The timing behaviour of radio pulsars George Hobbs Australia Telescope National

The timing behaviour of radio pulsars George Hobbs Australia Telescope National www.phwiki.com

The timing behaviour of radio pulsars George Hobbs Australia Telescope National

Gallen, Tim, Managing Editor has reference to this Academic Journal, PHwiki organized this Journal The timing behaviour of radio pulsars George Hobbs Australia Telescope National Facility george.hobbs@csiro.au Contents Radio pulsars Pulsar timing A few things that you can do with pulsar timing Young pulsars – a new (predictive) model as long as timing noise What has this to do with this conference – pulsars are compact objects – radio pulsar timing is a powerful technique as long as studying pulsars – can determine parameters of interest – neutron star masses, rotation rates etc. – can study the pulsar spin-down => implications as long as internal structure of neutron star. Let’s start at the beginning 08:35:20.61 -45:10:34.87

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Radio pulsars Animation: Michael Kramer Properties of radio pulsars Pulsar timing: The basics (see Hobbs, Edwards & Manchester 2006, MNRAS) Obtain pulse arrival times at observatory Model as long as pulsar spin down Form timing residuals – how good is the timing model at predicting the arrival times Improve timing model

What can we do with the timing model 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) Determine pulsar masses in addition to 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)

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 st in addition to ards Pulse propagation through the interstellar medium Orbital companions to the pulsar Gravitational waves! Errors in the planetary ephemeris Spin-down irregularities No angular signature Terrestrial time st in addition to ard irregularities Monopolar signature

Errors in the planetary ephemerides – e.g. error in the mass of Jupiter Dipolar signature What if gravitational waves exist Quadrapolar signature The post-fit planet ‘signal’: The effect of fitting CSIRO. Measuring the mass of Jupiter using pulsars Jupiter Mars Simulations of 10 years of pulsar residuals with an RMS of 100ns

Current status (Champion et al. 2009, in prep) Use data from Parkes, Arecibo, Effelsberg in addition to Nancay radio telescopes 9.54791915(11)x10-4 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 Pulsar timing residuals (fit as long as F0 in addition to F1)

Difficulties when categorising timing noise B1746-20 B1900+01 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. 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’ in addition to ‘psrtime’) Not terrestrial time scales/planetary ephemeris errors – too large Not ISM effect – not frequency dependent

Previous models of timing noise R in addition to om 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 r in addition to om, “noise-like” timing residuals 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. Timing noise in young pulsars caused by glitch recovery. Timing noise in older pulsars caused by something else! Globular cluster pulsar Periodicities: B1540-06 Significant 4.38yr periodicity If planet then Earth-mass. However, significant residuals remain in the timing after fitting as long as a planet

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Periodicities: B1642-03 Time between successive peaks range from 3.4yr to 6.6yr Radius of curvature smaller at local maxima than at minima Periodicities: B1818-04 Time between peaks ranges between 7 in addition to 10 years. No significant individual periodicities. Periodicities: B1826-17 Significant periodicity at 2.9yr (however time between peaks varies by ~10%). Local maxima have smaller curvature than minima

Periodicities: B1828-11 Significant periodicities – main periodicity at 500d. 3 components to the slow-down Modelled by Stairs et al. as free-precession Periodicities: B2148+63 Significant periodicity at 3.2yr, 7.1yr in addition to 2.1yr. Larger radius of curvature at maxima than at minima PSR B1931+24 PSR B1931+24 has recently been reported to undergo “extreme nulling” events (Kramer et al. 2006) Normal pulsar as long as 5 to 10 days Switches off as long as up to 35 days The pulsar spin-down rate changes by ~50% between the on in addition to off states (pulsar spinning down faster when “on”)

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!

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