The Virgo interferometer for Gravitational Wave detection

Francesco Fidecaro

EPFL, November 8, 2010

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Outline• Gravitational waves: sources and detection• The Virgo interferometer• The global network• Some LSC-Virgo results (for the LSC and Virgo

collaborations)• Advanced Virgo• Perspective

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Gravitational waves• Tiny perturbations of spacetime geometry

• Predicted by Einstein as consequence of General Relativity– Propagate at the speed of light

– Non relativistic approximation: generated by accelerated masses (quadrupole formula)

– Amplitude h decreases as 1/R (field, as opposed to 1/R2 for energy or particle counting)

– Order of magnitude: RS/R

– Detectable by measuring invariant separation between free falling masses

hg

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Gravitational wave detection• Measure variations in

curvature of space time• Use clocks on geodetics as

markers• Be careful of pitfalls of

Relativity! Measure only well defined, invariant quantities

1

d dx dxi

i

B

B

g

• Need precise clocks in

different places:– pulsar and atomic clock

t

A1

A2

A3 B1

B2

B3

x

• Need one precise clock in one place: laser

t

A1

A2

A3

B1

B2

B3

x

2d 0 : light rays

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Detection by time measurement

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Sources

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chirp

Compact binary systems

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Horizon and event rate

> 1 ev/yr

Predictions for the rates of compact binary coalescences observable … CQG, 10.1088/0264-9381/27/17/173001

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Impulsive events, final evolution of big mass starsCore collapses to NS or BH, GW emitted only in non-spherical collapseBig uncertainties, waveform “unpredictable”Coincidence detection necessary

Amplitude: optimistich~10-21 at 10 Mpc

non-axisymmetric collapse

Rate: several/year in the VIRGO cluster (how many detectable?)

GW emitted

Stellar core collapse (Supernova)

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1000 galactic pulsars knownPossible sources of GW

Pulsars

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Non-axisymmetric rotating NS emit periodic GW at f=2fspin but…weak

SNR increases with observation time T as T1/2, T can be monthsBut…

f ~ 10-6 Doppler correction of Earth motion:

f/f ~ 10-4 function of source position: Blind search limited by computing power

109 NS in the galaxy, ~1000 known

Ellipticity determination: EOS nuclear matter.Strange stars?

6

2

24527

10Hz 200g/cm 10

kpc 10103

fI

rh

Pulsars: rotating neutron stars

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Relic gravitons

Relic neutrinos

CMBR Imprinting of the early expansion of the universeNeed two correlated ITFsStandard inflation produces a background too lowString models ?

Relic stochastic background

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Dick Manchester, CSIRO

The Gravitational Wave Spectrum

LIGO/VIRGO

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Noise characterization

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Signal and noise

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The Virgo detector

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The Virgo Collaboration• Early efforts

– Brillet (optics)– Giazotto (suspensions)

• Collaboration started in 1992• LAPP Annecy• EGO Cascina• Firenze-Urbino• Genova• Napoli• OCA Nice• NIKHEF Amsterdam• LAL Orsay• LMA Lyon• APC Paris – ESPCI Paris• Perugia• Pisa• Roma La Sapienza• Roma Tor Vergata• Trento-Padova• IM PAN Warsaw• RMKI Budapest• LKB Paris• 18 groups• About 200 authors

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Noise in mass position

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Seismic isolation• Super-attenuators: multi-stage passive

seismic isolation system

MODEL

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marionetta

mirror

Superattenuator performance• Excitation at top• Use Virgo sensitivity

and stability• Integrate for several

hours• Upper limit for TF at

32 Hz:1,7 10-12

• In some configurations a signal was found, but also along a direction perpendicular to excitation: compatible with magnetic cross talk

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GW interferometers• Isolated/suspended mirrors:

– z at 10 Hz ~ 10-18 m– z at 100 Hz ~ 10-21 m

• Differential measurement to cancel phase noise

• Effective L ~ 102 km• = 1 m• Effective power ~ 1 kW ~ 1022 • Measurement noise ~ 10-11 rad

• for a 1 s measurement• Record a signal, if high SNR

there is a large information content

L

Light source

23shot 102

hL

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Issues in sensitivity (Virgo example)• h ~ 3 x 10-21 Hz-1/2 @ 10 Hz

• h ~ 7 x 10-23 Hz-1/2 @ 100 Hz

200 m fused silica suspension fibre

pioneered by Glasgow/GEO600

Mirror coating Beam size

High power laserMirror thermal lensing

compensation for high powerSignal recycling

Use of non standard light

Seismic attenuation

Local gravity fluctuations

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Virgo site in Cascina

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The European Gravitational ObservatoryPURPOSE• The Consortium shall have as its purpose the promotion of research

in the field of gravitation in Europe. • In this connection and in particular, the Consortium pursues the

following objectives:– ensures the end of the construction of the antenna VIRGO, its

operation, maintenance and the upgrade of the antenna as well as its exploitation;

– ensures the maintenance of the related infrastructures, including a computer centre and promotes an open co-operation in R&D;

– ensures the maintenance of the site;– carries out any other research in the field of gravitation of common

interest of the Members;– promotes the co-operation in the field of the experimental and

theoretical gravitational waves research in Europe;– promotes contacts among scientists and engineers, the dissemination of

information and the provision of advanced training for young researchers.

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EGO• 5 year renewal approved this year• Current members: CNRS, INFN participating equally to

budget (ca 10 M€ / year)• Management:

– EGO Council and its President– EGO Director– Board of auditors– Currently 48 staff, EGO Scientific Director, Adminstrative Head

• Scientific and Technical Advisory Committee– Experts of the field or of related questions

• VESF:Virgo-EGO Scientific Forum– Implementation of one of the EGO purposes– Gathers people interested in gravitational waves and their

detection

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Noise understanding

• Noise sources and coupling are well understood

• Low frequency shows more structures

• Noise reduction in advanced detectors achieved with proper design

• Virgo+ in 2010: fused silica suspensions and higher Finesse– risk reduction for

Advanced detectors

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Virgo sensitivity progress

VSR1: May 18-Sep 30 2007 4 month continuous data taking simultaneously with LIGO Analysis in progress

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Virgo & LIGO: 2008-09-10

Stability• Robust interferometer

– 95% Science Mode duty cycle – Good sensitivity

• Stable horizon:

8-8.5 Mpc (1.4-1.4 Ns-Ns) - averaged

42-44 Mpc (10-10 BH-BH) - averaged – fluctuating with input mirror etalon

effect• Low glitch rate: factor 10 lower than VSR1• Preparing for installation of monolithic

suspensions

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Environmental noises studiesInvestigations to understand the sources and the path to dark fringe

Coupling (paths) to dark fringe

- diffused light from in air optical benches

- diffused light related to Brewster window

- beam jitter on injection bench

Sources of environmental noise:

- air conditioning

- electronic racks

Laser

Brewster window

End benches

External bench

Injection bench

Detectionsuspended bench

Beam jitter

DAQ room

Need to work both on:- reduction of coupling- reduction of environmental noise

Elec

racks

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The global network

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Motivation for a Global GW Detector Network

LIGOGEO VIRGO TAMA

AIGO

t1

t2

t3 t5

t4

t6

• Time-of-flight to reconstruct source position

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Motivation for a Global GW Detector Network

source location

• Source location: – Ability to triangulate (or ‘N-angulate’) and more accurately pinpoint source

locations in the sky– More detectors provides better source localization Multi-messenger

astronomy

• Network Sky Coverage:– GW interferometers have a limited antenna pattern; a globally distributed

network allows for maximal sky coverage

• Detection confidence: – Redundancy – signals in multiple detectors

• Maximum Time Coverage - ‘Always listening’: – Ability to be ‘on the air’ with one or more detectors

• Source parameter estimation:– More accurate estimates of amplitude and phase– Polarization - array of oriented detectors is sensitive to two polarizations

• Coherent analysis: – Combining data streams coherently leads to better sensitivity ‘digging

deeper into the noise’– Also, optimal waveform and coordinate reconstruction

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LIGO

Abbott, et al., “The laser interferometer gravitational-wave observatory” http://stacks.iop.org/0034-4885/72/076901

38Credit: Albert Einstein Institute Hannover

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Large Cryogenic Gravitational wave TelescopeLCGT is almost entirely financed to be built underground at Kamioka, where the prototype CLIO detector is placed.

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World wide GW network: LV agreement• “Among the scientific benefits we hope to achieve from

the collaborative search are:– better confidence in detection of signals, better duty cycle and

sky coverage for searches, and better source position localization and waveform reconstruction. In addition, we believe that the intensified sharing of ideas will also offer additional benefits.”

• Collaborations keep their identities and independent governance

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LV Agreement (I)• “All data analysis activities will be open to all members of

the LSC and Virgo Collaborations, in a spirit of cooperation, open access, full disclosure and full transparency with the goal of best exploiting the full scientific potential of the data.”

• Joint committees set up to coordinate data analysis, review results, run planning, and computing. The makeup of these committees decided by mutual agreement between the projects.

• Joint publication of observational data whether data from Virgo, or LIGO (GEO) or both

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Some results from L-V

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Some results from LV

• MoU for data sharing: now common data analysis groups (Bursts, Coalescing Binaries, Periodic Sources, Stochastic Background), weekly (and more) telecons

• An Upper Limit on the Amplitude of Stochastic Gravitational-Wave Background of Cosmological Origin

• Joint searches for GRBs (LV)• GRB 070201 (LSC)• Crab spindown limit (LSC) and Vela (Virgo)

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Stochastic Background (SB)• A stochastic background can be

• a GW field which evolves from an initially random configuration: cosmological background

• the result of a superposition of many uncorrelated and unresolved sources : astrophysical background)

• Typical assumptions

• Gaussian, because sum of many contributions

• Stationary, because physical time scales much larger than observational ones

• Isotropic (at least for cosmological backgrounds)

If these are true, SB is completely described by its power spectrum

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Detection method• It is stochastic and presumably overwhelmed by noise• Need (at least) two detectors to check for statistical correlations

• Optimal filtering

SignalsUncorrelated

(?) noises

* 21 2 12

6,1 ,2

12

,

GWGW

GW

( ) ( ) ( ) ( )

( ) ( )

( ) : data from detector

( ) : overlap function between detectors

( ) : noise power spectrum in detector

( )

( )100Hz

GW

n n

i

n i

c

h f h f f fY df

f S f S f

h f i

f

S f i

dff

df

ff

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Detection performance

• Sensitivity improves as T1/2

• Better performances when coherence is high ( )– detectors near each

other compared to – detectors aligned

12

22

6,1 ,20

( ) ( )

( ) ( )GW

n n

f fSNR T df

f S f S f

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Isotropic search: results• Data collected during S5 run (one year integrated data of

LIGO interferometers)• Point estimate of Y: no evidence of detection integrating

over 40-170 Hz (99% of sensitivity)

60 6.9 10 95% C.L.

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Isotropic search: results• Now we are

beyond indirect BBN and CMB bounds

• We are beginning to probe models

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Joint LIGO/Virgo Search for GRBs• Gamma Ray Bursts (GRBs) - brightest EM emitters in the sky

– Long duration (> 2 s) bursts, high Z progenitors are likely core-collapse supernovae

– Short duration (< 2 s) bursts, distribution about Z ~ 0.5 progenitors are likely NS/NS, BH/NS, binary merger

– Both progenitors are good candidates for correlated GW emissions!

• 212 GRBs detected during S5/VSR1– 137 in double coincidence (any two of LIGO Hanford, LIGO Livingston, Virgo)

• No detections, we place lower limits on distance assuming EGW = 0.01 Mc2

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M31The Andromeda Galaxy

by Matthew T. RussellDate Taken:

10/22/2005 - 11/2/2005

Location:Black Forest, CO

Equipment:RCOS 16" Ritchey-Chretien

Bisque Paramoune MEAstroDon Series I Filters

SBIG STL-11000Mhttp://gallery.rcopticalsystems.com/gallery/m31.jpg

Refs:GCN: http://gcn.gsfc.nasa.gov/gcn3/6103.gcn3

GRB 070201

X-ray emission curves (IPN)

9 November 2007 GRB 2007 53

GRB070201: Not a Binary Merger in M31!

Inspiral (matched filter search:

Binary merger in M31 (770 kpc) scenario excluded at >99% level

Exclusion of merger at larger distances

90%

75%

50%

25%

Inspiral Exclusion Zone

99%

Abbott, et al. “Implications for the Origin of GRB 070201 from LIGO Observations”, Ap. J., 681:1419–1430 (2008).

Burst search:Cannot exclude an SGR in M31

SGR in M31 is the current best explanation for this emission

Upper limit: 8x1050 ergs (4x10-4 Mc2) (emitted within 100 ms for

isotropic emission of energy in GW at M31 distance)

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The Crab Pulsar: Beating the Spin Down Limit!• Remnant from supernova in year 1054

• Spin frequency EM = 29.8 Hz

gw = 2 EM = 59.6 Hz

• observed luminosity of the Crab nebula

accounts for < 1/2 spin down power

•spin down due to:

• electromagnetic braking

• particle acceleration

• GW emission?

• early S5 result: h < 3.9 x 10-25 ~ 4X below

the spin down limit (assuming restricted priors)

• ellipticity upper limit: < 2.1 x 10-4

• GW energy upper limit < 6% of radiated energy is in GWs

Abbott, et al., “Beating the spin-down limit on gravitational wave emission from the Crab pulsar,” Ap. J. Lett. 683, L45-L49, (2008).

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VSR2 sensitivity for CW searches

Targeted searches.

Vela

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5

5

5

4

4-

3

3

4

sup

109.8 04.124 6910-J0537

108.7 56.59 Crab

105.7 68.55 1011J1913

101.1 58.50 3252J1952

108.9 46.38 2809-J1747

101.1 32.32 1034-J1833

104.1 44.30 6449J0205

100.8 38.22 Vela

Name

gwf

Compatible with some ‘exotic’ EOS

Marginally compatible with standard EOS

(Vela spin-down limit in ~80 days)

may improve on Crab

VSR2 sensitivity

Spin-down limit can be beaten for a few pulsars

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Recent papers Burst• Search for gravitational-wave bursts associated with gamma-ray

bursts using data from LIGO Science Run 5 and Virgo Science Run 1Ap. J.:http://iopscience.iop.org/0004-637X/715/2/1438.

• All-sky search for gravitational-wave bursts in the first joint LIGO-GEO-Virgo runPhys. Rev. D.: Phys. Rev. D 81(2010) 102001

CBC• Search for gravitational-wave inspiralsignals associated with short

gamma-ray bursts during LIGO'sfifth and Virgo's first science runAp. J.:http://iopscience.iop.org/0004-637X/715/2/1453.

• Search for gravitational waves from compact binary coalescence in LIGO and Virgo data from S5 and VSR1provisionally accepted in Phys. Rev, D

CW• Searches for Gravitational Waves from Known Pulsars with S5 LIGO

Data”Ap. J. http://stacks.iop.org/0004-637X/713/67• First search for gravitational waves from the youngest known neutron

star”, accepted for publication in Ap. J.

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Prepare multi-messenger searches

• Multi-messenger astronomy - connecting different kinds of observations of the same astrophysical event or system

– Coincidence allows to decrease (somewhat) detection threshold– EM or particle presence may provide more information about the GW source

• Sky position, host galaxy type, distance, emission characteristics / astrophysical processes

• Require (at least) three operational and comparably sensitive GW detector sites

– LIGO Hanford, Livingston, GEOHF and Virgo

• With S6/VSR2 : begin connecting with other alert networks or provide data for immediate telescope pointing

– Requires rapid online analysis, data quality flagging – Ongoing development by LIGO Lab, Data Analysis Software Working

Group, and Search Groups– Example: P5 Swift ToO– Contacts with High Energy Neutrino detectors, pointing telescopes– Wide Optical Field telescopes

• Connection with Astroparticle community

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Advanced Virgo

6464

108 ly

Enhanced LIGO/Virgo+ Virgo/LIGO

Credit: R.Powell, B.Berger

Adv. Virgo/Adv. LIGO

2nd generation detectors– BNS inspiral range >10x

better than Virgo– Detection rate: ~1000x better

– 1 day of Adv data ≈ 3 yrs of data

2nd generation network. – Timeline: commissioning to

start in 2014.

Advanced detectors

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Advanced Virgo baseline design

• First orders placed. Plan to be backin 2015 with LIGO

Signal Recycling (SR)

Non degenerate rec. cavities

High power laser

High finesse3km FP cavities

Heavier mirrors

Large spot size on TM

Larger central linksCryotraps

Monolithicsuspensions

DC readout

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Perspective

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The Future – AIGO (Australia)

• A comparably sensitive detector in Australia will bring increased angular sensitivity and better sky coverage

• Australian Interferometer Gravitational- wave Observatory conceived as a 5 km interferometer

– will follow the AdvLIGO design• Possible variation in suspension and seismic isolation system• Likely location in Western Australia

– Aim for operation in 2017• 2 year lag behind AdvLIGO

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The future: go around shot noise• Squeezed vacuum states as a tool are becoming reality• 6 dB reduction in shot noise is equivalent to an increase

in power on beam splitter of 16 x• That reduction goes into radiation pressure fluctuations

that can be important at low frequency• Next steps: frequency dependent squeezing

GEO600

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The Future: The Einstein Telescope (Europe)

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Perspectives for third generation• Sources are waiting

– Systems at cosmological distance– High statistics in binary systems (inspiral waveforms, matter

distribution)– Increased sensitivity in merge and ringdown phase (GR, EOS)– Increased number of pulsars (EOS, population, )– Stochastic background (cosmological and astrophysical)– Coincidences with and X-ray satellites, observatories, …

(system dynamics)

• Gaining another factor 10 in sensitivity• Extending frequency down to a few Hz• Extending further frequency spectrum spectrum

– Pulsar timing– High frequency gravitational waves

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Sensitivity future evolution

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Einstein Telescope: time scale

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Conclusions• We are at the edge of starting a new, fascinating field of

science• After “first words”, there is room for a large expansion in

observations• Phenomenology, theory will follow• Room for unexpected• In spite of the size, the instrument can be run by a single

(clever) person• New developments will be first by table top experiments• High interdisciplinary views required• Will reward junior and senior scientists

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Thank you !

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The Fluctuation-Dissipation Theorem