Delensing Gravitational Wave Standard Sirens

Delensing Gravitational Wave Standard Sirens

Dr Martin Hendry

Astronomy and Astrophysics Group, Institute for Gravitational Research

Dept of Physics and Astronomy, University of Glasgow

Delensing Gravitational Wave Standard Sirens

Dr Martin Hendry

Astronomy and Astrophysics Group, Institute for Gravitational Research

Dept of Physics and Astronomy, University of Glasgow

With thanks to:

David Bacon, Chaz Shapiro, Ben Hoyle ICG, Portsmouth

See astro-ph/0907.3635; MNRAS in press

3

TG

Spacetime curvature

Matter (and energy)

Gravity in Einstein’s UniverseGravity in Einstein’s Universe

“The greatest feat of human thinking about nature, the most amazing combination of philosophical penetration, physical intuition and mathematical skill.” Max Born

Nottingham, March 2010

4


5

Spacetime tells matter how to move, and matter tells spacetime how to curve

Gravity in Einstein’s UniverseGravity in Einstein’s Universe


6

Gravitational Waves Produced by violent acceleration of mass in:

neutron star binary coalescences black hole formation and interactions cosmic string vibrations in the early universe (?)

and in less violent events: pulsars binary stars

Gravitational waves

‘ripples in the curvature of spacetime’

that carry information about changing gravitational fields – or fluctuating strains in space of amplitude h where:

L

Lh

~


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“Indirect” detection from orbital decay of binary pulsar: Hulse & Taylor

PSR 1913+16

Evidence for gravitational waves


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PulsedCompact Binary Coalescences: NS/NS; NS/BH; BH/BHStellar Collapse (asymmetric) to NS or BH

Continuous WavePulsarsLow mass X-ray binaries (e.g. SCO X1)Modes and Instabilities of Neutron Stars

StochasticInflationCosmic Strings

Gravitational Waves: possible sources


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Science goals of the gravitational wave field

Fundamental physics and GR

• What are the properties of gravitational waves?

• Is general relativity the correct theory of gravity?

• Is GR still valid under strong-gravity conditions?

• Are Nature’s black holes the black holes of GR?

• How does matter behave under extremes of

density and pressure?

Cosmology

• What is the history of the accelerating

expansion of the Universe?

• Were there phase transitions in the early

Universe?


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Astronomy and astrophysics• How abundant are stellar-mass black holes?

• What is the central engine that powers GRBs?

• Do intermediate mass black holes exist?

• Where and when do massive black holes form

and how are they connected to galaxy formation?

• What happens when a massive star collapses?

• Do spinning neutron stars emit gravitational waves?

• What is the distribution of white dwarf and

neutron star binaries in the galaxy?

• How massive can a neutron star be?

• What makes a pulsar glitch?

• What causes intense flashes of X- and gamma-

ray radiation in magnetars?

• What is the star formation history of the Universe?

Science goals of the gravitational wave field


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How can we detect them?

Gravitational wave amplitude h ~

L

L

L + L

L

Sensing the induced excitations of a large bar is one way to measure this

Field originated with J. Weber looking for the effect of strains in space on aluminium bars at room temperature

Claim of coincident events between detectors at Argonne Lab and Maryland – subsequently shown to be false


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VESF School on Gravitational Waves, Cascina May 25th - 29th 2009

How can we detect them?

Jim Hough andRon Drever, March 1978

L + L


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31 yrs on - Interferometric ground-based detectors


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laser

CONSTRUCTIVE(BRIGHT)

+

DESTRUCTIVE(DARK)

+

path 2p

ath

1

Michelson Interferometer

It’s all done with mirrors


15

Detecting gravitational waves

GW produces quadrupolar distortion of a ring of test particles

h 2L

LDimensionless strain

Expect movements ofless than 10-18 m over 4km


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Ground based Detector Network – audio frequency range

GEO600TAMA, CLIO

LIGO Livingston

LIGO Hanford

4 km2 km

600 m300 m100 m

P. Shawhan, LIGO-G0900080-v1

4 km

VIRGO 3 kmLIGO Livingston


Meudon, June 08

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State of the Universe: March 2010

Some key questions for cosmology:

• What is driving the cosmic acceleration?

• Why is 96% of the Universe ‘strange’ matter and energy?

• Is dark energy = Λ ?

• How, and when, did galaxies evolve?

• Big bang + inflation + gravity = LSS?


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State of the Universe: May 2010

From Kowalski et al (2008)

WMAP5

HSTKP

BAO: 2dFGRS+SDSS

SNIa: ‘union’ sample


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State of the Universe: March 2010

Some key questions for cosmology:

• What is driving the cosmic acceleration?

• Why is 96% of the Universe ‘strange’ matter and energy?

• Is dark energy = Λ ?

• How, and when, did galaxies evolve?

• Big bang + inflation + gravity = LSS?

What rôle could gravitational waves play in answering these questions?


Meudon, June 08

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Precision probe of relation on cosmological scales

zDL

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Gravitational Wave Sources as Cosmological Probes

Much recent interest in Following original idea in Schutz (1986);

‘Standard Sirens’ see also Cutler & Flanagan (1994)

time

ampl

itude

‘Chirping’ waveform

5/121

5/321 )(

mm

mmM

Measure

13/23/5 LDfMh

3/113/5 fMf

LDMffh ,,,

Chirp mass


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Much recent interest in ‘Standard Sirens’:

e.g. SMBHs at cosmological distances, for

which DL can in principle be determined to

exquisite accuracy.

Inspiral waveform strongly dependent on SMBH masses.

Since amplitude falls off linearly with (luminosity) distance, measured strain determines the distance of the source to high precision. Holz and Hughes 2005

Long tail due to parameter degeneracies



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What could we do with standard sirens?

• Completely independent, gravitational, calibration of the distance scale and the Hubble parameter

• Useful adjunct to existing constraints from CMBR, BAO, subject to completely different systematic errors.

• High precision probe of

• Extension of beyond the reach of SNIe and BAO.


)(zH

)(zw

Are these goals realistic?...


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Currently three major issues:

• Identification of E-M counterpart

• Impact of weak lensing

• Predicting merger event rates



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Determining source directions

Directions via 2 methods: AM & FM

FM: Frequency modulation due to orbital doppler shifts

Analogous to pulsar timing gives best resolution for f > 1 mHz

AM: Amplitude modulation due to change in orientation of array with respect to source over the LISA orbit

AM gives best resolution for f < 1 mHz

LISA will have sub-degree resolution for strong, SMBH sources

See e.g. Cutler (98), Hughes (02), Cornish &

Rubbo (03), Vecchio (04), Lang & Hughes (06)


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Identifying an E-M counterpart:

• GWs are redshifted, just like E-M radiation. Hence we determine (very precisely)

• If our goal is to probe e.g. how varies with we can assume and break the degeneracy. (See e.g. Hughes 02, Sesana et al. 07, 08)

)1( z

zDL z

• If we want to use sirens to measure , we must observe the E-M counterpart.

For this we need an accurate sky position!

zDL



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Lang & Hughes (2006) include spin-induced precession of the SMBHs

(See Vecchio 2004).

This significantly improves estimation of sky position and . LD

1z



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Lang & Hughes (2006) include spin-induced precession of the SMBHs

(See Vecchio 2004).

This significantly improves estimation of sky position and . LD

1z



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Lang & Hughes (2008) extend analysis to consider pre-merger evolution

Sky position error

ellipses shown at

28, 21, 14, 7, 4, 2,

1 and 0 days before

the merger.

Largest effect seen

during final day –

spin effects less

important earlier.

Similar analysis in

Kocsis et al (2007)



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So what exactly can we do with sirens?....

Adapted from Holz & Hughes (2005)



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So what exactly can we do with sirens?....


Adapted from Holz & Hughes (2005)


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GW sources will be (de-)magnified by weak lensing due to LSS.

Same effect as for SN

[ See e.g. Misner, Thorne &

Wheeler; Varvella et al (2004),

Takahashi (2006) ].

However, WL has much

greater impact for sirens,

because of their much

smaller intrinsic scatter.

Weak lensing may also limit identification of E-M counterpart



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Correcting for weak lensing?...

Weak lensing by intervening large-scale structure distorts images of background galaxies

Following Refregier 2003

Distortion matrix:

Convergence Shear

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• Observed siren brightness increased by magnification

• What can we expect?

• Can measure from shear maps derived from simulations

• Typically at

which means ~5% error in

• Could we correct individual sirens by mapping on small angular scales?

1.0~ 2z

LD


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• Dalal et al (2003) concluded cosmic shear maps too noisy on sub-arcminute scales.

Unlensed Lensed


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• Dalal et al (2003) concluded cosmic shear maps too noisy on sub-arcminute scales.

• Following Bacon (2008):

→ 3.8% at

• Templating? Jönsson et al (2006)

Find galaxies near to line of sight to siren. ‘Pin’ on realistic DM halos. → 2.5%

But what about ‘dark’ halos?...Systematics?...

Unlensed LensedLD 2z

LD


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• Shapiro et al (2009): Shear varies from place to place.

Gradient of shear → arcing, or flexion

see e.g. Bacon (2005)

• Can measure flexion from galaxy survey, giving better estimate of

matter density on small angular scales. → 1.8% at

→ 1.4% at

LD 2z

LD 1z


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• Shapiro et al (2009): Shear varies from place to place.

Gradient of shear → arcing, or flexion



→ 1.4% at


LD 2z

LDMajor ‘multimessenger’ challenge 1z


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No correction

Shear map only, ELT

Shear + flexion, ELT Shear + flexion,

ELT + Space



→ 1.4% at

LD 2z

LD 1zMajor ‘multimessenger’ challenge

EUCLID

EELT


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Dalal et al. (2006):

Short-duration GRBS, due to NS-NS mergers, will also be observed by ALIGO network.

What could be done from the ground?

First optical observation of a NS-NS merger?

GRB 080503 (Perley et al 2008)


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Dalal et al. (2006):

Short-duration GRBS, due to NS-NS mergers, will also be observed by ALIGO network.

Beaming of GRBs (blue curves), aligned with GW emission, could boost GW SNR.

All-sky monitoring of GRBs + 1 year operation of ALIGO network

H0 to ~2% ?



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Nissanke et al. (2009):

Very thorough treatment.

Considers impact of:

• siren true distance;

• no. of detectors in network;

Identifies strong degeneracy between distance and inclination.

Need E-M observations / beaming assumption to break this?

to 10 – 30% at 600 Mpc (NS-NS); 1400 Mpc (NS-BH).

Competitive with traditional ‘distance ladder’; probe of peculiar velocities?


LD


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Third Generation Network — Incorporating Low Frequency Detectors

Third-generation underground facilities are aimed at having excellent sensitivity from ~1 Hz to ~104 Hz.

This will greatly expand the new frontier of gravitational wave astrophysics.

Recently begun:

Three year-long European design study, with EU funding, underway for a 3rd-generation gravitational wave facility, the Einstein Telescope (ET).

Goal: 100 times better sensitivity than first generation instruments.

Looking ahead to the Einstein Telescope…


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Third Generation Network — Incorporating Low Frequency Detectors

Third-generation underground facilities are aimed at having excellent sensitivity from ~1 Hz to ~104 Hz.

This will greatly expand the new frontier of gravitational wave astrophysics.

Recently begun:

Three year-long European design study, with EU funding, underway for a 3rd-generation gravitational wave facility, the Einstein Telescope (ET).

Goal: 100 times better sensitivity than first generation instruments.



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Fit , ,


Sathyaprakash et al. (2009):

~106 NS-NS mergers observed by ET. Assume that E-M counterparts observed for ~1000 GRBs, 0 < z < 2.

Weak lensing De-lensed

Competitive with ‘traditional’ methods


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…And even further ahead to BBO…

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Cutler and Holz (2009):

~3 x 105 sirens observed, with unique E-M counterparts, for 0 < z < 5.


BBO schematic

Extremely good angular resolution, even at z = 5!

Robust E-M identification of host galaxy, for determining redshift


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Cutler and Holz (2009):

~3 x 105 sirens observed, with unique E-M counterparts, for 0 < z < 5.


Simulated Hubble diagram, including effects of lensing


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Hubble constant to ~0.1%

w0 to ~1%, wa to ~10%


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Hubble constant to ~0.1%

w0 to ~1%, wa to ~10%All of this lies far ahead, but the key is to work on

development of the science case now


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Opening a new window on the Universe


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Gravitational Waves????

Opening a new window on the Universe


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Delensing Gravitational Wave Standard Sirens

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