Status of VIRGO

Sipho van der Putten

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Contents

Introduction to gravitational waves VIRGO Pulsars: gravitational waves from periodic

sources Pulsars in binary systems Analysis approach

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Introduction to Gravitational Waves ‘Ripples’ in space-time

due to accelerating masses distorting space-time Two polarizations: ‘+’ & ‘x’ Measured in strain: h=dL/L

Extremely weak effects: Supernova (10 kpc, ~10

Msolar): h~10-22

Rotating deformed neutron star (~10 kpc, ~1 Msolar, 100 Hz): h~10-27

Ring of free falling masses

L

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VIRGO Science Run VSR1 complete

Oct ‘07 Combined LIGO & VIRGO

data taking ~5 months data

Current upgrade (VIRGO+) underway 5x better at low freq &

2x better at high freq Nikhef: Electronics, IMC VSR2 in mid 2009:

Combined run with eLIGO 1 year of data

Next upgrade AdvVirgo 10x better in sensitivity than

initial VIRGO design 2010 to 2012

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Periodic sources of gravity waves Pulsars: spinning

neutron stars Emitting GWs requires

quadrupole moment; symmetry axis is not rotation axis

Neutron stars: Isolated Binary systems

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0238

36

27

100

10

10101005.1

Hz

f

r

kpc

mkg

Ih rneutronsta

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Neutron stars in binary systems 2/3 of NS (f>10Hz) in a binary system

Mass transfer: Spin-up: f increases

Many parameters: Orbital: Sky Position: Source: ….

Doppler shift due to orbit of binary system: non stationary frequency Our goal: All-sky search for neutron stars in binary systems

,,/, 00 hdtdff ,

eaP p ,,

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Doppler shift Fixed point emits

stationary frequency Rotation of Earth (daily

motion) df/f~10-6

Earth’s orbit (yearly motion) df/f~10-4

Pulsars in binary system df/f~10-3

Hulse-Taylor system All shifts included

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Analysis binaries: spectral filtering Non stationary frequency:

FFT → power spread out, bad S/N

Spectral filtering: Identify the signal in the data

fsig= 203.1 Hz

fsig= 203.1 – 5*10-4 t Hz

sTHz fP

Pobssample

Noise

Signal 4096 , 4096 ,10 4

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Conceptual approach

Split the data in time stretches

Second order spectral filter

Each matching filter: f0,a,b,tavg

Pattern recognition using all the information available

20)( btatftf

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Simulations Simulated waveform:

Hulse-Taylor system Divide in time slices

1286 s Simple FFT each slice

Time (s)

Fre

quen

cy (

Hz) hrec

Time (s)

Fre

quen

cy

(Hz)

hrecP(noise)=100 P(sig)

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Spectral filtering Spectral filters:

2607 filters, applied ~109 times

Threshold 4x noise level CPU time: 1 day for ~10 h

data (0-400 Hz) Many improvements in

efficiency possible Non-stationary frequency not

an issue anymore To do:

Investigate higher order filters→ longer FFTs

Pattern recognition

Time (s)

Fre

quen

cy

(Hz)

hrecP(noise)=100 P(sig)

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Conclusions VIRGO & LIGO have 5 months of science-grade

data VIRGO+ & eLIGO upgrade underway and will be

ready in 2009 Analysis of binary pulsars:

Conceptual approach to analysis: spectral filtering S/N 0.1 easy with 2nd order filter Time dependent frequency no problem Todo: test idea on simulations and real data (higher

frequency signal, more noise) Todo: implement pattern recognition