Edwige Tournefier for the Virgo Collaboration The status of Virgo

July 20 th, 2007EPS Virgo optical scheme Laser 20 W Input Mode Cleaner (144 m) Output Mode Cleaner (4 cm) 3 km long Fabry-Perot cavities Power Recycling Input mirrors Dark fringe (Gravitationnal wave signal) Injection bench

July 20 th, 2007EPS Last years summary Sept 2003: start the commissioning of Virgo  Problem of back reflected light by the mode cleaner  Need to work at reduced power (0.8 instead of 8 Watts) End 2005: shutdown to upgrade the injection system + new PR mirror

July 20 th, 2007EPS shutdown New injection bench  Faraday isolator: protection against back-reflected light  Parabolic telescope New PR mirror  Better mechanical properties  Higher recycling gain New Inj. bench

July 20 th, 2007EPS Last years summary Sept 2003: start the commissioning of Virgo  Problem back reflected light by the injection system  Need to work at reduced power (0.8 instead of 8 Watts) End 2005: shutdown to upgrade the injection system + new PR mirror Early 2006: restart commissioning at full power  Thermal effects: absorption in the input mirrors  thermal lensing  Slow and complex lock acquisition (thermal transient)

July 20 th, 2007EPS Thermal effects Absorption in input mirrors  thermal lensing  change of recycling conditions  Need adjustment of the loop gains during the thermal transient Next: thermal compensation to obtain a uniform heating of the mirrors (Co2 laser) 15 minutes Powers inside the ITF Sidebandscarrier Loop unity gain frequency unity gain frequ. (Hz) Diff. arm Michelson Power recycling

July 20 th, 2007EPS Last years summary Sept 2003: start the commissioning of Virgo  Problem back reflected light by the injection system  Need to work at reduced power (0.8 instead of 8 Watts) End 2005: shutdown to upgrade the injection system + new PR mirror Early 2006: restart commissioning at full power  Thermal effects: absorption in the input mirrors  thermal lensing  Slow and complex lock acquisition (thermal transient) Sept 2006 – March 2007:  Stable lock, good enough sensitivity  make Weekend Science Runs May 2007: start first science run (VSR1) in coincidence with LIGO S5 run

July 20 th, 2007EPS Virgo science runs 10 Weekend Science Runs (WSRs) from Sept 2006 to March 2007:  Shake down organization and procedures  Check detector stability, data stationarity  Data analysis: »Detector characterization »Playground for searches »prepare joint analysis with LIGO VSR1 (May to September 2007) LSC-Virgo agreement  Data exchange  Data analysis groups merged  Joint DA committee and run organization committee

July 20 th, 2007EPS LIGO – Virgo sensitivities

July 20 th, 2007EPS Commissioning highlights Noise hunting Control noises Environmental noise: scattered light Controls: Suspensions

July 20 th, 2007EPS VSR1 noise budget Magnetic noise Environmental noise Longitudinal control noise Shot noise

July 20 th, 2007EPS Control noises: longitudinal + + (f) - Laser - PR B1 (GW channel) BS control loop Diff. end mirror control loop B5 Noise subtraction loop  = 0 mistuned  measured (f) GW signal Beam Splitter motion equivalent to end mirrors differential displacement  Beam Splitter control loop injects environmental noise  subtract injected noise (=re-inject with opposite sign on end mirrors)  Similar technique for PR control noise WE BS NE  Noise reduced by a factor 100

July 20 th, 2007EPS VSR1 noise budget Environmental noise: seismic, acoustic

July 20 th, 2007EPS Environmental noise: scattered light (I) Environmental noise acting on in air components + Scattered light from in air components = Phase noise in the interferometer (with the typical environmental-like noise structures) Laser Brewster windows End benches External bench Injection bench Detection suspended bench Actions: 1/ reduce diffused light on benches 2/ acoustic isolations around benches Before After 1/

July 20 th, 2007EPS Environmental noise: scattered light (II) bench seismic noise Acoustic isolations installed around all in air optical benches  Reduction of the impact of scattered light All in-air benches now have acoustic isolations GW signal Estimation of scattered light noise

July 20 th, 2007EPS Commissioning highlights Noise hunting Control noises Scattered light by environmental noise Controls: Suspensions

July 20 th, 2007EPS Detector stability: suspension control Suspensions control: compensation of non-linear z ->  coupling Under large seismic activity: large z correction sent to the mirror’s suspension  y recoil of the mirror suspension  Side effects on alignment (instabilities) Instabilities  data non-stationarity / unlocks Solution: compensate for z ->  y coupling Need a quadratic compensation: Dark fringe: alignment and total power - No compensation - With compensation  y =a*zM +b*zM 2 ( b=a/25) Under similar seismic activity :

July 20 th, 2007EPS VSR1 statistics 18/05 Horizon (average value) in Mpc 15/07 Duty cycle ~ 80% Horizon for NS-NS inspiral: 3.5 Mpc Longest lock: 66 hours Unlocks: mainly technical + earthquakes Some commissioning activities:  Noise reduction, improve duty cycle,… Lock duration

July 20 th, 2007EPS Data analysis highlights Event selection: experimental vetoes Coalescing binaries search Supernovae search

July 20 th, 2007EPS Event selection: experimental vetoes Experimental vetoes are used after the DA pipelines Vetoes based on: environmental or monitoring channels, auxiliary error signals,… Example:  GW events should be seen only in the dark fringe ‘in-phase’ signal (differential motion)  Veto events also seen in the ‘quadrature’ signal (typical for ‘dust events’)  WSR8 (Jan 2007): efficiency = 83% (SNR>10), dead time = 1.2%  Since then: beam path protected to reduced dust effects SNR Time (GPS)

July 20 th, 2007EPS Coalescing binaries search Topological cut in addition to experimental vetoes Hardware injections: check the analysis performances Dedicated searches in coincidence with GRBs  Train analysis and put upper limits 22 SNR Example: GRB070219A occurred during WSR9 (19/02) -Compare SNR distributions in the ON/OFF regions -No event for SNR>7.8 -Determine detection efficiency as a function of source distance SNR Distance (Mpc) Detection efficiency N events

July 20 th, 2007EPS PRELIMINARY Supernovae (burst) search Also dedicated searches in coincidence with GRBs All sky search: results for C7 run (Sept 2005) Goal  Understand loud events  Obtain upper limits on burst event rate as a function of strength  Develop the methodology to be applied in subsequent runs Science result  No signal detected  event rate limit as a function of h  Rate < 1.2 event/day at 90% C.L.  Limit on energy: EGW < 1.6x10 -6 Msun (for a source at Galactic Center)‏  Same sensitivity as LIGO S2

July 20 th, 2007EPS Conclusion Virgo switched to Science data taking mode with VSR1  The achievement of almost four years of commissioning  BNS average horizon distance at 3.5 Mpc level  Joint LSC-Virgo analysis of VSR1 and coincident S5 data Challenging and exciting time for data analysis! Detection probability is very low with the present sensitivity  Next step: Virgo+  Goal: improve the sensitivity by a factor 2 to 3  Upgrade of Virgo in 2008, start data taking mid-2009 (see G. Losurdo’s talk)

July 20 th, 2007EPS Next step: Virgo+ Goal  Sensitivity better than the Virgo design by a factor 2-3 Virgo+ baseline  New mirrors, higher finesse  New mirror reference mass  Higher laser power  Thermal compensation system  New control electronics  Monolithic suspension ? (see G. Losurdo’s talk) Time scale:  Next fall: select the options and adjust the planning  Spring 2008: Shutdown for Virgo+ upgrades  Mid-2009: start second science run (VSR2) in coincidence with enhanced-LIGO (S6) Next: Advanced Virgo (see G. Losurdo’s talk)

July 20 th, 2007EPS VSR1 noise budget Longitudinal control noise

July 20 th, 2007EPS Magnetic noise Dark fringe coherent with magnetic sensors Track sources of magnetic noises close to the input mirrors Move noisy power supplies  noise well reduced Further investigations ongoing dark fringe spectrum before / after Assembly mistake: All 4 magnets have the same polarity on input mirrors

July 20 th, 2007EPS Control noises: angular Beam not centered on the mirrors  any rotation induces a difference in the beam longitudinal path  the angular control noise couples to the dark fringe Noise reduction: Better centering of the beam on the mirrors (cm -> mm) Improved filters for controls  Angular control noise does not limit the sensitivity Further reduction is possible  z= d  x d Frequency (Hz) Strain sensitivity (Hz -1/2 ) Angular noise contributions to the sensitivity

July 20 th, 2007EPS Detector stability vs seismic activity Empirical formula: sea: Hz wind: Hz NS-NS Horizon (MPc) = H 0 (1 - a x sea – b x wind) - Measured horizon - Sea activity (a.u.) - Wind activity (a.u.) - Predicted horizon Horizon [MPc] WSR1 (09/2006) VSR1 (06/2007) Sea sensitivity a Wind sensitivity b Sensitivity to seismic activity well reduced Better robustness in bad weather conditions

July 20 th, 2007EPS