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VIRGO and the Network of Gravitational Wave Detectors

This article provides an introduction to gravitational wave detection using interferometric techniques, an overview of the VIRGO detector and its status, information on the network of detectors, and the future of gravitational wave research.

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VIRGO and the Network of Gravitational Wave Detectors

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  1. VIRGO and the Network ofGravitational Wave Detectors Stefano Braccini INFN Pisa e-mail: stefano.braccini@pi.infn.it

  2. 1) Introduction • 2) Principles of Interferometric Detection • 3) The VIRGO Status • 4) The Network • 5) The Future

  3. EinsteinField Equations gik»hik + hik |hik| « 1 Weak Field Approximation hik= 0 In a vacuum………. Wave Equation ruling the evolution of the perturbation What are Gravitational Waves ? A gravitational wave is a perturbation to the space-time metrics propagating at the speed of light

  4. L-DL L-DL L+DL L+DL h+ t = T /4 t = T/2 t = 3T /4 hX Radiation-Matter Interaction GW acting on a ring of freely falling masses

  5. Interferometric Detection t = 0 t = T /4 t = T/2 t = 3T /4 t = T

  6. L ~ 103m DL ~ 10-18m h ~ 10-21 (VIRGO Supernova) Interferometric Detection L-DL L+DL t = 0 t = T /4 t = T/2 t = 3T /4 t = T

  7. M~1.4 M0, R~20 km, r~10 Mpc, forb~500 Hz M R r h ~ 10-21 Sources of GW

  8. NS or BH Coalescing Binaries …minutes… kHz Hz chirp h Signals can be exactly computed (except for the final part) Time Sources of GW

  9. Sources of GW Supernova Bursts Pulse of ms duration (no template available)

  10. Emits periodic signals at f=2fspinbut ….weak Sources of GW Neutron Stars SNR can be increased by integrating the signal for long time (months) Importance of the low frequency sensitivity (Hz region)

  11. Wide variety of signals expected between fraction of Hz and a few kHz

  12. 1) Introduction • 2) Principles of Interferometric Detection • 3) The VIRGO Status • 4) The Network • 5) The Future

  13. A simple detector h = 10-21  Dfgw= 3·10-11 rad

  14. Fabry-Perot Cavities to increase the effect Increase beam phase shift by 2F/p

  15.  1 kW 20 W Optical Readout Noise An accurate measurement of the phase requires a large amount of photons…

  16. Thermal Noise • Fluctuation-dissipation theorem Reduce dissipations in the optical payload

  17. Seismic Noise • Suspend the mirror • Use multipendulums • Make them low frequency • Provide 6 d.o.f. isolation

  18. Seismic Attenuation Low Dissipations Recycling High Power Laser Summary of the technique Fabry-Perot photodiode Vacuum

  19. Seismic Thermal Shot What is a sensitivity curve ?

  20. 1) Introduction • 2) Principles of Interferometric Detection • 3) The VIRGO Status • 4) The Network • 5) The Future

  21. LAPP – Annecy • INFN – Firenze-Urbino • INFN – Frascati • LMA – Lyon • INFN – Napoli • NIKHEF - Amsterdam • OCA – Nice • LAL – Orsay • ESPCI – Paris • INFN – Perugia • INFN – Pisa • INFN – Roma VIRGO at EGO Site

  22. VIRGO Optical Scheme

  23. Vacuum • Requirements: • 10-9 mbar for H2 • 10-14 mbar for hydrocarbons

  24. VIRGO Mirrors 35 cm diameter, 10 cm thickness Absorption: 1 ppm Reflection Losses: <5 ppm Surface deformations: 0.01 micron

  25. Injection System Laser Cavity Laser Source 20 W Nd:YVO4 laser (l=1.064 mm)

  26. Injection System

  27. Superattenuators Magnetic antisprings Blade springs Extend the band down to a few Hz

  28. Thermal Noise Measured Upper Limit Seismic Attenuation

  29. Photodiode demodulated signal during resonance crossing HOOK CAVITIES AT RESONANCE USING MIRROR COIL-MAGNET ACTUATORS l/2 Resonance Crossing l /100 Interferometer Locking Mirror Optical Surface MIRROR SWING Specification Accuracy better than 10-11 m

  30. Mirror Position Control Mirror longitudinal swing reduced to tenths of mm/s by Inertial Damping Angular mirror displacements reduced to fraction of mrad by Local Controls

  31. Pre-Stabilized Beam Source Mirror Optical Surface Pre-Align mirrors by Local Controls to allow interference Reduce mirror swing by Inertial Damping Seismic Noise Suppression Summary

  32. We can start the “Commissioning”

  33. Photodiode demodulated signal during resonance crossing HOOK CAVITIES AT RESONANCE USING MIRROR COIL-MAGNET ACTUATORS l/2 Resonance Crossing l /100 Interferometer Locking 0.5 mm/s Mirror Optical Surface MIRROR SWING Specification Accuracy better than 10-11 m

  34. Use Quadrant Photodiodes to Close Automatic Alignment After Locking…. Specification Accuracy better than 10-8 rad

  35. C5 recycled May 27th, recycled Beam Splitter Control Improvements Photodiode Noise Reduction Reduced Beam Splitter DAC noise Noise Hunting and Reduction Measure the sensitivity  Identify the noise sources  Try to reduce the noise

  36. Virgo Sensitivity Evolution

  37. Virgo Sensitivity Evolution Under study

  38. 1) Introduction • 2) Principles of Interferometric Detection • 3) The VIRGO Status • 4) The Network • 5) The Future

  39. 3 km Interferometer Networks 600 m 4 & 2 km TAMA 4 km 300 m

  40. LIGO Commissioning LIGO is in action at the design sensitivity

  41. A few tons A few m long Resonant Detectors

  42. Auriga, Legnaro MiniGRAIL, Leiden (Olanda) Allegro, LSU Lousiana Explorer, CERN Schenberg, San Paolo (Bra) Nautilus, Frascati

  43. VIRGO - LIGO

  44. VIRGO-LIGO JOINT SCIENTIFIC RUN 18/05/2007 – 01/10/2007

  45. VSR1 duty cycle statistics Duty cycle: 84% Longest lock: 94 hours Avg. Lock duration: 11.2 hrs Lock Recovering Time: about 30 min

  46. VSR1 Unlock Type Time Distribution 197 unlocks from “Science Mode”

  47. VSR 1 Binary Neutron Star Horizon BNS range (Mpc)

  48. h Reconstruction Noise analysis & data quality Coalescing binaries Bursts Periodic sources Stochastic background VIRGO-LSC Data Analysis First results delivered in 2008

  49. -18 10 -19 10 -20 10 -21 10 -22 10 -23 10 -24 10 4 1 10 100 1000 10 Present Network Design 2006-2007 Network h/Hz1/2 LIGO Resonant Virgo Antennas Ultracryogenics Pulsars h , 1 year integration GEO BH-BH Merger max Oscillations @ 100 Mpc Core Collapse QNM from BH Collisions, @ 10 Mpc QNM from BH Collisions, 100 - 10 Msun, 150 Mpc 1000 - 100 Msun, z=1 BH-BH Inspiral, 100 Mpc NS-NS Merger Oscillations @ 100 Mpc BH-BH Inspiral, z = 0.4 -6 e NS, =10 , 10 kpc NS-NS Inspiral, 300 Mpc Hz A first detection is unlikely NS/NS HORIZON Around 10-20 Mpc

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