Detectors and their Capabilities Lee Samuel Finn Center for - - PowerPoint PPT Presentation

Detectors and their Capabilities

Lee Samuel Finn Center for Gravitational Wave Physics

Goals & Outline

• Goal: Introduction to gravitational wave

detectors through the prism of stellar population science

– Sources & observables, selection effects

• Outline

– Stellar populations and gravitational waves – Sources and observable source properties – Some sensitivity estimates

Stellar Populations and Gravitational Waves

• “Source”? Stellar populations

– Not necessarily an object!

• Relevant gravitational wave signals?

– Gravitational waves: coherent motion of mass

• Mostly time-varying quadrupole

– Obvious: isolated binaries (bh, ns, wd) – Less obvious: pulsars, rapidly rotating neutron stars, supernovae, GRBs (hypernovae, collapsars, AIC, binaries, etc.), nascent neutron stars, confusion-limit stochastic background, etc.

Observable Source Properties: Isolated Stars

• GRBs

– Possibly distinguish between binary, collapse models – Need advanced detectors, multi-spectrum observations, luck

• Supernovae and other collapse events
• Pulsars/rapidly rotating NS: non-axisymmetry,

precession

– Non-axisymmetry: εI/r, orientation; period, sky position – Precession: ε, I/r; period, sky position

• Accreting neutron stars

– Secular and dynamical instabilities in, e.g., LMXBs

• All signals likely weak …

– Low snr in context of prospective detectors

Observable Source Properties: Isolated Binaries

• Ground-based detectors (LIGO, Virgo, ?)

– Populations: NS/NS, solar mass BH binaries – “Chirp mass” M = µ3/5M2/5 determined with high precision – Component masses, spins, eccentricity information present but (much) less accurately determined – Sky position from time-of-arrival measurements in several detectors – Luminosity distance if localized in sky

Observable Source Properties: Isolated Binaries

• LISA

– Populations:

• Massive BH/BH binaries: (1+z)M > 103 M
• Solar mass BH/NS capture on 104–107 M BH
• WD/WD, WD/NS, WD/ M BH, NS/NS, NS/BH

– Orientation, sky position, eccentricity – Late inspiral captures on massive BHs, massive BH binaries: Chirp mass, eccentricity, luminosity distance – Merger of massive BHs, massive BH binaries: final mass, angular momentum – All signals strong: S/N ~ 100 or greater

Observable Source Properties: Confusion Limited Binaries

• Confusion limited?

– Superposition of unresolved galactic binaries

• Number in orbital frequency interval ~ 1/yr large

– Isolated binaries f > f0, confusion limited f < f0 – Orbital f0 ~ 10-3 Hz given estimated number binaries – S/N ~ 60 in confusion limited regime

• Transition frequency (resolved to confused),

confusion limit amplitude

– Related to number, space distribution, binary & binary component mass function

• Distribution on sky

– Amplitude, frequency, phase modulation owing to detector

• rbit about sun

Relevant Detectors and Basic Properties

• Relevant Detectors

– Ground-based detectors: GEO, LIGO, Virgo – Space-based detector: LISA

• Spectrum

– LIGO

• 1st gen.: 40 Hz - 4 KHz
• 2nd gen.: 10 Hz - 4 KHz

– Virgo – LISA: 10-3 Hz - 10-1 Hz

• Note Gap: 10-1 Hz - 10 Hz

– LISA arms too long, ground-base detectors limited by gravity-gradient noise

Relevant Detectors and Basic Properties

• Source localization

– Ground-based array

• Aperture synthesis for coherent

signals

• Arrival time analysis for burst

signals

• Antenna pattern modulates cw

signal as Earth rotates

– LISA

• Moving antenna pattern

modulates signal as detector

• rbits sun
• Also frequency, phase

modulation

• Map population distribution by

antenna pattern modulation

Antenna pattern for single IFO

Sensitivity Estimates: Binary Inspiral

• Science Reach: Survey volume

– Distance r such that observed rate of a uniformly distributed population is 4πr3n/3

• Parameters

– M = (1+z)µ3/5M2/5

• Reduced mass µ, total mass M,

redshift z

– Target false rate

• < 10–4/y corresponds to S/N ~ 8

– Three LIGO IFOs – rinit = 21 Mpc (M/1.2M)5/6 – radv = 300 Mpc (M /1.2M)5/6 – r ~ M5/6 for M<10M

inspiral coalescence ringdown

Periodic Signals

• Focus on pulsars

– fgw = 2fpulsar – h ∝ ε = (∆I/I)

• Reach: upper limit on ε

– 1 yr observation – 10 Kpc distance – Declination average – Significance: 95%

• Theoretical prejudice

– ε < ~ 10–6

• From pure Coulumb

lattice crust strength

• Observational

constraints

– ε < ~10–8 for old (recycled ms) pulsars

• γ-ray burst triggered by

formation of ~M bh

– Expect grav.-wave burst

• Individual grav.-wave

bursts not detectable

– Distance, amplitude, etc., conspire against – Adv. LIGO bound equiv to ~0.3M in grav.-waves at z = 1/2

γ-ray bursts

hDet

2 < h95% 2

= 1.35 ×10

−22

( )

2

2.5 ×10−23

( )

2

      T 0.2s 1000 Non      

1/ 2

LIGO I LIGO II

• Look for statistical

association:

Hypernovae; collapsars; NS/NS, NS/BH, He/BH, WD/BH mergers; AIC; … Black hole + debris torus Relativistic fireball γ-rays generated by internal or external shocks

Comments

• Ground-based detectors operate in regime of rare,

weak, isolated sources

– Except, perhaps, for ~ 10M/10M BH binaries

• LISA detectors operate in regime of many strong

sources

– Galactic binary sources unresolved in large part of band with snr ~ 60

• “In principle” is not yet “in practice”

– Analysis immature: much of what we know we can do in principle we don’t yet know how to do in practice – Especially true for LISA

• LISA science goals (and, thus, capabilities) still under

definition