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Optimization of the Advanced Virgo Sensitivity for astrophysical Sources

Optimization of the Advanced Virgo Sensitivity for astrophysical Sources. Stefan Hild , Giovanni Losurdo and Andreas Freise Virgo week July 2008. Overview. Motivation for sensitivity optimization Figures of merit for astrophysical sources Parameters used for optimization

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Optimization of the Advanced Virgo Sensitivity for astrophysical Sources

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  1. Optimization of the Advanced Virgo Sensitivity for astrophysical Sources Stefan Hild, Giovanni Losurdo and Andreas Freise Virgo week July 2008

  2. Overview • Motivation for sensitivity optimization • Figures of merit for astrophysical sources • Parameters used for optimization • Optimized configurations VIRGO week July 2008

  3. Motivation for sensitivity optimization • Reference is the AdV conceptual design. • In the meantime several things changed: • Thermo-optic noise • Ribbons (instead of cylindrical) Fibers • New code (Bench => GWINC) • So far optimization was done only for Inspiral sources Conceptual design: VIR-042A-07 Bench-GWINC note: VIR-055A-08 Conceptual design: SR-transmittance = 0.04, SR-tuning 0.07 BNS = 121 Mpc and BBH = 856 Mpc VIRGO week July 2008

  4. What do we want to do ?? Optimisation for as many different astrophysical sources… … and we want to scan the full parameter space of the detector. http://numrel.aei.mpg.de/Visualisations/ http://hubblesite.org/ VIRGO week July 2008

  5. Figure of merit: Inspiral • Inspiral ranges for BHBH and NSNS coalesence: • Parameters usually used: • NS mass = 1.4 solar masses • BH mass = 10 solar masses • SNR = 8 • Averaged sky location Frequency of last stable orbit (BNS = 1570 Hz, BBH = 220 Hz) Symmetric mass ratio Spectral weighting = f-7/3 Total mass Detector sensitivity [1] Damour, Iyer and Sathyaprakash, Phys. Rev. D 62, 084036 (2000). [2] B. S. Sathyaprakash, “Two PN Chirps for injection into GEO”, GEO Internal Document VIRGO week July 2008

  6. Figure of merit: Pulsars • Tried to find a figure of merit for Pulsars. Used the summed SNR of all detectable known pulsars. • We start from ANTF Pulsar Catalogue (about 1500 radio Pulsars), http://www.atnf.csiro.au/research/pulsar/psrcat/ Detector sensitivity Integrated detector sensitivity Observation time (we used 1yr) Spin down upper limit Figure of merrit: Summed SNR Detectibility threshold Factor 10.4 = all-sky, all polarisation average 95% upper limit for the Bayesian known pulsar pipeline VIRGO week July 2008

  7. Figure of merit: Bursts • Tried to find a figure of merit for Bursts. • Used the sum of the inverse sensitivity: • No spectral weighting. • in bad words: detector bandwidth / average sensitivity. Gives something like 1025 sqrt(Hz) No frequency cuts ! Width of the frequency bin Detector sensitivity VIRGO week July 2008

  8. Starting point of the optimization • Analysis based on Gravitational Wave Interferometer Noise Calculator (GWINC) • Using noise levels as presented in VIR-055A-08(S.Hild and G.Losurdo: “Advanced Virgo design: Comparison of the Advanced Virgo sensitivity from Bench 4 and GWINC (v1)”) • Figures of merrit: • Binary ranges (provided by gwinc) • Pulsar (our own Matlab function) • Burst (our own Matlab function) • Stochastic (provided by gwinc) • Multi-parameter analysis is done by Matlab-scripts querying GWINC. VIRGO week July 2008

  9. Optimization Parameter 1:Signal-Recycling (de)tuning • Frequency of pure optical resonance goes down with SR-tuning. • Frequency of opto-mechanical resonanced goes up with SR-tuning Advanced Virgo, Power = 125W, SR-transmittance = 4% Radiation pressure noise Shot noise Opto-mechanical resonance Pure optical resonance VIRGO week July 2008

  10. Optimization Parameter 2:Signal-Recycling mirror transmittance • Resonances are less developed for larger SR transmittance. Advanced Virgo, Power = 125W, SR-tuning = 0.07 VIRGO week July 2008

  11. Optimization Parameter 3:Laser-Input-Power • High frequency sensitivity improves with higher power (Shotnoise) • Low frequency sensitivity decreases with higher power (Radiation pressure noise) Advanced Virgo, SR-tuning=0.07, SR-transmittance = 4% VIRGO week July 2008

  12. Limits of the Parameter optimization • Our optimisation is limited by Coating thermal noise and Gravity Gradient noise. VIRGO week July 2008

  13. Example: Optimizing 2 Parameters • Inspiral ranges for free SR-tuning and free SRM-transmittance, but fixed Input power NSNS-range BHBH-range VIRGO week July 2008

  14. Example: Optimizing 2 Parameters Parameters for maximum • Different source usually have their maxima at different operation points. • It is impossible to get the maximum for BNS AND BBH both at the same time ! Maximum NSNS-range Parameters for maximum Maximum BHBH-range VIRGO week July 2008

  15. Comparison of Baseline and Single source type optimum • The crossing point of the black lines indicate the SR-operation point from the concep-tual design. • The parameters of the conceptual de-sign were chosen to give a compro-mise between BNS and BBH range. Conceptual design: SR-transmittance = 0.04, SR-tuning 0.07 BNS = 121 Mpc and BBH = 856 Mpc VIRGO week July 2008

  16. Example: Optimizing 3 Parameterfor Inspiral range • Scanning 3 parameter at the same time: • SR-tuning • SR-trans • Input Power • Using a video to display 4th dimension. VIRGO week July 2008

  17. Example: Inspiral ranges vs Power Already very low power (< initial Virgo) gives maximum range BBH sensitivity and 80% of the maximum BNS range. Please note: Each dot may represent Different SR-parameter. VIRGO week July 2008

  18. 2-Step approach for Advanced Virgo construction • The conceptual design proposes: • Start AdV without Signal-Recycling, but with high power. • At a later stage install Signal-Recycling. • We should investigate if it would not be easier to go for a different approach: • Start AdV with Signal-Recycling, but with only 5W (no TCS required) • At a later stage increase the power gradually Please note: Each dot may represent Different SR-parameter. VIRGO week July 2008

  19. Maximum we can achieve • We performed identical 3-para-meter optimization for Burst, Stochastic and Pulsar sources. • Traces show the maximum value achievable vs input power. All traces are normalized to their maximum value. Please note: Each dot may represent Different SR-parameter. • BNS and Burst have their maximum at high power. • BBH, Pulsars and Stochastic have their maximum at low power (3-5W). VIRGO week July 2008

  20. Optimal configurations Curves show the optimal sensitivity for a single source type. VIRGO week July 2008

  21. Optimal configurations Optimal REFERNCE Scenarios: VIRGO week July 2008

  22. Optimal configurations Optimal REFERNCE Scenarios: Using SR-parameters from Conceptual design with GWINC (new noise levels): VIRGO week July 2008

  23. Heavy mirror option (63kg)PRELIMINARY: non comprehensive Analysis !!! • Used the reference BNS scenario (pink) and only changed the mirror weight to 63 kg (green dashed). • High frequency performance unchanged, but significant improvement below 50 Hz. Preliminary 42kg: BNS= 152 Mpc BBH= 747 Mpc 63kg: BNS= 161 Mpc BBH= 961 Mpc Preliminary VIRGO week July 2008

  24. Summary • Recent results changed the noise boundaries of Advanced Virgo => new sensitivity optimization required. • Performed a detailed 3-parameter Optimization for 5 figures of merit (BNS, BBH, Burst, Pulsar, Stochastic). • Each source requires different parameters for optimal detection: • Can get optimal sensitivity only for a single source type. • Can get not optimal, but moderate sensitivity for more than one source type • We have now 5 optimized reference scenarios (optimal parameter sets + values of performance for each astrophysical source type). • Low power scenarios seem (at least for the beginning of Advanced Virgo) to be promising. VIRGO week July 2008

  25. Outlook Technical point of view: • Optimization is an continuous process … (until the design is fixed) • Include cavity finesse as 4th parameter into future optimization. • Proper modeling of suspension thermal noise (volunteers needed) • Investigate the effect of 62kg mirror option Scientific point of view: • Interaction with data analysis groups (Virgo and LSC): • How to make the trade-off between the different source-types? Can there be a sensible multi-source-type figure of merit? • Define the Science case (includes final figure of merit) VIRGO week July 2008

  26. More details … … will soon be available in: VIRGO week July 2008

  27. Acknowledgements • We wish to thank the LIGO Scientific Collaboration for making the GWINC code available for public use. • We are also very grateful to Matthew Pittkin (Glasgow) and Alberto Vecchio (Birmingham) for their help defining the figure of merit for pulsar sources. E N D VIRGO week July 2008

  28. Example: Optimising 3 Parameterfor Burst figure of merit • Scanning 3 parameter at the same time: • SR-tuning • SR-trans • Input Power • Using a video to display 4th dimension. VIRGO week July 2008

  29. Example: Optimising 3 Parameterfor the Pulsar figure of merit • Scanning 3 parameter at the same time: • SR-tuning • SR-trans • Input Power • Using a video to display 4th dimension. VIRGO week July 2008

  30. Figure of merrit: Stochastic • Omega is provided as standard output of GWinc VIRGO week July 2008

  31. Example: Optimising 3 Parameterfor 1/Omega(stochastic) • Scanning 3 parameter at the same time: • SR-tuning • SR-trans • Input Power • Using a video to display 4th dimension. VIRGO week July 2008

  32. Limited Parameter space • After we fixed the design of Advanced Virgo, there will probably some restrictions about accessible range of SR-parameter. • For instance: for very small SR detunings the errorsignals “vanish”. S Hild et al 2007 Class. Quantum Grav. 24 1513-1523 VIRGO week July 2008

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