Pulsar Timing Phenomenology

… an overview….

George HobbsAustralia Telescope National Facility

Sorry for being late!

Introduction

• Timing residuals for ‘normal’ pulsars (based on Jodrell Bank Observatory data)

• Timing residuals for millisecond pulsars (based on Parkes/Arecibo/GB/Nancay data)

Summary:

•Timing noise is wide-spread in pulsars

•Timing noise in millisecond pulsars is similar in structure to that seen in young pulsars

•The predicted amplitude of timing noise in some millisecond pulsars is low and provides hope for the detection of GWs

Pulsar timing: The basics

Obtain pulse arrival times at observatory

Model for pulsar spin down

Form timing residuals – how good is the timing model at predicting the arrival times

Improve timing model

Pulsar post-fit timing residuals

Fit for rotational period and its derivative (quadratic term)

PSR B1900+06

PSR B1828-11

Timing noise explained as free-precession due to periodicities and correlated pulse shape changes

Characterising the residuals (mag. dipole rad.)

‘n’ ranges between –2.6 x 108 and 2.5 x 108

46% of F2 measurements are negative

23v

vvn

•Strong correlation between amplitude of “timing noise” and first and second derivative of rotational frequency (also age)

•No correlation found so far with timescale of timing noise and any pulsar parameter.

•On average the timing residuals show sharper local maxima than local minima

30yr

Evolution of the characterisation

1 year 5 year

6 year11 year

35 year

Red noise simulations

AfP

Disproven theories of timing noise

• Off-line software

• Observatories/receiver systems …

• Frequency-dependent noise

• Timing noise is not correlated with “height above the Galactic plane, luminosity or pulse shape changes” – Cordes & Helfand (1980)

The cause of these structures in the timing residuals

• Unmodelled binary companions• Clouds of particles• Post-Newtonian orbital effects• Free-precession of the neutron star• Vortex creep• Accretion onto surface• Magnetospheric effects• Irregularities in terrestrial time standards• Inaccuracies in planetary ephemeris• Effects of gravitational waves

How do you tell?

• Expect (pseudo)-sinusoidal features for orbital/precessional effects

• Expect glitch-like phenomena in vortex creep models

• Expect particular power-spectrum for magnetospheric/phase noise/slowing-down noise

• Expect particular correlations between pulsars for GWs/time or solar system inaccuracies

• Theory provides expected amplitudes and time-scales

Timing noise in the millisecond pulsars

PSRs B1855+09 and B1937+21

Jodrell versus Arecibo residuals for B1937+21

Microglitch in B1821-24 (M24)

• Cognard, Backer (2004)

PSR B1744-24A (Nice, Arzoumanian, Thorsett), Terzan 5

Discussed possibilities:

Timing noise intrinsic to the pulsar (but many times larger than other millisecond pulsars)

Changes in the viewing geometry of the emission region (precession)

A “lumpy” disk around the binary system (precursor to planet formation)

Torques on the pulsar due to infalling matter

J0437-4715 and 35ns resultvan Straten (2001), Nature: arrival times averaged in 40 phase bins – rms residual of 35 ns

Current result: 450ns with 5 minute integrations

thesis, Splaver (2004) - areciboHotan: Parkes observations

Some systematic effect at ~100ns

Pulsar instabilities?Instrumental effects?

0437-4715

1909-3715

PSR J1909-3715• 5 minute integrations, rms = 200 ns, 5 minute integrations

Predicted amplitudes for the recycled pulsars

Backer (2005) – Aspen meeting

only Jodrell data

3yr spans

8 yr spans

3

108 ||6

1log t

where the spin frequency and its second derivative are measured over a 108 s interval.

0374.0056.010 94.2~ PPyrz

sigmaz at 10yrThanks to K.J. Lee

72 10hg

82 10hg

Conclusion

• Timing irregularities seen in both normal and millisecond pulsars

• “Amount” of timing noise correlated with Pdot (and age)

• Jodrell Bank observatory contains an archive of ~400 pulsars with data spanning up to 35 years

• Many theories of timing noise … how can we disprove some of these models?