Periodic sources of gravity waves

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Periodic sources of gravity waves

• Nikhef Jamboree 2007

Sipho van der Putten
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Contents

• Hulse-Taylor
• Pulsars gravitational waves from periodic
  sources
• Isolated pulsars
• Pulsars in binary systems

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Hulse - Taylor

• Hulse-Taylor (1974) binary PSR B191316
• Neutron star star (1.4 Msolar)
• Period 7.75 h
• Indirect detection of GWs
• Change in period over time and calculated from GR
  the energy loss
• Nobel prize 1993
• Direct detection VIRGO

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Periodic sources of gravity waves
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Periodic sources of gravity waves

• Pulsars spinning neutron stars
• Emitting GWs requires quadrupole moment
  symmetry axis is not rotation axis
• Strain (hdL/L) measured on earth

e Ellipticity ltlt 10-5 I3 3rd component moment
of inertia
hNS 10-27 Sensitivity 10-22
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Low amplitude, but

• Periodic signal ? Integrate over time
• Fourier transform
• hNS 10-27 ? 10-24
• Many neutron stars unknown and they can be
  nearby 2 kpc (Crab pulsar)
• hNS 10-24 ? 10-23
• All sky search
• 5 parameters

e.g. Neutron star rotating at 100 Hz and
observing it for 1 day gives a factor of 3x103
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Isolated pulsars simulations

• Simulated signal
• A(t) Amplitude modulation ? Detector acceptance
• F(a,d,t) Phase modulation ? Doppler shift,
  spindown
• Add simulated signal to detector output
• Reconstruct position amplitude of source
• Todo Reconstruct more realistic pulsars (h ?
  10-27)
• More involved analysis

hrec
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Neutron stars in binary systems
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Neutron stars in binary systems

• 2/3 of NS (fgt10Hz) in a binary system
• Mass transfer
• Spin-up f increases
• e increases (model dependent)
• 9 Search parameters

• Doppler shift due to orbit of binary system

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Analysis binaries spectral filtering

• Non stationary frequency FFT ? power spread out,
  bad S/N
• Spectral filtering Identify the signal in the
  data

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Templates for binaries

• Spectral filtering spread of power can be
  compensated
• Calculate expected signal
• Velocity of the detector relative to the SSB
• Velocity component of the binary in the direction
  of the detector
• Fourier transform calculated signal ? Template
• Own model
• Simulation package (R. Ebeling)
• Todo template search
• Template spacing 9 parameters !
• Computing power needed ? GRID

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Conclusions Outlook

• Isolated pulsars
• Simulations done/understood
• Analysis needs to be refined
• Binary pulsars
• Simulation in progress
• Conceptual approach to analysis spectral
  filtering
• Find the balance between FFT length and Template
  spacing in terms of available CPUs
• Developing GRID based analysis

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Backup slides
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Introduction to Gravitational Waves

• Ripples in space-time due to accelerating
  masses distorting space-time
• Two polarizations x
• Measured in strain hdL/L
• Extremely weak effects
• Supernova (10 kpc, 10 Msolar) h10-22
• Rotating deformed neutron star (10 kpc, 1
  Msolar, 100 Hz) h10-27

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VIRGO

• VIRGO 3km Michelson interferometer with resonant
  arm cavities
• Sensor (photodiode) tuned on dark fringe
• Gravitational wave
• Detector output

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Status of VIRGO
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Status of VIRGO
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Parameters Hulse Taylor

• PSR B191316
• Right ascension19h 13m 12.4655s
• Declination16 01' 08.189?
• AstrometryDistance21,000 ly (6.5 kpc)
• Mass1.441 Msolar
• Radius1.410-5
• Pulsar period 59.02999792988 ms
• Mass of companion 1.387 MSun
• Orbital period 7.751939106 hr
• Eccentricity 0.617131
• a1 sin i 2.34 LS
• Semimajor axis 1,950,100 km
• Periastron separation 746,600 km
• Apastron separation 3,153,600 km
• Orbital velocity of stars at periastron (relative
  to center of mass) 450 km/sec
• Orbital velocity of stars at apastron (relative
  to center of mass) 110 km/sec

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Detected frequency HT over 1 year
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Signal smearing

• Doppler shift power spread out over various
  frequency bins ? Lower S/N
• Get the signal back in 1 bin ? Adjust FFT length
• Isolated pulsars
• HT 7.4h ? 37 µHz
• J0034-0534 4800 s ? 208 µHz
• Binary pulsars
• HT 268 s ? 3.7 mHz
• J0034-0534 800 s ? 1.2 mHz