Brennan Hughey MIT Kavli Institute Postdoc Symposium 4-3-09 The Burst Analyses: Searching for Unmodeled Gravitational Wave Transients with LIGO Brennan Hughey MIT Kavli Institute Postdoc Symposium 4-3-09

LIGO and Friends LIGO Livingston (LA) L1 – 4km LIGO Hanford (WA) H1 – 4km H2 – 2km Virgo 3 km (Italy) Has data-sharing agreement with LSC GEO 600m (Germany) Part of the LSC

Sources And Methods This talk Template-less methods Matched filter Bursts Stochastic Background Template-less methods Compact Binary Inspirals Pulsars Matched filter Short duration Long This talk

Burst Analyses Sources of GW bursts include: Core-collapse supernovae Merger of binary compact objects Neutron star instabilities Cosmic string cusps and kinks Unexpected sources? Approaches: “All-sky” searches performed over whole sky and over all Collected data “Externally triggered” searches performed around the time Of Gamma-Ray Bursts or Soft Gamma Repeaters

Analysis Methods Excess Power: look for significant upward deviations from background expectation Perform coincidence test with other interferometers in network to reduce background Cross-correlation Look for consistency in waveforms observed in multiple interferometers Fully coherent methods: Reconstruct events hypothesizing sky locations and accounting for amplitude, time delay Coherent WaveBurst sensitivity for LIGO Network in Earth-centered, Earth-fixed coordinates

Data Quality Most triggers which stand out above background are of mundane origin (glitches) LIGO has hundreds of readout channels and auxiliary detectors to provide additional information about event seismic wind electromagnetic (power lines) acoustic Data quality flags remove periods of dubious quality Vetoes remove candidates in direct coincidence with specific channel

All-sky searches S5 all sky search 4 science runs of LIGO-GEO instruments in 2002-2005 35 days triple coincidence No event candidates Upper limit (90% confidence level on rate of detectable events) set S2 S4 LIGO S4 search: CQG 24 (2007) 5343 Preliminary S5 all sky search Analysis underway, split into 2 calendar years Order of magnitude more data and X2 sensitivity of S4 Exploiting coherent analysis methods and full network Detection Probability

High Frequency All Sky Searches All-sky searches previously limited to 2 kHz or lower New analyses extend range of analysis up to 6 kHz Most source types previously listed can have >2 kHz emission Use same methods as low frequency, adjusting as needed Takes full advantage of Virgo Clean, shot-noise dominated background

Triggered Searches GRB searches – 137 GRBs (with at least two active interferometers) analyzed during S5 Mostly reported by Swift satellite Analyzed using coherent methods GRB 070201 – Special case, earlier separate publication LIGO excludes compact merger within M31 as source at 99% CL SGR searches – Individual SGR Burst Search PRL 101, 211102 (2008) Sensitive to neutron star f-modes Stack-a-flare And other analyses not listed here

S5 analyses wrapping up, several papers coming out over next few months S5 Year 1 High Frequency Search paper should go to arXiv in late April or May

Data Analysis Prep for enhanced LIGO/Virgo+ Burst group is working on upgrades to pipelines to use with upgraded detector in enhanced LIGO/Virgo+ joint science run Biggest difference is move towards low-latency online analysis. Candidate events 10-30 minutes after initial processing There are several goals behind this effort: Assist detector characterization efforts Expedite offline analysis Work towards making LIGO/Virgo an integral part of the astronomical Community Quicker follow-up of events from other observatories Produce event candidates for follow-up at other astronomical observatories

Triggering other Detectors EM observatories: Wide-field optical telescopes: SkyMapper, ROTSE, TAROT, Quest, etc. Radio: LOFAR, Arecibo, VLA, etc. Gamma-ray/x-ray: Swift, etc. Neutrino telescopes: Super-k, IceCube, Antares, etc. both supernova neutrinos and high energy neutrino detectors don’t point, but sharing of data sets aids coincidence Details vary from collaboration to collaboration (e.g. Swift triggers will be much rarer than most of the ground-based telescopes) In all cases, majority of triggers will be false alarms and we are clearly communicating this Independent confirmation that an astrophysically interesting event is happening at the same time and place as our event candidate would greatly enhance our confidence – especially for the first direct gravitational wave detection

Analysis Flowchart

Summary Searches for gravitational wave transients have been conducted using a variety of methods Papers coming to publication over next few months Enhanced LIGO/Virgo+ science run starting around July “Online” low-latency analysis will enable much quicker turn-around and facilitate EM follow-ups