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A.Viceré – INFN Firenze/Urbino. The science potential of gravitational wave observation. Coupling constants. In SN collapse n withstand 10 3 interactions before leaving the star, the gravitational waves instead leave the core undisturbed Very early GW decoupling after Big Bang

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coupling constants
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze2/34Coupling constants
  • In SN collapse n withstand 103 interactions before leaving the star, the gravitational waves instead leave the core undisturbed
  • Very early GW decoupling after Big Bang
    • GW ~ 10-43 s (T ~ 1019 GeV)
    • n ~ 1 s (T ~ 1 MeV)
    • γ~ 1012 s (T ~ 0.2 eV)

GW emission: very energetic events but almost no interaction

Ideal information carrier,

Universe transparent to GW all the way back to the Big Bang!!

plausible target gw amplitude
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze3/34

Compactness C

1 for BH

0.3 for NS

10-4 for WD

h ~ 10-21

Plausible target GW amplitude
  • Luminosity:
  • Amplitude:

Efficient sources of GW must be asymmetric, compact and fast

GW detectors sensitivity expressed in amplitude h : 1/r attenuation

Example target amplitude:

coalescing NS/NS in the Virgo cluster

(r ~10 Mpc)

synopsis of sources
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze4/34Synopsis of sources

LONG DURATION

SHORT DURATION

Signal known

Coalescing compact binaries

Rotating NS

Signal partiallyor unknown

Stochastic GW

Supernovae

1 generation design sensitivity curves
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze5/341° generation design sensitivity curves

-18

10

1st generation detectors

h (Hz-1/2)‏

Pulsars

hmax – 1 yr integration

LIGO

-19

10

Virgo

-20

10

Resonant

antennas

GEO

BH-BH Merger

Oscillations

@ 100 Mpc

-21

10

Core Collapse

QNM from BH Collisions,

@ 10 Mpc

QNM from BH Collisions,

100 - 10 Msun, 150 Mpc

1000 - 100 Msun, z=1

BH-BH Inspiral, 100 Mpc

NS-NS Merger

-22

10

Oscillations

@ 100 Mpc

BH-BH Inspiral,

z = 0.4

-6

NS,

=10

, 10 kpc

-23

10

NS-NS Inspiral, 300 Mpc

-24

10

4

1

10

100

1000

10

Hz

Credit: P.Rapagnani

ligo and virgo detectors actual sensitivities
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze6/34LIGO and Virgo detectors actual sensitivities
  • LIGO at design sensitivity, Virgo close to it
  • Both detectors very stable  Science possible
science runs so far
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze7/34

368 days of triple-coincident LIGO data

Science Runs So Far
  • Since end of S5 / VSR1 :
    • ►Upgrading LIGO 4-km interferometers and Virgo
    • ►GEO and LIGO 2-km interferometer taking data whenever possible for “AstroWatch” vigil

2002

2003

2004

2005

2006

2007

LIGO:

S1 S2 S3 S4 S5

GEO:

Virgo:

VSR1

1st generation detection chances
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze8/34

1ST GENERATION INTERFEROMETERS CAN

DETECT A NS-NS COALESCENCE

AS FAR AS VIRGO CLUSTER (15 MPc)

1st generation detection chances

LOW EXPECTED EVENT RATE:

0.01-0.1 ev/yr (NS-NS)

FIRST DETECTION:

POSSIBLE BUT UNLIKELY

advanced detectors sensitivity
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze9/34

Enhanced LIGO/Virgo+

2009

Virgo/LIGO

108 ly

Adv. Virgo/Adv. LIGO

2014

Credit: R.Powell, B.Berger

Advanced detectors sensitivity
  • A factor of 10 in sensitivity  a factor 1000 in volume observed, OR event rate
  • Advanced LIGO funded, operational in 2014-15
  • Advanced Virgo to be approved; with less changes, possibly operational in same years
the supernovae
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze10/34The Supernovae

At the origin of most compact objects

Estimated rate: several /yr in the VIRGO cluster; a few / century in our galaxy

Integral has measured the gamma emission by Al26 isotope, whose abundance in our galactic centre confirms this rate

Latest to explode: Sanduleak, the well known 1987a, in the Magellanic clouds (50 kpc away)

supernovae and gw
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze11/34

GW emitted

Supernovae and GW
  • Dynamics and waveform from collapse hard to model
    • A variety of short bursts of GW are predicted. Actual observation will constrain the models
    • What is clear, is that GW and n emissions are almost simultaneous
    • Simulations suggest EGW~10-6 Mʘc2, while NS kick velocities suggest possible strong asymmetries. There could be surprises.

secs

hrs

[Zwerger, Muller]

what we know so far about gw and burst events
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze12/34What we know so far about GW and burst events
  • The most-recent published results use S4 data
  • LIGO-only search[ Classical and Quantum Gravity 24, 5343 (2007) ]
    • ►Searched 15.53 days of triple-coincidence data (H1+H2+L1)for short (<1 sec) signals with frequency content in range 64-1600 Hz
    • ►No event candidates observed
    • ►Upper limit on rate of detectable events: 0.15 per day (at 90% C.L.)
    • ►Sensitive to GW energy emission as small as ~10-7 M at 10 kpc,or ~0.25 M at the distance of the Virgo Cluster
  • LIGO-GEO joint search [ CQG 25, 245008 (2008) ]
    • First use of fully-coherent network analysis for burst signals
  • S5 / VSR1 all-sky search is currently under internal review
    • Factor of ~2 better amplitude sensitivity, and much longer observation time
    • Doing coherent network analysis using LIGO and Virgo data
targeting sne and low energy s
Targeting SNe and low energy 's
  • Boost detection confidence
    • Neutrino and GW expected within a few ms delay
    • Very tight coincidence can be required
  • Constrain  mass strongly
    • 1ms accuracy: m < 1eV constrain
coalescing binaries and psr1913 16
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze14/34

Nobel Prize 1993: Hulse and Taylor

Coalescing binaries and PSR1913+16
  • Pulsar bound to a “dark companion”, 7 kpc from Earth.
  • Relativistic clock: vmax/c ~10-3
  • GR predicts such a system to loose energy via GW emission: orbital period decrease
  • Radiative prediction of general relativity verified at 0.2% level
cb signals as probes of compact object dynamics
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze15/34CB signals as probes of compact object dynamics

[Campanelli et al., PRL, 2006]

  • Pairs of compact stars, like PSR1913+16, but close to the final “coalescence”
    • PBH: Primordial Black Holes (in the galactic halo): M in [0.2, 0.9]
    • BNS: Binary neutron stars: M in [0.9, 3.0]
    • BBH: Binary black holes: M in [3, 20]
    • NS-BH: mixed systems
  • Inspiral signal accurately predictable
    • Newtonian dynamics
    • Post-Newtonian corrections (3PN, (v/c)11/2) [L.Blanchet et al., 1996]
  • Recent big progress in merger 3D simulation [Baker et al 2006, Praetorious 2006]
    • Crucial to extract physics, mostly encoded in the merger phase
coalescing binaries as standard candles
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze16/34Coalescing binaries as standard candles

The signal instantaneous frequency is linked to the mass parameters of the system

The instantaneous GW luminosity is linked to the mass as well

Signal at Earth scales down by distance

From the multiple observation of the same signals, the signal strength at Earth can be determined, and translated into a distance

An alternative method to measure the Hubble constant

chirp

[Campanelli et al., PRL, 2006]

binary inspiral searches so far
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze17/34

100 Mpc

Binary inspiral searches so far
  • New result from first year of S5 data
  • No inspiral signals detected
  • Using population models,calculated 90% confidencelimits on coalescence rates:
  • For binary neutron stars:3.8×10–2per year per L10
  • For 5+5 M binary black holes:2.8×10–3
  • For BH-NS systems:1.9×10–2
  • (Slightly tighter limits if BHs are assumed to have no spin)

[ Preprint arXiv:0901.0302 ]

coalescing binaries and association with grb events
Coalescing binaries and association with GRB events
  • Swift now, Fermi (GLAST) keep looking at  rays from GRB
  • GRB powered by accretion disks on newly formed objects
    • Neutrino and GW expected within a few ms delay
  • Short GRB (< 2s) potentially related to BNS, BH-NS
  • Long GRB (>2s, average 30s) related to (classes of) SNe
    • Again, boost detection confidence
    • Provide insight in the fireball mechanism
the grb 070201 case
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze19/34The GRB 070201 case
  • Short, hard gamma-ray burst
    • Leading model for short GRBs: binary merger involving a neutron star
  • Position (by IPN  triangulation using time of arrival on different gamma satellites) consistent with being in M31
  • LIGO Hanford detectors were operating
    • Searched for inspiral & burst signals
  • Result from LIGO data analysis:No plausible GW signal found;therefore very unlikely to befrom a binary merger in M31
  • [ ApJ 681, 1419 (2008) ]
  • Hundreds of GRB occurred during the live time of LIGO and Virgo detectors: still under analysis
bns events can ground detectors see them
BNS events: can ground detectors see them?
  • Empirical models
    • Use observed (4) galactic binary systems coalescing on timescales comparable to Universe age
    • Infer # of events/Milky Way Equivalent Galaxy
    • Assume galactic density 0.01 Mpc-3
  • Population synthesis models
    • Use galactic luminosity to deduce star formation rate
    • Alternatively, use supernova events to calibrate the number of massive stars
    • Model binary formation and evolution to deduce # of systems coalescing in less than Hubble time
example range of predictions for bns in adv
Example: range of predictions for BNS in AdV
  • Wide range of variability
    • Empirical models uncertains because of the small number of systems observed
    • Population synthesis models vary because of physical assumptions and uncertainty in parameters
  • GW observations can constrain stellar evolution models
    • Each Advanced LIGO or AdV sees a BNS beyond 150 Mpc; will see sufficient events to shed light on stellar evolution models
even more uncertain binary black holes rates
Even more uncertain: binary black holes rates
  • Until recently, entirely based on models
    • Evolve populations of stars, based on current knowledge of massive star populations
    • Only masses < 10 M are simulated
  • BBH population synthesis very uncertain
    • Merger rates vary by factors of hundreds
    • If model A is true, prospects of detection are dim!
    • However ...
an empirical prediction about binary black holes
An empirical prediction about binary black holes
  • IC10 X-1
    • Binary system in local group (~ 700 kpc)‏
    • Includes a BH, m~24 Mo, and a massive Wolf-Rayet star, m~ 35 Mo
  • Allows to predict a rate (Bulik et al.)‏
    • The WR will evolve in BH, without disrupting the binary system
    • The resulting system should have Mchirp~14Mo
    • Such systems are detectable by AdV up to 1.1 Gpc ...
    • Rate for AdV should be ~ 250 /year
    • Rate for combined Advanced LIGO – AdV ~ 2500/year
another look at neutron stars
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze24/34Another look at neutron stars
  • Complicated objects
    • a solid crust of nuclear matter
    • an inner core which could be superfluid
    • Can sustain oscillation modes, whose f0 and Q are related to the structure and the equation of state of the NS matter
    • A strong magnetic field , O(108 T)
  • Numerous: 109 NS in the galaxy, 163 known in LIGO/Virgo band
spinning neutron stars
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze25/34Spinning Neutron Stars
  • Non-axisymmetric, triaxial rotating NS emit periodic GW at f=2fspin
  • Signal can be increased by integrating over long times (months)‏
  • Doppler correction of Earth motion needed (f/f  10-4)
    • Makes search more difficult, but
    • Makes the signal distinguishable from the (many) periodic noises present in the detectors
searches for periodic signals from known radio x ray pulsars
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze26/34

Crab

Searches for Periodic Signalsfrom Known Radio/X-ray Pulsars
  • Allow data demodulation, correcting for motion of detector
    • Doppler frequency shift, amplitude modulation from antenna pattern
  • S5 preliminary results(using first 13 months of data):
    • Place limits on strain h0and equatorial ellipticity e

► e limits as low as ~10–7

It’s plausible that an ordinary neutron star could sustain an ellipticity as large as ~10–6;Some models allow larger

known pulsars adv limits on h
Known pulsars: AdV limits on h
  • Dots: spin down limits.
  • Beaten by AdV for about 40 known objects
gw from soft gamma repeaters
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze28/34GW from Soft Gamma Repeaters
  • SGRs are believed to be magnetars
    • NS with exceedingly large magnetic fields, O(1011 T)
    • Occasional flares of soft gamma rays
    • May be associated with cracking of the crust that excitesvibration f-modes of the neutron star
  • LIGO searched for GW signals associated with SGR flares
    • Dec. 2004 “giant” flare of SGR 1806–20
    • 190 flares from SGR 1806–20 and SGR 1900+14 during first year of S5
    • Placed upper limits on GW signal energy for each flare
    • [ PRL 101, 211102 (2008) ]
    • Within the energy range predicted by some models
  • LIGO also searched for GW signals matching the quasiperiodic oscillations seen in X-rays in the tail of the Dec. 2004 giant flare
    • Placed upper limits [ PRD 76, 062003 (2007) ]
stochastic background of gravitational waves
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze29/34Stochastic Background of Gravitational Waves
  • Weak, random gravitational waves should be bathing the Earth
    • Left over from the early universe, analogous to CMBR ;ordue to overlapping signals from many astrophysical objects / events
  • Energy density
  • Characterized by log spectrum
  • Related to the strain power spectrum
  • Strain scale
stochastic background models and constrains
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze30/34Stochastic background models and constrains

LIGO S1, 2 wk data

h1002 < 23 PRD (2004)

Laser Interferometer

Space Antenna - LISA

LIGO S3, 2 wk data

h1002 < 8 x 10-4PRL (2005)‏

Nucleosynthesis

Pulsar

Initial LIGO, 1 yr data

Expectedh1002 < 2x10-6

Advanced IFOs, 1 yr data

Expectedh1002 < 7x10-10

CMB

Credit: B.Sathyaprakash

0

-2

-4

(0h1002)‏

Cosmic strings

-6

-8

Log

Pre-big bang

model

-10

EW or SUSY

Phase transition

Inflation

-12

Cyclic model

Slow-roll

-14

-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

6

8

-18

10

Log

( f [Hz])‏

astrophysical backgrounds
Astrophysical backgrounds
  • A network can locate point sources of random GW signals
    • Such could be objects of astrophysical interests, for instance very large black holes in active galaxies
    • A network of three detector sites, like the LIGO – Virgo network, with multiple baselines, allows to map the sky with good resolution
benefits by a gw detector network
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze32/34Benefits by a GW detector network

LIGO

VIRGO

False alarm rejection thanks to coincidence

Triangulation allowing to pinpoint the source

A network allows to deconvolve detector response and regress signal waveform -->measure signal parameters, including source distance for BNS signals

Joint operation yields a longer observation time, and a better sky coverage

slide33
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze33/34

10-22

10-23

10-24

10-25

Current detectors

LISA

3rd generation

Credit: B.Sathyaprakash

h (1/√Hz)‏

2008

2015

Adv detectors

2013

2020

0.1mHz 10mHz 1 Hz 100 10k

frequency f / binary black hole mass whose freq at merger=f

4x107 4x105 4x103 M 40 0.4

the role of new instruments
Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze34/34The role of new instruments
  • Better coverage of the frequency spectrum
    • To fill the gap between LISA and the ground based detectors
    • Some sources, like coalescing binaries, have much more signal at lower frequencies: for instance LISA can see BBH in the whole universe  requirements on sensitivity are less stringent
  • Increased number of detectors
    • To provide a better sky coverage  more events
    • To improve the detection capabilities  reject background
    • To reconstruct the signal more accurately  better science