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First Results from LIGO

First Results from LIGO. Keith Riles University of Michigan High Energy Physics Seminar Michigan State University – Feb. 24, 2004. Outline. Nature & Generation of Gravitational Waves Interferometric Gravitational Wave Detection The Initial LIGO Detector The LIGO Scientific Collaboration

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First Results from LIGO

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  1. First Results from LIGO Keith Riles University of Michigan High Energy Physics Seminar Michigan State University – Feb. 24, 2004

  2. Outline • Nature & Generation of Gravitational Waves • Interferometric Gravitational Wave Detection • The Initial LIGO Detector • The LIGO Scientific Collaboration • Science Run S1: Sensitivity & Data Quality • First analysis results and future prospects • Preparing for Advanced LIGO K. Riles - First Results from LIGO -2/24/04

  3. Example: Ring of test masses responding to wave propagating along z Nature of Gravitational Waves • Gravitational Waves = “Ripples in space-time” • Perturbation propagation similar to light (obeys same wave equation!) • Propagation speed = c • Two transverse polarizations - quadrupolar: +andx • Amplitude parameterized by (tiny) dimensionless strain h: DL ~ h(t) x L K. Riles - First Results from LIGO -2/24/04

  4. Why look for Gravitational Radiation? • Because it’s there! (presumably) • Test General Relativity: • Quadrupolar radiation? Travels at speed of light? • Unique probe of strong-field gravity • Gain different view of Universe: • Sources cannot be obscured by dust • Detectable sources some of the most interesting, least understood in the Universe • Opens up entirely new non-electromagnetic spectrum K. Riles - First Results from LIGO -2/24/04

  5. What will the sky look like? K. Riles - First Results from LIGO -2/24/04

  6. Generation of Gravitational Waves • Radiation generated by quadrupolar mass movements: (with Imn = quadrupole tensor, r = source distance) • Example: Pair of 1.4 Msolar neutron stars in circular orbit of radius 20 km (imminent coalescence) at orbital frequency 400 Hz gives 800 Hz radiation of amplitude: K. Riles - First Results from LIGO -2/24/04

  7. Generation of Gravitational Waves Major expected sources in 10-1000 Hz band: • Coalescences of binary compact star systems (NS-NS, NS-BH, BH-BH) • Supernovae (requires asymmetry in explosion) • Spinning neutron stars, e.g., pulsars (requires axial asymmetry or wobbling spin axis) Also expected (but probably exceedingly weak): • Stochastic background – Big Bang remnant K. Riles - First Results from LIGO -2/24/04

  8. Generation of Gravitational Waves • Sources well below LIGO bandwidth: • Binaries well before coalescence • Inspiral of stars into massive black holes • Coalescence of massive black holes • Stochastic background (e.g, big bang remnant, superposition of binaries) • Irreducible seismic noise argues for space-based system at low frequencies - LISA Three satellites forming interferometers with 5 x 106 km baselines (launch 2012?) K. Riles - First Results from LIGO -2/24/04

  9. Generation of Gravitational Waves • Strong indirect evidence for GW generation: Taylor-Hulse Pulsar System (PSR1913+16) • Two neutron stars (one=pulsar) in elliptical 8-hour orbit • Measured periastron advance quadratic in time in agreement with absolute GR prediction  Orbital decay due to energy loss K. Riles - First Results from LIGO -2/24/04

  10. Generation of Gravitational Waves Can we detect this radiation directly? NO - freq too low Must wait ~300 My for characteristic “chirp”: K. Riles - First Results from LIGO -2/24/04

  11. Generation of Gravitational Waves Coalescence rate estimates based on two methods: • Use known NS/NS binaries in our galaxy (two!) • A priori calculation from stellar and binary system evolution • Large uncertainties! For initial LIGO design “seeing distance” (~20 Mpc): Expect 1/(3000 y) to 1/(4 y)  Will need Advanced LIGO to ensure detection K. Riles - First Results from LIGO -2/24/04

  12. Generation of Gravitational Waves Most promising periodic source:Rotating Neutron Stars (e.g., pulsar) But axisymmetric object rotating about symmetry axis Generates NO radiation Radiation requires an asymmetry or perturbation: • Equatorial ellipticity (e.g., – mm-high “mountain”): h α εequat • Poloidal ellipticity (natural) + wobble angle: h α εpol x Θwobble (precession due to differentLand Ωaxes) Notation henceforth: ε = ( εequat or εpol x θwobble ) K. Riles - First Results from LIGO -2/24/04

  13. Periodic Sources of GW Serious technical difficulty: Doppler frequency shifts • Frequency modulation from earth’s rotation (v/c ~ 10-6) • Frequency modulation from earth’s orbital motion (v/c ~ 10-4) Additional, related complications: • Daily amplitude modulation of antenna pattern • Spin-down of source • Orbital motion of sources in binary systems Modulations / drifts complicate analysis enormously: • Simple Fourier transform inadequate • Every sky direction requires different demodulation  All-sky survey at full sensitivity = Formidable challenge K. Riles - First Results from LIGO -2/24/04

  14. Periodic Sources of GW But two substantial benefits from modulations: • Reality of signal confirmed by need for corrections • Corrections give precise direction of source • Difficult to detect neutron stars! • But search is nonetheless attractive & intriguing: • Unknown number of electromagnetically quiet, undiscovered neutron stars in our galactic neighborhood • Realistic values for ε unknown • A nearby source could be buried in the data, waiting for just the right algorithm to tease it into view K. Riles - First Results from LIGO -2/24/04

  15. Gravitational Wave Detection • Suspended Interferometers (IFO’s) • Suspended mirrors in “free-fall” • Broad-band response (~50 Hz to few kHz) • Waveform information (e.g., chirp reconstruction) • Michelson IFO is “natural” GW detector K. Riles - First Results from LIGO -2/24/04

  16. Gravitational Wave Detection Major Interferometers coming on line world-wide K. Riles - First Results from LIGO -2/24/04

  17. With Fabry-Perot arm cavities • Recycling mirror matches losses, enhances effective power by ~ 50x 4 km Fabry-Perot cavity recycling mirror 150 W LASER/MC 20000 W (~0.5W) LIGO Interferometer Optical Scheme Michelson interferometer end test mass 6W K. Riles - First Results from LIGO -2/24/04

  18. “Locking” the Inteferometer • Sensing gravitational waves requires sustained resonance in the Fabry-Perot arms and in the recycling cavity • Need to maintain half-integer # of laser wavelengths between mirrors • Feedback control servo uses error signals from imposed RF sidebands • Four primary coupled degrees of freedom to control • Highly non-linear system with 5-6 orders of magnitude in light intensity Also need to control mirror rotation (“pitch” & “yaw”) • Ten more DOF’s (but less coupled) And need to stabilize laser (intensity & frequency), keep the beam pointed, damp out seismic noise, correct for tides, etc.,… K. Riles - First Results from LIGO -2/24/04

  19. Gravitational Wave Detection Initial LIGO Design Sensitivity • Dominant noise sources: • Seismic below 50 Hz • Suspensions in 50-150 Hz • Shot noise above 150 Hz • Best design sensitivity: • ~3 x 10-23 Hz-1/2 @ 150 Hz K. Riles - First Results from LIGO -2/24/04

  20. LIGO Observatories Hanford Observation of nearly simultaneous signals 3000 km apart rules out terrestrial artifacts Livingston K. Riles - First Results from LIGO -2/24/04

  21. LIGO Detector Facilities • Stainless-steel tubes • (1.24 m diameter, ~10-8 torr) • Gate valves for optics isolation • Protected by concrete enclosure Vacuum System K. Riles - First Results from LIGO -2/24/04

  22. LIGO Detector Facilities LASER • Infrared (1064 nm, 10-W) Nd-YAG laser from Lightwave (now commercial product!) • Elaborate intensity & frequency stabilization system, including feedback from main interferometer Optics • Fused silica (high-Q, low-absorption, 1 nm surface rms, 25-cm diameter) • Suspended by single steel wire • Actuation of alignment / position via magnets & coils K. Riles - First Results from LIGO -2/24/04

  23. 102 100 10-2 10-6 Horizontal 10-4 10-6 10-8 Vertical 10-10 LIGO Detector Facilities Seismic Isolation • Multi-stage (mass & springs) optical table support gives 106 suppression • Pendulum suspension gives additional 1 / f 2 suppression above ~1 Hz K. Riles - First Results from LIGO -2/24/04

  24. Retrofit with active feed-forward isolation system (using technology developed for Advanced LIGO)  Work started January 2004 Solution: Livingston Problem -- Logging Livingston Observatory located in pine forest popular with pulp wood cutters Spiky noise (e.g. falling trees) in 1-3 Hz band creates dynamic range problem for arm cavity control K. Riles - First Results from LIGO -2/24/04

  25. Correlation between seismic noise and lock livetime (4-day weekend) K. Riles - First Results from LIGO -2/24/04

  26. Sampling of Milestones December 1999 First light in Hanford 2-km cavity & brief arm lock April 2000 Engineering run “E1” (1 day, one 2-km arm) October 2000 Hanford 2-km “First-Lock” (whole kit & caboodle) March 2001 Engineering run “E3” (3 days, one Livingston arm) January 2002 Eng. run “E7” (17 days, all IFO’s + GEO + ALLEGRO) September 2002 Science run “S1” (17 days, all IFO’s + GEO + TAMA)  Results reported here Feb. – April 2003 Science run “S2” (59 days, all IFO’s + TAMA) October 2003 Eng. run “E10” (7 days, all IFO’s) Nov 2003 – Jan 2004 Science run “S3” (66 days, all IFO’s + GEO + TAMA)  Just ended! K. Riles - First Results from LIGO -2/24/04

  27. The LIGO Scientific Collaboration (LSC) • LSC formed to • Determine the scientific needs of the project and set R&D priorities • Present the scientific case for the program • Carry out the scientific and technical research program • Carry out the data analysis and validate the scientific results • Maximize scientific returns in the operations of LIGO Laboratory facilities • Determine the relative distribution of observing and development time • Establish the long term needs of the field & set priorities for improvements • Modeled in part on the successful high energy physics arrangement between national facilities and user group collaborations: • LIGO Laboratory = Caltech + MIT + Hanford + Livingston K. Riles - First Results from LIGO -2/24/04

  28. University of Adelaide ACIGA Australian National University ACIGA Balearic Islands University California State Dominquez Hills Caltech LIGO Caltech Experimental Gravitation CEGG Caltech Theory CART University of Cardiff GEO Carleton College Cornell University Fermi National Laboratory University of Florida @ Gainesville Glasgow University GEO NASA-Goddard Spaceflight Center University of Hannover GEO Hobart – Williams University India-IUCAA IAP Nizhny Novgorod IUCCA India Iowa State University Joint Institute of Laboratory Astrophysics Salish Kootenai College LSC Membership (~400 scientists) LIGO Livingston Observatory (LLO) LIGO Hanford Observatory (LLO) Loyola New Orleans Louisiana State University Louisiana Tech University MIT LIGO Max Planck (Garching) GEO Max Planck (Potsdam) GEO University of Michigan Moscow State University NAOJ - TAMA Northwestern University University of Oregon Pennsylvania State University Southeastern Louisiana University Southern University Stanford University Syracuse University University of Texas@Brownsville Washington State University@ Pullman University of Western Australia ACIGA University of Wisconsin@Milwaukee K. Riles - First Results from LIGO -2/24/04

  29. Michigan LIGO Group Members Old fogeys: Dick Gustafson, Keith Riles Graduate students: Dave Chin, Vladimir Dergachev Research assistant: Jennifer Lindahl Undergraduates: Tim Bodiya, John Lucido, Jake Slutsky, Phil Szepietowski Former undergraduates: Jamie Rollins(now at MIT) Justin Dombrowski(now at seminary) Joseph Marsano(now at Harvard) Michael La Marca(now at Arizona State) K. Riles - First Results from LIGO -2/24/04

  30. Michigan Group – Main Efforts • Initial work -- R&D at Caltech 40-Meter Prototype Interferometer • Demonstration of “recycling” with suspended interferometer • Last major R&D milestone for LIGO project • Apprenticeship for Gustafson and Riles • Detector Characterization (leadership, instrumentation, software) • Riles, Gustafson, Chin, Dergachev, Bodiya, Lucido • Commissioning & Noise Reduction • Gustafson (in residence at Hanford), Chin • Control System Development • Gustafson, Lindahl, Szepietowski, Riles • Search for Periodic Sources (rotating neutron stars) • Chin, Dergachev, Riles, Gustafson, Slutsky K. Riles - First Results from LIGO -2/24/04

  31. Data Analysis • Four “upper limits groups” organized: (to become “search groups”) • Inspiraling binary systems • Unmodelled bursts • Periodic sources (e.g. pulsars) • Stochastic background (e.g., big-bang remnant) • First steps: • Limits not yet astrophysically interesting • Understanding detector artifacts • Defining analysis algorithms and strategy (e.g., acceptable single-IFO signal rate prior to coincidence searching) K. Riles - First Results from LIGO -2/24/04

  32. S1 Instrumental Sensitivities • LIGO S1 Run • ---------- • “First • Upper Limit • Run” • 23 Aug–9 Sept 2002 • 17 days • All IFOs in power recycling config LHO 2Km LHO 4Km LLO 4Km GEO in S1 RUN ---------- Ran simultaneously In power recycling Lesser sensitivity K. Riles - First Results from LIGO -2/24/04

  33. Science Run S1 Data Analysis • As expected, S1 data much improved over earlier engineering run data in • Sensitivity • Gaussianity • Stationarity • But significant residual artifacts remained and new problems emerged as the noise floor fell • Artifacts substantially complicated the data analysis K. Riles - First Results from LIGO -2/24/04

  34. S1 Data Quality(three hours of Livingston 4-km) Histograms vs time of filtered GW channel RAGGED DATA CLEAN DATA K. Riles - First Results from LIGO -2/24/04

  35. S1 Data Quality – Inspiral Range (kpc)(“seeing distance” for inspiraling binary system) Calibration not as stable as we wanted: (one day of S1 Hanford 4-km running) K. Riles - First Results from LIGO -2/24/04

  36. S1 Data Quality Despite commissioning improvements, occasional artifacts appeared: Hanford 4-km “heartbeat” Tracked down to undamped “side motion” of one end mirror kicked up by Oregon earthquake K. Riles - First Results from LIGO -2/24/04

  37. Science Run S1 Data Analysis • Will summarize here results from searches for four types of gravitational wave sources: • Inspiral coalescence of binary neutron star system • Periodic source (pulsar) • Stochastic gravitational wave background • Bursts K. Riles - First Results from LIGO -2/24/04

  38. S1 Results • Search for binary inspiral coalescence of two neutron stars • Reporting limit on inspiral rate / milky-way equivalent galaxy (per year) • Search method relies upon matched filtering (frequency domain) of bank of template waveforms against the data • Searching over grid of neutron star mass pairs with M1 < M2 < 3 MSUN • Efficiency depends on distance to binary system • Define “inspiral candle” range to be distance at which binary system of 2 × 1.4MSUN neutron stars can be detected with SNR=8 in optimal orientation K. Riles - First Results from LIGO -2/24/04

  39. Visible: Milky Way LMC, SMC S1 Ranges L1: 110 kpc < D < 210 kpc H1: 40 kpc < D < 75 kpc H2: 38 kpc < D < 70 kpc K. Riles - First Results from LIGO -2/24/04

  40. Inspiral Results:[gr-qc/0308069 – submitted to PRD] • Use all candidates from Hanford and Livingston: 236 hours • Cannot accurately assess background (be conservative, assume zero) • Use maximum signal-to-noise ratio statistic to establish the rate limit. • Monte Carlo simulation efficiency = 0.51 • 90% confidence limit = 2.3 / (efficiency * time) • Express the rate as a rate per Milky-Way Equivalent Galaxies (MWEG) R < 2.3 / (0.50 x 236 hr) =1.7 x 102 / yr / (MWEG) • Previous observational limits • Japanese TAMA  R < 30,000/ yr / MWEG • Caltech 40m  R < 4,000/ yr / MWEG • Theoretical prediction • R < 2 x 10-5 / yr / MWEG K. Riles - First Results from LIGO -2/24/04

  41. SNR vs time: χ2 vs time: Loudest Surviving Event Candidate • Not NS/NS inspiral event • 1 Sep 2002, 00:38:33 UTC • S/N = 15.9, c2/dof = 2.2 • (m1,m2) = (1.3, 1.1) Msun Study of auxiliary channels reveals: Photodiode Saturation! K. Riles - First Results from LIGO -2/24/04

  42. S1 Results (cont.) • Search for periodic sources of gravitational radiation • Chose to focus on single (fastest) pulsar: • J1939+2134  fGW = 1.28 kHz • Two independent searches carried out: • Time Domain (heterodyne with modulation correction) • Frequency Domain (FFT stitching with correction) • Doppler modulations and pulsar spin-down explicitly taken into account in these coherent targeted analyses K. Riles - First Results from LIGO -2/24/04

  43. Crab pulsar PSR J1939+2134 P = 0.00155781 s fGW = 1283.86 Hz P = 1.0511 10-19 s/s D = 3.6 kpc . Expectations for pulsar strain amplitude sensitivity <ho>= 11.4 [Sh(fo)/T]1/2 • Detectable amplitudes with a 1% false alarm rate and 10% false dismissal rate by the IFOs during S1 (colored curves) and at design sensitivities (black curves) • Upper limits on <ho> from spin-down measurements of known radio pulsars (filled circles) S1: NO DETECTION EXPECTED K. Riles - First Results from LIGO -2/24/04 Graphic by R. Dupuis, Glasgow

  44. IFO Frequentist FDS Bayesian TDS GEO(1.9  0.1) x 10-21(2.2  0.1) x 10-21 LLO(2.7  0.3) x 10-22 (1.4  0.1) x 10-22 LHO-2K(5.4  0.6) x 10-22 (3.3  0.3) x 10-22 LHO-4K(4.0  0.5) x 10-22 (2.4  0.2) x 10-22 Pulsar Results: [ gr-qc/0308050 –to appear in PRD] • No evidence of continuous wave emission from PSRJ1939+2134– As expected • Summary of 95% upper limits on h: • ho < 1.4 x 10-22 constrains ellipticity < 3 x 10-4 (M=1.4Msun, r=10km, R=3.6kpc) • Previous best result for PSR J1939+2134: ho < 10-20(Glasgow, Hough et al., 1983) K. Riles - First Results from LIGO -2/24/04

  45. S1 Results (cont.) Search for stochastic background of gravitational waves • Sources: early universe, many weak unresolved sources emitting gravitational waves independently  Random radiation described by its spectrum (isotropic, unpolarized, stationary and Gaussian) • Analysis goals: constrain contribution of stochastic radiation’s energy rGWto the total energy required to close the universe rcritical : K. Riles - First Results from LIGO -2/24/04

  46. Methods for the Stochastic Search • Optimally filteredcross-correlationof detector pairs: L1-H1, L1-H2 and H1-H2. • Detectorseparation and orientation reduce correlations at high frequencies (lGW > 2xBaseLine): overlap reduction function • H1-H2 best suited • L1-H1(H2) significant <50Hz • Achievable sensitivitiesto Wby detector pairs in S1 [assumes W(f) = W0 ] K. Riles - First Results from LIGO -2/24/04

  47. Previous best upper limits: • Measured: Garching-Glasgow interferometers : • Measured: EXPLORER-NAUTILUS (cryogenic bars): Results of Stochastic Search[ gr-qc/0312088 – submitted to PRD] • Non-negligible LHO 4km-2km (H1-H2) cross-correlation due to common acoustic coupling (now much improved!) Interferometer Pair 90% CL Upper Limit Tobs LHO 4km-LLO 4km WGW (40Hz - 314 Hz) < 55  11 64 hrs LHO 2km-LLO 4km WGW (40Hz - 314 Hz) < 23  5 51 hrs K. Riles - First Results from LIGO -2/24/04

  48. S1 Results (cont.) Search for gravitational wave bursts • Sources: Knownandunknown phenomenaemitting short transients of gravitational radiation of unknown waveform (e.g., supernovae, black hole mergers). • Analysis goals: Broad frequency bandsearch to (a) establish a bound on their rate at the instruments, (b) interpret bound in terms of a source and population model on a rate vs. strength exclusion plot. • Search method: Time-Frequency domain algorithm identifies regions in the time-frequency plane with excess power (threshold on pixel power and cluster size – “tfcluster”). K. Riles - First Results from LIGO -2/24/04

  49. basic assumption: multi-interferometerresponse consistent with a plane wave-front incident on network of detectors. design thecapability to veto data epochs and events based on quality criteria and auxiliary channels. essential: use temporal coincidence of the 3 interferometer’s ‘best candidates’ correlate frequency features of candidates (time-frequency domain analysis). Bursts Search Pipeline Search code generated events Epoch veto’ed K. Riles - First Results from LIGO -2/24/04 Can be veto’ed by auxiliary channels

  50. End result of analysis pipeline: number of triple coincidence events. Use time-shift experiments to establish number of background events. Use Feldman-Cousins to set 90% confidence upper limits on rate of foreground events: < 1.6 events/day Upper Limit on Rate of Bursts Background estimation for TFCLUSTERS in S1 Poisson fit of time shifted coincidences between the LIGO sites Zero-lag measurement K. Riles - First Results from LIGO -2/24/04

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