The International Pulsar Timing Array. Maura McLaughlin West Virginia University June

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1 The International Pulsar Timing Array Maura McLaughlin West Virginia University June

2 Outline Pulsar timing for gravitational wave detection Pulsar timing arrays EPTA, NANOGrav, PPTA The International Pulsar Timing Array Science Goals The International Pulsar Timing Array organization The future of the International Pulsar Timing Array

3 Gravitational Waves GWs are fluctuations in the fabric of spacetime traveling at the speed of light. plus-polarized cross-polarized h + h x We describe them by their strain (or amplitude) and their frequency. h = strain = ΔL/L = 0.5

4 Gravitational Wave Sources Masses with varying quadrupole moments will emit GWs. Which of the following are GW sources? - spinning spherical stars - pulsing stars - spinning bumpy spheres - stars in binary orbits - supernovae

5 Proof of Gravitational Radiation ( ) ( ) Hulse & Taylor, 1975, ApJ, 195, L51 Weisberg & Taylor, 1984, PRD, 52, 1348 P b = 192π ( ) 5/3 5 T 5/3 Pb m p m c f(e) 2π (m p + m c ) 1/3

6 How can we directly detect them? Search for light travel time changes between objects. LIGO LISA PTAs f ~ 1/ms ( Hz) f ~ 1/(mins-hrs) ( Hz ) f ~ 1/yrs ( Hz)

7 GW Sources Continuous Burst Stochastic

8 Pulsar Timing Arrays

9 PTAs depend on extreme stability of MPs Residual = measured expected pulse arrival times σ RMS = root-mean-square residual < 200 ns (3 x 10-5 P). At midnight on April 6 th 2001, the period was (2) ms!!!! J P = 5.75 ms Verbiest et al., 2008, ApJ, 400, 951

10 Pulsars for Direct GW Detection f ~ 1/weeks to 1/years ( Hz) h ~ σ rms /Τ ~ 100 ns/5 years ~ d t n i n j h ij (x, t)dr Δt ~ h/f and will have pulsar and Earth terms λ gw ~ 1-10 lyr; D psr ~ 1000 lyr 0 First discussed by Detweiler (1979, ApJ, 234,1100) and Sazhin (1978,SA,22,36).

11 Pulsars for Direct GW Detection P. Demorest

12 Single Source: 3C66B Proposed z=0.02 SMBH binary with period 1.05 yr and mass of 5x10 10 solar masses (Sudou et al. 2003). Pulsar term and Earth term

13 Single Source: 3C66B Proposed z=0.02 SMBH binary with period 1.05 yr and mass of 5x10 10 solar masses (Sudou et al. 2003). Analysis of the residuals from a single high-precision pulsar shows that this binary cannot exist (Jenet et al. 2004). Pulsar term and Earth term

14 Stochastic Background h c (f) =A ( f ) α yr 1 P. Demorest Model A α References Supermassive black holes /3 Jaffe & Backer, 2003, ApJ, 583, 616 Wyithe & Loeb, 2003, ApJ, 590, 691 Enoki et al., 2004, ApJ, 615, 19 Sesana et al., 2008, MNRAS, 290, 192 Relic GWs to -0.8 Grishchuk, 2005, PU, 48, 1235 Boyle & Buonanno, 2008,PRD, 78, Cosmic Strings /6 Maggiore, 2000, PR, 331, 283

15 Single Pulsar Limits h c < 2 x (f=1 yr -1 ) P (f) = 1 12π 2 1 f 3 h c(f) 2 f 13/3 0 P (f)df = σ 2 g Kaspi, Taylor, & Ryba, 1994, ApJ, 428, 713

16 Stochastic Background Limits from a Pulsar Timing Array Expected correlation of residuals for pairs of pulsars versus angular separation on sky. Pulsar terms uncorrelated. Earth terms correlated. r(θ) = 1 N N 1 i=0 R(t i, ˆk 1 )R(t i, ˆk 2 ) r(θ) = σ 2 gζ(θ) Jenet et al. 2005, ApJL, 625, 123 Clock errors monopole. Ephemeris errors dipole. GWs quadrupole. Hellings & Downs, 1983, ApJ, 265, L39

17 Sensitivity of a PTA T = total timespan of observations N TOAs = number of TOAs N PSR = number of pulsars σ rms = timing residual RMS PATIENCE HIGHER CADENCES (MORE TELESCOPE TIME) PULSAR SEARCHES (MORE TELESCOPE TIME) INTRINSIC and EXTRINSIC factors Intrinsic: rotational and emission stability, ISM, pulse shape, brightness Extrinsic: observation length, collecting area, bandwidth, frequency, instrumentation, algorithms Also depends on distribution of sources!

18 Sensitivity of a PTA A pulsar timing array is a detector (or telescope) just like LIGO is. We can calculate properties just like LIGO. Antenna response for the pulsar-earth system.

19 MSP Sky Distribution Galactic MSPs are local (distances ~ kly) and roughly isotropically distributed. There are roughly 100 MSPs (P < 20 ms) in our Galaxy.

20 Timing precision σtoa w Tsys 1 w SNR SPSR A BT w pulse width SNR - signal-to-noise ratio SPSR pulsar flux Tsys system temperature A telescope area B receiver bandwidth T integration time (1)

21 Pulsar Timing Array A pulsar timing array is a detector (or telescope) just like LIGO is. We can calculate properties just like LIGO. Antenna response for the pulsar-earth system.

22 Collaboration and Pooling of Data Necessary! NANOGRav includes 22 members from North America nanograv.org

23 Current Results J J < 100 ns RMS! P. Demorest 26 MSPs being timed with the Arecibo and Green Bank telescopes. 2-3 frequencies at each telescope. Bi-monthly to monthly observations. Residuals from 100 ns to 1.5 μs

24 NANOGrav Limit after Four Years h c < 7 x (f=1 yr -1 ) or P. Demorest

25 Sensitivity of a PTA T = total timespan of observations N TOAs = number of TOAs N PSR = number of pulsars σ rms = timing residual RMS PATIENCE HIGHER CADENCES (MORE TELESCOPE TIME) PULSAR SEARCHES (MORE TELESCOPE TIME) INTRINSIC and EXTRINSIC factors Intrinsic: rotational and emission stability, ISM, pulse shape, brightness Extrinsic: observation length, collecting area, bandwidth, frequency, instrumentation, algorithms

26 The International Pulsar Timing Array

27 The International Pulsar Timing Array

28 The International Pulsar Timing Array J. Verbiest

29 2012 Meeting Gravitational waves are a key prediction of general relativity. Their direct detection will allow us to probe new source classes. Both ground-based interferometers and PTAs are based on searching for changes in light travel time between objects. Source classes that will be studied by both are complementary. Detection is challenging and improvements are need to both interferometers and current PTAs. The IPTA has been formed to facilitate a detection with pulsars. Time to direct detection ~ 5-10 years.

30 Summary Gravitational waves are a key prediction of general relativity. Their direct detection will allow us to probe new source classes. Both ground-based interferometers and PTAs are based on searching for changes in light travel time between objects. Source classes that will be studied by both are complementary. Detection is challenging and improvements are need to both interferometers and current PTAs. The IPTA has been formed to facilitate a detection with pulsars. Time to direct detection ~ 5-10 years.