R. N. Manchester

1. Pulsars – Fascinating Objects and Marvellous Probes R. N. Manchester Australia Telescope National Facility, CSIRO, Sydney Australia • Pulsars – a short introduction • Parkes pulsar surveys – the double pulsar • Pulsars as probes the interstellar medium • Pulsars with the Fermi gamma-ray telescope • Detecting gravitational waves with pulsars

2. Spin-Powered Pulsars: A Census • Number of known pulsars: ~1820 • Number of millisecond pulsars: 181 • Number of binary pulsars: 139 • Number of AXPs: 13 • Number of pulsars in globular clusters: 107* • Number of extragalactic pulsars: 20 * Total known: 137 in 25 clusters (Paulo Freire’s web page) Data from ATNF Pulsar Catalogue, V1.33 (www.atnf.csiro.au/research/pulsar/psrcat; Manchester et al. 2005)

3. Pulsar Recycling - Millisecond Pulsars • Millisecond pulsars (MSPs) are very old (~109 years). • Most of them are members of a binary system - in orbit with another star • They have been recycled by accretion from an evolving binary companion. • This accretion spins up the neutron star to millisecond periods.

4. Pulsars as Clocks • Neutron stars are tiny (about 25 km across) but have a mass of about 1.4 times that of the Sun • They are incredibly dense and have gravity 1012 times as strong as that of the Earth • Because of this large mass and small radius, their spin rates - and hence pulsar periods - are incredibly stable e.g., PSR J0437-4715 had a period of : 5.757451831072007  0.000000000000008 ms • Although pulsar periods are very stable, they are not constant. Pulsars lose energy and slow down • Typical slowdown rates are less than a microsecond per year

5. . P vs P Galactic disk pulsars . • Most pulsars have P ~ 10-15 • MSPs have P smaller by about 5 orders of magnitude • Most MSPs are binary • Only a few percent of normal pulsars are binary • P/(2P) is an indicator of pulsar age • Most young pulsars are associated with supernova remnants . . ATNF Pulsar Catalogue (www.atnf.csiro.au/research/pulsar/psrcat)

6. The Parkes radio telescope has found more than twice as many pulsars as the rest of the world’s telescopes put together.

7. The Parkes Multibeam Pulsar Surveys • Multibeam receiver - 13 beams at 1.4 GHz - very efficient for pulsar surveys • Several independent surveys with different optimisations • More than 850 pulsars discovered with the multibeam system since 1997 • Excellent database for studies of pulsar Galactic distribution and evolution (Manchester et al. 2001)

8. The Parkes Multibeam Pulsar Surveys: Galactic Distribution

9. Parkes Multibeam Surveys: P vs P . J1119-6127 • New sample of young, high-B, long-period pulsars • Large increase in sample of mildly recycled binary pulsars • Three new double-neutron-star systems and the first-known double pulsar! J0737-3039

10. PSR J0730-3039A/B The first double pulsar! • Discovered at Parkes in 2003 • One of top ten science break-throughs of 2004 - Science • PA = 22 ms, PB = 2.7 s • Orbital period 2.4 hours! • Periastron advance 16.9 deg/yr! (Burgay et al., 2003; Lyne et al. 2004) Highly relativistic binary system!

11. PSR J0737-3039A/B Post-Keplerian Effects R: Mass ratio w: periastron advance g: gravitational redshift r & s: Shapiro delay Pb: orbit decay . . GR is OK! Consistent at the 0.05% level! Non-radiative test: distinct from PSR B1913+16 (Kramer et al. 2006)

12. PSR J0737-3039A Eclipses • Pulses from A eclipsed for ~30 sec each orbit • Eclipse by B magnetosphere – orbit seen nearly edge on • High-resolution observations show modulation of eclipse at rotation period of B pulsar! (McLaughlin et al., 2004)

13. PSR J0737-303A Eclipse Model • Synchrotron absorption by high-density plasma in the magnetospheric closed field-line region • Model fitted to observed eclipses to determine properties of eclipsing region (Lyutikov & Thompson 2005)

14. PSR J0737-3039A Eclipses: Evidence for Geodetic Precession of PSR J0737-3039B • Geodetic precession B spin axis with 75-year period expected from GR • Changing orientation of spin axis changes pattern of eclipse modulation • Lyutikov & Thompson eclipse model fitted to four-year data span • Evidence for change in longitude of spin axis – consistent with GR prediction (Breton et al. 2008)

15. Pulsars as Probes • Pulsars are: • Essentially point sources • Broad-band pulsed emitters • Highly polarised • Distributed through Galaxy at approximately known distances • These properties make them near ideal probes of the interstellar medium (ISM) • For example, scattering by small-scale irregularities in the ISM results in interstellar scintillation of pulsars • Interference pattern is function of frequency and, because of motion of the pulsar and the Earth, also of time – “dynamic spectrum” • Two-dimensional Fourier transform of dynamic spectrum gives a “secondary spectrum” • Can investigate ISM on scales as small as 0.1 A.U. (1010 m)

16. (Stinebring, 2006)

17. Probing the Galactic Magnetic Field with Pulsars • Pulsars are highly polarised – close to 100% linear polarisation in some cases • Faraday rotation of the plane of polarisation of pulsar emission is easily observed • The ratio of the Rotation Measure to the Dispersion Measure gives a direct measure of the mean line-of-sight magnetic field strength (weighted by the local electron density) : • Pulsars are spread through the Galaxy at approximately known distances, making possible three-dimensional tomography of the Galactic magnetic field • Rotation measures now available for nearly 400 pulsars (Pulse truncated at 20% of peak) PSR J0437-4715 1433 MHz Linear (Han et al. 2009, in prep.) Circular

19. The Gamma-ray Sky Vela Geminga Crab EGRET Sky survey: 1991-1995

20. Fermi Gamma Ray Space Telescope LAT In clean room before launch Launched June 11, 2008

21. Fermi – Three-month image

22. Fermi – Vela Pulsar Radio pulse (Abdo et al. 2009)

23. Fermi – CTA1 Pulsar First gamma-ray pulsar found in a blind search! (Abdo et al. 2008)

24. Fermi Pulsars 25 gamma-ray and radio pulsars (including 7 ms psrs) 13 gamma-ray only pulsars Pulses at 1/10th real rate High-confidence detections through 10/31/2008 EGRET pulsars young pulsars discovered using radio ephemeris pulsars discovered in blind search millisecond pulsars discovered using radio ephemeris (Credit: P. Michelson)

25. Detection of Gravitational Waves • Huge efforts over more than four decades to detect gravitational waves • Initial efforts used bar detectors pioneered by Weber • More recent efforts use laser interferometer systems, e.g., LIGO, VIRGO, LISA LIGO LISA • Two sites in USA • Perpendicular 4-km arms • Spectral range 10 – 500 Hz • Initial phase now operating • Advanced LIGO ~ 2011 • Orbits Sun, 20o behind the Earth • Three spacecraft in triangle • Arm length 5 million km • Spectral range 10-4 – 10-1 Hz • Planned launch ~2018

26. A Pulsar Timing Array • With observations of many pulsars widely distributed on the sky can in principle detect a stochastic gravitational wave background • Gravitational waves passing over the pulsars are uncorrelated • Gravitational waves passing over Earth produce a correlated signal in the TOA residuals for all pulsars • Requires observations of ~20 MSPs over 5 – 10 years; could give the first direct detection of gravitational waves! • A timing array can detect instabilities in terrestrial time standards – establish a pulsar timescale • Can improve knowledge of Solar system properties, e.g. masses and orbits of outer planets and asteroids Idea first discussed by Hellings & Downs (1983), Romani (1989) and Foster & Backer (1990)

27. Clock errors All pulsars have the same TOA variations: monopole signature • Solar-System ephemeris errors Dipole signature • Gravitational waves Quadrupole signature Can separate these effects provided there is a sufficient number of widely distributed pulsars

28. The Parkes Pulsar Timing Array Project Collaborators: • Australia Telescope National Facility, CSIRO, Sydney Dick Manchester, George Hobbs, David Champion, John Sarkissian, John Reynolds, Mike Kesteven, Warwick Wilson, Grant Hampson, Andrew Brown, Jonathan Khoo, (Russell Edwards, David Smith) • Swinburne University of Technology, Melbourne Matthew Bailes, Willem van Straten, Ramesh Bhat, Sarah Burke, Andrew Jameson • University of Texas, Brownsville Rick Jenet • University of California, San Diego Bill Coles • West Virginia University • Joris Verbiest • Franklin & Marshall College, Lancaster PA Andrea Lommen • University of Sydney, Sydney Daniel Yardley • National Observatories of China, Beijing Zhonglue Wen • Peking University, Beijing Kejia Lee • Southwest University, Chongqing Xiaopeng You • Curtin University, Perth Aidan Hotan

29. Sky Distribution of Millisecond Pulsars P < 20 ms and not in globular clusters

30. Recent Results for PSR J0437-4715 Rms timing residual 56 ns!!

31. Current PPTA Results • Timing for 20 MSPs • Four pulsars with timing residuals less than 200 ns and eleven less than 1 s These results are approaching the level needed to detect gravitational waves in 5 - 10 years! Still more work to be done to reduce systematic errors!

32. Future Prospects Single source detection Stochastic GW Background PPTA SKA 5 years, 100 ns Range of predicted amplitudes Predicted merger rates for 5 x 108 M binaries (Wen & Jenet 2008) (Jaffe & Backer 2003; Wyithe & Loeb 2003) Difficult to get sufficient observations with PPTA alone - international collaborations important! PPTA can’t detect individual binary systems - but SKA will!

33. The Gravitational Wave Spectrum