Interferometric Gravitational Wave Detectors Barry C. Barish Caltech "Colliding Black Holes" Credit: National Center for Supercomputing Applications (NCSA) LIGO-G030505-00-M TAUP 9-Sept-03 TAMA Japan 300m The Detectors LIGO Louisiana 4000m Virgo Italy 3000m GEO Germany
600m AIGO Australia future LIGO Washington 2000m & 4000m 9-Sept-03 TAUP 2 Detection on Earth network of detectors LIGO GEO decompose the polarization of detection locate theconfidence sources gravitational waves 9-Sept-03
TAUP Virgo TAMA AIGO 3 Interferometer Concept Laser used to measure Arms in LIGO are 4km relative lengths of two Measure difference in orthogonal arms length to one part in 1021 or 10-18 meters causing the interference pattern to change at the photodiode 9-Sept-03 As a wave Suspended
passes, the Masses arm lengths change in different ways. TAUP 4 Limiting Noise Sources Seismic noise & vibration limit at low frequencies Atomic vibrations (Thermal Noise) inside components limit at mid frequencies
Quantum nature of light (Shot Noise) limits at high frequencies Myriad details of the lasers, electronics, etc., can make problems above these levels 9-Sept-03 TAUP 5 LIGO Sensitivity Louisiana Interferometer First Science Run 17 days - Sept 02 May 01 Jan 03
Second Science Run 59 days - April 03 9-Sept-03 TAUP 6 Astrophysical Sources Compact binary inspiral: chirps NS-NS waveforms are well described BH-BH need better waveforms search technique: matched templates Supernovae / GRBs: bursts
burst signals in coincidence with signals in electromagnetic radiation prompt alarm (~ one hour) with neutrino detectors Pulsars in our galaxy: periodic search for observed neutron stars (frequency, doppler shift) all sky search (computing challenge) r-modes Cosmological Signals stochastic background 9-Sept-03 TAUP 7 Compact binary collisions
Neutron Star Neutron Star waveforms are well described Black Hole Black Hole need better waveforms Search: matched templates chirps 9-Sept-03 TAUP 8 Template Bank Covers desired region of mass param space Calculated based on L1 noise curve Templates placed for max mismatch of = 0.03
9-Sept-03 2110 templates Second-order post-Newtonian TAUP 9 Optimal Filtering frequency domain ~ Transform data to frequency domain : h (f) ~ Generate template in frequency domain : s( f ) Correlate, weighting by power spectral density of noise: ~* ~ s( f ) h ( f ) S h (| f |) Then inverse Fourier transform gives you the filter output
~* ~ at all times: s ( f ) h ( f ) 2 i f t z (t ) 4 e df S h (| f |) 0 Find maxima of | z (t ) | over arrival time and phase Characterize these by signal-to-noise ratio (SNR) and effective distance 9-Sept-03 TAUP 10 Matched Filtering 9-Sept-03 TAUP
11 Sensitivity neutron binary inspirals Star Population in our Galaxy Population includes Milky Way, LMC and SMC Neutron star masses in range 1-3 Msun LMC and SMC contribute ~12% of Milky Way Reach for S1 Data Inspiral sensitivity Livingston: = 176 kpc Hanford: = 36 kpc Sensitive to inspirals in Milky Way, LMC & SMC 9-Sept-03 TAUP 12 Loudest Surviving Candidate
Not NS/NS inspiral event 1 Sep 2002, 00:38:33 UTC S/N = 15.9, 2/dof = 2.2 (m1,m2) = (1.3, 1.1) Msun What caused this? Appears to be saturation of a photodiode 9-Sept-03 TAUP 13 Results of Inspiral Search Upper limit binary neutron star coalescence rate LIGO S1 Data R < 160 / 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 Detectable Range for S2 data will reach Andromeda! 9-Sept-03 TAUP 14 Astrophysical Sources Compact binary inspiral: chirps NS-NS waveforms are well described BH-BH need better waveforms search technique: matched templates Supernovae / GRBs: bursts
burst signals in coincidence with signals in electromagnetic radiation prompt alarm (~ one hour) with neutrino detectors Pulsars in our galaxy: periodic search for observed neutron stars (frequency, doppler shift) all sky search (computing challenge) r-modes Cosmological Signals stochastic background 9-Sept-03 TAUP 15
Detection of Burst Sources Known sources -- Supernovae & GRBs Coincidence with observed electromagnetic observations. No close supernovae occurred during the first science run Second science run We are analyzing the recent very bright and close GRB030329 NO RESULT YET Unknown phenomena Emission of short transients of gravitational radiation of unknown waveform (e.g. black hole mergers). 9-Sept-03 TAUP 16 Unmodeled Bursts GOAL search for waveforms from sources for which we cannot currently make an accurate prediction of the waveform shape.
METHODS Raw Data Time-domain high pass filter frequency Time-Frequency Plane Search TFCLUSTERS Pure Time-Domain Search SLOPE 8Hz 0.125s time 9-Sept-03 TAUP 17 Determination of Efficiency
To measure our Efficiency measured for tfclusters algorithm efficiency, we must pick a waveform. 1ms Gaussian burst amplitud e h 0 0 time (ms) 9-Sept-03 10 TAUP 18 Burst Upper Limit from S1
1ms gaussian bursts Result is derived using TFCLUSTERS algorithm Upper limit in strain compared to earlier (cryogenic bar) results: 90% confidence IGEC 2001 combined bar upper limit: < 2 events per day having h=1x10-20 per Hz of burst bandwidth. For a 1kHz bandwidth, limit is < 2 events/day at h=1x10-17 Astone et al. (2002), report a 2.2 excess of one event per day at strain level of h ~ 2x10-18 9-Sept-03 TAUP 19 Astrophysical Sources
Compact binary inspiral: chirps NS-NS waveforms are well described BH-BH need better waveforms search technique: matched templates Supernovae / GRBs: bursts burst signals in coincidence with signals in electromagnetic radiation prompt alarm (~ one hour) with neutrino detectors Pulsars in our galaxy: periodic search for observed neutron stars (frequency,
doppler shift) all sky search (computing challenge) r-modes Cosmological Signals stochastic background 9-Sept-03 TAUP 20 Detection of Periodic Sources Pulsars in our galaxy: periodic search for observed neutron stars all sky search (computing challenge) r-modes Frequency modulation of signal due to Earths motion relative to the Solar System Barycenter, intrinsic frequency changes. Amplitude modulation due to
the detectors antenna pattern. 9-Sept-03 TAUP 21 Directed searches NO DETECTION EXPECTED at present sensitivities Crab Pulsar h 0 11 .4 Sh f GW /TOBS Limits of detectability for rotating NS with equatorial ellipticity =I/Izz: 10-3 , 10-4 , 10-5 @ 8.5 kpc. PSR J1939+2134 9-Sept-03 TAUP 1283.86 Hz
22 Two Search Methods Frequency domain Best suited for large parameter space searches Maximum likelihood detection method + frequentist approach Time domain Best suited to target known objects, even if phase evolution is complicated Bayesian approach First science run --- use both pipelines for the same search for cross-checking and validation 9-Sept-03
TAUP 23 The Data time behavior Sh Sh days days Sh Sh days 9-Sept-03 days TAUP 24
The Data frequency behavior Sh Sh Hz Sh Sh Hz 9-Sept-03 Hz Hz TAUP 25 PSR J1939+2134 Frequency domain
Injected signal in LLO: h = 2.83 x 10-22 Fourier Transforms of time series Detection statistic: F , maximum likelihood ratio wrt unknown parameters use signal injections to measure Fs pdf Measured F statistic use frequentists approach to derive upper limit 9-Sept-03 TAUP 26 PSR J1939+2134 Data Time domain
Injected signals in GEO: h=1.5, 2.0, 2.5, 3.0 x 10-21 time series is heterodyned noise is estimated Bayesian approach in parameter estimation: express result in terms of posterior pdf for parameters of interest 9-Sept-03 95% h = 2.1 x 10-21 TAUP 27 Results: Periodic Sources No evidence of continuous wave emission from PSR J1939+2134. Summary of 95% upper limits on h:
IFO Frequentist FDS Bayesian TDS GEO (1.940.12)x10-21 (2.1 0.1)x10-21 LLO (2.830.31)x10-22 (1.4 0.1)x10-22 LHO-2K (4.710.50)x10-22 (2.2 0.2)x10-22 LHO-4K
(6.420.72)x10-22 (2.7 0.3)x10-22 Best previous results for PSR J1939+2134: ho < 10-20 (Glasgow, Hough et al., 1983), 9-Sept-03 TAUP 28 Upper limit on pulsar ellipticity J1939+2134 moment of inertia tensor 2 gravitational ellipticity of pulsar
2 8 G I zz f 0 h0 4 c R h0 < 3 10-22 < 3 10-4 R (M=1.4Msun, r=10km, R=3.6kpc) assuming emission due to deviation from axisymmetry: .. 9-Sept-03 TAUP 29 Astrophysical Sources Compact binary inspiral:
chirps NS-NS waveforms are well described BH-BH need better waveforms search technique: matched templates Supernovae / GRBs: bursts burst signals in coincidence with signals in electromagnetic radiation prompt alarm (~ one hour) with neutrino detectors Pulsars in our galaxy: periodic search for observed neutron stars (frequency, doppler shift) all sky search (computing challenge) r-modes
Cosmological Signals stochastic background 9-Sept-03 TAUP 30 Signals from the Early Universe stochastic background Cosmic Microwave background WMAP 2003 9-Sept-03 TAUP 31 Stochastic Background
Strength specified by ratio of energy density in GWs to total energy density needed to close the universe: GW ( f ) 1 critical dGW d(ln f ) Detect by cross-correlating output of two GW detectors: First LIGO Science Data Hanford - Livingston 9-Sept-03 Hanford - Hanford TAUP 32
Limits: Stochastic Search Interferometer Pair 90% CL Upper Limit Tobs LHO 4km-LLO 4km GW (40Hz - 314 Hz) < 72.4 62.3 hrs LHO 2km-LLO 4km GW (40Hz - 314 Hz) < 23 61.0 hrs Non-negligible LHO 4km-2km (H1-H2) instrumental cross-correlation; currently being investigated. Previous best upper limits: Measured: Garching-Glasgow interferometers : GW ( f ) 3 10 5
Measured: EXPLORER-NAUTILUS (cryogenic bars): 9-Sept-03 TAUP GW (907Hz) 60 33 Stochastic Background E7 results projected S1 S2 LIGO Adv LIGO 9-Sept-03
TAUP 34 LIGO Sensitivity Livingston 4km Interferometer First Science Run 17 days - Sept 02 May 01 Jan 03 Second Science Run 59 days - April 03 9-Sept-03 TAUP 35 Advanced LIGO 2007 +
Enhanced Systems laser suspension seismic isolation test mass Improvement factor in rate ~ 104 + narrow band optical configuration 9-Sept-03 TAUP 36 Gravitational Waves: Interferometers Terrestrial and Space Based Interferometers are being
developed Ground based interferometers in U.S.(LIGO), Japan (TAMA) and Germany (GEO) have done initial searches & Italy (Virgo) is beginning commissioning. New Upper limits already reported for neutron binary inspirals, a fast pulsar and stochastic backgrounds Sensitivity improvements are rapid -- second data run was 10x more sensitive and 4x duration Enhanced detectors will be installed in ~ 5 years, further increasing sensitivity Gravitational waves should be detected within the next decade ! 9-Sept-03 TAUP 37
