Gravity and the Unseen Sky Sydney J. Chamberlin Outline - PowerPoint PPT Presentation

Gravity and the Unseen Sky Sydney J. Chamberlin

Outline Gravitational-wave detectors Ti e road to detecting stochastic backgrounds with pulsar timing arrays Testing general relativity with pulsar timing arrays 2 February 17, 2015 California Institute of Technology

Gravitational wave spectrum and sources Moore et al. 2014 h February 17, 2015 California Institute of Technology 3

Gravitational wave (GW) experiments Ti e (detectable) gravitational wave spectrum Frequency (Hz) 10 -8 10 -6 10 -4 10 -2 10 10 2 |{z} |{z} |{z} supermassive black hole neutron star/black hole compact binary coalescence, binaries binaries supernovae, pulsars e.g. : European Pulsar Timing Array Parkes Pulsar Timing Array North American Nanohertz GW Observatory (NANOGrav) PTAs LISA LIGO All together: International Pulsar Timing Array 4 February 17, 2015 California Institute of Technology

Pulsar Timing Array TEMPO(2) D A B C D: GW perturb signals from all pulsars at Earth. B: GWs perturb space-time C: ionized gas in the interstellar medium A: GWs from e.g. supermassive Time of arrivals and residuals are calculated. at the pulsars as they transit disperses & scatters the light from pulsars BH binaries (also cosmic strings) Science! Gravitational Waves Stochastic Continuous Bursts Background Waves memory unmodeled isotropic anisotropic detect or limit Science! detect or limit detect or limit Funding Outreach C. M. F. Mingarelli (2015) February 17, 2015 5 California Institute of Technology

Pulsar timing preliminaries Millisecond Pulsars (MSPs) are used for GW detection because they are very stable (on the level of atomic clocks!!) MSPs are thought to be “recycled” pulsars — spun up through accretion in binary systems February 17, 2015 6 California Institute of Technology

Pulsar timing preliminaries pulse train GW A passing GW induces a redshift in the pulse train from the pulsar. Ti is redshift can be calculated with the geodesic equation. But important to note that the physical observable is not the redshift: is the timing residual r ( t ) = TOA actual − TOA expected Z t z ( t 0 ) dt 0 r ( t ) = 0 7 February 17, 2015 California Institute of Technology

Outline Gravitational-wave detectors Ti e road to detecting stochastic backgrounds with pulsar timing arrays Testing general relativity with pulsar timing arrays 8 February 17, 2015 California Institute of Technology

Stochastic GW searches with PTAs iments in strong-field situations [17, 18]. Hellings-Downs Curve First showed by Hellings and Downs in 1983 that a GW produces uniquely χ IJ correlated variations in the timing residuals of a set of pulsars So can search for GWs by fj tting this curve to the cross-correlated data (Jenet et al. 2005) ζ IJ Correlation between timing residuals for pulsar pairs as a function of the a Or, fj nd an optimized cross correlation that takes into account the GW spectrum and noise power spectra: r ⇤ r j ( f 0 ) i Ω gw ( f ) h ˜ i ( f )˜ δ ( f − f 0 ) ∝ χ ij <latexit 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