1. The science potential of gravitational wave observation
A.Viceré – INFN Firenze/Urbino

2. Coupling constants Ideal information carrier,
strong
e.m.
weak
gravity
0.1
1/137
10-5
10-39
GW emission: very energetic events but almost no interaction
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 ~ s (T ~ 1019 GeV)
n ~ s (T ~ 1 MeV)
γ ~ s (T ~ eV)
Ideal information carrier,
Universe transparent to GW all the way back to the Big Bang!!
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze 2/34

3. Plausible target GW amplitude
Luminosity:
Amplitude:
Compactness C
1 for BH
0.3 for NS
10-4 for WD
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)
h ~ 10-21
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze 3/34

4. Signal partially or unknown
Synopsis of sources
LONG DURATION
SHORT DURATION
Signal known
Rotating NS
Coalescing compact binaries
Signal partially or unknown
Stochastic GW
Supernovae
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze 4/34

5. 1° generation design sensitivity curves10
-24
-23
-22
-21
-20
-19
-18 1
100
1000 4
h (Hz-1/2)‏
Virgo
LIGO
Resonant
antennas Hz
GEO
Core Collapse
@ 10 Mpc
BH-BH Merger
Oscillations
@ 100 Mpc
Pulsars
hmax – 1 yr integration
BH-BH Inspiral,
z = 0.4
BH-BH Inspiral, 100 Mpc
QNM from BH Collisions,
Msun, z=1
NS, 
=10 -6
, 10 kpc
Msun, 150 Mpc
NS-NS Inspiral, 300 Mpc
NS-NS Merger
1st generation detectors
Credit: P.Rapagnani
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze 5/34

6. LIGO and Virgo detectors actual sensitivities
LIGO at design sensitivity, Virgo close to it
Both detectors very stable  Science possible
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze 6/34

7. 368 days of triple-coincident LIGO data
Science Runs So Far
368 days of triple-coincident LIGO data
2002
2003
2004
2005
2006
2007
LIGO:
S1 S2 S3 S4 S5
GEO:
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
Virgo:
VSR1
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze 7/34

8. 1st generation detection chances
1ST GENERATION INTERFEROMETERS CAN
DETECT A NS-NS COALESCENCE
AS FAR AS VIRGO CLUSTER (15 MPc)
LOW EXPECTED EVENT RATE:
ev/yr (NS-NS)
FIRST DETECTION:
POSSIBLE BUT UNLIKELY
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze 8/34

9. Advanced detectors sensitivity
108 ly
Enhanced LIGO/Virgo+
2009
Virgo/LIGO
Credit: R.Powell, B.Berger
Adv. Virgo/Adv. LIGO
2014
A factor of 10 in sensitivity  a factor 1000 in volume observed, OR event rate
Advanced LIGO funded, operational in
Advanced Virgo to be approved; with less changes, possibly operational in same years
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze 9/34

10. The 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)
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze /34

11. 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.
GW emitted
secs
hrs
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze /34
[Zwerger, Muller]

12. What 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 days of triple-coincidence data (H1+H2+L1) for short (<1 sec) signals with frequency content in range Hz
► No event candidates observed
► Upper limit on rate of detectable events: 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, (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
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze /34

13. 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

14. 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
Nobel Prize 1993: Hulse and Taylor
P (s)
(9)
dP/dt
-2.425(10)·10-12
dw/dt (º/yr)
(18) Mp
1.442 ± M Mc
1.386 ± M
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze /34

15. CB signals as probes of compact object dynamics
[Campanelli et al., PRL, 2006]
CB signals as probes of compact object dynamics
Pairs of compact stars, like PSR , 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
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze /34

16. Coalescing binaries as standard candles
[Campanelli et al., PRL, 2006]
Coalescing binaries as standard candles
chirp
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
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze /34

17. Binary inspiral searches so far
New result from first year of S5 data
No inspiral signals detected
Using population models, calculated 90% confidence limits on coalescence rates:
For binary neutron stars: ×10–2 per year per L10
For 5+5 M binary black holes: ×10–3
For BH-NS systems: ×10–2
(Slightly tighter limits if BHs are assumed to have no spin)
100 Mpc
Milky way is 1.7 L10
Rates could plausibly be as high as 5e-4 for BNS, 6e-5 for BBH or BHNS
i.e. about two orders of magnitude away from plausible rates
Also, S4 ringdown search paper in preparation
[ Preprint arXiv: ]
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze /34

18. 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

19. The 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 be from 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
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze /34

20. 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

21. 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

22. 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 ...

23. 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

24. Another 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
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze /34

25. Spinning 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
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze /34

26. Searches for Periodic Signals from 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 h0 and 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
Crab
Plot from Greg Mendell’s talk at Amaldi in July 2007
Lowest epsilon limit presented by Matt in April 2007 APS meeting; note that there was a correction after that, but in both cases the value was less than 1e-7.
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze /34

27. Known pulsars: AdV limits on h
Dots: spin down limits.
Beaten by AdV for about 40 known objects

28. GW 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 excites vibration f-modes of the neutron star
LIGO searched for GW signals associated with SGR flares
Dec “giant” flare of SGR 1806–20
190 flares from SGR 1806–20 and SGR during first year of S5
Placed upper limits on GW signal energy for each flare
[ PRL 101, (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 giant flare
Placed upper limits [ PRD 76, (2007) ]
Smallest gamma: 30
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze /34

29. Stochastic Background of Gravitational Waves
Weak, random gravitational waves should be bathing the Earth
Left over from the early universe, analogous to CMBR ; or due to overlapping signals from many astrophysical objects / events
Energy density
Characterized by log spectrum
Related to the strain power spectrum
Strain scale
BBN bound is 1.1e-5
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze /34

30. Stochastic background models and constrains
Credit: B.Sathyaprakash
LIGO S1, 2 wk data
h1002 < 23 PRD (2004)
LIGO S3, 2 wk data
h1002 < 8 x 10-4 PRL (2005)‏
Laser Interferometer
Space Antenna - LISA -2
CMB
Pulsar
Nucleosynthesis
(0h1002 )‏ -4
Cosmic strings
Initial LIGO, 1 yr data
Expected h1002 < 2x10-6 -6
Log -8
Advanced IFOs, 1 yr data
Expected h1002 < 7x10-10
Pre-big bang
model
-10
EW or SUSY
Phase transition
Inflation
-12
-14
Slow-roll
Cyclic model
-18
-16
-14
-12
-10 -8 -6 -4 -2 2 4 6 8 10
Log
( f [Hz])‏
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze /34

31. 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

32. Benefits 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
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze /34 32

33. frequency f / binary black hole mass whose freq at merger=f
Credit: B.Sathyaprakash
h (1/√Hz)‏
10-22
10-23
10-24
10-25
Current detectors
LISA
2008
2015
Adv detectors
2013
3rd generation
2020
0.1mHz mHz Hz k
frequency f / binary black hole mass whose freq at merger=f
4x x x103 M
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze /34

34. The 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
Arcetri – February 23rd, A.Viceré – Università di Urbino & INFN Firenze /34