LIGO Experiment - Searching for Gravitational Waves Myungkee Sung (Louisiana State University) December 15, 2009 at Seoul National University Myungkee Sung (Louisiana State University) December 15, 2009 at Seoul National University

Gravitational Waves Einstein’s theory of General Relativity (1916) – Geometrical Theory of Gravity. Gravitational interaction mediated by a deformation of space-time. Moving masses produce Gravitational Waves (GW) as a ripple in the curvature of space-time. Einstein’s theory of General Relativity (1916) – Geometrical Theory of Gravity. Gravitational interaction mediated by a deformation of space-time. Moving masses produce Gravitational Waves (GW) as a ripple in the curvature of space-time.

Hulse-Taylor Binary System Hulse-Taylor binary pulsar system (PSR B ) - loosing the energy with radiating GW. (1974, Nobel prize 1993) Gravitational Waves should exist! NO direct detection yet. Direct detection of GW will help understanding Gravity, GR, BH etc. Hulse-Taylor binary pulsar system (PSR B ) - loosing the energy with radiating GW. (1974, Nobel prize 1993) Gravitational Waves should exist! NO direct detection yet. Direct detection of GW will help understanding Gravity, GR, BH etc. [Weisberg & Taylor (2004)]

Detecting Gravitational Waves GW - Transverse waves travelling at the speed of light. Quadrupolar Distortions of Space between freely falling masses: GW as Dimensionless Strain: h(t) =  L(t) /L GW - Transverse waves travelling at the speed of light. Quadrupolar Distortions of Space between freely falling masses: GW as Dimensionless Strain: h(t) =  L(t) /L L+  L(t) To detect GW, measure  L(t) = h(t) L

Interferometer as GW Detector Interferometer for broadband antenna for gravitational waves - R. Weiss [1972]. Using interferometer to detect GWs - Gedanken experiment by P.A.E. Pirani (1956) Became Feasible with Advent of Lasers Interferometer for broadband antenna for gravitational waves - R. Weiss [1972]. Using interferometer to detect GWs - Gedanken experiment by P.A.E. Pirani (1956) Became Feasible with Advent of Lasers [MIT Quarterly Report (1972)]

Interferometer as GW Detector [MIT Quarterly Report (1972)] Servo System Conceptual Design of Broadband Antenna - Michelson Interferometer with long arms. Servo system Study on Various Noise Sources Conceptual Design of Broadband Antenna - Michelson Interferometer with long arms. Servo system Study on Various Noise Sources

Two LIGO Sites LIGO Hanford Observatory (LHO) Two interferometers (2, 4 km) LIGO Livingston Observatory (LLO) One interferometer (4km) LIGO Scientific Collaboration (LSC) - Over 60 institutions Caltech MIT 3002 km (L/c = 10 ms) Livingston LA Hanford WA

LIGO Scientific Collaboration Australian Consortium for Interferometric Gravitational Astronomy The Univ. of Adelaide Andrews University The Australian National Univ. The University of Birmingham California Inst. of Technology Cardiff University Carleton College Charles Sturt Univ. Columbia University Embry Riddle Aeronautical Univ. Eötvös Loránd University University of Florida German/British Collaboration for the Detection of Gravitational Waves University of Glasgow Goddard Space Flight Center Leibniz Universität Hannover Hobart & William Smith Colleges Inst. of Applied Physics of the Russian Academy of Sciences Polish Academy of Sciences India Inter-University Centre for Astronomy and Astrophysics Louisiana State University Louisiana Tech University Loyola University New Orleans University of Maryland Max Planck Institute for Gravitational Physics University of Michigan University of Minnesota The University of Mississippi Massachusetts Inst. of Technology Monash University Montana State University Moscow State University National Astronomical Observatory of Japan Northwestern University University of Oregon Pennsylvania State University Rochester Inst. of Technology Rutherford Appleton Lab University of Rochester San Jose State University Univ. of Sannio at Benevento, and Univ. of Salerno University of Sheffield University of Southampton Southeastern Louisiana Univ. Southern Univ. and A&M College Stanford University University of Strathclyde Syracuse University Univ. of Texas at Austin Univ. of Texas at Brownsville Trinity University Universitat de les Illes Balears Univ. of Massachusetts Amherst University of Western Australia Univ. of Wisconsin-Milwaukee Washington State University University of Washington

 Members from 2 National labs, 4 Universities  4 permanent members, 2 postdocs, 4 + PhD students, and 5 technical staff  Just joined LSC (last September).  Members from 2 National labs, 4 Universities  4 permanent members, 2 postdocs, 4 + PhD students, and 5 technical staff  Just joined LSC (last September). Seoul National U. National Institute for Mathematical Sciences [NIMS] Hanyang U. Lund U. Korea Institute of Science and Technology Information [KISTI] Pusan National U.

International GW Network Simultaneous detection - Detection confidence, Background Estimation, Better duty cycle Understanding detected GW signals better o Source polarization o Sky locations o Waveform extraction o Verify light speed propagation LIGO (LHO) LIGO (LLO)

Michelson Interferometer Pre-Stabilized Laser (PSL) Mode Cleaner Beam Splitter (BS) End Mirror (ETM) Nd:YAG = 1064nm 4-5W Photodiodes End Mirror (ETM) Fused Silica 10kg, 10cm thick D = 25cm Polished to /1000 (~1nm)

Fabry-Perot Michelson Interferometer Pre-Stabilized Laser (PSL) Mode Cleaner Fabry-Perot Cavity Input Mirrors (ITM) Beam Splitter (BS) End Mirror (ETM) Nd:YAG = 1064nm L = 4 km 4-5W Fabry-Perot Cavity: ~125 round trips  Effective optical path ~500km Photodiodes

LIGO Detector: Power-Recycled Fabry-Perot Michelson Interferometer Pre-Stabilized Laser (PSL) Mode Cleaner Fabry-Perot Cavity Recycling Mirror (RM) Input Mirrors (ITM) Beam Splitter (BS) End Mirror (ETM) Nd:YAG = 1064nm L = 4 km 4-5W W 12-15kW Power Recycling Cavity Power × 50

LIGO Detector: Power-Recycled Fabry-Perot Michelson Interferometer Pre-Stabilized Laser (PSL) Mode Cleaner Fabry-Perot Cavity Recycling Mirror (RM) Input Mirrors (ITM) Beam Splitter (BS) End Mirror (ETM) Nd:YAG = 1064nm L = 4 km 4-5W W 12-15kW Photodiodes ⇒ Gravitational Wave (GW) Channel D(t) More than 100 Control Servo Systems - Locking system using Pound–Drever–Hall (PDH) technique (1983) Ronald Drever (Caltech)

Gravitational Wave (Signal) Channel DARM_ERR: Only channel for GW signals, out of ~1000 channels. D(t) - Time series of ADC readout from DARM_ERR  Sampling rate – 2 14 measurements every seconds, or ~16 kHz.  Not the same as the strain, h(t), but detector response to the strain. DARM_ERR: Only channel for GW signals, out of ~1000 channels. D(t) - Time series of ADC readout from DARM_ERR  Sampling rate – 2 14 measurements every seconds, or ~16 kHz.  Not the same as the strain, h(t), but detector response to the strain. GW Channel Readout (arbitrary unit), D(t) Time [seconds]

Calibration of LIGO Data h(t) Calibration: Calculate/measure the Response function of the detector. h * (t) = R(f,t) × D(t) Calibration: Calculate/measure the Response function of the detector. h * (t) = R(f,t) × D(t) Response ft. R(f,t) CALIBRATION h * (t) LIGO Detector GW Channel Readout (arbitrary unit), D(t) Time [seconds]

h(t): Strain – Calibrated Data h(t) – Being produced in almost real time with the Time-Domain Calibration in the current run. [Rep. Prog. Phys. 72 (2009) ]

Sensitivity Limits – Noise Sources

Sensitivity and Science Runs  L = h(f)×L ~ m/  Hz Atomic nuclear size!! Sensitivity of required for potential strong sources of GWs in our galaxy or nearby galaxies Sensitive to frequency band of 40 ~ 7000 Hz

LIGO Milestones LIGO cofound by Kip Thorne, Ronald Drever (Caltech) and Rainer Weiss (MIT) in LIGO Detectors construction completed in The first Science Run (S1) in 2002 with sensitivity much better than any previous GW detectors. S5: November 2005 – September 2007 Achieved the designed sensitivity of the initial LIGO. Stable data taking for about 2 years. One year of triple coincidences. S6: Enhanced LIGO – Started July 2009.

GW Sources Coalescing Binary systems of Compact stars (CBC) Bursts – Supernovae, Gamma Ray Bursts (GRB) Continuous waves – Pulsars Stochastic backgrounds Binary Systems (NS, BH) Supernova Explosions Rotating Stars (Pulsars) Stochastic Background

GW Waveforms: Template Bank Known waveforms – CBCs, Supernovae, Known Pulsars and so on. Generic waveforms  Wavelets, Sine-Gaussians, Gaussians for burst search, Sine waves for pulsars.  Cover the parameter spaces in detector sensitivity Cross correlations – Stochastic background

Making Lists of Events Use techniques from the Signal Processing for each GW sources. Apply thresholds to the filtered outputs to make a list of potential candidates with outliers. Hardware and Software Injections  Understand detector performance  Evaluate Analysis Techniques – Efficiencies of Searching GWs.

Dealing with Background Events Background Events Accidental events from noise not from GW sources. Instrumental/environmental background Detector characterization, glitch study to understand backgrounds and detector responses. Auxiliary/Environmental channels which cannot have GW signals. Notes in Elog by shifters. Produce Vetoes/DQ flags. Most backgrounds are local – Multiple detectors!! Background Events Accidental events from noise not from GW sources. Instrumental/environmental background Detector characterization, glitch study to understand backgrounds and detector responses. Auxiliary/Environmental channels which cannot have GW signals. Notes in Elog by shifters. Produce Vetoes/DQ flags. Most backgrounds are local – Multiple detectors!! Hurricane Katrina August 29, 2005

All Sky Search and Triggered Searches All Sky Searches General searches for GWs from all directions of sky and polarizations. Use data from all Science Mode. Triggered Searches Use available information of potential GW sources like GRB, Supernovae, from other astronomical observations. Focusing on specific time.

Coalescing Compact Binaries Final stages of binary systems of neutron stars, black holes – inspiral & merger Inspiral waveforms - from Post-Newtonian (PN) model. S5 First year analysis [PRD 79,12200] 186 days of second year LIGO-only analysis [PRD 80, ] ~100 days of triple coincidences. No signals found for total masses between 2M  and 35 M . LIGO/Virgo joint analysis for the rest of S5 data will follow. Final stages of binary systems of neutron stars, black holes – inspiral & merger Inspiral waveforms - from Post-Newtonian (PN) model. S5 First year analysis [PRD 79,12200] 186 days of second year LIGO-only analysis [PRD 80, ] ~100 days of triple coincidences. No signals found for total masses between 2M  and 35 M . LIGO/Virgo joint analysis for the rest of S5 data will follow. [Phys. Rev. D ]

Burst Type Gravitational Waves Transient Gravitational Waves with short (< ~1s) duration Possible astrophysical sources - Core collapse of massive stars; Supernova explosion; Gamma Ray Burst (GRB), Unknown phenomenon. Waveforms – General waveforms like wavelets, Sine-Gaussians, Gaussians. Transient Gravitational Waves with short (< ~1s) duration Possible astrophysical sources - Core collapse of massive stars; Supernova explosion; Gamma Ray Burst (GRB), Unknown phenomenon. Waveforms – General waveforms like wavelets, Sine-Gaussians, Gaussians. All Sky Searches – No model for waveforms, All sky locations, All time. Triggered Searches – Trigger on astronomical observations such as GRBs, Soft Gamma Repeater (SGR) flares, Pulsar rotation glitches, Supernovae.

All Sky Burst Searches Low frequency search Frequency: 64 – 2000 Hz Result from S5 first year No burst signal found. Upper limit < 3.75 C.L. Analysis on full S5 data in progress. High frequency search Frequency up to 6 kHz Less noisy. Higher calibration uncertainty – Substantial systematic error. [PRD 80 (2009) ]

Triggered Burst Searches GRB [ APJ681, 1419 (2008) ] Position (from IPN) consistent with M31[Andromeda is the nearest spiral galaxy (2.5 M light-years)] Short, hard Gamma-Ray Burst - Leading model: Binary merger involving a neutron star? Both LIGO Hanford detectors were operating - Searched for inspiral & burst signals - Asymmetric 180 (-120/+60) second window about GRB trigger time. No plausible GW signal found ⇒ Very unlikely to be from a binary merger in M31

Continuous Waves - Pulsars Periodic sources with low amplitude. Continuous and quasi-monochromatic in frequency. Asymmetric spinning neutron stars. Waveform and position known for many pulsars. S5 UL for Crab pulsar: E GW < 4% of total energy loss [Ap. J. Lett. 683(2008) 45]. Blind Searches – General search for unknown pulsars in any sky locations. – Very expensive computationally ⇒ Early S5 results: [arXiv: ] Periodic sources with low amplitude. Continuous and quasi-monochromatic in frequency. Asymmetric spinning neutron stars. Waveform and position known for many pulsars. S5 UL for Crab pulsar: E GW < 4% of total energy loss [Ap. J. Lett. 683(2008) 45]. Blind Searches – General search for unknown pulsars in any sky locations. – Very expensive computationally ⇒ Early S5 results: [arXiv: ]

Stochastic GW Background Looking for cross-correlations between detectors from continuous random signals Gravitational wave background from big bang/early universe, predicted by most cosmological theories. Looking for cross-correlations between detectors from continuous random signals Gravitational wave background from big bang/early universe, predicted by most cosmological theories. [Phys. Rev. D 76 (2007) ]Phys. Rev. D 76 (2007)

Stochastic GW Background [Nature V460, 990]  0 < 6.9 x at 90% C.L. for ~100 Hz

Status of LIGO S5 achieved the design sensitivity for two years of data taking. S6, Enhanced LIGO (ELIGO) – Started in July, 2009, for one year data taking. Advanced LIGO (AdLIGO) approved and funding started April AdLIGO will improve sensitivity ×10. Low frequency boundary: 40Hz to 10Hz S5 achieved the design sensitivity for two years of data taking. S6, Enhanced LIGO (ELIGO) – Started in July, 2009, for one year data taking. Advanced LIGO (AdLIGO) approved and funding started April AdLIGO will improve sensitivity ×10. Low frequency boundary: 40Hz to 10Hz [Roadmap – Gravitational Waves International Committee (GWIC)]

Advanced LIGO: Second Generation Improve the isolation system, suspension system, test mass coating, laser power and so on. 180 W laser Seismic Isolation Quadruple Pendulum Suspensions

Science Runs and Inspiral Ranges

Advanced LIGO: Second Generation Range for binary neutron stars (2x1.4 M  ) increases from 10~20 Mpc to 200~350 Mpc. Ten times Improved sensitivity covers ×1000 larger volume. Estimated detection rate of binary neutron stars increases; 1/(50 years) ⇒ 40/year Expect to detect gravitational waves!! Range for binary neutron stars (2x1.4 M  ) increases from 10~20 Mpc to 200~350 Mpc. Ten times Improved sensitivity covers ×1000 larger volume. Estimated detection rate of binary neutron stars increases; 1/(50 years) ⇒ 40/year Expect to detect gravitational waves!!

Beyond AdLIGO: Third Generation [Physics, Astrophysics and Cosmology with Gravitational Waves, B.S. Sathyaprakash and B.F. Schutz Living Rev. Relativity 12, (2009), arXiv: ] LISA

Beyond AdLIGO [Roadmap, Gravitational Waves International Committee]

Timeline for Ground Based Detectors [Roadmap, Gravitational Waves International Committee]

Summary Overview of the LIGO Experiment LIGO Detectors LIGO Data GW searches with LIGO Status and Prospects of LIGO Roadmap of GW Physics Initial LIGO was successful by Achieving the design sensitivity as planned Developing various analysis techniques for gravitational waves from different sources. Second/Third generations are on schedule. Expect the direct detection of GWs in foreseeable future with the second generation. Overview of the LIGO Experiment LIGO Detectors LIGO Data GW searches with LIGO Status and Prospects of LIGO Roadmap of GW Physics Initial LIGO was successful by Achieving the design sensitivity as planned Developing various analysis techniques for gravitational waves from different sources. Second/Third generations are on schedule. Expect the direct detection of GWs in foreseeable future with the second generation.

Calibration of LIGO Data LIGO detector – Very sophisticated system with >100 feedback servo loops Calculate/measure the response function R(f,t) of the LIGO detector. LIGO detector – Very sophisticated system with >100 feedback servo loops Calculate/measure the response function R(f,t) of the LIGO detector. Response Function where G 0 (f) = D(f)A(f)C 0 (f)  (t) - Time-dependent coefficient. Actual calculation in frequency domain – complex functions D(t) s(t) = h(t) + n(t) Digital Filter Actuation Sensing DARM Servo Loop

Response function – Frequency Dependent Part Frequency dependent part of the response function: R(f) by setting  (t)=1 from Different models for different epochs, from measurements of each transfer functions, C(f), D(f), A(f). Understanding of the detector responses to both signals and background. Frequency dependent part of the response function: R(f) by setting  (t)=1 from Different models for different epochs, from measurements of each transfer functions, C(f), D(f), A(f). Understanding of the detector responses to both signals and background. Frequency [Hz] Amp(R(f)) Phase(R(f))

Time Dependent Coefficient:  (t) GPS Time Im(  (t)) Re(  (t)) Three calibration lines - ~50 Hz, ~400 Hz, ~1100 Hz Monitoring detector performance during data taking. Estimate Statistical and Systematic Uncertainties on Calibration – esp. Im(  ) Three calibration lines - ~50 Hz, ~400 Hz, ~1100 Hz Monitoring detector performance during data taking. Estimate Statistical and Systematic Uncertainties on Calibration – esp. Im(  ) Overall systematic error due to calibration < 10 %