Stefan Hild, Giovanni Losurdo and Andreas Freise
Virgo week July 2008
Optimization of the Advanced Virgo Sensitivity for
astrophysical Sources
Stefan Hild VIRGO week July 2008 Slide 2
Overview
Motivation for sensitivity optimization
Figures of merit for astrophysical sources
Parameters used for optimization
Optimized configurations
Stefan Hild VIRGO week July 2008 Slide 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 0.07BNS = 121 Mpc and BBH = 856 Mpc
Stefan Hild VIRGO week July 2008 Slide 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.
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Stefan Hild VIRGO week July 2008 Slide 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
[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
Frequency of last stable orbit (BNS = 1570 Hz, BBH = 220 Hz)
Spectral weighting = f-7/3Total mass
Symmetric mass ratio
Detector sensitivity
Stefan Hild VIRGO week July 2008 Slide 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/
Observation time(we used 1yr)
Integrated detectorsensitivity
Detector sensitivity
Figure of merrit:Summed SNR
Detectibility threshold
Factor 10.4 = all-sky, all polarisation average
95% upper limit for the Bayesian known pulsar pipeline
Spin down upper limit
Stefan Hild VIRGO week July 2008 Slide 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)
Detector sensitivity
Width of the frequency bin
No frequency cuts !
Stefan Hild VIRGO week July 2008 Slide 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.
Stefan Hild VIRGO week July 2008 Slide 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%
Pure opticalresonance
Opto-mechanicalresonance
Shot noise
Radiation pressurenoise
Stefan Hild VIRGO week July 2008 Slide 10
Optimization Parameter 2:Signal-Recycling mirror transmittance
Advanced Virgo, Power = 125W, SR-tuning = 0.07
Resonances are less developed for larger SR transmittance.
Stefan Hild VIRGO week July 2008 Slide 11
Optimization Parameter 3:Laser-Input-Power
Advanced Virgo, SR-tuning=0.07, SR-transmittance = 4%
High frequency sensitivity improves with higher power (Shotnoise) Low frequency sensitivity decreases with higher power (Radiation pressure noise)
Stefan Hild VIRGO week July 2008 Slide 12
Limits of the Parameter optimization
Our optimisation is limited by Coating thermal noise and Gravity Gradient noise.
Stefan Hild VIRGO week July 2008 Slide 13
Example: Optimizing 2 Parameters
Inspiral ranges for free SR-tuning and free SRM-transmittance, but fixed Input power
NSNS-range
BHBH-range
Stefan Hild VIRGO week July 2008 Slide 14
Example: Optimizing 2 Parameters
MaximumNSNS-range
MaximumBHBH-range
Parametersfor maximum
Parametersfor 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 !
Stefan Hild VIRGO week July 2008 Slide 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 0.07BNS = 121 Mpc and BBH = 856 Mpc
Stefan Hild VIRGO week July 2008 Slide 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.
Stefan Hild VIRGO week July 2008 Slide 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 representDifferent SR-parameter.
Stefan Hild VIRGO week July 2008 Slide 18
2-Step approach for Advanced Virgo construction
The conceptual design proposes:1. Start AdV without Signal-
Recycling, but with high power.
2. At a later stage install Signal-Recycling.
We should investigate if it would not be easier to go for a different approach:1. Start AdV with Signal-
Recycling, but with only 5W (no TCS required)
2. At a later stage increase the power gradually
Please note:Each dot may representDifferent SR-parameter.
Stefan Hild VIRGO week July 2008 Slide 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.
BNS and Burst have their maximum at high power. BBH, Pulsars and Stochastic have their maximum at low power (3-5W).
Please note:Each dot may representDifferent SR-parameter.
Stefan Hild VIRGO week July 2008 Slide 20
Optimal configurations
Curves show the optimal sensitivity for a single source type.
Stefan Hild VIRGO week July 2008 Slide 21
Optimal configurationsOptimal REFERNCE Scenarios:
Stefan Hild VIRGO week July 2008 Slide 22
Optimal configurations
Using SR-parameters from Conceptual design with GWINC (new noise levels):
Optimal REFERNCE Scenarios:
Stefan Hild VIRGO week July 2008 Slide 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.
42kg:BNS= 152 MpcBBH= 747 Mpc
63kg:BNS= 161 MpcBBH= 961 Mpc
Stefan Hild VIRGO week July 2008 Slide 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.
Stefan Hild VIRGO week July 2008 Slide 25
Outlook
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
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)
Technical point of view:
Scientific point of view:
Stefan Hild VIRGO week July 2008 Slide 26
More details …
… will soon be available in:
Stefan Hild VIRGO week July 2008 Slide 27
E N D
Acknowledgements
We wish to thank the LIGO Scientific Collaboration for making the GWINC code
We are also very grateful to Matthew Pittkin (Glasgow) and Alberto Vecchio
(Birmingham) for their help defining the figure of merit for pulsar sources.
available for public use.
Stefan Hild VIRGO week July 2008 Slide 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.
Stefan Hild VIRGO week July 2008 Slide 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.
Stefan Hild VIRGO week July 2008 Slide 30
Figure of merrit: Stochastic
Omega is provided as standard output of GWinc
Stefan Hild VIRGO week July 2008 Slide 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.
Stefan Hild VIRGO week July 2008 Slide 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