Hearing the Universe with Gravitational Waves

1. Hearing the Universe with Gravitational Waves Brennan Hughey ERAU Physics Seminar March 23rd 2010

2. Gravitational Waves • LIGO and Burst Analysis • III.Electromagnetic Follow-ups • of LIGO/Virgo Triggers

3. Astronomical Messengers • The Electromagnetic Spectrum: • Looking at the Universe • Visible Light (1st several centuries) • Radio • X-ray • Gamma ray • Beyond the • Electromagnetic Spectrum: • Reaching out with other “senses” • Cosmic rays • Neutrinos • Gravitational Waves Picture Credit: Spectra from Space by Neil Fetter

4. Astronomical Messengers • The Electromagnetic Spectrum: • Looking at the Universe • Visible Light (1st several centuries) • Radio • X-ray • Gamma ray • Beyond the • Electromagnetic Spectrum: • Reaching out with other “senses” • Cosmic rays • Neutrinos • Gravitational Waves Picture Credit: Spectra from Space by Neil Fetter Today’s Talk (but we’ll get back to the Electromagnetic spectrum too)

5. Gravitational Waves:Listening to the Universe • Predicted by Einstein’s General Theory of Relativity • When massive objects rapidly change shape or orientation, the • curvature of space-time also changes • The change propagates as a wave • traveling at the speed of light: • ripples in the fabric of space-time • Amplitude inversely proportional to • distance • 2 polarizations: “plus” (+) and • “cross” (x) (and any combination) + polarization

6. Simulated Wave Emission NASA

7. How “Loud” Are They? • Amplitude is described by dimensionless strain: stretching of space h = ΔL/L • Back-of-envelope calculation: • Laboratory dumbbell

8. How “Loud” Are They? • Amplitude is described by dimensionless strain: stretching of space h = ΔL/L • Back-of-envelope calculation: • Laboratory dumbbell (1 ton, 2m, 1kHz) h = 10-38 1 TON

9. How “Loud” Are They? • Amplitude is described by dimensionless strain: stretching of space h = ΔL/L • Back-of-envelope calculation: • Laboratory dumbbell (1 ton, 2m, 1kHz) h = 10-38 • Binary neutron star system (1.4 MO, 20km, 400 Hz) = 10-21 at a distance of 15 Mpc • So the search for gravitational waves requires objects of astrophysical mass, and even then is a hugely difficult problem 1 TON

10. So Are Gravitational Waves Real? Don’t take Einstein’s word for it. Gravitational waves haven’t been directly detected, but…. Indirect evidence from binary system including radio pulsar Shift in orbit matches GR predictions exactly Dantor 2007

11. The Gravitational Wave Spectrum Interferometers and Bars Pulsar Timing Arrays Lisa Figure credit: Hobbs 2008

12. Gravitational Waves • LIGO and Burst Analysis • III.Electromagnetic Follow-ups • of LIGO/Virgo Triggers

13. Building Ears: LIGO Laser Interferometer Gravitational-Wave Observatory Lasers split at 90 degree angle, bounced back and forth along detector arms, then recombined Compression and contraction of space-time due to passing Gravitational Waves can be reconstructed from interference pattern of the two laser beams

14. The Worldwide Network of Gravitational Wave Interferometers LIGO Hanford 4 km2 km 4 km LIGO Livingston

15. The Worldwide Network of Gravitational Wave Interferometers LIGO Hanford 4 km2 km 3 km 4 km LIGO Livingston VIRGO

16. GEO600 The Worldwide Network of Gravitational Wave Interferometers LIGO Hanford TAMA, CLIO 600 m 4 km2 km 300 m100 m 3 km 4 km LIGO Livingston VIRGO

17. LIGO Scientific Collaboration

18. Mirror in situ The Hardware Beam tube Vibration Isolation Vacuum System

19. Data Collection Shifts manned by resident “operators” and visiting “scientific monitors”

20. Science and Sensitivity S1 – 2002 1 month S2 – 2003 2 months S3 – 2004 2 months S4 – 2005 1 month S5 – 2007-2008 2 years Ground motion “Shot noise” Statistical fluctuations Suspension Thermal noise

21. S6 and the Road Ahead A new science run is currently underway: S6/VSR2 July 2009 to ~September 2010 (expected) with some commissioning breaks Virgo and recent LIGO data improved w.r.t S5/VSR1 Incorporates some new technology and methods These improvements are prototypes for…

22. Advanced LIGO Next generation of gravitational wave interferometers – 2015 10 times improved strain sensitivity – 1000 times volume of space

23. Long duration Short duration Matched filter Continuous Waves Compact Binary Inspirals Template-less methods Stochastic Background Bursts Sources And Methods

24. Continuous Waves • Crab pulsar spin rate is slowing down – why? • Energy loss could partly be due to GW emission • Integrate sinusoidal signal,correcting for motion of detector • Doppler frequency shiftand amplitude modulation fromantenna pattern of GW detector Gravitational wave emission is constrained to less than 2% of total power loss Constraint is factor of 7 in strain below spin-down limit 116 other known pulsars studied

25. Stochastic Weak, random gravitational waves should be bathing the Earth Left over from the early universe, analogous to CMBR ; orfrom overlapping signals from many astrophysical objects / events Results from S5 data analysis: Searched for isotropic stochastic signal with power-law spectrum For flat spectrum, set upper limit on energy density in gravitational waves: Energy density of stochastic GW background 0 < 6.9 × 10–6 around 100 Hz Starts to constrain cosmic (super)string and “pre-Big-Bang” models Below Big Bang Nucleosynthesis bound Or look for anisotropic signal:

26. Compact Binary Coalescence Matching to templates of systems of various mass

27. Bursts • Transient (usually less than 1 second) • Waveform not known in advance (could be modeled) • Zoo of potential sources: • Core collapse supernovae • Merger of two compact objects (e.g. short GRBs) • Neutron star instabilities • Cosmic string cusps and kinks NASA ESO/A Roquette Chandra Image Ken Olum gamma ray burst (artist’s conception) magnetar (artist’s conception) cosmic string cusp (computer simulation) supernova remnant

28. [Thompson et al. 2003, Rampp & Janka 2002, Liebendoerfer et al. 2002,2005] [Wilson 1985; Bethe & Wilson 1985] GW Burst Sources and Science Payoff: nuclear EOS / particle physics Core-Collapse Supernovae NS Structure Long GRBs Structure/Dynamics of Spacetime BH/BH, NS/NS, NS/BH merger GRB Central Engine(s) Short GRBs Core-Collapse Supernova Mechanism(s) NS Collapse SGRs/AXPs Exotic Theories Pulsar Glitches SGR Mechanism String Cusps Pulsar Glitch Mechanism Unexpected Unknown Unknowns

29. How do We Detect a “Burst” • 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 All methods require a network of detectors

30. Background • There are a huge variety of Earth-based disturbances • that cause “glitches” in the detector, so we have hundreds • of internal and external sensors set up to measure non • Gravitational wave effects Examples of noise sources: Wind Earthquakes Waves in gulf Power Lines Anthropogenic etc… Extreme example of an anthropogenic disturbance

31. Burst Results: S5 All Sky Search • Try to identify signal any time detector is on from anywhere • S5 results available in 2 papers: • 1st year LIGO (PRD 80:102001, 2009) • 2nd year LIGO + Virgo (arXiv:1002.1036) • Analyses tuned for ~0.1 event false alarm probability • using “time slide” method to remove real GW coincidence • No signals found (except a blind injection)

32. All Sky Sensitivity Sum of two polarizations Sample waveform: Gaussian-enveloped sine wave Q = 9 Efficiency Upper Limit

33. All Sky Sensitivity Efficiency corresponds to LIGO noise curve Efficiency Upper Limit

34. All Sky Sensitivity Efficiency corresponds to LIGO noise curve Curve determined by efficiency function Asymptote determined by live time Efficiency Upper Limit

35. High Frequency Search • Extend the all sky search to higher frequencies with similar methods • Not the most sensitive range of detectors, but: • Triples the frequency coverage from 2000 to 6000 kHz • “Shot-noise” dominated regime has low glitch rate • Numerous potential sources Baiotti et al. Waveform 1st year: excess power Followed by cross-correlation 2nd year: coherent analysis

36. Externally Triggered NASA • Start with a known observation, use timing to look for gravitational • waves in close coincidence in order to have smaller background • Possible sources include • Gamma Ray Bursts (short and long) • Soft Gamma Repeater flares • Pulsar glitches

37. GRB 070201 • Short, hard gamma-ray burst • Leading model for short GRBs: binary merger involving aneutron star • Position (from gamma-ray satellite data) is consistent with being in M31 • Both LIGO Hanford detectors were operating • Searched for inspiral & burst signals • Result from LIGO data analysis:No plausible GW signal found;therefore very unlikely to befrom a binary merger in M31

38. Gravitational Waves • LIGO and Burst Analysis • III. Electromagnetic Follow-ups • of LIGO/Virgo Triggers

39. Online Rapid Analysis Major effort amongst burst group and others in LIGO to produce rapid results in S6. • Interferometers produce • strain data with • preliminary calibration • Data transferred to • central site and • coherent burst • analysis is performed • Online data quality • standards cuts • generated and applied • Background estimated • with timeslides on cluster • First pass at data in ~10 minutes rather than months to years

40. Motivation • 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 NASA

41. Electromagnetic follow-ups Gravitational wave and electromagnetic emission from same source is not guaranteed, but many candidates exist (GRBs, SN, SGR….) and science payout could be huge: • Gravitational Wave Signal • Bulk motion dynamics • Luminosity distance • Progenitor mass • Light curve and spectrum • Host galaxy • Gas environment • Red shift distance • Confirm GW detection Multi-messenger astrophysics!! Map compact object hosts Full picture of progenitor physics

42. Partner Instruments TAROT Chile & France Swift Satellite QUEST camera onESO Schmidt Telescope • UV/optical telescope: 0.4x0.4 sq. deg. FOV • X-ray telescope: 0.3x0.3 sq. deg. FOV • 4.1 x 4.6 deg FOV • Survey telescope for supernovas, etc. • 1.85 x 1.85 deg. FOV • History of GRB follow-ups

43. Events for Follow-up • Automated event processing takes 5-10 minutes: • Events which meet False Alarm Rate criteria • (one per day* for QUEST / Tarot, one per month* for Swift) • and pass automated cuts trigger e-mails and text messages • Human component takes additional 20-35 minutes: • Designated human on-shift leaps into action, performing • sanity checks and talking to all 3 control rooms to vet event • Events which pass are then submitted for follow-up, and • observed as target of opportunity when able * Note that we’re not talking about gravitational wave detections here, just more interesting than average triggers

44. Position reconstruction • Formal study over a broad range of simulated signals added on S5/VSR1 and S6/VSR2 instrument data • Performance varies significantly with signal-to-noise ratio (SNR), morphology, analysis parameters • Several degree error angles (“ears” not “eyes”) Position error areas hide the fact that they may be broken down to multiple disjoint patches

45. Position Reconstruction Known mass sourcein local universe X Regions consistent with GW datamay be many disjoint regions Chosen telescope pointing based on mass distribution and GW data

46. December – January Run • After test period, program went live from • Dec 20th 2009 through Jan 8th 2010 • (ended by Virgo commissioning) • 8 events sent for follow-ups, 3 followed up by QUEST • and 1 by TAROT • 1 “Engineering run” Swift observation • Series of collected images currently being studied: • hands on study will help us understand challenges of • linking GW and EM observations

47. Future Prospects • 2nd observation period (hopefully) coming this summer • - criteria for follow-ups and mass targeting being refined • - will attempt to increase automation • Compact Binary Coalescence group working towards • inclusion in EM follow-ups program as well • Discussions ongoing with other experiments • - Pi of the Sky: improved sky coverage • - Radio telescopes • Successful program paves the way for Advanced detector era

48. Summary • Gravitational waves have the potential to let us hear the • universe in an entirely new way • LIGO and Virgo continue to pursue the detection of gravitational • waves through a variety of methods, including partnering with • more conventional telescopes. • Work now paves the way for the Advanced Detector era, with • a factor of 10 farther astrophysical reach

49. The End