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

3. Cascina – May. 6 th, 2003 G.Losurdo – INFN Firenze-Urbino PSR1913+16: GW Exist Pulsar bound to a “dark companion”, 7 kpc away. Extremely accurate clock: f  z,  f  t=10 -15 s -2 Relativistic clock: v max /c ~ 10 -3 GR predicts such a system to loose energy via GW emission  orbital period decrease

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

5. Cascina – May. 6 th, 2003 G.Losurdo – INFN Firenze-Urbino Energy-Time Scales In SN collapse withstand 10 3 interactions before leaving the star, GW leave the core undisturbed Decoupling after Big Bang –GW  10 -43 s (T ~ 10 19 GeV) –  1 s (T ~ 1 MeV) –e.m.  10 12 s (T ~ 0.2 eV) Coupling constants stronge.m.weakgravity 0.11/13710 -5 10 -39 GW brings unique information out of the Universe

6. Cascina – May. 6 th, 2003 G.Losurdo – INFN Firenze-Urbino Luminosity: Amplitude: M ~ 1.4 M , R ~ 20 km, r ~ 15 Mpc, f orb ~ 400 Hz Sources of GW h ~ 10 -21 R M r  E ~ 10 52 erg for NS/NS

7. Cascina – May. 6 th, 2003 G.Losurdo – INFN Firenze-Urbino 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] chirp

8. Cascina – May. 6 th, 2003 G.Losurdo – INFN Firenze-Urbino 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

9. Cascina – May. 6 th, 2003 G.Losurdo – INFN Firenze-Urbino 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 ~10 5 /yr within 100 Mpc is expected (Van Putten, PRL, 87, 2001)   GW

10. Cascina – May. 6 th, 2003 G.Losurdo – INFN Firenze-Urbino GW acting on a ring of freely falling masses Interferometric Detection of GW L-  L L+  L Measurable  L    m Target h   (NS/NS @10 Mpc) L    m

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

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

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

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

15. Cascina – May. 6 th, 2003 G.Losurdo – INFN Firenze-Urbino Vacuum Requirements: –10 -9 mbar for H 2, 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

16. Cascina – May. 6 th, 2003 G.Losurdo – INFN Firenze-Urbino 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 10 -14 @ 10 Hz

17. Cascina – May. 6 th, 2003 G.Losurdo – INFN Firenze-Urbino SA 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 Tide control LVDTs, accelerometers CCD ITF

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

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

20. Cascina – May. 6 th, 2003 G.Losurdo – INFN Firenze-Urbino Injection System 20 W laser 144 m MC cavity to reduce jitter noise and select TEM 00 mode

21. Cascina – May. 6 th, 2003 G.Losurdo – INFN Firenze-Urbino 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 Output mode cleaner External bench Suspended bench

22. Cascina – May. 6 th, 2003 G.Losurdo – INFN Firenze-Urbino 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 Coater VIRGO Absorption, Birefringence, wavefront measurement

23. Cascina – May. 6 th, 2003 G.Losurdo – INFN Firenze-Urbino 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

24. Cascina – May. 6 th, 2003 G.Losurdo – INFN Firenze-Urbino Environment Monitoring NINI BSBS IB B WI PRPR DBDB SRSR Temperature probes, 88, 1 Hz Humidity probes, 4, 1 Hz Pressure probes, 4, 1 Hz Episensors, 6, 1 kHz Accelerometers, 9, 10 kHz Magnetometers, 3, 20 kHz Microphones, 3, 10 kHz Night-day seismic noise on site

25. Cascina – May. 6 th, 2003 G.Losurdo – INFN Firenze-Urbino 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

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

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

28. Cascina – May. 6 th, 2003 G.Losurdo – INFN Firenze-Urbino 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!  L = 2 · 10 -12 m RMS 2·10 -12 m

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

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

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

32. Cascina – May. 6 th, 2003 G.Losurdo – INFN Firenze-Urbino 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

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

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

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