Binary Neutron Star Merger – GW170817

Thomas Dent Galician Gravitational Wave Week 2019 Lecture 4 Plan of lecture

— Detection and sky localization of GW170817 with �–ray space detectors & LIGO–Virgo

— Followup by optical telescopes and discovery of ‘kilonova’ — source of many heavy elements via ‘r–process nucleosynthesis’ — Bounds on deviations from GR — Hubble constant estimate from host galaxy — Measured properties of the binary, NS deformability and equation of state

2 Detection of GW170817/ GRB 170817A

3 GW signal

— Slower waveform evolution than all BBH systems we observed — Implies much lower chirp mass — Signal spends ~100 sec in the LIGO sensitive band (>20 Hz) — Clear signals in LIGO detectors, not obvious in Virgo — BNS horizon distances (Mpc) 218 (L1), 107 (H1), 58 (V1) — In Virgo’s blind spot — triangulation is still possible — Total SNR: 32.4 — Loudest GW signal detected! 4 GammaRayBurst detection

— Fermi GBM: 90% of burst fluence

observed over T90 = 2.0 ± 0.5 s — Fast main pulse – ~0.5 sec long – Comptonized spectrum (power law + exponential) – peak energy 185 ± 62 keV — Followed by a weak tail – ~1 sec long – 10 keV – blackbody spectrum — Integral observation consistent — 3:1 odds for ‘short’ vs. ‘long’ GRB 5

Glitch removal & triangulation

— Problem : low latency data contained loud transient (glitch) in LLO

— reprocess ‘by hand’ to window out & filter data again

6 Sky map comparisons

— GBM map from directional sensitivity

— Fermi/Integral band from time delay

— GW map uses H–L time delay and H/L/V signal amplitudes

https://dcc.ligo.org/DocDB/0146/G1702012/003/antenna-patterns.mp4

7 Probability of chance coincidence

— Rate of sGRBs detected by GBM ~0.1/day — Probability that unrelated sGRB detected with peak within ±1.74 ~ 5×10−6

— Probability that GW/Fermi–GBM sky maps are as consistent for unrelated sGRB ~ 0.01

— Chance probability for both time and direction : 5×10−8 ~ “5.3 �”

⇒ Clear association of BNS merger with (one) sGRB

8 Followup campaign with optical telescopes

9 Optical counterpart & host

— Campaign by dozens of observatories

— New source seen within a few hours

— Host galaxy NGC 4993 − distance ~40Mpc � = 0.0097

10 ‘Kilonova’ emission

— Early ‘blue’ emission quickly transitions to ‘red’

— Large number of ‘light’ / ‘heavy’ element nuclear transitions

— Material travelling with high velocity

11 ‘r-process’ nucleosynthesis

— Large fraction of heavier metal elements made in BNS mergers

12 Bounds on non‐GR theories

— GRB recorded ~2s after BNS merger time — GW and light travel at the same average speed ! — GW and light experience same delay travelling through gravitational potential ! LVC+Fermi-GBM+INTEGRAL ApJL (2017)

Rules out many non‐GR theories proposed to avoid dark matter/dark energy 13 Ezquiaga & Zumalacárregui PRL (2017) Hubble constant measurement

— Luminosity distance determined from GW amplitude — “standard siren”

— �H ‘Hubble flow velocity’ : average recession velocity of galaxies at given distance

— estimated via redshifts of surrounding group & bulk flow peculiar velocity

14 GW as tie‐breaker on H0 ? ) — Inclination is largest � uncertainty on H0 measurement Inclinationcos(

Hubble constant H0 )

— Consistent with both 0 CMB-based and distance ladder determinations Probability p(H Probability 15 NS masses from the GW signal

— Assume NS spins are � < 0.05

(weaker bounds if high spin allowed)

16 NS tidal deformability

— NS in (static) tidal field will develop a nonzero quadrupole moment

— Λ : dimensionless deformability — Affects evolution of orbit and GW emission when NS approach close to each other — Leading contribution to GW phase prop. to

17 Bounds for ‘independent’ Λ’s

— low spins assumed

18 Parameterized EOS bounds

— ‘Spectral model’ of NS energy & density as functions of pressure (Lindblom et al.) — polynomials in � imposing physical constraints — must allow � ≥ 1.97 M☉

19 NS mass and radius

— For parameterized EOS find & same constraint for R2 20 Desmorest et al. 2010 21 The next few years

LVCK, Living Rev. Relativity 2018 22 Upcoming science runs

Projections from Living Rev. Relativity vol.19 (2016) 1 — O3 run to start ~early 2019, duration ~1 year — Advanced LIGO design sensitivity by 2021-22 23 Extending the network

~ 2017+

2022+ with LIGO-India 24 ‘A+’ aLIGO mid scale upgrade

● Upgrade to aLIGO that leverages existing technology and infrastructure, with minimal new investment and moderate risk ● Target: average 1.7x increase in range over aLIGO è ~ 5x greater event rate than Advanced LIGO ~ 40 times greater than current Advanced LIGO sensitivity ● Stepping stone to future detector technologies ● Two year down time; back online by A+ key parameters 2023 12 dB injected squeezing 15% readout loss 100 m filter cavity (FC) 20 ppm round trip FC loss Coating Thermal Noise half of aLIGO 25 Further on: Voyager, Einstein Telescope, Cosmic Explorer

Longer Arm Length Interferometers LIGO Voyager – exploiting the LIGO Observatory facility limits

Einstein Telescope

A future GW observatory in the EU

λ = 2 µm Cosmic Explorer – A future GW observatory in the US

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