1. The Virgo interferometer for Gravitational Wave detection
Francesco Fidecaro
EPFL, November 8, 2010

2. 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

3. 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

4. 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 t A1 A2 A3 B1 B2 B3 x t A1 A2 A3 B1 B2 B3 x
Need precise clocks in different places:
pulsar and atomic clock
Need one precise clock in one place: laser

5. Detection principle tB O A B tA t0 t1 O A B

6. Detection by time measurement

7. Sources

8. Compact binary systems
chirp

9. Horizon and event rate > 1 ev/yr
Predictions for the rates of compact binary coalescences observable … CQG, / /27/17/173001

10. Stellar core collapse (Supernova)
Impulsive events, final evolution of big mass stars
Core collapses to NS or BH,
GW emitted only in non-spherical collapse
Big uncertainties, waveform “unpredictable”
Coincidence detection necessary
Amplitude: optimistic
h~10-21 at 10 Mpc
non-axisymmetric collapse
Rate:
several/year in the VIRGO cluster
(how many detectable?)
GW emitted

11. Pulsars
1000 galactic pulsars known
Possible sources of GW

12. Pulsars: rotating neutron stars
Non-axisymmetric rotating NS emit periodic GW at f=2fspin but…weak
SNR increases with observation time T as T1/2, T can be months
But…
Df ~ 10-6
Doppler correction of Earth motion:
Df/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?

13. Relic stochastic background
CMBR
Relic gravitons
Relic neutrinos
Imprinting of the early expansion of the universe
Need two correlated ITFs
Standard inflation produces a background too low
String models ?

14. The Gravitational Wave Spectrum
Dick Manchester, CSIRO
LIGO/VIRGO

15. Noise characterization

16. Signal and noise

17. Wideband detectors

18. The Virgo detector

19. 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

20. Noise in mass position

21. Seismic isolation
Super-attenuators: multi-stage passive seismic isolation system
MODEL

22. Superattenuator performance
marionetta
mirror
Excitation at top
Use Virgo sensitivity and stability
Integrate for several hours
Upper limit for TF at 32 Hz:1,
In some configurations a signal was found, but also along a direction perpendicular to excitation: compatible with magnetic cross talk

23. GW interferometers L Isolated/suspended mirrors:
sz at 10 Hz ~ m
sz at 100 Hz ~ m
Differential measurement to cancel phase noise
Effective L ~ 102 km
l = 1 mm
Effective power ~ 1 kW ~ 1022 g
Measurement noise ~ rad
for a 1 s measurement
Record a signal, if high SNR there is a large information content L
Light source

24. The Virgo interferometer

25. Issues in sensitivity (Virgo example)
200 mm fused silica suspension fibre pioneered by Glasgow/GEO600
Mirror coating Beam size
h ~ 3 x Hz-1/2 @ 10 Hz
h ~ 7 x Hz-1/2 @ 100 Hz
High power laser
Mirror thermal lensing compensation for high power
Signal recycling
Use of non standard light
Seismic attenuation
Local gravity fluctuations

26. Virgo site in Cascina

27. The European Gravitational Observatory
PURPOSE
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.

28. 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

29. 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

30. Virgo sensitivity progress
VSR1: May 18-Sep month continuous data taking simultaneously with LIGO Analysis in progress

31. Virgo & LIGO:

32. Stability Robust interferometer 95% Science Mode duty cycle
Good sensitivity
Stable horizon:
8-8.5 Mpc ( 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

33. Environmental noises studies
Investigations 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
Need to work both on:
reduction of coupling
reduction of environmental noise
End benches
Elec
racks
Injection bench
Laser
Beam jitter
Brewster window
DAQ room
Detection
suspended bench
External bench

34. The global network

35. Motivation for a Global GW Detector Network
Time-of-flight to reconstruct source position t3 t5 t1 t4 t2
GEO
VIRGO
LIGO
TAMA t6
AIGO

36. Motivation for a Global GW Detector Network
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
source
location

37. LIGO
Abbott, et al., “The laser interferometer gravitational-wave observatory”

38. Credit: Albert Einstein Institute Hannover

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

40. 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

41. 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

42. LV Agreement (II)
“Author lists are to be separately established according to the rules ofeach collaboration, and maintained by them. When papers are published, the author lists will be combined in a manner established by mutual agreement between the collaborations.”
Joint collaboration meetings 4 times/year alternating between Europe and US
Bi-weekly meeting of LIGO and Virgo leadership
Organization of joint data analysis described in detail in 7 page attachment to MOU

43. Some results from L-V

44. 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 (LSC)
Crab spindown limit (LSC) and Vela (Virgo)

46. 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

47. Uncorrelated (?) noises
Detection method
It is stochastic and presumably overwhelmed by noise
Need (at least) two detectors to check for statistical correlations
Optimal filtering
Uncorrelated (?) noises
Signals 47

48. Detection performance
Sensitivity improves as T1/2
Better performances when coherence is high ( )
detectors near each other compared to l
detectors aligned

49. 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 Hz (99% of sensitivity)

50. Isotropic search: results
Now we are beyond indirect BBN and CMB bounds
We are beginning to probe models

51. 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 Mc2

52. GRB 070201 Refs: GCN: http://gcn.gsfc.nasa.gov/gcn3/6103.gcn3
X-ray emission curves (IPN)
Home Brew:
The error box:
Refs:
GCN:
Alex: /Inspiral:
“…The error box area is sq. deg. The center of the box is
1.1 degrees from the center of M31, and includes its spiral
arms. This lends support to the idea that this exceptionally
intense burst may have originated in that galaxy (Perley and
Bloom, GCN 6091)…” from GCN6013
----
M31 The Andromeda Galaxy
by Matthew T. Russell
Date Taken: 10/22/ /2/2005 Location: Black Forest, CO Equipment: RCOS 16" Ritchey-Chretien Bisque Paramoune ME AstroDon Series I Filters SBIG STL-11000M
M31 The Andromeda Galaxy
by Matthew T. Russell
Date Taken: 10/22/ /2/2005 Location: Black Forest, CO Equipment: RCOS 16" Ritchey-Chretien Bisque Paramoune ME AstroDon Series I Filters SBIG STL-11000M

53. GRB070201: Not a Binary Merger in M31!
Abbott, et al. “Implications for the Origin of GRB from LIGO
Observations”, Ap. J., 681:1419–1430 (2008).
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%
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 Mc2) (emitted within 100 ms for isotropic emission of energy in GW at M31 distance)
9 November 2007
GRB 2007

54. The Crab Pulsar: Beating the Spin Down Limit!
Remnant from supernova in year 1054
Spin frequency nEM = 29.8 Hz
 ngw = 2 nEM = 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  ~ 4X below
the spin down limit (assuming restricted priors)
ellipticity upper limit: e < 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).
Has LIGO detected a gravitational wave? Not yet. When? “Predictions are difficult, especially about the future”
Pulsars are spinning neutron stars that beam radio bursts which sweep around at the spin frequency of the star.
Pulsars are born spinning fast and ‘brake’ or slow down due to energy radiation due to magnetic dipole radiation, particle acceleration in the magnetosphere, or possibly gravitational wave radiation if the pulsar has radial asymmetry (bump) or elliptical shape and orbital wobble – anything that leads to a time-dependent quadrapole.
The Crab is interesting because it is young and spinning down fast. Born almost 1000 years ago as a supernova remnant. The predicted GW emission frequency is 59.8 Hz (not a great frequency from an experimentalist’s standpoint if you live in the US). One can predict a ‘spin down’ limited strain, assuming all of the braking were due to GW emission.
The search integrates over long times, taking into account Doppler shifts due to the diurnal rotation of the earth and the yearly orbit of the earth around the sun.
Using 9 months of data from the S5 science run, we can put an strain upper limit 4x below the spindown limit, corresponding to < 6% of the energy being carrier away by gravitational waves. (In addition, an upper limit on the ellipticity of < 2 x 10^-4. Physically, this means that the Crab Pulsar deviates from a perfect sphere less than 1 m on a 10 km radius.)

55. VSR2 sensitivity for CW searches
Targeted searches.
Vela

56. VSR2 sensitivity Spin-down limit can be beaten for a few pulsars
(Vela spin-down limit in ~80 days)
Compatible with some ‘exotic’ EOS
may improve on Crab
Marginally compatible with standard EOS

57. Recent papers
Burst
Search for gravitational-wave bursts associated with gamma-ray bursts using data from LIGO Science Run 5 and Virgo Science Run 1 Ap. J.:
All-sky search for gravitational-wave bursts in the first joint LIGO-GEO-Virgo run Phys. Rev. D.: Phys. Rev. D 81(2010)
CBC
Search for gravitational-wave inspiralsignals associated with short gamma-ray bursts during LIGO'sfifth and Virgo's first science run Ap. J.:
Search for gravitational waves from compact binary coalescence in LIGO and Virgo data from S5 and VSR1 provisionally accepted in Phys. Rev, D CW
Searches for Gravitational Waves from Known Pulsars with S5 LIGO Data”Ap. J.
First search for gravitational waves from the youngest known neutron star”, accepted for publication in Ap. J.

62. 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

63. Advanced Virgo

64. Credit: R.Powell, B.Berger
Advanced detectors
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.
108 ly
Enhanced LIGO/Virgo+
Virgo/LIGO
Credit: R.Powell, B.Berger
Adv. Virgo/Adv. LIGO 64

65. Advanced Virgo baseline design
First orders placed. Plan to be backin 2015 with LIGO
Heavier mirrors
Larger central links
Cryotraps
High finesse
3km FP cavities
Large spot size on TM
Non degenerate
rec. cavities
Monolithic
suspensions
High power laser
Signal Recycling (SR)
DC readout

67. Perspective

68. 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

69. 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

70. The Future: The Einstein Telescope (Europe)

71. 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 g and X-ray satellites, n 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

72. Sensitivity future evolution

73. Einstein Telescope: time scale

74. 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

75. Thank you !

76. The Fluctuation-Dissipation Theorem