Virgo status

LISA

Virgo status

Jo van den Brand

SAC, Nikhef: April 20, 2007

Contents



Progress with Virgo commissioning



Comparison to LIGO, GEO600 and bar detectors



NIKHEF activities in Virgo



Discovery potential



Future

LISA

VIRGO Optical Scheme

Laser 20 W

Input Mode Cleaner (144 m)

Power Recycling

3 km long Fabry-Perot Cavities

Output Mode Cleaner (4 cm)

Sensitivity evolution

LISA

Sensitivity evolution

Sensitivity today

Hardware Limit

LISA

Sensitivity today

Hardware Limit

Length Control

Sensitivity today

Hardware Limit

Length Control

Angular Control

LISA

Sensitivity today

Hardware Limit

Length Control

Angular Control

Acoustics

LIGO: meeting the challenge

 LIGO

– Two 4 km interferometers

– One 2 km interferometer

 LIGO started commissioning first arm in 1999

 All detectors at design sensitivity

 Science run (S5) in progress

LISA

Virgo sensitivity compared to LIGO and GEO600

Virgo - Bars joint analysis



Burst events and stochastic signals



LIGO and Virgo now at ~10

around 900 Hz



Keep bars operational during LIGO and Virgo upgrades

1.510

at 3 kHz

NIKHEF activities

Upgrades to Virgo+ (2008)



Commissioning upgrades before Virgo+ :

– Scattered light mitigation

– New Automatic Alignment electronics

– New coil drivers

– Thermal compensation



Virgo+ upgrades:

– The laser input power will be higher (50 W, vs 20 W now)

– Pre-mode cleaner

– The test masses will be replaced

– Ta2O₅/SiO₂ coating layers with TiO₂ dopants

– Finesse of the arms may be higher (about 150, vs 50 now);

– Larger end Mode Cleaner mirror (140 mm instead of present 80 mm)

– New DSP and DAQ electronics

– Monolithic suspensions

– Input Mode Cleaner input mirrors

– DC read-out (?)

LISA

NIKHEF: Linear alignment of VIRGO

N W

EOM



Phase modulation of input beam



Demodulation of photodiode signals at different output beams

– => longitudinal error signals



Quadrant diodes in output beams

– => Alignment information

– (differential wavefront sensing)

Thermal effects on FP cavities



Thermal lensing of mirrors

–

Optical instabilities

–

Operate with reduced power

–

Problem for upgrade



FEM studies

–

Sipho van der Putten

–

Eric Hennes

5540 5545 5550 5555 5560 5565 5570 5575 5580 5585

10^-20 10^-19 10^-18 10^-17 10^-16 10^-15 10^-14

Pr_B1_ACp FFT

GPSstart840240000

Gaussian distribution yields df/dT = 0.055 Hz/K

0.000 0.002 0.004 0.006

-0.01 0.00 0.01 0.02 0.03 0.04 0.05

T [K] from FEM

GPStime [s]

T from FEM (0.7ppm/cm+1.25ppm)

T [K] from mirror mode

WI T from mirror mode

0.000 0.002 0.004 0.006

-0.01 0.00 0.01 0.02 0.03 0.04 0.05

T [K] from FEM

GPStime [s]

T from FEM (0.7ppm/cm+1.25ppm)

T [K] from mirror mode

WI T from mirror mode

LISA

Suspended Injection Bench

Critical suspended IO components

Remotely rotated waveplate

Faraday modifications: remote isolation tuning, thermal focal length Dihedron: movements, clipping, scattering, …

Dihedron

Focal

compensator

LISA

Dihedron

End MC mirror

Suprasil mirrors,

80mm30mm, contacted on Zerodur prism, 180100 mm

Leaning on three thin steel

legs (“kinematic” mount)

Dihedron

Mains concerns:



Movements



Scattering



Beam clipping



Mechanical resonances



IMC alignment coupling with ITF beam pointing

Possibile solutions:



Block the dihedron to the bench



Better mirrors (and new dihedron, blocked or not blocked)



Suspend the mirrors (and make them larger): preferred solution

All being evaluated (review in April)

LISA

New Mode-Cleaner mirror



Larger diameter (140 vs 80 mm)



Larger thickness (40 vs 30 mm)



Heavier (2 kg vs 0.360 kg): radiation pressure effects reduction



Better polishing (less scattered light)



Heavier Reference Mass and thinner Reference Mass coils electrical wires (pendulum mode dominated)

Three mirrors are being polished

(GSI-General Optics)

Virgo analysis at NIKHEF

LISA

Detection of Periodic Sources

• Pulsars in our galaxy: “periodic”

•

search for observed neutron stars

28 Radio Sources

h ~ GIf



/cr < 10

Periodic Sources – all sky search – Roma / NIKHEF

• Doppler shifts

•

Frequency modulation: due to Earth’s motion relative to the Solar System Barycenter, intrinsic frequency changes

•

Amplitude modulation: due to the detector’s antenna pattern.

•

The original frequency is 100 Hz and the maximum variation fraction is of the order of 0.0001

•

Note the daily variations.

•

Because of the frequency

variation, the energy of the

wave doesn’t go in a single

bin, so the SNR is highly

reduced.

LISA

Optimal detection by re-sampling procedure

•

Use a non-uniform sampling of the received data: if the sampling frequency is proportional to the (varying) received frequency, the

samples, seen as uniform, represent a constant frequency sinusoid and the energy goes only in one bin of their FFT.

•

Every point of the sky (and every spin-down or spin-up behavior) needs a particular re-sampling and FFT.

Original data:

The frequency is varying, we sample non-uniformly

(about 13 samples per period).

The non-uniform samples, seen as uniform, give a perfect sinusoid and the

periodogram of the samples has a single “excited” bin.

1 year FFT length (number of points) 3.1E+10

Sky points 3.1E+13

Spin-down points (1st ) 3.1E+06

Spin-down points (2nd ) 3.2E+02

Freq. points (500 Hz) 1.6E+10

Total points 4.8E+32

Comp. power (Tflops) 3.6E+19

ALL SKY SEARCH

enormous computing challenge

Rotational frequency of all observed pulsars

The dark histogram indicates members of binary systems

Include binary system in analysis

Discovery potential

GW Source: Coalescing Binary



End of the life of compact binary systems

– Neutron Stars or Black Hole



Rare events:

– ~ 0.1 event/year (@20Mpc) ±1 order of magnitude



Typical amplitude (NS-NS): h ~ 10

@20 Mpc



“Known” waveform

– Search with matched filtering

– General Relativity test

– Standard candles: get the distance from the waveform

– Coincidence with short gamma ray burst?

LISA

GW source : Supernovae



Non-spherical star collapse



Impulsive events

–

Duration < 10 ms



Required coincidences

– GW, optical, neutrino detectors



Waveform and amplitude difficult to predict

– h  10^-21 @ 10 Mpc (?)

Example of expected waveforms



Rates:

– 1/50 year in Milky Way

– 10/year in the Virgo cluster

SN 1604 @ 6kpc SN 1572 @ 2.3 kpc

SN 1054 @ 2.3 kpc

 Rotating asymmetric neutron star

 GW Amplitude function of the unknown asymmetry

– ε = star asymmetry = ??

– Upper limit set by the pulsar spin down

 A few pulsars around a few 100 Hz

– Only 800 pulsars plotted out of 10⁹ in the galaxy

 Weak signal but could be integrated for months

– But a complex problem due to the Doppler effect

– CPU issues

GW Source: pulsars

 

 



 



 



 



 



 



 



 



2 2

45 27

10 200

10 10 10

3 

Hz f cm

g I r

h kpc

f (Hz) N

LIGO: <10% of energy in GW

Crab pulsar

LISA

Virgo: what for?

 First (?) direct observation of gravity waves

 Better understanding of gravity

– GW produced in high density area

– Strong field

– Tests GR

 Open a new window on the universe

– GW very weakly absorbed

– Standard candle: Hubble constant

– GW + Gamma Ray Bursts?

– Supernova understanding?

– Neutron stars/black hole physics?

– Early universe picture??

 Pushing interferometer techniques to their limits

The future ?

Supernovae – with present detector only sensitive to Milky Way

Coalescent binaries – with present detector

LISA

Post S5: Virgo+



Fall 2007: Additional commissioning

– Emphasis on the low frequency side



2008 Virgo+:

– Virgo+ main features

– 50W laser,

– Monolithic suspension, – New digital electronics …

– Horizon improvement: 2 – 5 (depends of noise model)

– Detailed schedule not yet decided

– Depend on:

– Noise budget; Virgo+ readiness; LIGO schedule – Review of Virgo+ on April 3rd



2009

– Commissioning Virgo+

– Goal: Online at the same time of enhanced LIGO

Advanced Virgo



Target sensitivity improvement:

– One order of magnitude compared to Virgo



Time scale: Shutdown around 2011



Bigger changes compared to Virgo+:

– New beam topology:

– Flat beam? Change the beam waist? Signal recycling??

– Progress on internal thermal noise:

– Material? Coating? Monolithic suspension?

– Newtonian noise subtraction?

– …



But Smaller Changes than Advanced LIGO

– keep the seismic isolation.

A possible sensitivity

LISA

LIGO and VIRGO: scientific evolution



At present hundreds of galaxies in range for 1.4 M

NS-NS binaries



Enhanced program

–

In 2009 about 10 times more galaxies in range



Advanced detectors

–

About 1000 times more galaxies in range

–

In 2014 expect 1 signal per day or week

–

Start of gravitational astrophysics

–

Numerical relativity will

provide templates for

interpreting signals

Third generation detector

Rüdiger, ‘85



Two order of magnitude compared to initial Virgo



Underground site



Multiple interferometers:

– 3 Interferometers; triangular configuration?

– 10 km long

– 2 polarization + redundancy



Design study part of ILIAS & FP7



Construction: 2010-16 ?

LISA

Gravitational wave antenna in space - LISA

–

3 spacecraft in Earth-trailing solar orbit separated by 5 x10

km.

–

Measure changes in distance between fiducial masses in each spacecraft

–

Partnership between NASA and ESA

–

Launch date ~2016+

Complementarity of Space- & Ground- Based Detectors

Rotating Neutron Stars

Difference of 10

in wavelength:

Like difference between X-rays and IR!

VIRGO LISA

LISA will see all the compact white-dwarf and

neutron-star binaries in the Galaxy (Schutz)

LISA

LISA Interferometry

 “LISA is essentially a Michelson Interferometer in Space”

 However

– No beam splitter

– No end mirrors

– Arm lengths are not equal

– Arm lengths change continuously

– Light travel time ~17 seconds

– Constellation is rotating and

translating in space

Summary



Gravitational waves physics is new & exciting



Detectors sensitivity is improving fast

–

MOU on data sharing between LIGO and Virgo



Virgo close to start a first science run



More progress to come soon…