VIRGO and the search for Gravitational Waves Giovanni Losurdo INFN Firenze-Urbino e-mail:...

VIRGO and the search for Gravitational Waves

Giovanni Losurdo

INFN Firenze-Urbino

e-mail: [email protected]

Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino

PSR1913+16: GW Exist

• Pulsar bound to a “dark companion”, 7 kpc away.

• Extremely accurate clock: fz, ft=10-15 s-2

• Relativistic clock: vmax/c ~ 10-3

• GR predicts such a system to loose energy via GW emission orbital period decrease

0035.00032.1.

th

obs

P

corrP


• Linearized Einstein eqs. (far from big masses) admit wave solutions (perturbations to the background geometry)

Ripples in the Cosmic Sea

01

1 with 2

2

22

htc

hhg


Energy-Time Scales

• In SN collapse withstand 103 interactions before leaving the star, GW leave the core undisturbed

• Decoupling after Big Bang – GW 10-43 s (T ~ 1019 GeV)– 1 s (T ~ 1 MeV)– e.m. 1012 s (T ~ 0.2 eV)

Coupling constants

strong e.m. weak gravity

0.1 1/137 10-5 10-39

GW brings unique information out of the Universe

c

Gmp

2


• Luminosity:

• Amplitude:

• M ~ 1.4 M, R ~ 20 km, r ~ 15 Mpc, forb ~ 400 Hz

Sources of GW

h ~ 10-21 R

M

r

6259

5 s

erg104

5

c

v

R

RQQ

c

GP S

ijij

12

44 r

E

c

GQ

rc

Gh ns

E ~ 1052 erg for NS/NS


Coalescing Binaries

• Compact stars (NS/NS, NS/BH, BH/BH)

• Inspiral signal accurately predictable– Newtonian dynamics– Post-Newtonian corrections (3PN, (v/c)11/2) [L.Blanchet et al., CQG

13, 1996]

chirp


Supernovae

• Final evolution of big mass stars

• Core collapses to NS or BH

• Neutrinos and GW emission

• Rate: several per year in the VIRGO cluster

GW emitted


Kerr Black Holes – Torus System

• A BH-torus system may originate in a NS-BH coalescence

• GRBs can be emitted during BH accretion by torus matter

• A non-axisymmetric spinning torus, powered by BH angular momentum, is expected to emit a GW burst of T~15 sec, f~1-2/(1+z) kHz

• If the observed GRBs are originated in such events a rate of ~105 /yr within 100 Mpc is expected

(Van Putten, PRL, 87, 2001)

GW

GW


• GW acting on a ring of freely falling masses

Interferometric Detection of GW

L-L

L+L

hLL2

1

Measurable L m

Target h

(NS/NS @10 Mpc)

L m


Noise in Interferometric Detectors

• Suspended mirrors (free falling test masses)

• GW induce ITF phase shift:

• Shot noise:

• Thermal noise:

hL 4

2

hLL

2

hLL

P

2~

)(4)(~2 fTkfF B


• 3 km vacuum performance within requirements

• Final mirrors suspended

• Start of commissioning: June 2003

• Data taking: 2004+


Sensitivity Goal

seismic

thermal

shot

bars


A Real Interferometer


Vacuum

• Requirements:– 10-9 mbar for H2, 10-14 mbar for hydrocarbons– 10-6 mbar in the suspension chambers – Outgassing rate: 5 10-15 mbar l s-1 cm-2

• Status:– Whole tube welded, leak-tested and baked– 160 steel baffles for reflected light shielding installed– Vacuum performance within requirements

1.00E-14

1.00E-13

1.00E-12

1.00E-11

1.00E-10

1.00E-09

1.00E-08

1.00E-07

0 10 20 30 40 50 60 70 80 90 100

mass/charge

pa

rtia

l pre

ssu

re,

mb

ar

After bake

before bake

Residual Gases in tube900m - 1500m N

October 2001 Ptot=3E-8 mbar

Ptot=2E-10 mbar

2: hydrogen18: water12,28: carbon monoxide44: carbon dioxide55, 57: hydrocarbon contamination


Superattenuators

• Goal: move the seismic wall down to a few Hz

• Expected attenuation: 10-14 @ 10 Hz

• 3 actuation points for hierarchical control of the mirror: inverted pendulum,marionette, recoil mass

• Inertial damping on IP, angular local controls on marionette

10-14 @ 10 Hz


SA Control

• Residual low frequency motion of the mirrors ~ 10-4 m

• Mirror motion after local control < 10-6 m

• Mirror motion after locking ~ 10-12 m

Inertialdamping

Angularcontrols

Pendulumdamping

Tidecontrol

LVDTs,accelerometers

CCD

ITF


Inverted pendulum

Marionette

Mirror – ref. mass

filters


The superattenuator and the VIRGO vacuum system


Injection System

• 20 W laser

• 144 m MC cavity to reduce jitter noise and select TEM00 mode


Detection

• Suspended bench with optics for beam adjustement and output mode cleaner

• Detection, amplification and demodulation on the external bench

• Output mode cleaner locked in CITF

Output mode cleaner

External bench

Suspended bench


Mirrors

• Coater VIRGO in a class 1 clean room, unique in the world (2.2*2.2*2.4 m)

• Coating features:– very low losses: scattering < 5 ppm, absorption < 1 ppm– Uniformity on large dimension: < 10-3 400 mm

• Optical metrology adapted to large components

• Type of controls: scattering, absorption (bulk, surface), birefringence, reflection, transmission, wavefront (stitching), roughness, defects detection

Coater VIRGO Absorption, Birefringence, wavefront measurement


Global Control

• Receives the photodiodes (10 kHz) and quadrants (500 Hz) signals

• Simple implementation of complex algorithm for lock acquisition

• Computes lengths and angles, applies filters

• Sends corrections to mirrors

• Used in the CITF commissioning

• Working robustly over long periods


Environment Monitoring

NI

BS

IBB

WI

PR

DB

SR

Temperature probes, 88, 1 Hz

Humidity probes, 4, 1 Hz

Pressure probes, 4, 1 Hz

Episensors, 6, 1 kHz

Accelerometers, 9, 10 kHz

Magnetometers, 3, 20 kHz

Microphones, 3, 10 kHz

Night-day seismic noise on site


Data Acquisition/Storage

• Data flow: 4.1 Mbytes/sec– 39 % from detection channels (detection bench + global

control)– 46 % from suspension channels– 15 % from monitoring channels

• Storage:– Last 6 months (~64 Tbytes) to be stored on disk at site– Last 2 years stored on disk at Bologna and Lyon– All data copied on tapes on site

– 20 Tbytes on disk will be available on site by the end of 2002


The Central Interferometer

• 6 m recycled Michelson. Commissioning: april 2001-june 2002

• Integration of most of the VIRGO subsystems

• 5 engineering runs (E0-E4)


CITF Progress

Duty cycles:98% 85% 98% 98% 73%


Locking Accuracy

• How good we are in keeping the mirror “still”?

• The dark fringe signal at low frequency measures the relative motion of the mirrors:

• VIRGO requirement fulfilled!

L = 2 · 10-12 m

RMS

2·10-12 m


A long way to go…


Network

• False alarm rejection will require coincidences

• ITFs have little directionality: 3 well separated detectors are necessary to reconstruct the source direction

TAMA600 m

300 m4 & 2 km

4 km

AIGO

3 km


The Other Detectors

• TAMA and LIGO are close to the target sensitivity

• 2003: LIGO-TAMA S2 science run

LIGO

TAMA


How Many Events

• Expected rate of coalescences: 3/yr out of 40 200 Mpc [Grishchuk et al. Astro-ph/0008481]

• VIRGO can detect a NS/NS event at ~ 20 Mpc

• Detection rate, best estimates:– <1/yr for NS/NS– 2-3/yr for BH/BH

• Estimated rate of supernovae: several /yr in the VIRGO cluster, but the efficiency of GW emission is strongly model dependent


Expanding the Accessible Universe

• Thermal noise reduction: – Fused silica fibers – Sapphire test masses– Cryogenic interferometers?

• Shot noise: – High power laser– Better optics

seismic

thermal

shot

Where and how can we reduce the detector noise?


Advanced Interferometers

Initial Interferometers

Advanced Interferometers

Open up wider band

~ 15 in h ~3000 in rate

NS/NS

dete

ctab

le @

300

Mpc

From LIGO


LISA

• Space interferometer

• LISA will explore a different frequency range

• Launch of test mission SMART 2: 2006

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VIRGO and the search for Gravitational Waves Giovanni Losurdo INFN Firenze-Urbino e-mail:...

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