Crab pulsar photometry and the signature of free precession

Čadež, A.; Vidrih, S.; Galicic, M.; Carramiñana, A.

doi:10.1051/0004-6361:20000283

Cited by 14 publications

(10 citation statements)

References 11 publications

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“…Ulmer et al (1994) reported that the intensity ratio of the two peaks in the gamma‐ray pulse of the Crab seems to vary sinusoidally with a period of ≈14 yr in both the 50–500 keV and 50 MeV bands (but not in the optical). However, the 14‐yr period differs from that observed by Lyne et al (1988) and a 60‐s modulation of the Crab’s optical pulses found by Čadež et al (1997).…”

Section: Application To Observationscontrasting

confidence: 69%

“…Tentative reports also exist of oscillatory variations in Crab and Vela timing residuals (e.g. Lyne, Pritchard & Smith 1988; McCulloch et al 1990; Čadež, Galičič & Calvani 1997), and some authors have inferred changes in α on the braking time‐scale from braking‐index measurements (Allen & Horvath 1997; Link & Epstein 1997) and the evolution of pulsar radio beam statistics (Tauris & Manchester 1998).…”

Section: Introductionmentioning

confidence: 99%

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Radiative precession of an isolated neutron star

Melatos

2000

Monthly Notices of the Royal Astronomical Society

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Euler’s equations of motion are derived exactly for a rigid, triaxial, internally frictionless neutron star spinning down electromagnetically in vacuo. It is shown that the star precesses, but not freely: its regular precession relative to the principal axes of inertia couples to the component of the radiation torque associated with the near‐zone radiation fields and is modified into an anharmonic wobble. The wobble period τ1 typically satisfies τ1≲10−2τ0, where τ0 is the braking time‐scale; the wobble amplitude evolves towards a constant non‐zero value, oscillates, or decreases to zero, depending on the degree of oblateness or prolateness of the star and its initial spin state; the (negative) angular frequency derivative ω˙ oscillates as well, exhibiting quasi‐periodic spikes for triaxial stars of a particular figure. In light of these properties, a young, Crab‐like pulsar ought to display fractional changes of order unity in the space of a few years in its pulse profile, magnetic inclination angle and ω˙. Such changes are not observed, implying that the wobble is damped rapidly by internal friction, if its amplitude is initially large upon crystallization of the stellar crust. If the friction is localized in the inner and outer crusts, the thermal luminosity of the neutron star increases by a minimum amount ΔL≈3×1031(ε/10−12)(ω/103 rad s−1)2(τd/1 yr)−1 erg s−1, where ε is the ellipticity, and τd is the damping time‐scale, with the actual value of ΔL determined in part by the thermal conduction time τcond. The increased luminosity is potentially detectable as thermal X‐rays lasting for a time ≈ max(τd,τcond) following crystallization of the crust.

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Section: Application To Observationscontrasting

confidence: 69%

Section: Introductionmentioning

confidence: 99%

Radiative precession of an isolated neutron star

Melatos

2000

Monthly Notices of the Royal Astronomical Society

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“…Optical photometry of PSR 0531+21 over the last seven years [19] have confirmed the existence of variations of the pulsar emission with a period of ∼60 s. The observed period and its time dependence agree well with a free-precession model. Along with the short-period variations, analysis of observations of PSR 0531+021 has revealed longterm, quasi-periodic oscillations with a period of 15 to 30 months [10].…”

Section: Monitoring Of Pulsarssupporting

confidence: 67%

10.1007/s11444-008-1007-0

2010

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Assuming that the observed periodic variations of pulsar emission are due to the free precession of the spin axis, we investigate the evolution of the rotation of a two-layer neutron star using the Hamiltonian method of Getino. We model the dynamical characteristics of a rotating neutron star using the observed variations of the emission of seven pulsars. We estimate the dependence of the period of the Chandler wobble, the period of precession of the spin axis, and the dynamical ellipticity of a neutron star on the model used to describe the super-dense neutron matter and the mass of the star.

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“…More recently, evidence has been presented for a 60‐s modulation in the Crab pulsar's amplitude and phase residual, both in the optical band (Čadež & Galičič 1996a,b; Čadež, Galičič & Calvini 1997). This is by far the shortest free precession period to have been proposed in the literature.…”

Section: Analysis Of Observations Of Free Precessionmentioning

confidence: 99%

Freely precessing neutron stars: model and observations

Jones

Andersson

2001

Monthly Notices of the Royal Astronomical Society

133

235

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We present a model of a freely precessing neutron star, which is then compared against pulsar observations. The aim is to draw conclusions regarding the structure of the star, and to test theoretical ideas of crust±core coupling and superfluidity. We argue that, on theoretical grounds, it is likely that the core neutron superfluid does not participate in the free precession of the crust. We apply our model to the handful of proposed observations of free precession that have appeared in the literature. Assuming crust-only precession, we find that all but one of the observations are consistent with there being no pinned crustal superfluid at all; the maximum amount of pinned superfluid consistent with the observations is about 10 210 of the total stellar moment of inertia. However, the observations do not rule out the possibility that the crust and neutron superfluid core precess as a single unit. In this case the maximum amount of pinned superfluid consistent with the observations is about 10 28 of the total stellar moment of inertia. Both of these values are many orders of magnitude less than the 10 22 value predicted by many theories of pulsar glitches. We conclude that superfluid pinning, at least as it affects free precession, needs to be reconsidered.

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Crab pulsar photometry and the signature of free precession

Cited by 14 publications

References 11 publications

Radiative precession of an isolated neutron star

Radiative precession of an isolated neutron star

10.1007/s11444-008-1007-0

Freely precessing neutron stars: model and observations

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