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The Virgo interferometer for Gravitational Wave detection Francesco Fidecaro EPFL, November 8, 2010 Outline • • • • Gravitational waves: sources and detection The Virgo interferometer The global network Some LSC-Virgo results (for the LSC and Virgo collaborations) • Advanced Virgo • Perspective 2 Gravitational waves • Tiny perturbations of spacetime geometry g h • Predicted by Einstein as consequence of General Relativity – Propagate at the speed of light – Non relativistic approximation: generated by accelerated masses (quadrupole formula) – Amplitude h decreases as 1/R (field, as opposed to 1/R2 for energy or particle counting) – Order of magnitude: RS/R – Detectable by measuring invariant separation between free falling masses 3 Gravitational wave detection • Measure variations in curvature of space time • Use clocks on geodetics as markers • Be careful of pitfalls of Relativity! Measure only well defined, invariant quantities B3 B2 t B1 ds 2 0 : light ray Bi 1 d Bi g dx dx • Need one precise precise clocks in different clock in one places: place: laser – pulsar and atomic clock B3 B2 A3 B1 A2 A1 4 xx Detection by time measurement 6 Sources 7 Compact binary systems chirp 8 Horizon and event rate > 1 ev/yr 9 Predictions for the rates of compact binary coalescences observable … CQG, 10.1088/0264-9381/27/17/173001 Stellar core collapse (Supernova) Impulsive events, final evolution of big mass stars Core collapses to NS or BH, GW emitted only in nonspherical collapse Big uncertainties, waveform “unpredictable” GW emitted Coincidence detection necessary Amplitude: optimistic h~10-21 at 10 Mpc non-axisymmetric collapse Rate: several/year in the VIRGO cluster (how many detectable?) 10 Pulsars 1000 galactic pulsars known Possible sources of GW 11 Pulsars: rotating neutron stars Non-axisymmetric rotating NS emit periodic GW at f=2fspin but…weak f I 10 kpc 45 6 2 r 10 g/cm 200 Hz 10 2 h 3 10 27 SNR increases with observation time T as T1/2, T can be months But… Df ~ 10-6 Doppler correction of Earth motion: Df/f ~ 10-4 function of source position: Blind search limited by computing power 109 NS in the galaxy, ~1000 known Ellipticity determination: EOS nuclear matter. Strange stars? 12 Relic stochastic background CMBR Imprinting of the early expansion of Relic neutrinos Relic gravitons the universe Need two correlated ITFs Standard inflation produces a background too low String models ? 13 The Gravitational Wave Spectrum Dick Manchester, CSIRO LIGO/VIRGO 14 Noise characterization 15 Signal and noise 16 The Virgo detector 18 The Virgo Collaboration • Early efforts – – • • • • • • • • • • • • • • • • • • • • • Brillet (optics) Giazotto (suspensions) Collaboration started in 1992 LAPP Annecy EGO Cascina Firenze-Urbino Genova Napoli OCA Nice NIKHEF Amsterdam LAL Orsay LMA Lyon APC Paris – ESPCI Paris Perugia Pisa Roma La Sapienza Roma Tor Vergata Trento-Padova IM PAN Warsaw RMKI Budapest LKB Paris 18 groups About 200 authors 19 Noise in mass position 20 Seismic isolation • Super-attenuators: multi-stage passive seismic isolation system MODEL 21 Superattenuator performance • Excitation at top • Use Virgo sensitivity and stability • Integrate for several hours • Upper limit for TF at 32 Hz:1,7 10-12 • In some configurations a signal was found, but also along a direction perpendicular to excitation: compatible with magnetic cross talk marionetta mirror 22 GW interferometers • Isolated/suspended mirrors: – – • • • • • Differential measurement to cancel phase noise Effective L ~ 102 km l = 1 m Effective power ~ 1 kW ~ 1022 g Measurement noise ~ 10-11 rad h • • sz at 10 Hz ~ 10-18 m sz at 100 Hz ~ 10-21 m l s shot L 2 L Light source 1023 for a 1 s measurement Record a signal, if high SNR there is a large information content 23 m fused silica Issues in sensitivity200 (Virgo example) suspension fibre by-1/2 @ 10 Hz • h pioneered ~ 3 x 10-21 Hz • Glasgow/GEO600 h ~ 7 x 10-23 Hz-1/2 @ 100 Hz Mirror coating Beam size High power laser Mirror thermal lensing compensation for high power Signal recycling Use of non standard light Seismic attenuation Local gravity fluctuations 25 Virgo site in Cascina 26 The European Gravitational Observatory PURPOSE • The Consortium shall have as its purpose the promotion of research in the field of gravitation in Europe. • In this connection and in particular, the Consortium pursues the following objectives: – ensures the end of the construction of the antenna VIRGO, its operation, maintenance and the upgrade of the antenna as well as its exploitation; – ensures the maintenance of the related infrastructures, including a computer centre and promotes an open co-operation in R&D; – ensures the maintenance of the site; – carries out any other research in the field of gravitation of common interest of the Members; – promotes the co-operation in the field of the experimental and theoretical gravitational waves research in Europe; – promotes contacts among scientists and engineers, the dissemination of information and the provision of advanced training for young researchers. 27 EGO • 5 year renewal approved this year • Current members: CNRS, INFN participating equally to budget (ca 10 M€ / year) • Management: – – – – EGO Council and its President EGO Director Board of auditors Currently 48 staff, EGO Scientific Director, Adminstrative Head • Scientific and Technical Advisory Committee – Experts of the field or of related questions • VESF:Virgo-EGO Scientific Forum – Implementation of one of the EGO purposes – Gathers people interested in gravitational waves and their detection 28 Noise understanding • Noise sources and coupling are well understood • Low frequency shows more structures • Noise reduction in advanced detectors achieved with proper design • Virgo+ in 2010: fused silica suspensions and higher Finesse – risk reduction for Advanced detectors 29 Virgo sensitivity progress VSR1: May 18-Sep 30 2007 4 month continuous data taking simultaneously with LIGO Analysis in progress 30 Virgo & LIGO: 2008-09-10 31 Stability • Robust interferometer – 95% Science Mode duty cycle – Good sensitivity • Stable horizon: 8-8.5 Mpc (1.4-1.4 Ns-Ns) - averaged 42-44 Mpc (10-10 BH-BH) - averaged – fluctuating with input mirror etalon effect • Low glitch rate: factor 10 lower than VSR1 • Preparing for installation of monolithic suspensions Environmental noises studies Investigations to understand the sources and the path to dark fringe Coupling (paths) to dark fringe - diffused light from in air optical benches Need to work both on: - diffused light related to Brewster window reduction of coupling reduction of environmental noise - beam jitter on injection bench Sources of environmental noise: - air conditioning - electronic racks End benches Elec racks Injection bench Laser Beam jitter Brewster window DAQ room Detection suspended bench External bench 33 The global network 34 Motivation for a Global GW Detector Network • Time-of-flight to reconstruct source position t3 t1 t2 LIGO t5 t4 GEO VIRGO TAMA t6 AIGO 35 Motivation for a Global GW Detector Network • Source location: – – • Network Sky Coverage: – • Ability to be ‘on the air’ with one or more detectors Source parameter estimation: – – • Redundancy – signals in multiple detectors Maximum Time Coverage - ‘Always listening’: – • GW interferometers have a limited antenna pattern; a globally distributed network allows for maximal sky coverage Detection confidence: – • Ability to triangulate (or ‘N-angulate’) and more accurately pinpoint source locations in the sky More detectors provides better source localization Multimessenger astronomy More accurate estimates of amplitude and phase Polarization - array of oriented detectors is sensitive to two polarizations source location Coherent analysis: – – Combining data streams coherently leads to better sensitivity ‘digging deeper into the noise’ Also, optimal waveform and coordinate reconstruction 36 LIGO Abbott, et al., “The laser interferometer gravitational-wave observatory” http://stacks.iop.org/0034-4885/72/076901 37 38 Credit: Albert Einstein Institute Hannover Large Cryogenic Gravitational wave Telescope LCGT is almost entirely financed to be built underground at Kamioka, where the prototype CLIO detector is placed. 39 World wide GW network: LV agreement • “Among the scientific benefits we hope to achieve from the collaborative search are: – better confidence in detection of signals, better duty cycle and sky coverage for searches, and better source position localization and waveform reconstruction. In addition, we believe that the intensified sharing of ideas will also offer additional benefits.” • Collaborations keep their identities and independent governance 40 LV Agreement (I) • “All data analysis activities will be open to all members of the LSC and Virgo Collaborations, in a spirit of cooperation, open access, full disclosure and full transparency with the goal of best exploiting the full scientific potential of the data.” • Joint committees set up to coordinate data analysis, review results, run planning, and computing. The makeup of these committees decided by mutual agreement between the projects. • Joint publication of observational data whether data from Virgo, or LIGO (GEO) or both 41 Some results from L-V 43 Some results from LV • MoU for data sharing: now common data analysis groups (Bursts, Coalescing Binaries, Periodic Sources, Stochastic Background), weekly (and more) telecons • An Upper Limit on the Amplitude of Stochastic Gravitational-Wave Background of Cosmological Origin • Joint searches for GRBs (LV) • GRB 070201 (LSC) • Crab spindown limit (LSC) and Vela (Virgo) 44 45 Stochastic Background (SB) • A stochastic background can be • a GW field which evolves from an initially random configuration: cosmological background • the result of a superposition of many uncorrelated and unresolved sources : astrophysical background) • Typical assumptions • Gaussian, because sum of many contributions • Stationary, because physical time scales much larger than observational ones • Isotropic (at least for cosmological backgrounds) If these are true, SB is completely described by its power spectrum 46 Detection method • It is stochastic and presumably overwhelmed by noise • Need (at least) two detectors to check for statistical correlations Signals • Optimal filtering Uncorrelated (?) noises * 2 h1 ( f )h 2 ( f )g 12 ( f )GW (f) Y df f 6 S n ,1 ( f ) S n ,2 ( f ) hi ( f ) : data from detector i g 12 ( f ) : overlap function between detectors S n ,i ( f ) : noise power spectrum in detector i f d GW GW ( f ) c df f GW ( f ) 100Hz 47 Detection performance SNR 2 T df 0 g 2 ( f )GW ( f ) 12 f 6 Sn,1 ( f ) Sn,2 ( f ) • Sensitivity improves as T1/2 • Better performances when coherence is high ( ) – detectors near each other compared to l – detectors aligned 48 Isotropic search: results • Data collected during S5 run (one year integrated data of LIGO interferometers) • Point estimate of Y: no evidence of detection integrating over 40-170 Hz (99% of sensitivity) 0 6.9 10 6 95% C.L. 49 Isotropic search: results • Now we are beyond indirect BBN and CMB bounds • We are beginning to probe models 50 Joint LIGO/Virgo Search for GRBs • Gamma Ray Bursts (GRBs) - brightest EM emitters in the sky – Long duration (> 2 s) bursts, high Z progenitors are likely core-collapse supernovae – Short duration (< 2 s) bursts, distribution about Z ~ 0.5 progenitors are likely NS/NS, BH/NS, binary merger – Both progenitors are good candidates for correlated GW emissions! • 212 GRBs detected during S5/VSR1 – 137 in double coincidence (any two of LIGO Hanford, LIGO Livingston, Virgo) • No detections, we place lower limits on distance assuming EGW = 0.01 Mc2 51 GRB 070201 Refs: GCN: http://gcn.gsfc.nasa.gov/gcn3/6103.gcn3 X-ray emission curves (IPN) M31 The Andromeda Galaxy by Matthew T. Russell Date Taken: 10/22/2005 - 11/2/2005 Location: Black Forest, CO Equipment: RCOS 16" Ritchey-Chretien Bisque Paramoune ME 52 I Filters AstroDon Series SBIG STL-11000M http://gallery.rcopticalsystems.com/gallery/m31.jpg GRB070201: Not a Binary Merger in M31! Inspiral (matched filter search: Abbott, et al. “Implications for the Origin of GRB 070201 from LIGO Observations”, Ap. J., 681:1419–1430 (2008). Binary merger in M31 (770 kpc) scenario excluded at >99% level Inspiral Exclusion Zone 25% 50% Exclusion of merger at larger distances 75% 90% 99% Burst search: Cannot exclude an SGR in M31 SGR in M31 is the current best explanation for this emission Upper limit: 8x1050 ergs (4x10-4 Mc2) (emitted within 100 ms for isotropic emission of energy in GW at M31 distance) 9 November 2007 GRB 2007 53 The Crab Pulsar: Beating the Spin Down Limit! • Remnant from supernova in year 1054 • Spin frequency EM = 29.8 Hz gw = 2 EM = 59.6 Hz Abbott, et al., “Beating the spin-down limit on gravitational wave emission from the Crab pulsar,” Ap. J. Lett. 683, L45-L49, (2008). • observed luminosity of the Crab nebula accounts for < 1/2 spin down power •spin down due to: • electromagnetic braking • particle acceleration • GW emission? • early S5 result: h < 3.9 x 10-25 ~ 4X below the spin down limit (assuming restricted priors) • ellipticity upper limit: < 2.1 x 10-4 • GW energy upper limit < 6% of radiated energy is in GWs 54 VSR2 sensitivity for CW searches Targeted searches. Vela 55 VSR2 sensitivity Spin-down limit can be beaten for a few pulsars Name f gw sup Vela 22.38 8.0 10 4 J0205 6449 30.44 1.4 10 3 J1833 - 1034 32.32 1.1 10 3 J1747 - 2809 38.46 8.9 10-4 J1952 3252 50.58 1.1 10 4 J1913 1011 55.68 7.5 10 5 5 Crab 59.56 7.8 10 J0537 - 6910 124.04 8.9 10 5 (Vela spin-down limit in ~80 days) Compatible with some ‘exotic’ EOS may improve on Crab Marginally compatible with standard EOS 56 Recent papers Burst • Search for gravitational-wave bursts associated with gamma-ray bursts using data from LIGO Science Run 5 and Virgo Science Run 1 Ap. J.:http://iopscience.iop.org/0004-637X/715/2/1438. • All-sky search for gravitational-wave bursts in the first joint LIGOGEO-Virgo run Phys. Rev. D.: Phys. Rev. D 81(2010) 102001 CBC • Search for gravitational-wave inspiralsignals associated with short gamma-ray bursts during LIGO'sfifth and Virgo's first science run Ap. J.:http://iopscience.iop.org/0004-637X/715/2/1453. • Search for gravitational waves from compact binary coalescence in LIGO and Virgo data from S5 and VSR1 provisionally accepted in Phys. Rev, D CW • Searches for Gravitational Waves from Known Pulsars with S5 LIGO Data”Ap. J. http://stacks.iop.org/0004-637X/713/67 • First search for gravitational waves from the youngest known neutron star”, accepted for publication in Ap. J. 57 58 59 60 61 Prepare multi-messenger searches • Multi-messenger astronomy - connecting different kinds of observations of the same astrophysical event or system – Coincidence allows to decrease (somewhat) detection threshold – EM or particle presence may provide more information about the GW source • Sky position, host galaxy type, distance, emission characteristics / astrophysical processes • Require (at least) three operational and comparably sensitive GW detector sites – LIGO Hanford, Livingston, GEOHF and Virgo • With S6/VSR2 : begin connecting with other alert networks or provide data for immediate telescope pointing – Requires rapid online analysis, data quality flagging – Ongoing development by LIGO Lab, Data Analysis Software Working Group, and Search Groups – Example: P5 Swift ToO – Contacts with High Energy Neutrino detectors, pointing telescopes – Wide Optical Field telescopes • Connection with Astroparticle community 62 Advanced Virgo 63 Advanced detectors 2nd generation detectors – – – Enhanced LIGO/Virgo+ Virgo/LIGO BNS inspiral range >10x better than Virgo Detection rate: ~1000x better 1 day of Adv data ≈ 3 yrs of data 108 ly 2nd generation network. – Timeline: commissioning to start in 2014. Adv. Virgo/Adv. LIGO Credit: R.Powell, B.Berger 6464 Advanced Virgo baseline design • First orders placed. Plan to be backin 2015 with LIGO Heavier mirrors High finesse 3km FP cavities Larger central links Cryotraps Large spot size on TM Non degenerate rec. cavities High power laser Signal Recycling (SR) Monolithic suspensions DC readout 65 66 Perspective 67 The Future – AIGO (Australia) • • A comparably sensitive detector in Australia will bring increased angular sensitivity and better sky coverage Australian Interferometer Gravitational- wave Observatory conceived as a 5 km interferometer – will follow the AdvLIGO design • Possible variation in suspension and seismic isolation system • Likely location in Western Australia – Aim for operation in 2017 • 2 year lag behind AdvLIGO 68 The future: go around shot noise • Squeezed vacuum states as a tool are becoming reality • 6 dB reduction in shot noise is equivalent to an increase in power on beam splitter of 16 x • That reduction goes into radiation pressure fluctuations that can be important at low frequency • Next steps: frequency dependent squeezing GEO600 69 The Future: The Einstein Telescope (Europe) 70 Perspectives for third generation • Sources are waiting – Systems at cosmological distance – High statistics in binary systems (inspiral waveforms, matter distribution) – Increased sensitivity in merge and ringdown phase (GR, EOS) – Increased number of pulsars (EOS, population, ) – Stochastic background (cosmological and astrophysical) – Coincidences with g and X-ray satellites, observatories, …(system dynamics) • Gaining another factor 10 in sensitivity • Extending frequency down to a few Hz • Extending further frequency spectrum spectrum – Pulsar timing – High frequency gravitational waves 71 Sensitivity future evolution 72 Einstein Telescope: time scale 73 Conclusions • We are at the edge of starting a new, fascinating field of science • After “first words”, there is room for a large expansion in observations • Phenomenology, theory will follow • Room for unexpected • In spite of the size, the instrument can be run by a single (clever) person • New developments will be first by table top experiments • High interdisciplinary views required • Will reward junior and senior scientists 74 Thank you ! 75 The Fluctuation-Dissipation Theorem 76