perego DISCRETE conference, 26/11/2018 14 / 34

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Tidal deformation during the inspiral phase

NS in external, inhomegeneous gravitational field ⇒ tidal deformation

Bernuzzi et al PRD 2012

Qi,j = −λEi,j λ = 2 3 R5 G k2

  • ◮ Qi,j quadrupolar moment

◮ Ei,j = ∂2 i,jΦ

tidal field

◮ k2 quadrupolar tidal

polarizability

◮ R radius of the star ◮ tidal deformation enhances GW emission ◮ ≥ 5th PN order correction to point particle dynamics ◮ leading term ∝ ˜

Λ(MA, MB, EOS)

˜ Λ = 16 13

  • (MA + 12MB)M4

AΛ(A) 2

(MA + MB)5 + (A ↔ B)

  • ; Λ(i)

2

=

  • c2

Mi 5 λ(i); i = A, B

see, e.g., Damour, Les Houches Summer School on Gravitational Radiation 1982; Flanagan & Hinderer PRD 77 2008, Bernuzzi et al PRD 2012 Albino Perego DISCRETE conference, 26/11/2018 15 / 34

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NS mass, radius and EOS from GW170817

Idea: Measure the NS tidal deformation from GW170817 inspiral signal to probe cold NS EOS above ρnuc

LVC PRL 121 2018

Relevant assumptions:

◮ same parametrized EOS for the two NSs

e.g. Lindblom & Indik PRD 89 2014

◮ Mmax,TOV > 1.97M⊙

Antoniadis et al Science 340 2013 LVC PRL 121 2018

◮ marginalized posteriors for Λ1,2 ◮ same EOS for the two NSs

improves results compared with previous analysis

Albino Perego DISCRETE conference, 26/11/2018 16 / 34

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SLIDE 17

NS mass, radius and EOS from GW170817

Idea: Measure the NS tidal deformation from GW170817 inspiral signal to probe cold NS EOS above ρnuc

LVC PRL 121 2018

Relevant assumptions:

◮ same parametrized EOS for the two NSs

e.g. Lindblom & Indik PRD 89 2014

◮ Mmax,TOV > 1.97M⊙

Antoniadis et al Science 340 2013 LVC PRL 121 2018

◮ marginalized posteriors for

p = p(ρ)

◮ GW signal favors softer EOS ◮ MTOV,max > 1.97M⊙: EOS

stiffening at high density

Albino Perego DISCRETE conference, 26/11/2018 17 / 34

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SLIDE 18

NS mass, radius and EOS from GW170817

Idea: Measure the NS tidal deformation from GW170817 inspiral signal to probe cold NS EOS above ρnuc

LVC PRL 121 2018

Relevant assumptions:

◮ same parametrized EOS for the two NSs

e.g. Lindblom & Indik PRD 89 2014

◮ Mmax,TOV > 1.97M⊙

Antoniadis et al Science 340 2013 LVC PRL 121 2018

◮ simultaneous NS M − R

measurements

◮ R1 = 11.9+1.4 −1.4 km

m1[M⊙] ∈ [1.36, 1.58]

◮ R2 = 11.9+1.4 −1.4 km

m2[M⊙] ∈ [1.18, 1.36]

Albino Perego DISCRETE conference, 26/11/2018 18 / 34

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Weak interaction in BNS merger

Albino Perego DISCRETE conference, 26/11/2018 19 / 34

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Weak interaction in hot and dense matter

◮ most relevant neutrino production processes (inverse: absorption)

u d u u d d e− νe W p n

p + e− → n + νe

d u u u d d e+ νe W n p

n + e+ → p + ¯ νe

e+ νe e− νe W e+ ν e− ν Z0

e− + e+ → ν + ¯ ν

N N N N ν ν π Z0

N + N → N + N + ν + ¯ ν ◮ most relevant scattering processes

d d d d u u ν ν Z0 n n

n + ν → n + ν

u u u u d d ν ν Z0 p p

p + ν → p + ν νe νe e+ e+ W

(−)

ν

(−)

ν e± e± Z0

e± + ν → e± + ν

Tubbs & Schramm ApJ 75; Lamb & Pethick ApJ 76; . . . Burrows, Reddy & Thompson NuPhA 06; Bacca, Hally, Liebend¨

  • rfer, Perego et al. ApJ 12

Albino Perego DISCRETE conference, 26/11/2018 20 / 34

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Reaction rates in hot and dense matter

◮ plasma (n, p, e±, γ) in thermal and NSE (NS matter EOS) ◮ ν production rates: boosted by high temperatures & densities

λe− ∝ npT5F4(µe/T) λe+ ∝ nnT5F4(−µe/T)

λe− =

  • d3pν

(2πc)3 jνe(Eν) ≈   nn − np exp µp−µn+∆

kBT

  • − 1

  ∞ 4πσ0c (2πc)3 E + ∆ me 2 fe−(E + ∆) E2dE σ0 = 4G2

F(mec2)2(c2 v + 3c2 a)

π(c)4 ≈ 2.43×10−44 cm2 ∼ 2×10−20σt,e Fk(η) = ∞ xk 1 + exp(x − η) dx

e.g. Bruenn ApJ 1985; Rosswog & Liebend¨

  • rfer MNRAS 2003

Albino Perego DISCRETE conference, 26/11/2018 21 / 34

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Reaction rates in hot and dense matter

◮ plasma (n, p, e±, γ) in thermal and NSE (NS matter EOS) ◮ ν production rates: boosted by high temperatures & densities

λe− ∝ npT5F4(µe/T) λe+ ∝ nnT5F4(−µe/T)

◮ ν absorption/scattering rates: neutrino diffusion

ℓνe = c κνe ≈ 2.36 × 103cm

  • ρ

1014 g/cm3 −1 Eν 10 MeV −2 ≪ RNS κνe(Eνe) = exp Eνe − (µp + µe − µn) kBT

  • j(Eνe) ≈ nNσν

c σν ∼ σ0 Eν mec2 2 ⇒ Radiative transfer problem

Albino Perego DISCRETE conference, 26/11/2018 22 / 34

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Reaction rates in hot and dense matter

◮ plasma (n, p, e±, γ) in thermal and NSE (NS matter EOS) ◮ ν production rates: boosted by high temperatures & densities

λe− ∝ npT5F4(µe/T) λe+ ∝ nnT5F4(−µe/T)

◮ ν absorption/scattering rates: neutrino diffusion

ℓνe ≪ RNS

◮ matter composition:

◮ W-mediated processes can change ratio between n and p, i.e. Ye:

n + e+ ↔ p + ¯ νe p + e− ↔ n + νe

  • Ye = ne/nB ≈ np/
  • np + nn
  • → direct impact on nucleosynthesis

Albino Perego DISCRETE conference, 26/11/2018 23 / 34

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Impact of ν absorption on dynamical ejecta

◮ dynamical ejecta: matter promptly expelled in a BNS merger

◮ τej,dyn 5 ms ◮ Mej,dyn 10−4 - 10−3M⊙ ◮ vej,dyn ∼ 0.3c

◮ in the past, ν-matter interactions assumed to be negligile ◮ however, ν-matter interactions increase Ye (n + νe → p + e−)

w/o neutrino absorption

20 40 60 80 θ 0.1 0.2 0.3 0.4 Ye LS220 M135135 LK 10−4 10−3 10−2 M/Mej

w neutrino absorption

20 40 60 80 θ 0.1 0.2 0.3 0.4 Ye LS220 M135135 M0 10−4 10−3 10−2 M/Mej

Perego, Radice, Bernuzzi ApJL 2017; Radice, Perego, Hotokezaka et al arXiv:1809.11161 Albino Perego DISCRETE conference, 26/11/2018 24 / 34

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Impact of ν absorption on dynamical ejecta

◮ dynamical ejecta: matter promptly expelled in a BNS merger

◮ τej,dyn 5 ms ◮ Mej,dyn 10−4 - 10−3M⊙ ◮ vej,dyn ∼ 0.3c

◮ in the past, ν-matter interactions assumed to be negligile ◮ however, ν-matter interactions increase Ye (n + νe → p + e−)

ejecta Ye for increasing Lν

10-7 10-6 10-5 10-4 Mass [M ] capture low luminosity 0.0 0.1 0.2 0.3 0.4 Electron fraction at 8.0 GK 10-7 10-6 10-5 10-4 Mass [M ] medium luminosity 0.0 0.1 0.2 0.3 0.4 0.5 Electron fraction at 8.0 GK high luminosity

→ r-process nucleosynthesis

10

7

10

6

10

5

10

4

10

3

Abundance Y capture low luminosity 50 100 150 200 Mass number A 10

7

10

6

10

5

10

4

10

3

Abundance Y medium luminosity 50 100 150 200 Mass number A high luminosity

Martin, Perego, Kastaun & Arcones CQG 2018 Albino Perego DISCRETE conference, 26/11/2018 25 / 34

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SLIDE 26

ν-driven winds from BNS merger

◮ wind ejection driven by energy

& momentum deposition

◮ τej,wind ∼ tens ms ◮ Mej,wind 10−2M⊙ ◮ vej,wind 0.1c ◮ first 3D

radiation-hydrodynamics simulation

◮ ejecta analysis and

nucleosynthesis calculations

◮ kilonova prediction: blue & red

kilonova

Perego, Rosswog, Cabezon et al MNRAS 2014; Martin, Perego, Arcones et al ApJ 2015 Albino Perego DISCRETE conference, 26/11/2018 26 / 34

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SLIDE 27

ν-driven winds from BNS merger

◮ wind ejection driven by energy

& momentum deposition

◮ τej,wind ∼ tens ms ◮ Mej,wind 10−2M⊙ ◮ vej,wind 0.1c ◮ first 3D

radiation-hydrodynamics simulation

◮ ejecta analysis and

nucleosynthesis calculations

◮ kilonova prediction: blue & red

kilonova

Perego, Rosswog, Cabezon et al MNRAS 2014; Martin, Perego, Arcones et al ApJ 2015 Albino Perego DISCRETE conference, 26/11/2018 27 / 34

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Multi-Component Anisotropic Kilonova Model

◮ kilonova model that includes our present knowledge about ejecta ◮ different ejection channels → multi-component ◮ explicit dependency on polar angle → anisotropic & viewing angle ◮ homologous expansion + γ diffusion

Perego, Radice, Bernuzzi 2017, ApjL 2 4 6 8 10 12 14 Time [days] 18 16 14 12 10 8 6 AB magnitude @ 10 pc [-] Light curves for best fits: near-IR bands

i z J H Ks

Mej,tot ∼ 0.05M⊙, θobs ≈ 30o

Albino Perego DISCRETE conference, 26/11/2018 28 / 34

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Multimessenger constraints on nuclear EOS

◮ can GW signal + EM signature + NR simulations constrain NS EOS?

Radice, Perego, Zappa, Bernuzzi ApJL 17

10−4 10−3 10−2 10−1 Mdisk + Mej [M⊙] AT2017gfo 102 103 ˜ Λ 100 101 tBH [ms]

BHBΛφ DD2 LS220 SFHo

◮ ˜

Λ describes BNS deformation: ˜ Λ = ˜ Λ(EOS, M1, M2)

◮ NR results suggest ˜

Λ 400 to account for 0.05M⊙ of ejecta

◮ application to GW170817/AT2017gfo ◮ ˜

Λ(EOS, Mchirp = 1.118M⊙, q)

◮ calculation of ˜

Λ for different EOSs

◮ MM constraints from GW & EM+NR

exclude very stiff & soft EOSs

0.5 0.6 0.7 0.8 0.9 1.0 q 200 400 600 800 1000 ˜ Λ GW170817 AT2017gfo Mchirp = 1.188 M⊙

H4 HB DD2 BHBΛφ ALF2 LS220 MPA1 ENG SFHo SLy APR4 FPS

Albino Perego DISCRETE conference, 26/11/2018 29 / 34

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Conclusions

◮ MM astrophysics can answer fundamental questions: compact binary

mergers as laboratory for fundamental physics

◮ interpretation of MM observation requires sophisticated models

including all the necessary physics

◮ weak reactions and neutrinos play a central role in MM astrophysics ◮ joint GW+EM detections can set stringent limits, e.g. ◮ interaction speed ◮ equivalence principle ◮ Hubble constant ◮ EOS of nuclear matter

LVC PRL 121 2018 2 4 6 8 10 12 14 Time [days] 18 16 14 12 10 8 6 AB magnitude @ 10 pc [-] Light curves for best fits: near-IR bands

i z J H Ks

Perego, Radice, Bernuzzi, ApJL 2017 Albino Perego DISCRETE conference, 26/11/2018 30 / 34

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BNS merger in a nutshell

Credit: D. Radice; see Rosswog IJMP 2015 for a recent review

◮ Massive NS (→ BH)

ρ 1012g cm−3, T ∼ a few 10 MeV

◮ thick accretion disk

M ∼ 10−2 − 0.2M⊙, Ye 0.20 T ∼ a few MeV

◮ intense ν emission

Lν,tot ∼ 1053erg s−1, Eν 10 MeV

  • Ye = ne/nB ≈ np/
  • np + nn
  • Albino Perego

DISCRETE conference, 26/11/2018 31 / 34

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NS radii and EOS from GW170817: basic idea

Idea: Measure the NS tidal deformation from GW170817 inspiral signal to probe cold NS EOS above ρnuc, assuming the same EOS for the two NSs

LVC PRL 121 2018

Hypothesis:

◮ NS mass and spin consistent with astro constraints & expectations ◮ same EOS for the two NSs

Methods:

◮ Bayesan analysis of GW data against waveforms models generated by

PhenomPNRT with different {Λ1, Λ2} choices

e.g., Schmidt et al. PRD 86 2012; Kahn et al. PRD 93 2016, Dietrich, Bernuzzi, Tichy PRD 2017

◮ two methods to generate {Λ1, Λ2}:

  • 1. EOS-insensitive empirical relations involving Λ1,2

e.g. Yanu & Yuges CQG 33 2016

  • 2. general, parametrized version of the NS EOS, satisfying basic constraints

e.g. Lindblom & Indik PRD 89 2014 ◮ causality ◮ thermodynamical stability ◮ MTOV,max > 1.97M⊙ Antoniadis et al Science 340 2013 Albino Perego DISCRETE conference, 26/11/2018 32 / 34

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SLIDE 33

NS radii and EOS from GW170817: results

LVC PRL 121 2018

◮ marginalized posteriors for Λ1,2 ◮ same EOS for the two NSs

improves results compared with previous analysis

◮ marginalized posteriors for

p = p(ρ)

◮ GW signal favors softer EOS ◮ MTOV,max > 1.97M⊙: EOS

stiffening at high density

LVC PRL 121 2018 Albino Perego DISCRETE conference, 26/11/2018 33 / 34

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SLIDE 34

NS radii and EOS from GW170817: results

◮ simultaneous M-R measurments

LVC PRL 121 2018

◮ EOS-independent Λ1,2 relations ◮ R1 = 10.8+2.0

−1.7 km

m1[M⊙] ∈ [1.36, 1.62]

◮ R2 = 10.7+2.1

−1.5 km

m2[M⊙] ∈ [1.15, 1.36]

◮ parametrized EOS ◮ R1 = 11.9+1.4

−1.4 km

m1[M⊙] ∈ [1.36, 1.58]

◮ R2 = 11.9+1.4

−1.4 km

m2[M⊙] ∈ [1.18, 1.36]

Albino Perego DISCRETE conference, 26/11/2018 34 / 34