Keith Riles University of Michigan

To Catch a Wave – The Hunt for Gravitational Radiation with LIGO

REU seminar

June 24, 2013

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Outline

Nature & Generation of Gravitational Waves

Detecting Gravitational Waves with the LIGO Detector

Data Runs and Results to Date

Looking Ahead – Advanced LIGO

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Gravitational Waves = “Ripples in space-time”

Perturbation propagation similar to light (obeys same wave equation!) Propagation speed = c Two transverse polarizations - quadrupolar: + and x

Amplitude parameterized by (tiny) dimensionless strain h: ΔL ~ h(t) x L

Nature of Gravitational Waves

Example:

Ring of test masses

responding to wave

propagating along z

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Why look for Gravitational Radiation?

Because it’s there! (presumably)

Test General Relativity: Quadrupolar radiation? Travels at speed of light? Unique probe of strong-field gravity

Gain different view of Universe: Sources cannot be obscured by dust Detectable sources some of the most interesting,

least understood in the Universe Opens up entirely new non-electromagnetic spectrum

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What will the sky look like?

Has BICEP-2 seen fossil GWs?

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Generation of Gravitational Waves

Radiation generated by quadrupolar mass movements:

(with I = quadrupole tensor, r = source distance)

Example: Pair of 1.4 Msolar neutron stars in circular orbit of radius 20 km (imminent coalescence) at orbital frequency 400 Hz gives 800 Hz radiation of amplitude:

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Generation of Gravitational Waves Strong indirect evidence for GW generation:

Taylor-Hulse Pulsar System (PSR1913+16)Two neutron stars (one=pulsar)

in elliptical 8-hour orbitMeasured periastron advance

quadratic in time in agreement with

absolute GR prediction

Orbit decay due to GW energy loss

17 / sec

~ 8 hr

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Generation of Gravitational Waves

Can we detect this radiation directly?

NO - freq too low

Must wait ~300 My for characteristic “chirp”:

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What makes Gravitational Waves?

• Compact binary inspiral: “chirps”– NS-NS waveforms are well described– Recent progress on BH-BH waveforms

• Supernovae / GRBs: “bursts” – burst signals in coincidence with signals in electromagnetic

radiation / neutrinos– all-sky untriggered searches too

• Pulsars in our galaxy: “periodic”– search for observed neutron stars – all-sky search (computing challenge)

• Cosmological Signals “stochastic background”

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Generation of Gravitational Waves

Most promising periodic source: Rotating Neutron Stars (e.g., pulsar)

Poloidal ellipticity (natural) + wobble angle (precessing star):

h α εpol x Θwobble

(precession due to different L and Ω axes)

Need an asymmetry or perturbation:

Equatorial ellipticity (e.g., – mm-high “mountain”):

h α εequat

But axisymmetric object rotating about symmetry axis

Generates NO radiation

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Periodic Sources

Serious technical difficulty: Doppler frequency shifts Frequency modulation from earth’s rotation (v/c ~ 10-6) Frequency modulation from earth’s orbital motion (v/c ~ 10-4)

Additional, related complications: Daily amplitude modulation of antenna pattern Spin-down of source Orbital motion of sources in binary systems

Modulations / drifts complicate analysis enormously: Simple Fourier transform inadequate Every sky direction requires different demodulation

All-sky survey at full sensitivity = Formidable challenge

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Periodic Sources of GW

But two substantial benefits from modulations: Reality of signal confirmed by need for corrections Corrections give precise direction of source

Difficult to detect spinning neutron stars!

But search is nonetheless intriguing:

Unknown number of electromagnetically quiet, undiscovered

neutron stars in our galactic neighborhood

Realistic values for ε unknown

A nearby source could be buried in the data, waiting for just the

right algorithm to tease it into view

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Outline

Nature & Generation of Gravitational Waves

Detecting Gravitational Waves with the LIGO Detector

Data Runs and Results to Date

Preparing for Advanced LIGO

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Gravitational Wave Detection

Suspended Interferometers (IFO’s)

Suspended mirrors in “free-fall”

Michelson IFO is

“natural” GW detector

Broad-band response

(~50 Hz to few kHz)

Waveform information

(e.g., chirp reconstruction)

Top view

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The Global Interferometer NetworkThe three (two) LIGO, Virgo and GEO interferometers are part of a Global Network.

Multiple signal detections will increase detection confidence and provide better precision on source locations and wave polarizations

LIGO GEO Virgo

KAGRAH1, H2

G1L1

K1

V1

LIGO – India (approved)

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LIGO Observatories

Livingston

Hanford

Observation of nearly simultaneous signals 3000 km apart rules out terrestrial artifacts

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LIGO Detector Facilities

Vacuum System

•Stainless-steel tubes

(1.24 m diameter, ~10-8 torr)

•Gate valves for optics isolation

•Protected by concrete enclosure

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LIGO Detector Facilities

LASER Infrared (1064 nm, 10-W) Nd-YAG laser from Lightwave (now commercial product!) Elaborate intensity & frequency stabilization system, including feedback from main

interferometer

Optics Fused silica (high-Q, low-absorption, 1 nm surface rms, 25-cm diameter) Suspended by single steel wire Actuation of alignment / position via magnets & coils

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LIGO Detector Facilities

Seismic Isolation Multi-stage (mass & springs) optical table support gives 106 suppression Pendulum suspension gives additional 1 / f 2 suppression above ~1 Hz

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100

10-2

10-4

10-6

10-8

10-10

Horizontal

Vertical

10-6

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What Limits the Sensitivityof the Interferometers?

• Seismic noise & vibration limit at low frequencies

• Atomic vibrations (Thermal Noise) inside components limit at mid frequencies

• Quantum nature of light (Shot Noise) limits at high frequencies

• Myriad details of the lasers, electronics, etc., can make problems above these levels

Best design sensitivity:

~ 3 x 10-23 Hz-1/2 @ 150 Hz

achieved

< 2 x 10-23

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The road to design sensitivity at Hanford…

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Harder road at Livingston…

Livingston Observatory located in pine forest popular with pulp wood cutters

Spiky noise (e.g. falling trees) in 1-3 Hz band creates dynamic range problem for arm cavity control

40% livetime

Solution:Retrofit with active feed-forward isolation system (using technology developed for Advanced LIGO)

Fixed

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LIGO Scientific CollaborationAustralian Consortiumfor InterferometricGravitational AstronomyThe Univ. of AdelaideAndrews UniversityThe Australian National Univ.The University of BirminghamCalifornia Inst. of TechnologyCardiff UniversityCarleton CollegeCharles Sturt Univ.Columbia UniversityEmbry Riddle Aeronautical Univ.Eötvös Loránd UniversityUniversity of FloridaGerman/British Collaboration forthe Detection of Gravitational WavesUniversity of GlasgowGoddard Space Flight CenterLeibniz Universität HannoverHobart & William Smith CollegesInst. of Applied Physics of the Russian Academy of SciencesPolish Academy of SciencesIndia Inter-University Centrefor Astronomy and AstrophysicsLouisiana State UniversityLouisiana Tech UniversityLoyola University New OrleansUniversity of MarylandMax Planck Institute for Gravitational Physics

University of MichiganUniversity of MinnesotaThe University of MississippiMassachusetts Inst. of TechnologyMonash UniversityMontana State UniversityMoscow State UniversityNational Astronomical Observatory of JapanNorthwestern UniversityUniversity of OregonPennsylvania State UniversityRochester Inst. of TechnologyRutherford Appleton LabUniversity of RochesterSan Jose State UniversityUniv. of Sannio at Benevento, and Univ. of SalernoUniversity of SheffieldUniversity of SouthamptonSoutheastern Louisiana Univ.Southern Univ. and A&M CollegeStanford UniversityUniversity of StrathclydeSyracuse UniversityUniv. of Texas at AustinUniv. of Texas at BrownsvilleTrinity UniversityUniversitat de les Illes BalearsUniv. of Massachusetts AmherstUniversity of Western AustraliaUniv. of Wisconsin-MilwaukeeWashington State UniversityUniversity of Washington

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Michigan LIGO Group MembersOld fogeys:

Dick Gustafson, Keith Riles

Graduate students:

Santiago Caride, Grant Meadors, Jaclyn Sanders

Undergraduates / high school students:

Weigang Liu, Daniel Mantica, Pranav Rao, Curtis Rau / David Groden

Graduated Ph.D. students:

Dave Chin (now medical physicist)

Vladimir Dergachev* (now postdoc at Caltech)

Evan Goetz* (now postdoc at Albert Einstein Institute – Hanover, Germany)

Former undergraduates:

Jamie Rollins* (Caltech postdoc) Alistair Hayden (Boston U.)

Joseph Marsano (Chicago postdoc) Michael La Marca (Arizona State G.S.)

Jake Slutsky* (A.E.I. postdoc) Phil Szepietowski (U. Virginia postdoc)

Tim Bodiya* (MIT G.S.) Courtney Jarman (Wisconsin G.S.)

Ramon Armen (industry) Alex Nitz* (Syracuse G.S.)

*Continued GW research after graduating

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Michigan Group – Main Efforts

Search for Periodic Sources (rotating neutron stars)

Riles, Caride, Meadors, Sanders, Liu, Mantica, Rao

Detector Characterization (instrumentation, software)

Riles, Gustafson, Caride, Meadors, Liu, Groden

Commissioning & Noise Reduction

Gustafson, Meadors, Sanders (when in residence at Hanford)

Controls System Development

Gustafson

Public Outreach

Riles, Meadors, Rau

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LIGO Scientific CollaborationAustralian Consortiumfor InterferometricGravitational AstronomyThe Univ. of AdelaideAndrews UniversityThe Australian National Univ.The University of BirminghamCalifornia Inst. of TechnologyCardiff UniversityCarleton CollegeCharles Sturt Univ.Columbia UniversityEmbry Riddle Aeronautical Univ.Eötvös Loránd UniversityUniversity of FloridaGerman/British Collaboration forthe Detection of Gravitational WavesUniversity of GlasgowGoddard Space Flight CenterLeibniz Universität HannoverHobart & William Smith CollegesInst. of Applied Physics of the Russian Academy of SciencesPolish Academy of SciencesIndia Inter-University Centrefor Astronomy and AstrophysicsLouisiana State UniversityLouisiana Tech UniversityLoyola University New OrleansUniversity of MarylandMax Planck Institute for Gravitational Physics

University of MichiganUniversity of MinnesotaThe University of MississippiMassachusetts Inst. of TechnologyMonash UniversityMontana State UniversityMoscow State UniversityNational Astronomical Observatory of JapanNorthwestern UniversityUniversity of OregonPennsylvania State UniversityRochester Inst. of TechnologyRutherford Appleton LabUniversity of RochesterSan Jose State UniversityUniv. of Sannio at Benevento, and Univ. of SalernoUniversity of SheffieldUniversity of SouthamptonSoutheastern Louisiana Univ.Southern Univ. and A&M CollegeStanford UniversityUniversity of StrathclydeSyracuse UniversityUniv. of Texas at AustinUniv. of Texas at BrownsvilleTrinity UniversityUniversitat de les Illes BalearsUniv. of Massachusetts AmherstUniversity of Western AustraliaUniv. of Wisconsin-MilwaukeeWashington State UniversityUniversity of Washington

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GEO600

Work closely with the GEO600 Experiment (Germany / UK / Spain)

• Arrange coincidence data runs when commissioning schedules permit

• GEO members are full members of the LIGO Scientific Collaboration

• Data exchange and strong collaboration in analysis now routine

• Major partners in proposed Advanced LIGO upgrade

600-meter Michelson Interferometer just outside Hannover, Germany

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Virgo

Have begun collaborating with Virgo colleagues (Italy/France)

Took data in coincidence for parts of last two science runs

Data exchange and joint analysis

Will coordinate closely on detector upgrades and future data taking3-km Michelson Interferometer just outside Pisa, Italy

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Outline

Nature & Generation of Gravitational Waves

Detecting Gravitational Waves with the LIGO Detector

Data Runs and (small sampling of ) Results to Date

Looking Ahead – Advanced LIGO

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Data Runs

S1 run: 17 days (Aug / Sept 2002) – Rough but good practice

Have carried out a series of Engineering Runs (E1–E14) and Science Runs (S1—S6) interspersed with commissioning & upgrades

S2 run: 59 days (Feb—April 2003) – Many good results

S3 run:

70 days (Oct 2003 – Jan 2004) -- Ragged S4 run:

30 days (Feb—March 2005) – Another good runS5 run:

23 months (Nov 2005 – Sept 2007) – Great!

S6 run:

“16” months (Jul 2009 – Oct 2010) – Better sensitivity but uneven

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hrms = 3 10-22

S1 S5 Sensitivities

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Factor of 2 improvement above 300 Hz

“Enhanced LIGO” (July 2009 – Oct 2010)

S5

S6

Displacement spectral noise

density

Searching for Gravity Waves

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Binary Inspirals Continuous waves (NS-NS, NS-BH, BH-BH) (Spinning NS)

Bursts Stochastic background (Supernovae, “mergers”) (Cosmological, astrophysical)

Long-LivedShort-Lived

Known waveform

Unknown waveform

Spinning black-hole / SGR ringdowns Young pulsars high-mass inspirals (glitchy)

Today

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Crab Pulsar

Upper limits on GW strain amplitude h0

Single-template, uniform prior: 3.4 × 10–25

Single-template, restricted prior: 2.7 × 10–25

Multi-template, uniform prior: 1.7 × 10–24

Multi-template, restricted prior: 1.3 × 10–24

Ch

and

ra im

age

Mo

de

l

Searching for continuous wavesSearching for continuous waves

Implies that GW emission accountsfor ≤ 4% of totalspin-down power

Ap. J. Lett 683 (2008) 45

Use coherent, 9-month, time-domain matched filterStrain amplitude h0

Bayesian PDF

Searching for continuous wavesSearching for continuous waves

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Same algorithm applied to 195 known pulsars over LIGO S5/S6 and Virgo VSR2/VSR4 data

Lowest upper limit on strain:

h0 < 2.1 × 10−26

Lowest upper limit on ellipticity:

ε < 6.7 × 10-8

Crab limit at 1% of total energy loss

Vela limit at 10% of total energy loss

arXiv:1309.4027 (Sept 2013)

All-sky search for unknown isolated neutron stars

Semi-coherent, stacks of 30-minute, demodulated power spectra

(“PowerFlux”)

Linearly polarized

Circularly polarized

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Searching for continuous wavesSearching for continuous waves

Phys. Rev. Lett. 102 (2009) 111102

Carried out by Michigan graduate student Vladimir Dergachev (now at Caltech)

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Latest full-S5 all-sky results Semi-coherent, stacks of 30-minute, demodulated power spectra (“PowerFlux”)

Astrophysical reach

Recent resultsRecent results

Phys. Rev. D85 (2012) 022001

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First all-sky search for unknown binary CW sourcesUses TwoSpect* algorithm:

*E. Goetz & K. Riles, CQG 28 (2011) 215006

Sample spectrogram (30-minute FFTs) for simulated strong signal (Earth’s motion already demodulated)

Result of Fourier transforming each row of spectrogram

Concentrates power in orbital harmonics

Searching for continuous wavesSearching for continuous waves

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Initial search uses 30-minute FFTs Favors longer orbital periods:

Search is severely computationally bound

Upper limits based on summing power in harmonics

Templates used only in follow-up

Not so limited in directed searches, e.g., for Scorpius X-1

Period (hr)

Mo

d. D

epth

(H

z)

Searching for continuous wavesSearching for continuous waves

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GEO-600 Hannover LIGO Hanford LIGO Livingston Current search

point Current search

coordinates Known pulsars Known supernovae

remnants

http://www.einsteinathome.org/

Your computer can help

too!

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Outline

Nature & Generation of Gravitational Waves

Detecting Gravitational Waves with the LIGO Detector

Data Runs and Results to Date

Looking Ahead – Advanced LIGO

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Looking Ahead

Both LIGO and Virgo underwent significant upgrades since first joint science run (S5/VSR1):

Initial LIGO “Enhanced LIGO”

Initial Virgo “Virgo +”

LIGO schedule: S6 data run July 2009 – October 2010 Began Advanced LIGO installation October 2010

Aim for first data run fall (summer?) 2015

Virgo schedule: VSR2/3 data runs July 2009 – October 2010 Virgo+ upgrade ongoing

VSR4 data run – Summer 2011 Began Advanced Virgo installation fall 2011

On schedule for 2016 data run

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Advanced LIGO

Increased test mass:

10 kg 40 kg

Compensates increased radiation pressure noise

Increased laser power:

10 W 200 W

Improved shot noise (high freq)

Higher-Q test mass:

Fused silica with better optical coatings

Lower internal thermal noise in band

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Advanced LIGO

New suspensions:

Single Quadruple pendulum

Lower suspensions thermal noise in bandwidth

Improved seismic isolation:

Passive Active

Lowers seismic “wall” to ~10 Hz

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Neutron Star Binaries:Average range ~ 200 Mpc Most likely rate ~ 40/year

The science from the first 3 hours of Advanced LIGO should be comparable to 1 year of initial LIGO

Advanced LIGO

(Range x ~10 Volume x ~1000)

But that sensitivity will not be achieved instantly…

arXiv: 1304.0670

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SummaryBottom line:

No GW signal detected yet

But

• Not all S5-6 VSR1-4 searches completed

• Advanced LIGO / Virgo will bring major sensitivity improvements with orders of magnitude increase in expected event rates

Extra Slides

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LIGO Interferometer Optical Scheme

end test mass

LASER/MC

6W

recyclingmirror

•Recycling mirror matches losses, enhances effective power by ~ 50x

150 W

20000 W(~0.5W)

Michelson interferometer

4 km Fabry-Perot cavity

With Fabry-Perot arm cavities

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Generation of Gravitational Waves

Coalescence rate estimates based on two methods: Use known NS/NS binaries in our galaxy (three!) A priori calculation from stellar and binary system evolution

Will need Advanced LIGO to ensure detection

For initial LIGO design “seeing distance” (~15 Mpc):

Expect 1/(70 y) to 1/(4 y)

Large uncertainties!

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Generation of Gravitational Waves

Examples of SN waveforms

Tony Mezzacappa -- Oak Ridge National Laboratory

Super-novae (requires asymmetry in explosions)

May not know exactly what to look for – must be open-minded with diverse algorithms

LIGO

Livingston, Louisiana & Hanford, Washington

2 x 4000-m

(1 x 2000-m)

Completed 2-year data run at design sensitivity –

“enhanced” – running again

VIRGO

Near Pisa, Italy1 x 3000-m

Took ~4 months coincident data with LIGO – near design sensitivity - running

GEO

Near Hannover, Germany 1 x 600-mTook data during L-V downtime, undergoing

upgrade

TAMA

Tokyo, Japan 1 x 300-mUsed for R&D aimed at

future underground detector

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Major Interferometers world-wide

Use calculated templates for inspiral phase (“chirp”) with optimal filtering.

Search for systems with different masses: Binary neutron stars (~1-3 solar masses):

~15 sec templates, 1400 Hz end freq Binary black holes (< ~30 solar masses):

shorter templates, lower end freq Primordial black holes (<1 solar mass):

longer templates, higher end freq

Search for binary systemsSearch for binary systems

John Rowe, CSIRO

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Searching for binariesSearching for binaries

Use two or more detectors: search for double or triple coincident “triggers” Can infer masses and “effective” distance. Estimate inverse false alarm probability of resulting candidates: detection?

John Rowe, CSIRO

S5 Year 1 Search for “Low-Mass” Inspirals

Blue – CoincidentGray – Time lag

Triple Double Double

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Searching for binariesSearching for binaries

No evidence of excess Use detection efficiency and surveyed galaxies Set upper limit vs stellar mass

Phys. Rev. D 79 (2009) 122001

John Rowe, CSIRO

BH-BH NS-BH

L10 = 1010 × blue solar luminosityMilky Way = 1.7 L10

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GRB 070201

Short, hard gamma-ray burst A leading model for short GRBs:

binary merger involving aneutron star

Position (from IPN) consistent with being in M31 (Andromeda)

LIGO H1 and H2 were operating

Result from (several) LIGO searches:No plausible GW signal found;therefore very unlikely to befrom a binary merger in M31

Ap. J. 681 (2008) 1419

Likely was SGR giant flare in M31

Searching for burstsSearching for bursts

IPN 3-sigma error region from Mazets et al., ApJ 680, 545

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Searching for bursts Searching for bursts (untriggered)(untriggered)

hRSS

S5 Year 1 Search for Untriggered Bursts

Sampling of efficiency curves:

Search for double or triple coincident triggers (three algorithms) Check waveform consistency among interferometers – apply vetoes Set a threshold for detection for low false alarm probability Evaluate efficiency for variety of simple waveforms

2 2 2(| ( ) | | ( ) | )RSSh h t h t dt

Parametrize strength in terms of “root sum square of h” : hRSS

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Searching for bursts Searching for bursts (untriggered)(untriggered)

Detected triggers and expected background for one algorithm (Coherent WaveBurst – wavelet-based) for triple-coincident triggers with fcentral > 200 Hz

Threshold

No candidates found above threshold in any of the searches Set upper limits on rate vs hRSS

Coherent network amplitude arXiv:0905.0020 (May 2009)

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A primordial isotropic GW stochastic background is predicted by most cosmological theories.

Given an energy density spectrum gw(f), there is a strain power spectrum:

The signal can be searched from cross-correlations in different pairs of detectors: L1-H1 and H1-H2.

The farther the detectors, the lower the frequencies that can be searched.

NASA, WMAP

Searching for a stochastic Searching for a stochastic backgroundbackground

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Early-S5 H1-L1 Bayesian 90% UL:

Ω90% = 6.9 × 10-6 (42-169 Hz)

Searching for a stochastic Searching for a stochastic backgroundbackground

NASA, WMAP

Nature 460 (2009) 990

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Other S5 Searches Other S5 Searches (released)(released)

Search for Gravitational Wave Bursts from Soft Gamma RepeatersPhys Rev Lett 101 (2008) 211102 Search for High Frequency Gravitational Wave Bursts in the First Calendar Year of LIGO's Fifth Science Run arXiv:0904.4910

Stacked Search for Gravitational Waves from the 2006 SGR 1900+14 StormarXiv:0905.0005

Search for Gravitational Waves from Low Mass Compact Binary Coalescence in 186 Days of LIGO's fifth Science Run arXiv:0905.3710

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Other S5 Other S5 (S6) (S6) Searches Underway Searches Underway (planned)(planned)

Inspirals:High-mass, spinning black holesYear 2, joint LIGO-VirgoRingdownsGRBs

Bursts:Year 2, Joint LIGO-VirgoGRBs

Continuous wave:Full-S5 all-sky searches (semi-coherent, Einstein@Home)Directed searches (Cassiopeia A, globular clusters, galactic center, SN1987A)“Transient CW” sourcesAll-sky binary – Evan Goetz Ph.D. dissertation – this year

Stochastic:Full-S5 isotropic – imminentDirected (anisotropic)H1-H2 High-frequency (37 kHz – LIGO arm free spectral range)