stefan hild, giovanni losurdo and andreas freise virgo week july 2008 optimization of the advanced...

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


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


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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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


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


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


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)


Width of the frequency bin

No frequency cuts !


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.


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


Optimization Parameter 2:Signal-Recycling mirror transmittance

Advanced Virgo, Power = 125W, SR-tuning = 0.07

Resonances are less developed for larger SR transmittance.


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)


Limits of the Parameter optimization

Our optimisation is limited by Coating thermal noise and Gravity Gradient noise.


Example: Optimizing 2 Parameters

Inspiral ranges for free SR-tuning and free SRM-transmittance, but fixed Input power

NSNS-range

BHBH-range


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 !


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


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.


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.


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



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).



Optimal configurations

Curves show the optimal sensitivity for a single source type.


Optimal configurationsOptimal REFERNCE Scenarios:


Optimal configurations

Using SR-parameters from Conceptual design with GWINC (new noise levels):

Optimal REFERNCE Scenarios:


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


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.


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:


More details …

… will soon be available in:


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.


Example: Optimising 3 Parameterfor Burst figure of merit




Example: Optimising 3 Parameterfor the Pulsar figure of merit




Figure of merrit: Stochastic

Omega is provided as standard output of GWinc


Example: Optimising 3 Parameterfor 1/Omega(stochastic)




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

stefan hild, giovanni losurdo and andreas freise virgo week july 2008 optimization of the advanced...

Documents

mpc slide

configurations slide

devisualisations slide

stefan hildvirgo week

upper limit slide

advanced virgo sensitivity

figure of merit

inverse sensitivity