search for gravitational wave transientsmoriond.in2p3.fr/j11/transparents/robinet.pdf · search for...

Search for Gravitational Wave Transients

Florent RobinetOn behalf of the LSC and Virgo Collaborations

Rencontres de Moriond - March 2011 1

Gravitational WavesGravitational Waves

Black hole merger

Gravitational wavesGravitational waves = "ripples" in spacetime = "ripples" in spacetime

Weak field approximation :Weak field approximation :

Wave equation, speed Wave equation, speed cc

Solution with 2 d.o.f. : Solution with 2 d.o.f. :

Dimensionless amplitude given by Dimensionless amplitude given by hh

Signal strength:Signal strength:

Production of gravitational waves

A good GW source : is compact and massive is asymmetric has a relativistic speed

c5

G

2R s

R 2

vc 6

ℒ =

Lab production : Lab production : h ~ 10 h ~ 10 – 39– 39

Astrophysical sources : Astrophysical sources : h ~ 10 h ~ 10 – 21– 21

g=h ∣h∣≪1

Rencontres de Moriond - March 2011 2 Florent Robinet

h= h+hx

hrss=∫-∞

+∞∣h+t ∣

2∣hx t ∣

2dt

Gravitational Wave SourcesGravitational Wave Sources


?

Pulsars(asymmetric rotations, instabilities)

Compact binary coalescence of neutron stars &/or black holes

Supernovae(asymmetric core bounce)

Cosmic strings

Stochastic background

The unexpected

A Network of DetectorsA Network of Detectors

Virgo (3 km)

Geo (600 m)

Livingston (4 km)

Hanford (4&2 km)

LSC – Virgo collaboration– Full data sharing since May 2007– Common analyses and papers– Common tools



tLivingston

tHanford

tHanford

tVirgo

SOURCE

SOURCE POINTING● Source location within ~ tens of square degrees● Serious candidates followup (EM, neutrinos...)

GHOST




Hanford sky coverage – Antenna pattern



Livingstone sky coverage – Antenna pattern



Virgo sky coverage – Antenna pattern



Network sky coverage – Antenna pattern

LIGO / Virgo Science RunsLIGO / Virgo Science Runs


2005 2006 2007 2008 2009 2010 2011 2012

S4 S5 S6

VSR2VSR1 VSR3 VSR4?

AdvancedDetectors

Many Publications Analyses in progressPublications in preparation

com

mis

sion

ing

LIGO / Virgo Science RunsLIGO / Virgo Science Runs


S5 - VSR1

S6 - VSR2

Analysis GroupsAnalysis Groups

Compact Binary Coalescence(CBC)

Short Signals(Bursts)

Continuous Waves Stochastic

?


See C. Palomba's talk

Analysis GroupsAnalysis Groups

Compact Binary Coalescence(CBC)

Short Signals (Bursts)

?

All sky

GRB-triggered

SGR Flares

EM Follow-upBinary Mergers

PulsarsGlitches

Supernovae

Multi-MessengerAstronomy

Low Mass High Mass

Inspiral-Merger-Ringdown (IMR)

ParameterEstimation

Cosmic Strings

Rencontres de Moriond - March 2011 Florent Robinet

CBC vs. BurstsCBC vs. Bursts


Compact Binary Coalescence (CBC)

The Signals● Modeled signals● Inspiral – Merger – Ringdown

The search● Template search (selective)● Waveform parameter estimation

Science goals● Detection● Upper limits on GW emission● Multi-messenger (EM, neutrino...)● Parameter estimation● Study gravity● Study populations● Study dense matter● Study GRBs

Burst Signals

The Signals● Short-duration signals (<1s)● Modeled and unmodeled signals● Large variety of sources

The search● Robust signal detection methods● Excess power (unmodeled)● Template search (modeled)

Science goals● Detection● Upper limits on GW emission● Multi-messenger (EM, neutrino...)● Parameter estimation● Star equation of state● Study populations

Analysis MethodsAnalysis Methods


Data Detector 1

Data Detector 2

Triggers

Triggers

Coincidence

Selection+

DataQuality

Significance?

Data stream

COINCIDENT PIPELINE



Data Detector 1

Data Detector 2

Triggers

Triggers

Coincidence

Selection+

DataQuality

Significancewrt

background

Data Detector 2time-shifted wrt 1 Data stream

Background stream

DETECTION?NO?→ Upper limits

COINCIDENT PIPELINE



Data Detector 1

Data Detector 2

Triggers

Triggers

Coincidence

Selection+

DataQuality

Significancewrt

background

Signal injections

Data Detector 2time-shifted wrt 1

Search efficiency

Data streamInjection streamBackground stream

DETECTION?

UPPER LIMITS

The number of detectors can be increased (up to 4) Various coincidence schemes: union of configurationsIncreasing the number of coincidences enables to be more selective (but less efficient)

COINCIDENT PIPELINE



Data Detector 1

Data Detector 2

TriggersCoherent combination

Selection+

DataQuality

Significancewrt

background

Signal injections

Data Detector 2time-shifted wrt 1

Search efficiency

Data streamInjection streamBackground stream

DETECTION?

UPPER LIMITS

The data of multiple detectors can be combined coherentlySky positions are scanned to take into account the time of arrival and the antenna pattern of each detectors

COHERENT PIPELINE

Analysis Methods: Template SearchesAnalysis Methods: Template Searches


Detector whitened Strain h(t)Noise + inspiral hardware injection

A template bank covering the parameter space is slid over the data

t ∝∫0

∞ h f f Shf

e−2i f t df

Signal-to-noise ratio time serie:

Template waveformSensitivity

An event is defined when Given by the background estimation(+ additional clustering in time and frequency)

t Threshold

This method is used for:

● CBC searches● Pulsar ringdown search● Cosmic string burst search

Sh

Analysis Methods: Excess Power SearchesAnalysis Methods: Excess Power Searches


Injected Inspiral Signal

The time-frequency plane is tiled with pixels

An event is defined when the energy of multiple pixels exceeds a given threshold

This method is used for:

● Most of the burst searches

Data QualityData Quality


The noise of the detector displays a non-Gaussian behavior

Transient glitches removal is crucial to improve the sensitivity of the searches

Noise understanding for each detector have been performed for each science run

Many glitch families have been understood

Specific vetoes based on auxiliary channels have been produced to remove specific glitch families

Veto safety have been carefully checked(we don't want to flag real signals!)

Example: Virgo, VSR2Deadtime ~ 10%Removal efficiency ~ 80% (SNR>8)

SNR10 100

Magnetic sensor

Detection channel

CBC SearchesCBC Searches


"Realistic" observable BNS coalescence rate ~ 0.02 per year (large uncertainty)

BNSBBHBHNS

S5/VSR1 data have been analyzed and results are published

S6/VSR2-3 analyses are in progressPreliminary results are releasedSee T. Dent's talk

CBC: Low Mass SearchCBC: Low Mass Search


Description of the search:

● Non-spinning templates● Post-Newtonian up to the innermost stable orbit● Mass region 2 < M

total < 35 M

sun

BNS/BBH Upper limits NS/BH Upper limits

No Detection

Phys. Rev. D 82(2010) 102001

http://prd.aps.org/abstract/PRD/v82/i10/e102001

CBC: High Mass SearchesCBC: High Mass Searches


High-Mass● Effective One Body (EOB) waveforms● Inspiral-Merger-Ringdown is covered● No spin● Mass region 25 < M

total < 100 M

sun

● Uncertainty on the waveforms● LIGO only search (Virgo is not sensitive enough for High mass systems)

Ringdown search ● In progress for S5● LIGO only search● Mass region

75 < MBH

< 750 Msun

● Spin is included● The ringdown contains most of the GW energy● More reliable waveforms

arXiv:1102.3781

http://arxiv.org/abs/1102.3781

CBC & Burst Signals: GRB Triggered SearchesCBC & Burst Signals: GRB Triggered Searches


Powerful bursts of highly energetic gamma raysTwo populations: short and long duration

Short: possibly produced by the merging of binary objects → CBC colored search

Long: possibly produced by violent stellar collapse (hypernovae)

Short-duration GRBsLong-duration GRBs

Use mainly Swift and Fermi triggers to get a source location a timing and sometimes a distance

Background reductionBetter sensitivity

During S5/VSR1 137 GRBs were analyzed by the burst coherent pipeline (short and long). See M. Was's talk

22 GRBs were analyzed by a CBC pipeline. See N. Christensen's talk

20Num

ber

of B

urst

s

40

60

0.1 1 10T90 (seconds)

CBC & Burst Signals: GRB Triggered SearchesCBC & Burst Signals: GRB Triggered Searches


GRB 070201

Short and hard GRB detected by 4 satellites in Feb. 2007 in direction of the Andromeda galaxy

The binary merger scenario is excluded with a 99% confidence level!

90%

75%

50%

25%

Inspiral Exclusion Zone

99%

Astrophys. J. 681(2008) 1419

http://www.iop.org/EJ/abstract/0004-637X/681/2/1419/

Burst Signals: All-Sky SearchBurst Signals: All-Sky Search


Description of the search● Multiple Algorithms● Broad-band frequency search● Coincident and coherent searches● Very large variety of waveforms● Robustness

Upper limit (sine-gaussian)

Rate (90% C.L.) vs. frequencyNo detection

With a 90% confidence level, the rate of burst signals with 50 < f < 2048 Hz is lower than 2 events per year

Phys. Rev. D 81(2010) 102001

~8e-7 yr-1 Mpc-3

1e-2 yr-1 Mpc-3

100 f(Hz) 1000

(EGW

= Msun

c2)

http://prd.aps.org/abstract/PRD/v81/i10/e102001

Burst Signals: Neutron StarsBurst Signals: Neutron Stars


2006/08/12: timing glitch observed in the radio emission of the Vela pulsar

Quasi-normal mode oscillations GW

Both Hanford detectors were up at that timeRingdown signal is searched → No detectionUpper limits on GW energy released by mono-harmonic modes

Phys. Rev. D83(2011) 042001

Soft Gamma Repeaters (SGR) / Anomalous X-ray Pulsars (AXP)

Neutron stars powered by extreme magnetic fields (magnetars)

6 magnetars have been analyzed by a dedicated pipeline (excess power)

SGR 1900+14SGR 0418+5729SGR 1627-41SGR 1806-20SGR 0501+4516AXP 1E 1547.0-4508

arXiv:1011.407946 52

http://link.aps.org/doi/10.1103/PhysRevD.83.042001

http://arxiv.org/abs/1011.4079

GW

GW

Burst Signals: Cosmic String CuspsBurst Signals: Cosmic String Cusps


When 2 cosmic string segments meet they can reconnect and produce loops. The main mechanism for the loop to loose its energy is to radiate gravitationally.

GW radiation is the most promising signature to detect cosmic strings.

Points of the string can acquire a large Lorentz boost and form a "cusp"→ GW burst

S4

S5 Projection

Well-modeled signalTemplate burst searchDedicated pipeline

Upper limits on the cosmic string parameter space:

Gμ: String tensionε: loop size parameterp: reconnection probability

GμPhys Rev D 80(2009) 062002 10 –610 –7

http://link.aps.org/doi/10.1103/PhysRevD.80.062002

Online SearchesOnline Searches

Rencontres de Moriond - March 2011 Florent Robinet

Low latency searches took place during S6 / VSR2-3 for both CBC and burst searches

Most significant events were sent to telescopes / satellites(14 events for S6/VSR2-3)

Sky localization is performed with a resolution of ~tens of square degrees for events at threshold

Image analysis is performed within the collaboration

See M. Branchesi's talk

Hanford Livingstone Virgo

Central Location

CBC pipelineMBTA

Burst pipelineOmega

Burst pipelineCoherent Waveburst

CandidateDatabase

Most significantCandidate selection

h(t) h(t) h(t)

h(t)h(t)h(t)

event event event

~ 30 min

Swift Zadko ROTSE

S6/VSR2-3 Science RunS6/VSR2-3 Science Run


Improved sensitivity

~ 200 days of live-time with at least 2 detectors up

Big challenge: run analyses online– 3 pipelines were running (2 bursts + 1 CBC)– The data quality was performed with low latency (< 1 min)– EM follow-up by partner telescopes

Offline analyses are in progress (some results are released)

Analyses pipelines and data quality tools have been improved for a better sensitivity

Blind hardware injection challenge was successful(we detected it with great confidence). See T. Dent's talk

Preparation for Advanced Detectors EraPreparation for Advanced Detectors Era


Sensitivity improvement by a factor 10

This translates into a detection rate up to 40 neutron star binary events per year

Science should resume in 2015Design sensitivity achieved by 2019

What are we going to do in the meantime ?

Virgo might run this summer (VSR4) along with the GEO detector Similar sensitivity at high frequencyThis run could be of some interest for external triggered searches

Then GEO will run alone in astrowatch mode during the construction of Adv. detectors (2012-2015)

Some mock data runs are planned to test and improve our searches

A lot of work is required to optimize the EM-followup procedures

Summary - ConclusionsSummary - Conclusions


A large variety of physical results have been produced from the LIGO-Virgo data

There is no detection yet but upper limits can be used to constrain astrophysical

models

The first generation of detectors is close to the end.

– Analysis pipeline have greatly improved over the last years to perform

optimized and sensitive searches on GW data

– Data quality is a great challenge. Multiple tools have been developed to reject

noise events efficiently.

– GW astronomy is on its way: online searches, Multi-messengers, EM followup

Now, the big challenge is to be fully ready for the Advanced Detectors Era

search for gravitational wave transientsmoriond.in2p3.fr/j11/transparents/robinet.pdf · search for...

Documents