– Results from O2 run – Multi-messenger observations of a binary neutron star merger GW170817 Loïc Rolland for t"e #irgo an! L$GO collaborations %&minaire au LA(( #irgo web site* "tt+*,,+ubli .virgo-gw-eu, 10 novembre 2017 LIGO web site: "tt+*,,))).ligo.org/ What is a gravitational wave? GW origin Masses in motion %+a e-time !eformation ➢ transversal plane wave ➢ +ro+agation at t"e lig"t s+ee! Gravitational )ave ➢ t)o +olarisation states /0 an! 12 Detectable effect on free fall masses y L0 h(t) x * am+litu!e of t"e GW h Illustration of the metric variation with free fall masses initially located along / "as no !imension2 a circle, for a + polarised GW propagating along z L. Rolland - 10 novembre 2017 - LAPP 2 A gravitational wave interferometer time For GW170814, first #irgo detecte! event* " 7 5110-22 9 :L = ; 0.8 x 10-18 m L. Rolland - 10 novembre 2017 - LAPP 3 An international networ< of detectors Net)or< wor<ing as a single !ete tor since 2007 The network is a “Gravitational wave telescope” ✔ Reje tion of spurious lo al noise / oinci!ence2 9 better sensitivity ✔ %ource localisation (triangulation) → astronomy ✔ Wave polari>ation L. Rolland - 10 novembre 2017 - LAPP 4 GW150914 Binary neutron stars Binary black holes 09 12/09/2015 2015 LVT151012 10 O1 11 GW151226 12 Summary of O1 O2and runs Summary of O1 O2and runs 01 19/01/2016 02 03 04 05 06 L. RollandL. 10 - novembre 2017 - LAPP 2016 07 08 09 10 11 GW170104 30/11/2016 12 01 O2 run duty cycles: 02 ● ● ● Virgo V1: ~80%Virgo (O2b) LIGO L1: ~60% LIGO H1: ~60% 03 04 O2a 05 + multi-messenger detections! 2017 06 First Virgo Firstevent! Virgo 07 GW170814 GW170817 01/08/2017 O2b 08 25/08/2017 09 10 NOW! 5 August 14,GW170814: 2017 at 10h30m43s UTC the first Virgo event! Combined SNR = 18 False alarm rate < 1 per 27000 years False alarm rate: → a binary bla < hole merer5 similar to the first ever detecte! event GW150914 L. Rolland - 10 novembre 2017 - LAPP 6 $mprovements with Virgo data Better sky source localisation First tests of GW polarisation General Relativity → 2 polarization modes for GW Generic metric theories of gravity → 6 modes allowed Using only two LIGO detectors: 700 deg2 Including Virgo detector: 80 deg2 New tests with GW170814 2D localisation Interferometer sensitive to GW projected onto the → sky area reduced by factor ~10 detector local + mode Can study GW polarization modes using multiple 3D localisation detectors with different orientations → sky volume reduced by factor ~20 → pure + and x modes favoured wrt pure scalar of vector polarizations (polarization mixtures no tested yet) Abbott et al., Phys. Rev. Lett. 119, 141101 (2017) L. Rolland - 10 novembre 2017 - LAPP 7 Binary compact objects masses Binary black holes Binary neutron stars L. Rolland - 10 novembre 2017 - LAPP 8 $n brief: physics w/ binary black holes Formation of massive stars? Inference of BBH population distribution and merger rate Astrophysical Formation of BBH implications Estimation of GW From binary stars stochastic background (disfavoured?) from BBH mergers From isolated BHs Check waveform internal consistency Bound on graviton mass and Lorentz violation Tests of General Relativity Search for deviations from GR in waveform L. Rolland - 10 novembre 2017 - LAPP 9 The first multi-messenger detection of a binary neutron star merger: GW170817 ● GW data alone ● GRB association ● Electro-magnetic follow-up and kilonova ● Measurement of the Hubble constant ● Searching for neutrinos L. Rolland - 10 novembre 2017 - LAPP 10 ● GW data alone ● GRB association ● Electro-magnetic follow-up and kilonova ● Measurement of the Hubble constant ● Searching for neutrinos L. Rolland - 10 novembre 2017 - LAPP 11 AugustChe 17, 2017 BNSat 12h41m04.4s merger UTC Abbottin et al.,L$GO-#irgo PRL, 119, 161101 (2017) data Combined SNR = 32.4 False alarm rate < 1 per 8x104 years Low signal in Virgo: Worse sensitivity + worse sky direction → do not participate to detection → significant effect on parameter estimation, sky localisation in particular 10-21 SNR = 18.8 10-22 10-23 SNR = 26.4 Virgo LIGO-Hanford LIGO-Livingston 102 103 Frequency (Hz) Antenna responses SNR = 2.0 projected on Earth (darker → less sensitive) LIGO (Livingston) Virgo Signal duration: 100 s (from 24 Hz) L. Rolland - 10 novembre 2017 - LAPP 12 GW170817 source localisation ● Sky location: - rapid loc. with HL: 190 deg2 - rapid loc. with HLV: 31 deg2 - final loc. with HLV: 28 deg2 +8 ● Luminosity distance: 40 -14 Mpc (~120 millions of light-years) → 3D position: 380 Mpc3 This is the closest and most precisely localized gravitational-wave signal! → triggered follow-up observations → and identification of NGC4993 as host galaxy Abbott et al., PRL, 119, 161101 (2017) L. Rolland - 10 novembre 2017 - LAPP 13 Comparing the detected GW signals Binary black hole mergers short signals (<2 s) in the detector frequency band maximum frequency: few 100’s hertz Binary neutron star merger longer signals (~100 s) in the detector frequency band maximum frequency: ~1 kHz Shape of the GW signal → information on the source type and parameters L. Rolland - 10 novembre 2017 - LAPP 14 Estimation of intrinsic parameters Bayesian fit of the waveform Spin limit consistent with Theoretical observed population spin limit Mass parameters Dimensionless tidal deformability Masses of the objects Equation of state of the neutron stars Degeneracy between mass ratio Imprint on the and aligned spin components shape of the Tidal field of Deformation of gravitational wave, the companion the neutron star from f>600 Hz (→ parameter Λ) → Masses < 2.3 M⨀ ● Collision happens earlier than w/o tidal effect ● Modified final spin → disfavour equations of state of neutron stars that predict less compact stars: radius < 15 km → masses consistent with two neutron stars Abbott et al., PRL, 119, 161101 (2017) L. Rolland - 10 novembre 2017 - LAPP 15 Expected electro-magnetic counterparts? Short gamma-ray burst (sGRB): ● Jet → prompt γ-ray emission - few seconds after merger - last for <2 s - beamed ● Interaction of jet with interstellar medium → afterglow emission - few days after merger - evolves from X-ray to radio Kilonova ● Conversion of hot ejected matter into r- processed elements, disintegration and thermal emission → black body continuum + broad structures - few hours-days after merger - visible in UV, optical, IR - rapid spectral evolution Metzger & Berger, ApJ, 746, 48 (2012) L. Rolland - 10 novembre 2017 - LAPP 16 ● GW data alone ● Gamma-tray burst association ● Electro-magnetic follow-up and kilonova ● Measurement of the Hubble constant ● Searching for neutrinos L. Rolland - 10 novembre 2017 - LAPP 17 'ssociation wit" a gamma-ray burst GRB170817A detected by Fermi and INTEGRAL GRB sky localisation (90% CL) - γ-ray emission started ~1.7 s after merger time - 3 times more likely to be a short GRB than a long GRB Fermi-GBM (1100 deg2) Fermi and INTEGRAL (deg2) LIGO-Virgo (28 deg2) Time and localisation association chance probability: 5.0 x 10-8 → association validated within 5.3 σ → First direct evidence that binary neutron star mergers are progenitors of (at least some) short gamma-ray bursts! Abbot at al., ApJ, 848, 13 (2017) L. Rolland - 10 novembre 2017 - LAPP 18 GW170817?ew waveform insight → loose limit on into BNS viewing gamma-ray angle, but degeneracy with burstssource distance ● F < 56° from GW data alone ● F < 36° using the known distance to the host galaxy NGC 4993 → compatible with jet pointing towards Earth GRB170817A: ● the closest short GRB with know distance (z~0.008) (previous closest, GRB061201: z ~0;11) ● 102 to 106 times less energetic than other bursts → implications/questions on the structure of the jet Prediction of detection rates ● higher rate than previously expected for sGRB to be seen in gamma-rays ● 1-50 BNS mergers expected in LIGO-Virgo during run O3 (wrt previously estimated 0.04-100) → 0.1 to 1.4 joint detections for GW and Fermi sGRB during run O3 (end 2018-2019) Abbot at al., ApJ, 848, 13 (2017) L. Rolland - 10 novembre 2017 - LAPP 19 GW,GRB association and s+ee! of gravity Emission Propagation Detection on Earth at the binary neutron star merger Along at least 26 Mpc → GW and γ-ray signals → GW and γ-rays (85x106 light-years) GW γ- rays Assumption: γ-rays detected γ-rays emitted between 1.74 ; 0.05 s 0 and 10 s after GW after GW merger Previous constraints were allowing a time Difference between speed of gravity and speed of light: difference of 1000 years! [-3x10-15 ; +7x10-16] x c Abbot at al., ApJ, 848, 13 (2017) L. Rolland - 10 novembre 2017 - LAPP 20 ● GW data alone ● GRB association ● Electro-magnetic follow-up and kilonova ● Measurement of the Hubble constant ● Searching for neutrinos L. Rolland - 10 novembre 2017 - LAPP 21 The electro-magnetic follow-up campaign T0 T0 + 1,7 s T0 + 5 h T0 + 11 h T0 + 11 h T0 + 9 d T0 + 16 d GW GRB GW Optical Host galaxy X-ray radio-ray detection detection localisation counterpart NGC4993 counterpart counterpart +8 + distance: 40 -14 Mpc Identification of the host galaxy: 30’’ NGC4993, at ~40 Mpc Abbott et al., The Astrophysical Journal Letters, 848:L12 (2017) L. Rolland - 10 novembre 2017 - LAPP 22 3ollowing the optical transient Light curves in different bands Time evolution of light spectrum (blue to near-infrared) Black body 5000 K r ~ 8x1014 cm v ~ 0.2 c 18 August rapid cooling a r t c e p s y l Near IR i a d f o red e m i T UV/blue 27 August blue near-IR mid-IR → Decrease of light flux, → and spectral evolution faster at UV/blue than at NIR wavelengths - colour changed from blue to red black body - with apparition of lines → rapid cooling of ejecta (0.01 to 0.05 M ) G Abbot et al., Astrophys.