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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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