Gravitational waves from neutron star mergers

Output predictions

S.BernuzziTCAN workshop July 2020

www.computational-relativity.org

Merger dynamics

Annual Reviews of Nuclear and Particle Science Radice, SB, Perego [ https://arxiv.org/abs/2002.03863 ]

https://arxiv.org/abs/2002.03863

The gravitational-wave spectrum

What is needed?● Broad-band waveforms from adiabatic quasicircular inspiral to merger and postmerger

– Beyond regimes covered by post-Newtonian / numerical relativity (need connection)● Identify key parameters characterizing merger and postmerger dynamics

● Predictions of the remnants

– Prompt-collapse to black hole

– Input physics uncertainties● Accuracy requirements for high-precision measurements (EOS constraints)

Review on Neutron Star Merger Remnants [https://arxiv.org/abs/2004.06419]

https://arxiv.org/abs/2004.06419

EOB waveforms w/ tides● Effective-one-body (EOB) formalism (backup slides)

○ 4+ Post-Newtonian conservative point-mass dynamics ○ NNLO spin dynamics (incl. self-spin)○ Tides (NR-verified [https://arxiv.org/abs/1412.4553])○ Mulitpolar waveform○ Resummation of post-Newtonian series

● Only 2 groups/independent EOB models: ○ AEI (Buonanno +) ○ IHES/Jena/Torino (Damour/SB/Nagar +) [*]

● Most of the current analysis conducted with phenomenological representation of these EOB models + NR fitting (Dietrich,SB,Tichy [https://arxiv.org/abs/1706.02969])

● Postmerger EOB-completions Breschi+ [https://arxiv.org/abs/1908.11418]○ Based on NR phenomenologial relations between tidal

parameters & characteristic frequencies (next slides)SB+ [https://arxiv.org/abs/1504.01764]

[*] Nagar+ [https://arxiv.org/abs/1806.01772] Akcay+ [https://arxiv.org/abs/1812.02744] Nagar+[https://arxiv.org/abs/1812.07923]

Credit: L.Barak

https://arxiv.org/abs/1412.4553https://arxiv.org/abs/1706.02969https://arxiv.org/abs/1908.11418https://arxiv.org/abs/1504.01764https://arxiv.org/abs/1806.01772https://arxiv.org/abs/1812.02744https://arxiv.org/abs/1812.07923

Systematics at design sensitivity aLIGO-aVirgo

[Gamba, Breschi + (In Prep)]

NS Radius uncertaintyΔR

1.4 >~ 500m

Injection:TEOBResumS

Relative difference in the reduced tidal parameter as measured by different approximants

Damour+ [https://arxiv.org/abs/1203.4352]

Source parameters measurements

Tides

Chirp mass

https://arxiv.org/abs/1203.4352

Faithfulness of NR merger waveforms

[SB+ https://arxiv.org/abs/1109.3611 ; Gamba, Breschi + (In Prep)]

https://arxiv.org/abs/1109.3611

Merger parametrization (aka quasiuniversality)● Well understood from theory point of view

(not phenomenological)

● Well quantified for nonspinning mergers w\simple extension to capture “large” mass ratios

● Understood but not well quantified for spin case

● Why useful? ○ Lower bounds for energy, angular momentum,

radiated to merger (at the end of chirp)○ GW merger frequency/amplitude

(not predicted by post-Newtonian methods)○ Upper bounds for remnant's energy,

ang.momentum

SB+ [https://arxiv.org/abs/1402.6244]

https://arxiv.org/abs/1402.6244

Prompt collapse to BH

Hotokezaka+ [https://arxiv.org/abs/1105.4370], Bauswein+ [https://arxiv.org/abs/1307.5191] + more data avail to date and collected in Agathos+ [https://arxiv.org/abs/1908.05442]

https://arxiv.org/abs/1105.4370https://arxiv.org/abs/1307.5191https://arxiv.org/abs/1908.05442

Zappa+ [ https://arxiv.org/abs/1712.04267 ]

Prompt collapse to BH /2

PC well described by tidal parameter

https://arxiv.org/abs/1712.04267

Inferring BH formation from inspiral GW

Agathos+ [https://arxiv.org/abs/1908.05442]

● Two methods, w/ NR-based prompt collapse criteria (consistent results)

– EOS inference + Threshold mass

– Tidal parameter + Λ-Threshold ● GW170817: quantitatively support the

“mainstream” interpretation of counterparts

● GW190425: P(prompt collapse) ~ 97%

LVC [https://arxiv.org/abs/2001.01761]

P(prompt collapse|M

Prompt collapse to BH /3

SB+ [ https://arxiv.org/abs/2003.06015 ]

All models fail for high-mass ratios (“accretion-induced PC”)

https://arxiv.org/abs/2003.06015

Post-merger parametrization

● Merger parametrization can be extended to postmerger frequenciesSB+ [https://arxiv.org/abs/1402.6244]

● Basic reason: efficiency of early postmerger GW emission. GW energy emitted in short time at f ~ const = 2x rotation (No discrete freqs!)SB+ [https://arxiv.org/abs/1512.06397]

● Phenomenological description○ Pro: connect to pre-merger○ Con: dependent on simulations' input EOS!

● Other, similar proposals exist, but retain same “con.” See work by Bauswein+, Hotokezaka+, Stergioulas+, Takami+, ...

Breschi+ [https://arxiv.org/abs/1908.11418]

https://arxiv.org/abs/1402.6244https://arxiv.org/abs/1512.06397https://arxiv.org/abs/1908.11418

NRPM: Postmerger waveform (EOB-completion)

[Breschi+ https://arxiv.org/abs/1908.11418]

https://arxiv.org/abs/1908.11418

● Model selection to identify PC/PM signal: min SNR ~ 9-12

→ GW170817-like events for 3G

(Cf. Torres-Rivas [https://arxiv.org/abs/1811.08931 ])

● High-precision measurements of NS masses, radius, tidal parameter will be available from inspiral-merger

→ want new info? parameters ~ ⍴max ● Examples

– NS minimum radius (Cf. Bauswein+ [https://arxiv.org/abs/1403.5301 ] )

– EOS softness effects (next slides)

GW from NS remnants (kHz)

Breschi+ [ https://arxiv.org/abs/1908.11418 ]

https://arxiv.org/abs/1811.08931https://arxiv.org/abs/1403.5301https://arxiv.org/abs/1908.11418

Softness effects at extreme densities

Radice+ [ https://arxiv.org/abs/1612.06429 ]

https://arxiv.org/abs/1612.06429

Softness effects: High-mass case

Breschi+ [ https://arxiv.org/abs/1908.11418 ]

https://arxiv.org/abs/1908.11418

Summary● Accurate & complete GW models are essential for multimessenger observations.

– Use EOB models (accelerate evaluation + efficient data analysis infrastructures)

– Explore systematics in GW models (“piece-by-piece” analysis)

– Verify resummation techniques with high-precision NR data

– Explore use & conceptual limitations of NR-informed postmerger models● Detailed NR simulations promise to fill several gaps between theory and observations.

– Improved NR waveforms to merger with dedicated methods

– Explore prompt collapse scenarios and improve current PC models

– Explore longer timescales w\ neutrino transport and MHD effects

– Future simulations require improved scaling

CoRe [ http://www.computational-relativity.org/ ]

http://www.computational-relativity.org/

Additional slides

Factorized (resummed) PN waveform [Damour,Iyer,Nagar 2008]Includes test-mass limit (i.e. particle on Schwarzschild)Includes post-Newtonian and self-force resultsUses resummation techniques → predictive strong-field regimeIncludes tidal interactions (→ BNS) [Damour&Nagar PRD 2010]Flexible framework → NR informed

[Buonanno&Damour PRD 2000a, 2000b]

Credit: A.Taracchini/AEI

Effective-one-body framework in a nutshell

Credit: L.Barak

[Hinderer 2007, Damour&Nagar 2009a, Binnington&Poisson 2009]

Love numbers depends on EOS and NS compactness

Relativistic Tides

[Damour&Nagar 2009b]

Hamiltonian(Newtonian limit):

Waveform:

Tides are attractive and short range

Key point: No other binary parameter (mass, radii, etc) enter separately the formalism at LO

“Tidal coupling constant”

TEOBResumS● Effective-one-body model for tidally interacting and spinning compact binaries

● Pade' resummed A-potential for conservative dynamics

● 5PN effective information from BBH NR

● Spin-orbits and spin-spin effects blended together by the centrifugal radius [Damour&Nagar 2014]

● NR-based phenomenological description of postmerger waveform

● Multipolar waveform and fluxes

● Tidal sector based on PN+GSF potential w\ gravitoelectric and magnetic terms up to ell=4

– [BiniDamourFaye 2012, SB+ 2012, Bini&Damour 2013, SB+ 2015, Akcay+ 2018]

● EOS-dependent self-spin terms up to NNLO [Nagar,SB+ 2018, Nagar+ 2018]

● Fast evaluation through post-adiabaic approximation [Rettegno+ 2018]

● Code available at https://bitbucket.org/eob_ihes/teobresums/src/master/

https://arxiv.org/abs/1406.6913https://arxiv.org/abs/1202.3565https://arxiv.org/abs/1205.3403https://arxiv.org/abs/1409.6933https://arxiv.org/abs/1412.4553https://arxiv.org/abs/1812.02744https://arxiv.org/abs/1806.01772https://arxiv.org/abs/1812.07923https://arxiv.org/abs/1805.03891https://bitbucket.org/eob_ihes/teobresums/src/master/

[Zappa+ https://arxiv.org/abs/1712.04267]

● BBH events ~ 3 − 4 × 10^56 erg/s● Simple description of all simulated BNS based on tidal parameter● Estimate for GW170817:

GW Luminosity

https://arxiv.org/abs/1712.04267

● Upper limit on total energy → postmerger is not detectable for GW170817● BBH events ~ 1-3 Msun c^2

Upper limit:

[Zappa+ https://arxiv.org/abs/1712.04267]

Energy per mass unit

https://arxiv.org/abs/1712.04267

Softness effects: Low-mass case

Breschi+ [ https://arxiv.org/abs/1908.11418 ]

https://arxiv.org/abs/1908.11418

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