The timing behaviour of radio pulsars

1. The timing behaviour of radio pulsars George Hobbs Australia Telescope National Facility george.hobbs@csiro.au

2. Contents • Radio pulsars • Pulsar timing • A few things that you can do with pulsar timing • Young pulsars - a new (predictive?) model for timing noise • What has this to do with this conference? - pulsars are compact objects - radio pulsar timing is a powerful technique for studying pulsars - can determine parameters of interest - neutron star masses, rotation rates etc. - can study the pulsar spin-down => implications for internal structure of neutron star. CSIRO. Gravitational wave detection

3. Let’s start at the beginning 08:35:20.61 -45:10:34.87 CSIRO. Gravitational wave detection

4. Radio pulsars Animation: Michael Kramer CSIRO. Gravitational wave detection

5. Properties of radio pulsars CSIRO. Gravitational wave detection

6. Must average many thousands of pulses together to obtain stable profile Must convert to conform with terrestrial time standards Must convert to reference frame suitable for the timing model – e.g. solar system barycentre Must convert to arrival times at infinite frequency Must add extra propagation delays e.g. through the solar system Pulsar timing: The basics(see Hobbs, Edwards & Manchester 2006, MNRAS) Model for pulsar spin down Improve timing model Obtain pulse arrival times at observatory Form timing residuals – how good is the timing model at predicting the arrival times CSIRO. Gravitational wave detection

7. What can we do with the timing model? CSIRO. Gravitational wave detection

8. Some examples: pulsar velocities • With long data spans can get accurate pulsar proper motions - with a distance estimate can obtain velocities. • Mean space velocity ~ 400km/s (Hobbs et al. 2005) CSIRO. Gravitational wave detection

9. Determine pulsar masses and testing GR • Champion et al. (2008) Science: PSR J1903+0327, NS mass = 1.74 ± 0.04 Mo (unusually large) • Double pulsar (B) has mass 1.25 Mo - significantly smaller (Lyne et al. 2004 Sci) CSIRO. Gravitational wave detection

10. What can we do with the timing residuals? • Residuals are a measure of unmodelled physics • Are these residuals from … • The pulsar spin-down • Terrestrial time standards • Pulse propagation through the interstellar medium • Orbital companions to the pulsar • Gravitational waves! • Errors in the planetary ephemeris • … CSIRO. Gravitational wave detection

11. Spin-down irregularities No angular signature CSIRO. Gravitational wave detection

12. Terrestrial time standard irregularities Monopolar signature CSIRO. Gravitational wave detection

13. Errors in the planetary ephemerides - e.g. error in the mass of Jupiter Dipolar signature CSIRO. Gravitational wave detection

14. What if gravitational waves exist? Quadrapolar signature CSIRO. Gravitational wave detection

15. The post-fit planet ‘signal’: The effect of fitting Jupiter Simulations of 10 years of pulsar residuals with an RMS of 100ns Mars CSIRO. Gravitational wave detection CSIRO. Measuring the mass of Jupiter using pulsars

16. Current status (Champion et al. 2009, in prep) • Use data from Parkes, Arecibo, Effelsberg and Nancay radio telescopes 9.54791915(11)x10-4 CSIRO. Gravitational wave detection

17. The timing residuals of young pulsars • 76-m Lovell Radio Telescope • 366 pulsars with tspan > 10yr • Hobbs, Lyne & Kramer (2004) Not high time precision experiments CSIRO. Gravitational wave detection

18. Pulsar timing residuals (fit for F0 and F1) CSIRO. Gravitational wave detection

19. Difficulties when categorising timing noise • B1746-20 • B1900+01 CSIRO. Gravitational wave detection

20. Difficulties when categorising timing noise: depends on data span • PSR B1818-04 • Any simple classification scheme would change with data span. • Most large-scale analyses of timing noise used ~3 yr of data. CSIRO. Gravitational wave detection

21. What timing noise is not! • Not observatory dependent - many pulsars also observed at other observatories - see same timing noise • Not off-line processing (use ‘tempo2’ and ‘psrtime’) • Not terrestrial time scales/planetary ephemeris errors - too large • Not ISM effect - not frequency dependent CSIRO. Gravitational wave detection

22. Previous models of timing noise • Random walks in the pulse frequency or its derivatives • Free-precession of the neutron star • Unmodelled planetary companions • Asteroid belts • Magnetospheric effects • Interstellar/interplanetary medium effects • Unmodelled Post-Keplerian orbital parameters • Accretion onto the pulsar’s surface • Large numbers of small glitch events • These models were based on short data sets • Mainly model random, “noise-like” timing residuals CSIRO. Gravitational wave detection

23. Significant F2 values (= cubics in timing residuals) • Glitch events => F2 > 0 (Lyne, Shemar & Graham-Smith 2000) • All pulsars with c < 105 yr have F2 > 0 • For older pulsars 52% have F2 > 0. • Globular cluster pulsar • Timing noise in young pulsars caused by glitch recovery. • Timing noise in older pulsars caused by something else! CSIRO. Gravitational wave detection

24. Periodicities: B1540-06 • Significant 4.38yr periodicity • If planet then Earth-mass. However, significant residuals remain in the timing after fitting for a planet CSIRO. Gravitational wave detection

25. Periodicities: B1642-03 • Time between successive peaks range from 3.4yr to 6.6yr • Radius of curvature smaller at local maxima than at minima CSIRO. Gravitational wave detection

26. Periodicities: B1818-04 • Time between peaks ranges between 7 and 10 years. No significant individual periodicities. CSIRO. Gravitational wave detection

27. Periodicities: B1826-17 • Significant periodicity at 2.9yr (however time between peaks varies by ~10%). • Local maxima have smaller curvature than minima CSIRO. Gravitational wave detection

28. Periodicities: B1828-11 • Significant periodicities - main periodicity at 500d. • 3 components to the slow-down • Modelled by Stairs et al. as free-precession CSIRO. Gravitational wave detection

29. Periodicities: B2148+63 • Significant periodicity at 3.2yr, 7.1yr and 2.1yr. • Larger radius of curvature at maxima than at minima CSIRO. Gravitational wave detection

30. PSR B1931+24 • PSR B1931+24 has recently been reported to undergo “extreme nulling” events (Kramer et al. 2006) • Normal pulsar for 5 to 10 days • Switches off for up to 35 days • The pulsar spin-down rate changes by ~50% between the on and off states (pulsar spinning down faster when “on”) CSIRO. Gravitational wave detection

31. Directly looking at F1 values • PSR J2043-2740 • First pulsar we looked at: • Has 2 F1 values • Has correlated pulse shape changes CSIRO. Gravitational wave detection

32. Modelling B1828-11 • Implication: B1828-11 is not undergoing free-precession! • Undergoes mode 1, 2, 3, 2 …. CSIRO. Gravitational wave detection

33. More 1828-11 simulations CSIRO. Gravitational wave detection

34. PSR J1107-5907 • Recently discovered pulsar with three pulse profiles: • 1) a very strong profile (brightness rivals that of Vela) • 2) weak profile • 3) completely undetectable • => some pulsars exhibit 3 “magnetospheric modes” - have not yet checked to look for correlated slow-down rates. CSIRO. Gravitational wave detection

35. The implications of the model • Have a link between various time-dependent phenomena in pulsars: long-term moding/extreme nulling/intermittency/free-precession/timing noise • Timing noise linked to magnetospheric changes • Quasi-random nature of the mode switches => a random walk in F1 => large scale cubics can exist in the timing residuals • Note: have no understanding of the process creating multiple spin-down rates, but it seems that large changes in spin-down rate => large pulse shape changes. • 50% change in spin-down rate B1931-24 (large shape changes) • ~% change in spin-down rate B1828-11 (moderate shape changes) • Fraction of a % change in spin-down rate B1540-06 (small shape changes?) CSIRO. Gravitational wave detection

36. Glitches CSIRO. Gravitational wave detection

37. An aside: slow glitches • Zou et al. (2004) reported a new phenomenon known as “slow glitches” • No difference between “slow glitches” and timing noise! • B1822-09 (vertical lines are slow-glitches according to Shabanova (2007) CSIRO. Gravitational wave detection

38. Glitches • Sudden speedup in rotation period, relaxing back in days to years • The pulse structure is not notably affected by a glitch => phenomena internal to the neutron star • Current model is that superfluid vortices in the neutron star ‘pin’ to the surface/crust. Catastrophic unpinning leads to a glitch event. • 285 glitches published in 101 objects. • 65% of the glitching pulsars have only glitched once • PSR J1740-3015 has glitched 33 times CSIRO. Gravitational wave detection

39. Glitches • Melatos, Peralta & Wyithe (2008, ApJ) suggest that glitch events follow an avalanche model. • Waiting time between glitches is consistent with a Poissionian process. • … we’re writing a new paper containing more pulsar glitches … • What would you like us to present? Clearly, the glitches are telling us something about the interior of the pulsar … but how do we extract the information? CSIRO. Gravitational wave detection

40. Conclusion • You can do lots of physics/astronomy with radio pulsar timing observations • Most millisecond pulsars are very stable rotators • The spin-down of the youngest pulsars is dominated by glitch recovery • The spin-down of most pulsars is dominated by a quasi-periodic phenomenon. • This is probably telling us something about the interior of the neutron star! CSIRO. Gravitational wave detection