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VIRGO and the search for Gravitational Waves

VIRGO and the search for Gravitational Waves. Giovanni Losurdo INFN Firenze-Urbino e-mail: losurdo@fi.infn.it. PSR1913+16: GW Exist. Pulsar bound to a “dark companion”, 7 kpc away. Extremely accurate clock: f =17 H z, D f /D t =10 -15 s -2 Relativistic clock: v max /c ~ 10 -3.

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VIRGO and the search for Gravitational Waves

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  1. VIRGO and the search for Gravitational Waves Giovanni Losurdo INFN Firenze-Urbino e-mail: losurdo@fi.infn.it

  2. PSR1913+16: GW Exist • Pulsar bound to a “dark companion”, 7 kpc away. • Extremely accurate clock: f=17 Hz, Df/Dt=10-15 s-2 • Relativistic clock: vmax/c ~ 10-3 • GR predicts such a system to loose energy via GW emission  orbital period decrease Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  3. Ripples in the Cosmic Sea • Linearized Einstein eqs. (far from big masses) admit wave solutions (perturbations to the background geometry) Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  4. Energy-Time Scales Coupling constants • In SN collapse n withstand 103 interactions before leaving the star, GW leave the core undisturbed • Decoupling after Big Bang • GW ~ 10-43 s (T ~ 1019 GeV) • n ~ 1 s (T ~ 1 MeV) • e.m. ~ 1012 s (T ~ 0.2 eV) GW brings unique information out of the Universe Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  5. DE ~ 1052 erg for NS/NS M R r h ~ 10-21 Sources of GW • Luminosity: • Amplitude: • M~1.4 M, R~20 km, r~15 Mpc, forb~400 Hz Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  6. chirp Coalescing Binaries • Compact stars (NS/NS, NS/BH, BH/BH) • Inspiral signal accurately predictable • Newtonian dynamics • Post-Newtonian corrections (3PN, (v/c)11/2) [L.Blanchet et al., CQG 13, 1996] Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  7. Supernovae • Final evolution of big mass stars • Core collapses to NS or BH • Neutrinos and GW emission • Rate: several per year in the VIRGO cluster GW emitted Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  8. g GW GW g Kerr Black Holes – Torus System • A BH-torus system may originate in a NS-BH coalescence • GRBs can be emitted during BH accretion by torus matter • A non-axisymmetric spinning torus, powered by BH angular momentum, is expected to emit a GW burst of T~15 sec, f~1-2/(1+z) kHz • If the observed GRBs are originated in such events a rate of ~105 /yr within 100 Mpc is expected (Van Putten, PRL, 87, 2001) Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  9. L-DL L+DL L ~ 103m Measurable DL ~ 10-18m Target h ~ 10-21 (NS/NS @10 Mpc) Interferometric Detection of GW • GW acting on a ring of freely falling masses Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  10. Noise in Interferometric Detectors • Suspended mirrors (free falling test masses) • GW induce ITF phase shift: • Shot noise: • Thermal noise: Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  11. 3 km vacuum performance within requirements • Final mirrors suspended • Start of commissioning: June 2003 • Data taking: 2004+ Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  12. seismic bars thermal shot Sensitivity Goal Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  13. A Real Interferometer Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  14. Vacuum • Requirements: • 10-9 mbar for H2, 10-14 mbar for hydrocarbons • 10-6 mbar in the suspension chambers • Outgassing rate: 5 10-15 mbar l s-1 cm-2 • Status: • Whole tube welded, leak-tested and baked • 160 steel baffles for reflected light shielding installed • Vacuum performance within requirements Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  15. 10-14 @ 10 Hz Superattenuators • Goal: move the seismic wall down to a few Hz • Expected attenuation: 10-14 @ 10 Hz • 3 actuation points for hierarchical control of the mirror: inverted pendulum,marionette, recoil mass • Inertial damping on IP, angular local controls on marionette Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  16. LVDTs, accelerometers CCD ITF SA Control Tide control • Residual low frequency motion of the mirrors ~ 10-4 m • Mirror motion after local control < 10-6 m • Mirror motion after locking ~ 10-12 m Inertial damping Angular controls Pendulum damping Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  17. Inverted pendulum Marionette Mirror – ref. mass filters Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  18. The superattenuator and the VIRGO vacuum system Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  19. Injection System • 20 W laser • 144 m MC cavity to reduce jitter noise and select TEM00 mode Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  20. Output mode cleaner External bench Suspended bench Detection • Suspended bench with optics for beam adjustement and output mode cleaner • Detection, amplification and demodulation on the external bench • Output mode cleaner locked in CITF Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  21. Mirrors • Coater VIRGO in a class 1 clean room, unique in the world (2.2*2.2*2.4 m) • Coating features: • very low losses: scattering < 5 ppm, absorption < 1 ppm • Uniformity on large dimension: < 10-3 400 mm • Optical metrology adapted to large components • Type of controls: scattering, absorption (bulk, surface), birefringence, reflection, transmission, wavefront (stitching), roughness, defects detection Absorption, Birefringence, wavefront measurement Coater VIRGO Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  22. Global Control • Receives the photodiodes (10 kHz) and quadrants (500 Hz) signals • Simple implementation of complex algorithm for lock acquisition • Computes lengths and angles, applies filters • Sends corrections to mirrors • Used in the CITF commissioning • Working robustly over long periods Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  23. Temperature probes, 88, 1 Hz NI Humidity probes, 4, 1 Hz SR DB Pressure probes, 4, 1 Hz WI BS Episensors, 6, 1 kHz Accelerometers, 9, 10 kHz Magnetometers, 3, 20 kHz PR Microphones, 3, 10 kHz Night-day seismic noise on site IBB Environment Monitoring Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  24. Data Acquisition/Storage • Data flow: 4.1 Mbytes/sec • 39 % from detection channels (detection bench + global control) • 46 % from suspension channels • 15 % from monitoring channels • Storage: • Last 6 months (~64 Tbytes) to be stored on disk at site • Last 2 years stored on disk at Bologna and Lyon • All data copied on tapes on site • 20 Tbytes on disk will be available on site by the end of 2002 Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  25. The Central Interferometer • 6 m recycled Michelson. Commissioning: april 2001-june 2002 • Integration of most of the VIRGO subsystems • 5 engineering runs (E0-E4) Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  26. CITF Progress Duty cycles: 98%85%98%98%73% Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  27. RMS Locking Accuracy • How good we are in keeping the mirror “still”? • The dark fringe signal at low frequency measures the relative motion of the mirrors: • VIRGO requirement fulfilled! DL = 2 · 10-12 m 2·10-12 m Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  28. A long way to go… Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  29. 3 km Network • False alarm rejection will require coincidences • ITFs have little directionality: 3 well separated detectors are necessary to reconstruct the source direction 600 m TAMA 4 & 2 km 300 m AIGO 4 km Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  30. The Other Detectors • TAMA and LIGO are close to the target sensitivity • 2003: LIGO-TAMA S2 science run LIGO TAMA Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  31. How Many Events • Expected rate of coalescences: 3/yr out of 40  200 Mpc [Grishchuk et al. Astro-ph/0008481] • VIRGO can detect a NS/NS event at ~ 20 Mpc • Detection rate, best estimates: • <1/yr for NS/NS • 2-3/yr for BH/BH • Estimated rate of supernovae: several /yr in the VIRGO cluster, but the efficiency of GW emission is strongly model dependent Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  32. Thermal noise reduction: Fused silica fibers Sapphire test masses Cryogenic interferometers? Shot noise: High power laser Better optics seismic thermal shot Expanding the Accessible Universe Where and how can we reduce the detector noise? Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  33. Open up wider band ~ 15 in h ~3000 in rate Advanced Interferometers NS/NS detectable @300 Mpc Initial Interferometers Advanced Interferometers From LIGO Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

  34. LISA • Space interferometer • LISA will explore a different frequency range • Launch of test mission SMART 2: 2006 Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

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