We provide an analysis of timing irregularities observed for 366 pulsars. Observations were obtained using the 76-m Lovell radio telescope at the Jodrell Bank Observatory over the past 36 years. ...These data sets have allowed us to carry out the first large-scale analysis of pulsar timing noise over time-scales of >10 yr, with multiple observing frequencies and for a large sample of pulsars. Our sample includes both normal and recycled pulsars. The timing residuals for the pulsars with the smallest characteristic ages are shown to be dominated by the recovery from glitch events, whereas the timing irregularities seen for older pulsars are quasi-periodic. We emphasize that previous models that explained timing residuals as a low-frequency noise process are not consistent with observation.
Abstract
Braking index measurements offer the opportunity to explore the processes affecting the long-term spin evolution of pulsars and possible evolutionary connections between the various pulsar ...populations. In most cases, such measurements are difficult because of the presence of short-term phenomena, such as glitches and timing noise, which obscure the long-term trends. In particular, recoveries from large glitches are the main obstacle to measuring the braking indices of young pulsars like the Vela and Crab pulsars. We present a new method to overcome this problem and report on braking index measurements for the Vela-like pulsars, PSR B1800−21 and PSR B1823−13, together with an updated measurement for Vela. Additionally, the use of the method is extended to six more young glitching pulsars observed at Jodrell Bank Observatory and we are able to estimate four new braking indices. Values of braking indices describe the long-term evolution of the pulsars across the P–
$\dot{P}$
diagram. Despite some measurements being affected by considerable uncertainties, there is evidence for a common trend among young glitching pulsars, characterized by low braking indices n ≤ 2. Such values introduce a new variant in the evolution of young pulsars, and their relationship with other populations in the P–
$\dot{P}$
diagram, and imply that these pulsars could be a few times older than indicated by standard formulae. In this context, we analyse the case of PSR B1757−24 and conclude that the pulsar could be old enough to be related to the supernova remnant G5.4−1.2. Between glitches, the short-term evolution of Vela-like pulsars is characterized by large interglitch braking indices n
ig > 10. We interpret both short- and long-term trends as signatures of the large glitch activity, and speculate that they are driven by short-term post-glitch re-coupling and a cumulative long-term decoupling of superfluid to the rotation of the star.
The rotation of more than 700 pulsars has been monitored using the 76-m Lovell Telescope at Jodrell Bank. Here we report on a new search for glitches in the observations, revealing 128 new glitches ...in the rotation of 63 pulsars. Combining these new data with those already published, we present a data base containing 315 glitches in 102 pulsars. The data base was used to study the glitch activity among the pulsar population, finding that it peaks for pulsars with a characteristic age τc∼ 10 kyr and decreases for longer values of τc, disappearing for objects with τc > 20 Myr. The glitch activity is also smaller in the very young pulsars (τc≲ 1 kyr). The cumulative effect of glitches, a collection of instantaneous spin-up events, acts to reduce the regular long-term spin-down rate
of the star. The percentage of
reversed by glitch activity was found to vary between 0.5 and 1.6 per cent for pulsars with spin-down rates
between 10−14 and 3.2 × 10−11 Hz s−1, decreasing to less than 0.01 per cent at both higher and lower spin-down rates. These ratios are interpreted in terms of the amount of superfluid involved in the generation of glitches. In this context, the activity of the youngest pulsar studied, the Crab pulsar, may be explained by quake-like activity within the crust. Pulsars with low spin-down rates seem to exhibit mostly small glitches, matching well the decrease of their crustal superfluid.
Through the analysis of glitch sizes, it was found that the particular glitching behaviour of PSR J0537−6910 and the Vela pulsar may be shared by most Vela-like pulsars. These objects present most of their glitches with characteristic frequency and frequency derivative jumps, occurring at regular intervals of time. Their behaviour is different from other glitching pulsars of similar characteristic age.
A statistical study of 233 pulsar proper motions Hobbs, G.; Lorimer, D. R.; Lyne, A. G. ...
Monthly notices of the Royal Astronomical Society,
July 2005, Letnik:
360, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We present and analyse a catalogue of 233 pulsars with proper motion measurements. The sample contains a wide variety of pulsars including recycled objects and those associated with globular clusters ...or supernova remnants. After taking the most precise proper motions for those pulsars for which multiple measurements are available, the majority of the proper motions (58 per cent) are derived from pulsar timing methods, 41 per cent using interferometers and the remaining 1 per cent using optical telescopes. Many of the one-dimensional (1D) and two-dimensional (2D) speeds (referring to speeds measured in one coordinate only and the magnitudes of the transverse velocities, respectively) derived from these measurements are somewhat lower than earlier estimates because of the use of the most recent electron density model in determining pulsar distances. The mean 1D speeds for the normal and recycled pulsars are 152(10) and 54(6) km s−1, respectively. The corresponding mean 2D speeds are 246(22) and 87(13) km s−1. PSRs B2011+38 and B2224+64 have the highest inferred 2D speeds of ~1600 km s−1. We study the mean speeds for different subsamples and find that, in general, they agree with previous results. Applying a novel deconvolution technique to the sample of 73 pulsars with characteristic ages less than 3 Myr, we find the mean three-dimensional (3D) pulsar birth velocity to be 400(40) km s−1. The distribution of velocities is well described by a Maxwellian distribution with 1D rms σ = 265 km s−1. There is no evidence for a bimodal velocity distribution. The proper motions for PSRs B1830-08 and B2334+61 are consistent with their proposed associations with the supernova remnants W41 and G114.3+0.3, respectively.
Abstract
PSR B1820−30A is located in the globular cluster NGC 6624 and is the closest known pulsar to the centre of any globular cluster. We present more than 25 yr of high-precision timing ...observations of this millisecond pulsar and obtain four rotational frequency time derivative measurements. Modelling these higher order derivatives as being due to orbital motion, we find solutions that indicate the pulsar is in either a low-eccentricity (0.33 ≲ e ≲ 0.4) smaller orbit with a low-mass companion (such as a main-sequence star, white dwarf, neutron star or stellar mass black hole) or a high-eccentricity (e ≳ 0.9) larger orbit with a massive companion. The cluster mass properties and the observed properties of 4U 1820−30 and the other pulsars in the cluster argue against the low-eccentricity possibility. The high-eccentricity solution reveals that the pulsar is most likely orbiting around an intermediate-mass black hole (IMBH) of mass >7500 M⊙ located at the cluster centre. A gravitational model for the globular cluster, which includes such a central BH, predicts an acceleration that is commensurate with that measured for the pulsar. It further predicts that the model-dependent minimum mass of the IMBH is ∼60 000 M⊙. Accounting for the associated contribution to the observed period derivative indicates that the γ-ray efficiency of the pulsar should be between 0.08 and 0.2. Our results suggest that other globular clusters may also contain central BHs and they may be revealed by the study of new pulsars found sufficiently close to their centres.
We report on the high-precision timing of 42 radio millisecond pulsars (MSPs) observed by the European Pulsar Timing Array (EPTA). This EPTA Data Release 1.0 extends up to mid-2014 and baselines ...range from 7–18 yr. It forms the basis for the stochastic gravitational-wave background, anisotropic background, and continuous-wave limits recently presented by the EPTA elsewhere. The Bayesian timing analysis performed with temponest
yields the detection of several new parameters: seven parallaxes, nine proper motions and, in the case of six binary pulsars, an apparent change of the semimajor axis. We find the NE2001 Galactic electron density model to be a better match to our parallax distances (after correction from the Lutz–Kelker bias) than the M2 and M3 models by Schnitzeler. However, we measure an average uncertainty of 80 per cent (fractional) for NE2001, three times larger than what is typically assumed in the literature. We revisit the transverse velocity distribution for a set of 19 isolated and 57 binary MSPs and find no statistical difference between these two populations. We detect Shapiro delay in the timing residuals of PSRs J1600−3053 and J1918−0642, implying pulsar and companion masses
$m_{\rm p}=1.22_{-0.35}^{+0.5}\ {\rm M}_{{\odot }}$
,
$m_{\rm c} = 0.21_{-0.04}^{+0.06}\ {\rm M}_{{\odot } }$
and
$m_{\rm p}=1.25_{-0.4}^{+0.6}\ {\rm M}_{{\odot }}$
,
$m_{\rm c} = 0.23_{-0.05}^{+0.07}\ {\rm M}_{{\odot } }$
, respectively. Finally, we use the measurement of the orbital period derivative to set a stringent constraint on the distance to PSRs J1012+5307 and J1909−3744, and set limits on the longitude of ascending node through the search of the annual-orbital parallax for PSRs J1600−3053 and J1909−3744.
45 years of rotation of the Crab pulsar Lyne, A. G; Jordan, C. A; Graham-Smith, F ...
Monthly notices of the Royal Astronomical Society,
01/2015, Letnik:
446, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The 30-Hz rotation rate of the Crab pulsar has been monitored at Jodrell Bank Observatory since 1984 and by other observatories before then. Since 1968, the rotation rate has decreased by about ...0.5 Hz, interrupted only by sporadic and small spin-up events (glitches). 24 of these events have been observed, including a significant concentration of 15 occurring over an interval of 11 yr following MJD 50000. The monotonic decrease of the slowdown rate is partially reversed at glitches. This reversal comprises a step and an asymptotic exponential with a 320-d time constant, as determined in the three best-isolated glitches. The cumulative effect of all glitches is to reduce the decrease in slowdown rate by about 6 per cent. Overall, a low mean braking index of 2.342(1) is measured for the whole period, compared with values close to 2.5 in intervals between glitches. Removing the effects of individual glitches reveals an underlying power-law slowdown with the same braking index of 2.5. We interpret this value in terms of a braking torque due to a dipolar magnetic field in which the inclination angle between the dipole and rotation axes is increasing. There may also be further effects due to a monopolar particle wind or infalling supernova debris.
On the origin of a highly dispersed coherent radio burst Keane, E. F.; Stappers, B. W.; Kramer, M. ...
Monthly notices of the Royal Astronomical Society. Letters,
September 2012, 2012-09-01, 20120901, Letnik:
425, Številka:
1
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
We discuss the possible source of a highly dispersed radio transient discovered in the Parkes Multibeam Pulsar Survey (PMPS). The pulse has a dispersion measure of 746 cm−3 pc, a peak flux ...density of 400 mJy for the observed pulse width of 7.8 ms and a flat spectrum across a 288‐MHz band centred on 1374 MHz. The flat spectrum suggests that the pulse did not originate from a pulsar, but is consistent with radio‐emitting magnetar spectra. The non‐detection of subsequent bursts constrains any possible pulsar period to ≳1 s, and the pulse energy distribution to being much flatter than typical giant pulse emitting pulsars. The burst is also consistent with the radio signal theorized from an annihilating mini black hole. Extrapolating the PMPS detection rate provides a limit of on the density of these objects. We investigate the consistency of these two scenarios, plus several other possible solutions, as potential explanations to the origin of the pulse, as well as for another transient with similar properties: the Lorimer burst.
Timing observations from the Parkes 64-m radio telescope for 165 pulsars between 1990 and 2011 have been searched for period glitches. Data spans for each pulsar ranged between 5.3 and 20.8 yr. From ...the total of 1911 yr of pulsar rotational history, 107 glitches were identified in 36 pulsars. Out of these glitches, 61 have previously been reported whereas 46 are new discoveries. Glitch parameters, both for the previously known and the new glitch detections, were measured by fitting the timing residual data. Observed relative glitch sizes Δνg/ν range between 10−10 and 10−5, where ν = 1/P is the pulse frequency. We confirm that the distribution of Δνg/ν is bimodal with peaks at approximately 10−9 and 10−6. Glitches are mostly observed in pulsars with characteristic ages between 103 and 105 yr, with large glitches mostly occurring in the younger pulsars. Exponential post-glitch recoveries were observed for 27 large glitches in 18 pulsars. The fraction Q of the glitch that recovers exponentially also has a bimodal distribution. Large glitches generally have low Q, typically just a few per cent, but large Q values are observed in both large and small glitches. Observed time constants for exponential recoveries ranged between 10 and 300 d with some tendency for longer time-scales in older pulsars. Shorter time-scale recoveries may exist but were not revealed by our data which typically have observation intervals of 2-4 weeks. For most of the 36 pulsars with observed glitches, there is a persistent linear increase in
(i.e. decrease in the slow-down rate
) in the interglitch interval. Where an exponential recovery is also observed, the effects of this are superimposed on the linear increase in
. In some but not all cases, the slope of the linear recovery changes at the time of a glitch. The
values characterizing the linear changes in
are almost always positive and, after subtracting the magnetospheric component of the braking, are approximately proportional to the ratio of
and the interglitch interval, as predicted by vortex-creep models.
We describe observations of Rotating Radio Transients (RRATs) that were discovered in a re-analysis of the Parkes Multibeam Pulsar Survey (PMPS). The sources have now been monitored for sufficiently ...long to obtain seven new coherent timing solutions to make a total of 14 now known. Furthermore, we announce the discovery of seven new transient sources, one of which may be extragalactic in origin (with z∼ 0.1) and would then be a second example of the so-called 'Lorimer burst'. The timing solutions allow us to infer neutron star characteristics such as energy-loss rate, magnetic field strength and evolutionary time-scales, as well as facilitating multiwavelength followup by providing accurate astrometry. All of this enables us to consider the question of whether or not RRATs are in any way special, i.e. a distinct and separate population of neutron stars, as has been previously suggested. We see no reason to consider 'RRAT' as anything other than a detection label, the subject of a selection effect in the parameter space searched. However, single-pulse searches can be utilized to great effect to identify pulsars difficult, or impossible, to find by other means, in particular those with long periods (half of the PMPS RRATs have periods greater than 4 s), high magnetic field strengths (B≳ 1013 G) and pulsars approaching the 'death valley'. The detailed nulling properties of such pulsars are unknown but the mounting evidence suggests a broad range of behaviour in the pulsar population. The group of RRATs fits in to the picture where pulsar magnetospheres switch between stable configurations.
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