Vuk Mandic for the LIGO Scientific Collaboration

University of Minnesota

10/03/12

Gravitational Wave Detectors in the Next Decade

Produced by accelerating mass distribution of quadrupole (or higher) moment. » Two polarizations: “plus” and “cross”.

Gravity is weak, have to look at most energetic events in the Universe.

Transient sources, typically 1-sec long (or less): » Compact binary coalescences » Bursts: transient emissions during Supernovae, GRBs…

Continuous sources: » Periodic sources: pulsars » Stochastic sources: cosmological and astrophysical

Unexpected?

Sources of Gravitational Waves

“+” “x”

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Gravitational wave effectively stretches one arm while compressing the other.

Interferometer measures the arm-length difference. » Suspended mirrors act as

“freely-falling”. In practice:

» Optical cavities in arms. » Power recycling. » Control of length and

angular degrees of freedom = hundreds of feedback loops.

Time

Interferometers as Gravitational Wave Detectors

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Network of Gravitational-Wave Detectors

Strain Sensitivities

LIGO reached design strain sensitivity in November 2005.

S5 science run: 2005-2007. Upgraded to Enhanced LIGO in

2007-2008. S6 science run: 2009-2010. Virgo reached similar strain

sensitivities on similar time-scales.

Significant coincident running with LIGO.

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Advanced Detector Era Network in 2015?

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Advanced LIGO

Keep the same facilities, but redesign all subsystems. » 10x better strain sensitivity

over the whole frequency range.

» ~1000x more sources! » Push down to 10 Hz.

Signal recycling:

» Allows tuning sensitivity for a particular frequency range.

Currently ~75% completed, expect

first data in 2014.

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Binary Neutron Star Merger Localization: Hanford-Livingston-Virgo-India-KAGRA

5 site network

S. Fairhurst, “Improved source localization with LIGO India”, arXiv:1205.6611v1

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Compact Binary Coalescences

Inspiral

Merger

Ringdown

Two neutron stars and/or black holes emit GWs as they inspiral, and merge.

R. Spero

Deep in this noise stream:

Search: optimal Wiener filtering with matched templates

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Binary Coalescence Searches

Predicted rates

Latest LIGO-Virgo upper limits

LIGO and Virgo Collaborations, Phys. Rev D85 (2012) 082002 10

Current Guess for BNS Sensitivity Evolution

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Bursts Many potential transient sources:

» Supernovae: probe the explosion mechanisms. » Gamma Ray Bursts: collapse of rapidly rotating

massive stars or neutron star mergers. » Pulsar glitches: accretion. » Cosmic strings cusps.

Models are ok, but not essential: » Search for power excess in the data. » Search for any short signal with measurable strain

signal.

Aspherical outflows

Anisotropic ν-flows Rotational instabilities

Convection

C. Ott 12

Long Transients

New category of sources. » Tens of seconds or longer. » Use cross-correlation technique.

Long GRBs (Piro & Pfahl): » In-falling material circularizes and

falls into the black hole via an accretion disk.

» Strong cooling from helium photodisintegration leads to disk fragmentation, and GWs.

Magnetars: » ~10% of neutron stars, strong

magnetic fields (1014 – 1016 G). » B-field/accretion can induce tri-

axial deformation – GWs.

A. Pyro 13

Searching for Power Excess

Typically look at the time-frequency maps. » Either power in one detector, or cross-power in two detectors.

Various pattern recognition algorithms search through maps. Require consistency between detectors.

ADI simulated signal added to real data.

ADI signal as recovered by the STAMP burst-cluster algorithm.

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Externally Triggered Burst Searches

Multi-messenger Astronomy » Use EM or neutrino observations to simplify the search.

Know when and where on the sky to look. » May even know what kind of signal to look for and how far it is.

Or, a GW trigger can be used to point telescopes. » Signed MOUs with a number of radio, optical, X-ray

telescopes, neutrino observatories... For example, observation of optical or X-ray afterglow could

indicate the host galaxy of a Supernova or a GRB. » Coincident GW observation could then provide additional

information about the source – such as the central engine of a short GRB.

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Short Gamma Ray Bursts (GRBs): intense flashes of gamma rays, lasting <2s. » Nearby: soft gamma-ray repeaters (SGRs). » Distant: neutron star and/or black hole

merger. GRB 070201 was observed in the direction of

Andromeda galaxy (M31) by several spacecraft (Konus-Wind, Integral, Messenger, Swift).

Two LHO detectors operational at the time. » Search -120/+60 sec around the GRB time. » No gravitational-wave candidate was found.

Inspiral search for compact binary merger (M⊙<m1<3M ⊙, M ⊙ <m2<40M ⊙): » In M31 (770 kpc) excluded at 99%

confidence. » Excluded at 90% confidence out to 3.5

Mpc. Un-modeled burst: SGR in M31 not excluded. IPN3 error box overlaps with M31

Externally Triggered Burst Searches

Astrop. J. 681, 1419 (2008)

Add up contributions from many GW sources throughout the universe: » Binary coalescences. » Magnetars. » Neutron star instabilities. » Core collapse.

Resulting energy density may be observed by the second-generation detectors.

Constrain model parameters: » Rate of binaries. » Equation of state in

neutron stars.

Stochastic Background

Catalog of models: http://homepages.spa.umn.edu/~gwplotter/

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Triggered searches for gamma-ray bursts

Data from LIGO S6 and Virgo VSR 2,3 Modeled search for NS-NS, NS-BH

coalescences » TaylorF2 3.5 PN order templates, [2,

40) M total mass range

Unmodeled search for GW bursts » Coherent network analysis (‘X-

pipeline’); time-frequency clustering 404 GRBs from Swift, Fermi, MAXI,

SuperAGILE, INTEGRAL Require 2 detectors in science mode

154 GRB triggers analyzed

LIGO Scientific and Virgo Collaborations, Briggs, et al., arXiv:1205.2216

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Advanced Virgo

Advanced Virgo will undergo similar improvements to Advanced LIGO: » More powerful laser. » Signal recycling. » Vacuum improvements.

Very similar sensitivity to Advanced LIGO.

Expected start similar to Advanced LIGO: 2014/2015.

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KAGRA

Recently, Japan funded the KAmioka GRAvitational-wave observatory (KAGRA).

Main characteristics: » Underground: Kamioka

mine, seismically quiet. » 3km long arms. » High-power laser. » Cryogenic mirrors. » Vibration-isolation

system. Similar sensitivity to

Advanced LIGO and Virgo. Expected start: ~2016?

Projected LCGT Sensitivity

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Einstein Telescope

EU funded a design study to define the scientific scope and conceptual design of a third-generation detector.

Xylophone concept: several detectors, focusing on different frequency bands.

10km arms, triangle configuration. Underground to improve on seismic

and Newtonian noise. Novel optical configurations,

squeezing, more powerful laser (500W).

Cryogenic mirrors, novel coatings, larger beams to reduce thermal noise. 23

Searches for GWs from nearby GRB sources

GRB050311, GRB070201: short GRBs with sky localizations that overlap nearby galaxies

» GRB050311 overlap with M81 (3.6 Mpc) » GRB070201 overlap with M31 (770 kpc)

Binary coalescence in M31 excluded at >99% confidence level

Binary coalescence in M81 excluded at 98% confidence level

M81 GRB 051103

M31, GRB 070201

LIGO Scientific Collaboration, K. Hurley, Astrophys. J. 681 (2008) 1419 LIGO Scientific Collaboration, arXiv:1201.4413

GRB051103

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