Pulsar Timing Phenomenology … an overview…. George Hobbs Australia Telescope National Facility

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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 B

PSR B 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 10 8 and 2.5 x % of F2 measurements are negative 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 year 11 year 35 year

Red noise simulations

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 B and B Jodrell versus Arecibo residuals for B

Microglitch in B (M24) Cognard, Backer (2004)

PSR B A (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

J and 35ns result van 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) - arecibo Hotan: Parkes observations Some systematic effect at ~100ns Pulsar instabilities? Instrumental effects?

PSR J 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 where the spin frequency and its second derivative are measured over a 10 8 s interval.

sigmaz at 10yrThanks to K.J. Lee

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?