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Goals and status of the burst searches

Antony SearleLIGO Lab, Caltech

November 2008

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Outline

• Scientific motivation• Science goals• Data in hand• Recent results• Status of S5 analyses• Plans for S6 analyses

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Gravitational wave bursts

• Short-lived signals, lasting only a few cycles within the frequency band of the instruments

» Typically from few milliseconds to few seconds and with 100-few kHz frequency content

» Unknown or poorly known waveforms

• Sources» Core-collapse supernova» Merger phase of binary compact

objects» Neutron star instabilities» Cosmic string cusps and kinks» The unexpected!

• Need to make minimal assumptions about the candidate signal

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Dimmelmeier et al., astro-ph/0702305

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Burst search goals

• Direct detection of gravitational wave bursts from astrophysical sources

• Set upper limits on the rate and energy of gravitational wave bursts

• “Eyes wide open” or “untriggered” searches» Minimal assumptions about their waveform details» Search the whole sky and all times with collected data

• “Directed” or “triggered” searches guided by astronomical observations in the electromagnetic spectrum » Search around the directions and approximate times of Gamma-Ray

Bursts (GRBs) and Soft Gamma Repeaters (SGRs)

• Low-latency analysis of data to:» To provide detector characterization input» To allow electromagnetic follow-ups of candidates

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What data do we have in hand?

• LIGO-GEO (LSC) Fifth Science Run (S5)» Nov 4, 2005 – Oct 1, 2007» >365 days of 3-instrument coincidences» >400 days of 2-site coincidences

• Virgo Science Run 1 (VSR1)» May 18, 2007 – Oct 1, 2007» >75 days of 3-site coincidences» >95 days of 2-site coincidences

• LSC-Virgo started data-sharing on May 18, 2007» All data collected by the instruments after that day are being

analyzed jointly

• Instruments at or close to their design sensitivities

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Instrument sensitivities

Traditional burst searches

High frequency searches

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Burst group publications in 2008• Search for Gravitational Waves Associated with 39 Gamma-Ray

Bursts Using data from the Second, Third, and Fourth LIGO Runs Phys. Rev. D 77 (2008) 062004

• A Joint Search for Gravitational Wave Bursts with AURIGA and LIGO Class. Quantum Grav. 25 (2008) 095004

» S3; first transient joint search with a bar detector

• First joint search for gravitational-wave bursts in LIGO and GEO600 data (to appear in CQG) arXiv:0807.2834

» S4; first three-site coherent network analysis

• Implications for the Origin of GRB 070201 from LIGO Observations Astrophys. J. 681 (2008) 1419 (jointly with Inspiral group)

» S5; confidently excluded an inspiral in M31 (Andromeda) as the source

• Search for Gravitational Wave Bursts from Soft Gamma Repeaters (to appear in PRL) arXiv:0808.2050

» S5 externally triggered search; constrained some SGR models

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Burst searches in a nutshell

• Is the multi-interferometer response consistent with a plane gravitational wave?

» For two sites:» Times of arrival must be less than light travel times between different sites» Frequencies (or other basis parameters) must be consistent (coincident

analysis)» For three or more sites: » Times of arrival must determine a physical direction» Phases and amplitudes must be consistent with instrument responses for that

direction (coherent analysis)

• What is the background?» Time-shift the data so these properties of gravitational waves are violated,

producing O(100) signal-free datasets to assess the significance of an observation in the unshifted “zero lag” data

• What is the sensitivity?» Add a variety of simulated signals into the time-shifted datasets and measure

the efficiency with which they are recovered

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Main burst searches on S5/VSR1

• Untriggered all-sky all time» “Low” frequency (64-2048 Hz)» “High” frequency (1024-6500

Hz)

• Electromagnetically triggered» Gamma-Ray Bursts» Soft Gamma Repeaters

• Broken into two epochs» S5 Year 1» S5 Year 2 / VSR2

• Most are nearing completion

• GEO is used as a follow-up instrument

• Multi-methods approach» Including coherent

network techniques

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S5 data quality and vetoes

From Q-pipeline:excess w/r/t gaussian ofunclustered triggers with SNR>5

A random H1 day, no data quality flags applied

preliminary

• Extensive data quality and event-by-event veto studies based on ~300 auxiliary channels yielded significant veto flags that were used in a hierarchical way in the detection and upper-limit setting steps of the searches

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All-sky search in S5-year1

f<200 Hz f>200 Hz

red dots – zero lag triggersblack dots – time shifted triggers

No eventsabove threshold No events

above threshold

Correlated SNR

Chosen thresholds

Searched for un-modeled bursts in the 64-2048Hz frequency regime

Three methods were involved (BlockNormal, coherent-WaveBurst and Q-pipeline) based on incoherent, coherent and hierarchical approaches to data analyses

No signal consistent with a gravitational wave burst found

Correlated SNR

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All-sky search in S5 Year 1

• Analysis complete, paper is being drafted• Paper to be presented to the collaboration at the December 2008 meeting

and submitted for publication shortly after» A factor of 2 improvement in sensitivity with respect to S4 (2 x 10–8 M

at 10 kpc or 0.05 M emitted at Virgo Cluster), a factor of 10 in upper limit

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S5 Year 2 / VSR1 all-sky search

• Extends methodology established in the corresponding S5 Year 1 search

• Incoherent (coincidence-based), fully coherent and hierarchical methods are being applied to joint data

• Virgo can make significant contributions in the search above 300Hz where its sensitivity becomes comparable to LIGO’s

• May contain an artificial signal added blindly to the instruments using the hardware injection system

• Nearing completion

• Similar “high” frequency searches in the 1-6.5 kHz band

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Searches triggered by GRBs

• 213 GRB triggers from satellites during S5 run• Known direction and approximately known time

allows us to compare on-source and off-source correlations between the sites

• S5Y1 consistent with background; upper limits set» Excluded a merger in Andromeda as the source of GRB 070201

• S5Y2/VSR1 underway with Virgo and the more advanced coherent methods it permits

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Other S5 and pre-S6 activities

• Astrophysically and cosmologically motivated searches» Targeting point sources, e.g., galactic center» Bursts from cosmic strings» Specialized searches for binary black holes, core-collapse supernovae

• Searches in varying stage of maturity and probability for completion in the next 12 months

• An “Astrowatch” run currently collects data with the 2-km LIGO Hanford detector and GEO; an insurance policy for a nearby supernova» Data being analyzed primarily for detector monitoring and

characterization purposes as close to real time as possible» More in-depth analysis expected to take place for significant events

reported by electromagnetic (or particle) observations» Test-bed for real-time analyses expected to start with S6

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Goals and plans for S6

• LIGO and Virgo are currently undergoing upgrades that will provide a x2 sensitivity improvement in ~mid-2009 at which time S6 and VSR2 will commence

• Main S5 searches are expected to remain the group’s priority in S6 » Three-site network lets us continue to expand the use of coherent analysis

• Emphasis in setting up infrastructure and defining protocol for low latency burst searches in S6 and VSR2» Hours-to-minutes scale latency targeted

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Low latency searches in S6

• Do everything faster and more automatically» Generate calibrated data with low latency» Generate triggers with low latency at LIGO and Virgo sites» Transfer triggers and/or data from LIGO and Virgo sites to a central

location with low latency

• Make a useful product for followup with ground and space-based telescopes» Accurately (~1 degree) reconstruct direction, at detection threshold

SNR, with low latency– Position Reconstruction group very active

» Associate triggers with nearby galaxies» Provide error regions to “tile” with instrument FOVs» Control false rate to make good use of limited followup “slots”

• Make a useful product for detector characterization» Low-latency feedback to operators and for commissioning

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LIGO Lab’s role in bursts(Sep 2007-Aug 2008)

• Group Leadership (Katsavounidis, co-chair, with Shawhan (Maryland) & Hello (Orsay))

• Review Committees Membership (O’Reilly, Robertson, Cannon, Blackburn, Zweizig, Chatterji)

• Participation in Science (Blackburn, Brunet, Cannon, Chatterji, Garofoli, Hoak, Hughey, Katsavounidis, Markowitz, O’Reilly, Raab, Robertson, Searle, Shi, Stein, Stuver, Torres, Whitcomb, Yakushin, Zweizig) » all-sky searches for unmodeled bursts,» externally triggered searches,» astrophysically and cosmologically motivated searches,» detector characterization, data quality and veto investigations,» algorithmic development for hierarchical and fully-coherent searches,» LSC-Virgo joint analysis activities.

• Calibration Team Membership (O’Reilly, Hughey)

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Conclusions

• Burst searches of the LIGO, GEO and Virgo data from the S5/VSR1 runs are well underway» Flagship searches are expected to complete within the next 6

months

• We are preparing for S6/VSR2» Enhanced detectors at three sites will greatly increase the science

we can do» Low-latency external triggers a challenge and a priority

• LIGO Laboratory personnel contribute to all strands and lead many of them

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