1. Sarah Burke Spolaor Jet Propulsion Laboratory, California Institute of Technology Gravitational Wave Detection with Pulsar Timing Arrays: Status and Prospects © 2013 California Institute of Technology, Government Sponsorship Acknowledged

2. Millisecond pulsars Spinning up to ~700 times per second

3. “Timing Residuals” Model pulsar  Observe  Correct? Model – Actual Arrival Phase (ms) Time (relative MJD) residual measurement error Figure of Merit: RMS scatter of residuals. BEST: <50ns WORST: few  s Fit for known effects

4. Example pulsar model PSR J0437-4715 Also referenced: JPL Planetary ephemeris TAI international atomic time standard

5. Pulsar Earth Jenet et al. (2004)

6. Pulsar Timing Array Monopolar signature? Atomic time standards (Hobbs et al. 2012) Telescope issues Dipolar signature? Planetary ephemeris errors (Champion et al. 2010) Quadrupolar signature? Gravitational waves

8. GW Spectrum Adapted from Yardley et al. (2009) log [ dimensionless GW strain ] Stochastic SMBH Binary Background

9. UNTIL RECENTLY: “Working on our sensitivity” CURRENTLY & UPCOMING: Meaningful upper limits + Detection

10. GW Background Normalized Distribution Strain Amplitude at f = (1 year) -1 ALL MODELS Fiducial models Low-mass BCG High-mass BCG Adapted from Sesana et al (2013)

11. GW Background Van Haasteren et al. 2013 Shannon et al. (accepted to Science) Normalized Distribution Strain Amplitude at f = (1 year) -1 ALL MODELS Fiducial models Low-mass BCG High-mass BCG Rules out standard Millennium Simulation binary presecription to 50% confidence

12. Sensitivity scaling law S/N Number of pulsars Average residual RMS Number of observations Length of experiment Scaling law from Siemens et al. (2013)  = 13/3 for SMBH binary background

13. Recent Sensitivity Improvements: Gaussian & Non-stationary Noise

14. Recent Sensitivity Improvements: Detection Algorithms Coherently seek correlations using all pulsars More sensitive statistical analysis Resolved sources: Corbin+Cornish10; Finn+Lommen+10; Lee+11; Ellis+12; Boyle+Pen12; Mingarelli+12; Ellis13 … Sky localization (~2000 deg 2 ; Ellis 2013) Parameter estimation (M, e, D, P …) Measuring Spin-orbit Precession

15. Recent Sensitivity Improvements: Detection Algorithms Incoherent spectral analysis (Yardley+09) Bayesian inference (Ellis et al. in prep) Thanks to J. Ellis for figure Yardley et al. (2009) data set: two algorithms

16. Recent Sensitivity Improvements: Detection Algorithms Coherently seek correlations using all pulsars More sensitive statistical analysis GW Backgrounds: van Haasteren+11; Demorest+12; Shannon et al (accepted) IPTA data challenge (12 distinct submissions, paper in prep)

17. Recent Sensitivity Improvements: International Pulsar Timing Array Nanohertz Observatory for Gravitational Waves (NANOGrav; North America) European Pulsar Timing Array (Europe) Parkes Pulsar Timing Array (Australia)

18. Recent Sensitivity Improvements: International Pulsar Timing Array DOUBLE number of pulsars [~40 total] LONGER data sets [up to 30 years] LOWEST RMS RESIDUALS pulsars [many under 500ns] LARGE NUMBER OF DATA POINTS S/N Number of pulsars Average residual RMS Number of observations Length of experiment Scaling law from Siemens et al. (2013)  = 13/3 for SMBH binary background

19. 100 Pulsars 10 yr per pulsar Coherent Optimistic timing precision The Future: Resolved SMBH Binaries z = 0.001 z = 0.01 z = 0.1 Optimistic Future timing array with Square Kilometre Array Burke-Spolaor (2013; CQG Special issue on Pulsar Timing Arrays) Confusion limit? (Boyle & Pen 2012) 2e9M sun at International Timing Array 2014 + Ellis+12 Bayesian algorithm Yardley et al. (2010)

20. The Future: GW Background Shannon et al. (submitted) Square Kilometre Array 100 pulsars, RMS < 100ns, for 10 years Normalized Distribution Strain Amplitude at f = (1 year) -1 ALL MODELS Fiducial models Low-mass BCG High-mass BCG IPTA est.

21. The Future: GW Background With three new pulsar discoveries per year Continuing without improvement Only NANOGrav considered here (Siemens et al. 2013)

22. Summary Galactic-scale gravitational wave observatory Supermassive black hole binaries anticipated first detection: Individual/Stochastic Background Gravitational waves in ~9 years WITHOUT improvements. IPTA formation Enhanced algorithms and more pulsars Improved instrumentation + understanding of “detector” (pulsar) Timing Array science not covered: Multi-messenger targets Strongest observational limits on cosmic string tension Testing alternate theories of gravity Detecting trans-Neptunian objects Spacecraft naviation with timing arrays

24. Grab-bag: Alternative gravity theories Lee+08

25. Where to look? Burke-Spolaor (2013; CQG Special issue) References: Comerford+09, Liu+10, Shen+11, Komossa+03, Fabbiano+11, Graham04, Milosavljevic+Phinney05, Sesana+11, Tanaka+12, Eracleous+11, Burke-Spolaor11, Gower82, Volonteri+08, and more Red: not yet confirmed

26. Grab-bag: Astrophysics with GW limits 3C66B (Sudou+03, Jenet+04) 1.06 year orbit (P gw = ½ year) Total mass > 10 10 M sun Simulated 3C66B signal… Actually saw…