Transcript The Virgo interferometer for Gravitational Wave detection

The Virgo interferometer for Gravitational
Wave detection
Francesco Fidecaro
EPFL, November 8, 2010
Outline
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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
g      h
• 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
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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
B3
B2
t
B1
ds 2  0 : light ray
Bi1
 d  
Bi
g  dx  dx
• Need one
precise
precise
clocks in
different
clock
in one
places:
place:
laser
– pulsar and atomic clock
B3
B2
A3
B1
A2
A1
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Detection by time measurement
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Sources
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Compact binary systems
chirp
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Horizon and event rate
> 1 ev/yr
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Predictions for the rates of compact binary coalescences observable … CQG, 10.1088/0264-9381/27/17/173001
Stellar core collapse (Supernova)
Impulsive events, final
evolution of big mass stars
Core collapses to NS or BH,
GW emitted only in nonspherical collapse
Big uncertainties, waveform
“unpredictable”
GW emitted
Coincidence detection
necessary
Amplitude: optimistic
h~10-21 at 10 Mpc
non-axisymmetric collapse
Rate:
several/year in the VIRGO
cluster
(how many detectable?)
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Pulsars
1000 galactic pulsars known
Possible sources of GW
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Pulsars: rotating neutron stars
Non-axisymmetric rotating NS emit periodic GW at f=2fspin but…weak
 f    
I
 10 kpc 
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 45
  6 
2 
 r  10 g/cm  200 Hz   10 
2
h  3 10
 27
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?
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Relic stochastic background
CMBR Imprinting of the early expansion of
Relic neutrinos
Relic gravitons
the universe
Need two correlated ITFs
Standard inflation produces a
background too low
String models ?
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The Gravitational Wave Spectrum
Dick Manchester, CSIRO
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
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Early efforts
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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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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
marionetta
mirror
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GW interferometers
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Isolated/suspended mirrors:
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Differential measurement to
cancel phase noise
Effective L ~ 102 km
l = 1 m
Effective power ~ 1 kW ~ 1022 g
Measurement noise ~ 10-11 rad
h
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sz at 10 Hz ~ 10-18 m
sz at 100 Hz ~ 10-21 m
l s shot
L 2
L
Light source
1023
for a 1 s measurement
Record a signal, if high SNR
there is a large information
content
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m fused silica
Issues in sensitivity200
(Virgo
example)
suspension fibre
by-1/2 @ 10 Hz
• h pioneered
~ 3 x 10-21 Hz
• Glasgow/GEO600
h ~ 7 x 10-23 Hz-1/2 @ 100 Hz
Mirror coating
Beam size
High power laser
Mirror thermal lensing
compensation for high power
Signal 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 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.
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EGO
• 5 year renewal approved this year
• Current members: CNRS, INFN participating equally to
budget (ca 10 M€ / year)
• Management:
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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
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Stability
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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
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
Need to work both on:
- diffused light related to Brewster window
reduction of coupling
reduction of environmental noise
- beam jitter on injection bench
 Sources of environmental noise:
- air conditioning
- electronic racks
End benches
Elec
racks
Injection bench
Laser
Beam jitter
Brewster window
DAQ room
Detection
suspended bench
External bench
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The global network
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Motivation for a Global GW Detector Network
• Time-of-flight to reconstruct source position
t3
t1
t2
LIGO
t5
t4
GEO
VIRGO
TAMA
t6
AIGO
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Motivation for a Global GW Detector Network
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Source location:
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Network Sky Coverage:
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Ability to be ‘on the air’ with one or more detectors
Source parameter estimation:
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Redundancy – signals in multiple detectors
Maximum Time Coverage - ‘Always listening’:
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GW interferometers have a limited antenna pattern; a globally
distributed network allows for maximal sky coverage
Detection confidence:
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Ability to triangulate (or ‘N-angulate’) and more accurately
pinpoint source locations in the sky
More detectors provides better source localization  Multimessenger astronomy
More accurate estimates of amplitude and phase
Polarization - array of oriented detectors is sensitive to two
polarizations
source
location
Coherent analysis:
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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
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Credit: Albert Einstein Institute Hannover
Large Cryogenic Gravitational wave Telescope
LCGT 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
Signals
• Optimal filtering
Uncorrelated (?)
noises
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2
h1 ( f )h 2 ( f )g 12 ( f )GW
(f)
Y   df
f 6 S n ,1 ( f ) S n ,2 ( f )
hi ( f ) : data from detector i
g 12 ( f ) : overlap function between detectors
S n ,i ( f ) : noise power spectrum in detector i
f d GW
GW ( f ) 
c df

 f 
GW ( f )   

 100Hz 
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Detection performance

SNR 2  T  df
0
g 2 ( f )GW ( f )
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f 6 Sn ,1 ( f ) Sn ,2 ( f )
• Sensitivity improves as T1/2
• Better performances when
coherence is high (
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– detectors near each
other compared to l
– detectors aligned
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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)
0  6.9 10
6
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
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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!
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212 GRBs detected during S5/VSR1
– 137 in double coincidence (any two of LIGO Hanford, LIGO Livingston, Virgo)
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No detections, we place lower limits on distance assuming EGW = 0.01 Mc2
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GRB 070201
Refs:
GCN: http://gcn.gsfc.nasa.gov/gcn3/6103.gcn3
X-ray emission curves (IPN)
M31
The Andromeda Galaxy
by Matthew T. Russell
Date Taken:
10/22/2005 - 11/2/2005
Location:
Black Forest, CO
Equipment:
RCOS 16" Ritchey-Chretien
Bisque Paramoune ME
52 I Filters
AstroDon Series
SBIG STL-11000M
http://gallery.rcopticalsystems.com/gallery/m31.jpg
GRB070201: Not a Binary Merger in M31!
Inspiral (matched
filter search:
Abbott, et al. “Implications for the Origin of GRB 070201 from LIGO
Observations”, Ap. J., 681:1419–1430 (2008).
Binary merger in M31
(770 kpc) scenario
excluded at >99%
level
Inspiral Exclusion Zone
25%
50%
Exclusion of merger at
larger distances
75%
90%
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
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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
Abbott, et al., “Beating the spin-down limit on gravitational wave
emission from the Crab pulsar,” Ap. J. Lett. 683, L45-L49, (2008).
• 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
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VSR2 sensitivity for CW searches
Targeted searches.
Vela
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VSR2 sensitivity
Spin-down limit can be beaten for a few pulsars
Name
f gw
 sup
Vela
22.38
8.0 10  4
J0205  6449
30.44
1.4 10 3
J1833 - 1034
32.32
1.1 10 3
J1747 - 2809
38.46
8.9 10-4
J1952  3252
50.58
1.1 10  4
J1913  1011
55.68
7.5 10 5
5
Crab
59.56
7.8 10
J0537 - 6910
124.04
8.9 10 5
(Vela spin-down limit in ~80 days)
Compatible with some ‘exotic’ EOS
may improve on Crab
Marginally compatible with standard EOS
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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 1
Ap. J.:http://iopscience.iop.org/0004-637X/715/2/1438.
• All-sky search for gravitational-wave bursts in the first joint LIGOGEO-Virgo run
Phys. 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 run
Ap. 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 VSR1
provisionally 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
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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
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Require (at least) three operational and comparably sensitive GW
detector sites
– LIGO Hanford, Livingston, GEOHF and Virgo
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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
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Connection with Astroparticle community
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Advanced Virgo
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Advanced detectors
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2nd generation detectors
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Enhanced LIGO/Virgo+
Virgo/LIGO
BNS inspiral range >10x
better than Virgo
Detection rate: ~1000x better
1 day of Adv data ≈ 3 yrs
of data
108 ly
2nd generation network.
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Timeline: commissioning to
start in 2014.
Adv. Virgo/Adv. LIGO
Credit: R.Powell, B.Berger
6464
Advanced Virgo baseline design
• First orders placed. Plan to be backin 2015 with LIGO
Heavier mirrors
High finesse
3km FP cavities
Larger central links
Cryotraps
Large spot size on TM
Non degenerate
rec. cavities
High power laser
Signal Recycling (SR)
Monolithic
suspensions
DC readout
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Perspective
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The Future – AIGO (Australia)
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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 g 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
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