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Interferometric Gravitational Wave Detectors

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					  Interferometric Gravitational
                Wave Detectors



                                                         Barry C. Barish
                                                                Caltech

"Colliding Black Holes"                                            TAUP
Credit:                                                          9-Sept-03
National Center for Supercomputing Applications (NCSA)
TAMA Japan          The                              LIGO Louisiana
                                                         4000m
  300m
                  Detectors
                    Virgo Italy
                      3000m




                                               GEO Germany
 AIGO Australia                                   600m
    future


                             LIGO Washington
                              2000m & 4000m




9-Sept-03                    TAUP                             2
            Detection on Earth
            network of detectors
LIGO                GEO          Virg
                                 o      TAMA




 decompose the polarization of      AIGO
      locate the sources
     detection confidence
      gravitational waves
9-Sept-03              TAUP                3
              Interferometer Concept
ß Laser used to measure ß Arms in LIGO are 4km
  relative lengths of two ß Measure difference in
  orthogonal arms
                            length to one part in 1021 or
                            10-18 meters
   …causing the
interference pattern                           As a wave
  to change at the                            Suspended
                                              passes, the
     photodiode                                 Masses
                                              arm lengths
                                               change in
                                                different
                                                ways….




  9-Sept-03                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
                                               May 01
                              First Science
                                   Run
                              17 days - Sept
                                    02

                                               Jan 03




         Second Science
              Run
        59 days - April 03

9-Sept-03                    TAUP               6
              Astrophysical Sources
ß   Compact binary inspiral:         “chirps”
      » NS-NS waveforms are well described
      » BH-BH need better waveforms
      » search technique: matched templates

ß   Supernovae / GRBs:               “bursts”
      » burst signals in coincidence with signals in
        electromagnetic radiation
      » prompt alarm (~ one hour) with neutrino detectors

ß   Pulsars in our galaxy:           “periodic”
      » search for observed neutron stars (frequency,
        doppler shift)
      » all sky search (computing challenge)
      » r-modes

ß   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

                      2110 templates
ß Covers desired
                      Second-order
  region of mass
                      post-Newtonian
  param space
ß Calculated
  based on L1
  noise curve
ß Templates
  placed for
  max mismatch
  of d = 0.03




  9-Sept-03               TAUP         9
                  Optimal Filtering
                 frequency domain
 ß Transform data to frequency domain : h ( f )
                                                    ~
 ß Generate template in frequency domain :      ~( f )
                                                s
 ß Correlate, weighting by power spectral density of noise:
                                  ~
                         ~( f ) h * ( f )
                         s
                            S h (| f |)
Then inverse Fourier transform gives you the filter output
at all times:       •~     ~*
                          s ( f ) h ( f ) 2p i f t
             z (t ) = 4 Ú                 e        df
                        0
                              S h (| f |)
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
ß Population includes Milky Way, LMC and SMC
ß Neutron star masses in range 1-3 Msun
ß LMC and SMC contribute ~12% of Milky Way

                                            Reach for S1 Data
                                     ß Inspiral sensitivity
                                        Livingston: <D> = 176 kpc
                                        Hanford:      <D> = 36 kpc
                                     ß Sensitive to inspirals in
                                        » Milky Way, LMC & SMC




   9-Sept-03                  TAUP                           12
              Loudest Surviving Candidate
ß Not NS/NS inspiral event
ß 1 Sep 2002, 00:38:33 UTC
ß S/N = 15.9, c2/dof = 2.2
ß (m1,m2) = (1.3, 1.1) Msun




                                          What caused this?
                                     ß 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
ß Previous observational limits
   » Japanese TAMA ‡        R < 30,000 / yr / MWEG
   » Caltech 40m ‡          R < 4,000 / yr / MWEG
ß Theoretical prediction    R < 2 x 10-5 / yr / MWEG

 Detectable Range for S2 data will reach Andromeda!
9-Sept-03                    TAUP                         14
              Astrophysical Sources
ß   Compact binary inspiral:         “chirps”
      » NS-NS waveforms are well described
      » BH-BH need better waveforms
      » search technique: matched templates

ß   Supernovae / GRBs:               “bursts”
      » burst signals in coincidence with signals in
        electromagnetic radiation
      » prompt alarm (~ one hour) with neutrino detectors

ß   Pulsars in our galaxy:           “periodic”
      » search for observed neutron stars (frequency,
        doppler shift)
      » all sky search (computing challenge)
      » r-modes

ß   Cosmological Signals “stochastic background”


9-Sept-03                            TAUP                   15
              Detection of Burst Sources

ß 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

ß 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



        Time-Frequency Plane Search                Pure Time-Domain Search
              ‘TFCLUSTERS’                                 ‘SLOPE’
     frequency




                                       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

      h
 amplitud
 e




     0

            0               10
                time (ms)




      9-Sept-03                  TAUP                            18
            Burst Upper Limit from S1
                 1ms gaussian bursts
        Result is derived using ‘TFCLUSTERS’ algorithm

             90% confidence            Upper limit in strain
                                       compared to earlier
                                       (cryogenic bar) results:

                                          • 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 s excess of one
                                          event per day at strain level
                                          of h ~ 2x10-18
9-Sept-03                      TAUP                             19
              Astrophysical Sources
ß   Compact binary inspiral:         “chirps”
      » NS-NS waveforms are well described
      » BH-BH need better waveforms
      » search technique: matched templates

ß   Supernovae / GRBs:               “bursts”
      » burst signals in coincidence with signals in
        electromagnetic radiation
      » prompt alarm (~ one hour) with neutrino detectors

ß   Pulsars in our galaxy:           “periodic”
      » search for observed neutron stars (frequency,
        doppler shift)
      » all sky search (computing challenge)
      » r-modes

ß   Cosmological Signals “stochastic background”


9-Sept-03                            TAUP                   20
          Detection of Periodic Sources
ß Pulsars in our galaxy: “periodic”
   » search for observed neutron stars
   » all sky search (computing challenge)
   » r-modes

                                 ß Frequency modulation of signal
                                 due to Earth’s motion relative to
                                 the Solar System Barycenter,
                                 intrinsic frequency changes.

                                 ßAmplitude modulation due to
                                 the detector’s 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 e = dI/Izz: 10-3 , 10-4 ,
                                   10-5 @ 8.5 kpc.




                                                  PSR J1939+2134
                                                  1283.86 Hz
9-Sept-03                 TAUP                                    22
                 Two Search Methods

         Frequency domain                     Time domain


•      Best suited for large             • Best suited to target
       parameter space searches          known objects, even if
                                         phase evolution is
•      Maximum likelihood
                                         complicated
       detection method +
       frequentist approach              • 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          days

9-Sept-03                 TAUP                   24
                     The Data
                 frequency behavior
            Sh               Sh




                     Hz           Hz
            Sh               Sh




                     Hz           Hz

9-Sept-03                 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 F’s pdf                                  Measured
                                                 F statistic

• use frequentist’s approach to
derive upper limit



    9-Sept-03                     TAUP                                              26
                       PSR J1939+2134

                                       Data   Injected signals in GEO:
                                              h=1.5, 2.0, 2.5, 3.0 x 10-21
         Time domain
• time series is heterodyned
• noise is estimated
• Bayesian approach in
parameter estimation:                 95%
express result in terms of
posterior pdf for parameters
                                                h = 2.1 x 10-21
of interest




   9-Sept-03                   TAUP                             27
                Results: Periodic Sources

ß No evidence of continuous wave emission from PSR J1939+2134.
ß Summary of 95% upper limits on h:

          IFO      Frequentist FDS        Bayesian TDS
          GEO      (1.94±0.12)x10-21      (2.1 ±0.1)x10-21
          LLO      (2.83±0.31)x10-22      (1.4 ±0.1)x10-22
          LHO-2K   (4.71±0.50)x10-22      (2.2 ±0.2)x10-22
          LHO-4K   (6.42±0.72)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
                                         gravitational
                                         ellipticity of
                 2            2          pulsar
          8p G I zz f 0
      h0 = 4            e
           c       R
   h0 < 3 10-22 Ë e < 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
ß   Compact binary inspiral:         “chirps”
      » NS-NS waveforms are well described
      » BH-BH need better waveforms
      » search technique: matched templates

ß   Supernovae / GRBs:               “bursts”
      » burst signals in coincidence with signals in
        electromagnetic radiation
      » prompt alarm (~ one hour) with neutrino detectors

ß   Pulsars in our galaxy:           “periodic”
      » search for observed neutron stars (frequency,
        doppler shift)
      » all sky search (computing challenge)
      » r-modes

ß   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
ß   Strength specified by ratio of energy density in GWs to total energy
    density needed to close the universe:
                                            1         drGW
                          WGW ( f ) =
                                        r critical   d(ln f )
ß    Detect by cross-correlating output of two GW detectors:
                            First LIGO Science Data
             Livingston
    Hanford -†                                            Hanford - Hanford




9-Sept-03                                  TAUP                               32
                Limits: Stochastic Search

  Interferometer Pair        90% CL Upper Limit                     Tobs



  LHO 4km-LLO 4km         WGW (40Hz - 314 Hz) < 72.4             62.3 hrs
  LHO 2km-LLO 4km          WGW (40Hz - 314 Hz) < 23              61.0 hrs


ß Non-negligible LHO 4km-2km (H1-H2) instrumental cross-correlation;
  currently being investigated.
ß Previous best upper limits:
   » Measured: Garching-Glasgow interferometers :         WGW ( f ) < 3 ¥10 5

   » Measured: EXPLORER-NAUTILUS (cryogenic bars):         WGW (907Hz) < 60

                                                  †
    9-Sept-03                     TAUP                                     33

                                                      †
               Stochastic Background

                                 E7
            results
            projected
                                S1
                                S2
                               LIGO

                                      Adv LIGO




9-Sept-03               TAUP               34
                 LIGO Sensitivity
            Livingston 4km Interferometer
                                               May 01
                              First Science
                                   Run
                              17 days - Sept
                                    02

                                               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
ß Terrestrial and Space Based Interferometers are
  being developed
ß Ground based interferometers in U.S.(LIGO), Japan
  (TAMA) and Germany (GEO) have done initial
  searches & Italy (Virgo) is beginning commissioning.
ß New Upper limits already reported for neutron binary
  inspirals, a fast pulsar and stochastic backgrounds
ß Sensitivity improvements are rapid -- second data
  run was 10x more sensitive and 4x duration
ß Enhanced detectors will be installed in ~ 5 years,
  further increasing sensitivity
ß Gravitational waves should be detected within the
  next decade !
  9-Sept-03               TAUP                      37

				
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