arXiv subjects

R. N. Manchester

Publications and source records attributed to R. N. Manchester.

At least 55 records · Page 3Linked to original sources

arXiv2018

Search for a Radio Pulsar in the Remnant of Supernova 1987A

We have observed the remnant of supernova SN~1987A (SNR~1987A), located in the Large Magellanic Cloud (LMC), to search for periodic and/or transient radio emission with the Parkes 64\,m-diameter radio telescope. We found no evidence of a radio pulsar in our periodicity search and derived 8$σ$ upper bounds on the flux density of any such source of $31\,μ$Jy at 1.4~GHz and $21\,μ$Jy at 3~GHz. Four candidate transient events were detected with greater than $7σ$ significance, with dispersion measures (DMs) in the range 150 to 840\,cm$^{-3}\,$pc. For two of them, we found a second pulse at slightly lower significance. However, we cannot at present conclude that any of these are associated with a pulsar in SNR~1987A. As a check on the system, we also observed PSR~B0540$-$69, a young pulsar which also lies in the LMC. We found eight giant pulses at the DM of this pulsar. We discuss the implications of these results for models of the supernova remnant, neutron star formation and pulsar evolution.

astro-ph.HE↗

arXiv2018

Single-pulse observations of the Galactic Center magnetar PSR J1745$-$2900 at 3.1 GHz

We report on single-pulse observations of the Galactic Center magnetar PSR J1745$-$2900 that were made using the Parkes 64-m radio telescope with a central frequency of 3.1 GHz at five observing epochs between 2013 July and August. The shape of the integrated pulse profiles was relatively stable across the five observations, indicating that the pulsar was in a stable state between MJDs 56475 and 56514. This extends the known stable state of this pulsar to 6.8 months. Short term pulse shape variations were also detected. It is shown that this pulsar switches between two emission modes frequently and that the typical duration of each mode is about ten minutes. No giant pulses or subpulse drifting were observed. Apparent nulls in the pulse emission were detected on MJD 56500. Although there are many differences between the radio emission of magnetars and normal radio pulsars, they also share some properties. The detection of mode changing and pulse nulling in PSR J1745$-$2900 suggests that the basic radio emission process for magnetars and normal pulsars is the same.

astro-ph.HE↗

arXiv2017

Pulsar Rotation Measures and Large-scale Magnetic Field Reversals in the Galactic Disk

We present the measurements of Faraday rotation for 477 pulsars observed by the Parkes 64-m radio telescope and the Green Bank 100-m radio telescope. Using these results along with previous measurements for pulsars and extra-galactic sources, we analyse the structure of the large-scale magnetic field in the Galactic disk. Comparison of rotation measures of pulsars in the disk at different distances as well as with rotation measures of background radio sources beyond the disk reveals large-scale reversals of the field directions between spiral arms and interarm regions. We develop a model for the disk magnetic field, which can reproduce not only these reversals but also the distribution of observed rotation measures of background sources.

astro-ph.GA↗

arXiv2017

Long-term observations of pulsars in the globular clusters 47 Tucanae and M15

Multi-decade observing campaigns of the globular clusters 47 Tucanae and M15 have led to an outstanding number of discoveries. Here, we report on the latest results of the long-term observations of the pulsars in these two clusters. For most of the pulsars in 47 Tucanae we have measured, among other things, their higher-order spin period derivatives, which have in turn provided stringent constraints on the physical parameters of the cluster, such as its distance and gravitational potential. For M15, we have studied the relativistic spin precession effect in PSR B2127+11C. We have used full-Stokes observations to model the precession effect, and to constrain the system geometry. We find that the visible beam of the pulsar is swiftly moving away from our line of sight and may very soon become undetectable. On the other hand, we expect to see the opposite emission beam sometime between 2041 and 2053.

astro-ph.HE↗

arXiv2017

Millisecond Pulsars, their Evolution and Applications

Millisecond pulsars (MSPs) are short-period pulsars that are distinguished from "normal" pulsars, not only by their short period, but also by their very small spin-down rates and high probability of being in a binary system. These properties are consistent with MSPs having a different evolutionary history to normal pulsars, viz., neutron-star formation in an evolving binary system and spin-up due to accretion from the binary companion. Their very stable periods make MSPs nearly ideal probes of a wide variety of astrophysical phenomena. For example, they have been used to detect planets around pulsars, to test the accuracy of gravitational theories, to set limits on the low-frequency gravitational-wave background in the Universe, and to establish pulsar-based timescales that rival the best atomic-clock timescales in long-term stability. MSPs also provide a window into stellar and binary evolution, often suggesting exotic pathways to the observed systems. The X-ray accretion-powered MSPs, and especially those that transition between an accreting X-ray MSP and a non-accreting radio MSP, give important insight into the physics of accretion on to highly magnetised neutron stars.

astro-ph.HE↗

arXiv2017

TMRT observations of 26 pulsars at 8.6 GHz

Integrated pulse profiles at 8.6~GHz obtained with the Shanghai Tian Ma Radio Telescope (TMRT) are presented for a sample of 26 pulsars. Mean flux densities and pulse width parameters of these pulsars are estimated. For eleven pulsars these are the first high-frequency observations and for a further four, our observations have a better signal-to-noise ratio than previous observations. For one (PSR J0742-2822) the 8.6~GHz profiles differs from previously observed profiles. A comparison of 19 profiles with those at other frequencies shows that in nine cases the separation between the outmost leading and trailing components decreases with frequency, roughly in agreement with radius-to-frequency mapping, whereas in the other ten the separation is nearly constant. Different spectral indices of profile components lead to the variation of integrated pulse profile shapes with frequency. In seven pulsars with multi-component profiles, the spectral indices of the central components are steeper than those of the outer components. For the 12 pulsars with multi-component profiles in the high-frequency sample, we estimate the core width using gaussian fitting and discuss the width-period relationship.

astro-ph.HE↗

arXiv2017

Long-term observations of the pulsars in 47 Tucanae - II. Proper motions, accelerations and jerks

This paper is the second in a series where we report the results of the long-term timing of the millisecond pulsars (MSPs) in 47 Tucanae with the Parkes 64-m radio telescope. We obtain improved timing parameters that provide additional information for studies of the cluster dynamics: a) the pulsar proper motions yield an estimate of the proper motion of the cluster as a whole ($μ_α\, = \, 5.00\, \pm \, 0.14\, \rm mas \, yr^{-1}$, $μ_δ\, = \, -2.84\, \pm \, 0.12\, \rm mas \, yr^{-1}$) and the motion of the pulsars relative to each other. b) We measure the second spin-period derivatives caused by the change of the pulsar line-of-sight accelerations; 47 Tuc H, U and possibly J are being affected by nearby objects. c) For ten binary systems we now measure changes in the orbital period caused by their acceleration in the gravitational field of the cluster. From all these measurements, we derive a cluster distance no smaller than $\sim\,$4.69 kpc and show that the characteristics of these MSPs are very similar to their counterparts in the Galactic disk. We find no evidence in favour of an intermediate mass black hole at the centre of the cluster. Finally, we describe the orbital behaviour of the four "black widow" systems. Two of them, 47 Tuc J and O, exhibit orbital variability similar to that observed in other such systems, while for 47 Tuc I and R the orbits seem to be remarkably stable. It appears, therefore, that not all "black widows" have unpredictable orbital behaviour.

astro-ph.HE↗

arXiv2017

Determination of the Sun's Offset from the Galactic Plane Using Pulsars

We derive the Sun's offset from the local mean Galactic plane($z_\odot$) using the observed $z$ distribution of young pulsars. Pulsar distances are obtained from measurements of annual parallax, HI absorption spectra or associations where available and otherwise from the observed pulsar dispersion and a model for the distribution of free electrons in the Galaxy. We fit the cumulative distribution function for a ${\rm sech}^2(z)$ distribution function, representing an isothermal self-gravitating disk, with uncertainties being estimated using the bootstrap method. We take pulsars having characteristic age $τ_c<10^{6.5}$~yr and located within 4.5~kpc of the Sun, omitting those within the local spiral arm and those significantly affected by the Galactic warp, and solve for $z_\odot$ and the scale height, $H$, for different cutoffs in $τ_c$. We compute these quantities using just the independently determined distances, and these together with DM-based distances separately using the YMW16 and NE2001 Galactic electron density models. We find that an age cutoff at $10^{5.75}$~yr with YMW16 DM-distances gives the best results with a minimum uncertainty in $z_\odot$ and an asymptotically stable value for $H$ showing that, at this age and below, the observed pulsar $z$-distribution is dominated by the dispersion in their birth locations. From this sample of 115 pulsars, we obtain $z_\odot=13.4\pm$4.4~pc and $H=56.9\pm$6.5~pc, similar to estimated scale heights for OB stars and open clusters. Consistent results are obtained using the independent-only distances and using the NE2001 model for the DM-based distances.

astro-ph.SR↗

arXiv2017

Comparison of Pulsar Positions from Timing and Very Long Baseline Astrometry

Pulsar positions can be measured with high precision using both pulsar timing methods and very-long-baseline interferometry (VLBI). Pulsar timing positions are referenced to a solar-system ephemeris, whereas VLBI positions are referenced to distant quasars. Here we compare pulsar positions from published VLBI measurements with those obtained from pulsar timing data from the Nanshan and Parkes radio telescopes in order to relate the two reference frames. We find that the timing positions differ significantly from the VLBI positions (and also differ between different ephemerides). A statistically significant change in the obliquity of the ecliptic of $2.16\pm0.33$\,mas is found for the JPL ephemeris DE405, but no significant rotation is found in subsequent JPL ephemerides. The accuracy with which we can relate the two frames is limited by the current uncertainties in the VLBI reference source positions and in matching the pulsars to their reference source. Not only do the timing positions depend on the ephemeris used in computing them, but also different segments of the timing data lead to varying position estimates. These variations are mostly common to all ephemerides, but slight changes are seen at the 10$μ$as level between ephemerides.

astro-ph.HE↗

arXiv2016

Wide-band Profile Domain Pulsar Timing Analysis

We extend profile domain pulsar timing to incorporate wide-band effects such as frequency-dependent profile evolution and broadband shape variation in the pulse profile. We also incorporate models for temporal variations in both pulse width and in the separation in phase of the main pulse and interpulse. We perform the analysis with both nested sampling and Hamiltonian Monte Carlo methods. In the latter case we introduce a new parameterisation of the posterior that is extremely efficient in the low signal-to-noise regime and can be readily applied to a wide range of scientific problems. We apply this methodology to a series of simulations, and to between seven and nine yr of observations for PSRs J1713$+$0747, J1744$-$1134, and J1909$-$3744 with frequency coverage that spans 700-3600MHz. We use a smooth model for profile evolution across the full frequency range, and compare smooth and piecewise models for the temporal variations in DM. We find the profile domain framework consistently results in improved timing precision compared to the standard analysis paradigm by as much as 40% for timing parameters. Incorporating smoothness in the DM variations into the model further improves timing precision by as much as 30%. For PSR J1713+0747 we also detect pulse shape variation uncorrelated between epochs, which we attribute to variation intrinsic to the pulsar at a level consistent with previously published analyses. Not accounting for this shape variation biases the measured arrival times at the level of $\sim$30ns, the same order of magnitude as the expected shift due to gravitational-waves in the pulsar timing band.

astro-ph.IM↗

arXiv2016

Pulse profiles and timing of PSR J1757$-$2421

Pulse arrival time measurements over fourteen years with the Nanshan 25-m and Parkes 64-m radio telescopes have been used to determine the average profile and timing properties for PSR J1757$-$2421 (B1754$-$24). Analysis of the radio profile data shows a large variation of spectral index across the profile and an unusual increase in component separation with increasing frequency. The timing observations show that PSR B1754$-$24 underwent a large glitch with a fractional increase in spin frequency of $Δν_{\rm g}/ν\sim 7.8\times10^{-6}$ in May 2011. At the time of the glitch there was a large permanent jump in the rotational frequency accompanied by two exponential recovery terms with timescales of 15(6) and 97(15) days, respectively.

astro-ph.HE↗

arXiv2016

A New Electron Density Model for Estimation of Pulsar and FRB Distances

We present a new model for the distribution of free electrons in the Galaxy, the Magellanic Clouds and the intergalactic medium (IGM) that can be used to estimate distances to real or simulated pulsars and fast radio bursts (FRBs) based on their dispersion measure (DM). The Galactic model has an extended thick disk representing the so-called warm interstellar medium, a thin disk representing the Galactic molecular ring, spiral arms based on a recent fit to Galactic HII regions, a Galactic Center disk and seven local features including the Gum Nebula, Galactic Loop I and the Local Bubble. An offset of the Sun from the Galactic plane and a warp of the outer Galactic disk are included in the model. Parameters of the Galactic model are determined by fitting to 189 pulsars with independently determined distances and DMs. Simple models are used for the Magellanic Clouds and the IGM. Galactic model distances are within the uncertainty range for 86 of the 189 independently determined distances and within 20\% of the nearest limit for a further 38 pulsars. We estimate that 95\% of predicted Galactic pulsar distances will have a relative error of less than a factor of 0.9. The predictions of YMW16 are compared to those of the TC93 and NE2001 models showing that YMW16 performs significantly better on all measures. Timescales for pulse broadening due to interstellar scattering are estimated for (real or simulated) Galactic and Magellanic Cloud pulsars and FRBs.

astro-ph.GA↗

arXiv2016

The disturbance of a millisecond pulsar magnetosphere

Pulsar timing has enabled some of the strongest tests of fundamental physics. Central to the technique is the assumption that the detected radio pulses can be used to accurately measure the rotation of the pulsar. Here we report on a broad-band variation in the pulse profile of the millisecond pulsar J1643-1224. A new component of emission suddenly appears in the pulse profile, decays over 4 months, and results in a permanently modified pulse shape. Profile variations such as these may be the origin of timing noise observed in other millisecond pulsars. The sensitivity of pulsar-timing observations to gravitational radiation can be increased by accounting for this variability.

astro-ph.HE↗

arXiv2016

Long-term observations of the pulsars in 47 Tucanae. I. A study of four elusive binary systems

For the past couple of decades, the Parkes radio telescope has been regularly observing the millisecond pulsars in 47 Tucanae (47 Tuc). This long-term timing program was designed to address a wide range of scientific issues related to these pulsars and the globular cluster where they are located. In this paper, the first of a series, we address one of these objectives: the characterization of four previously known binary pulsars for which no precise orbital parameters were known, namely 47 Tuc P, V, W and X (pulsars 47 Tuc R and Y are discussed elsewhere). We determined the previously unknown orbital parameters of 47 Tuc V and X and greatly improved those of 47 Tuc P and W. For pulsars W and X we obtained, for the first time, full coherent timing solutions across the whole data span, which allowed a much more detailed characterization of these systems. 47 Tuc W, a well-known tight eclipsing binary pulsar, exhibits a large orbital period variability, as expected for a system of its class. 47 Tuc X turns out to be in a wide, extremely circular, 10.9-day long binary orbit and its position is ~3.8 arcmin away from the cluster center, more than three times the distance of any other pulsar in 47 Tuc. These characteristics make 47 Tuc X a very different object with respect to the other pulsars of the cluster.

astro-ph.HE↗

arXiv2016

Proper motions of 15 pulsars: a comparison between Bayesian and frequentist algorithms

We present proper motions for 15 pulsars which are observed regularly by the Nanshan 25-m radio telescope. Two methods, the frequentist method (Coles et al.2011) and the Bayesian (Lentati et al. 2014) method, are used and the results are compared. We demonstrate that the two methods can be applied to young pulsar data sets that exhibit large amounts of timing noise with steep spectral exponents and give consistent results. The measured positions also agree with very-long-baseline interferometric positions. Proper motions for four pulsars are obtained for the first time, and improved values are obtained for five pulsars.

astro-ph.IM↗

arXiv2016

Investigation of nulling and subpulse drifting properties of PSR J1727$-$2739

Aims. To make a detailed study of the nulling and subpulse drifting in PSR J1727$-$2739 for investigation of its radiation properties. Methods. The observations were carried out on 20 March, 2004 using the Parkes 64-m radio telescope, with a central frequency of 1518 MHz. A total of 5568 single pulses were analysed. Results. This pulsar shows well defined nulls with lengths lasting from 6 to 281 pulses and separated by burst phases ranging from 2 to 133 pulses. We estimate a nulling fraction of around 68\%. No emission in the average pulse profile integrated over all null pulses is detected with significance above $3σ$. Most transitions from nulls to bursts are within a few pulses, whereas the transitions from bursts to nulls exhibit two patterns of decay: decrease gradually or rapidly. In the burst phase, we find that there are two distinct subpulse drift modes with vertical spacing between the drift bands of $9.7 \pm 1.6$ and $5.2 \pm 0.9$ pulse periods, while sometimes there is a third mode with no subpulse drifting. Some mode transitions occur within a single burst, while others are separated by nulls. Different modes have different average pulse profiles. Possible physical mechanisms are discussed.

astro-ph.HE↗

arXiv2016

Characterising the rotational irregularities of the Vela pulsar from 21 yr of phase-coherent timing

Pulsars show two classes of rotational irregularities that can be used to understand neutron-star interiors and magnetospheres: glitches and timing noise. Here we present an analysis of the Vela pulsar spanning nearly 21 yr of observation and including 8 glitches. We identify the relative pulse number of all of the observations between glitches, with the only pulse-number ambiguities existing over glitch events. We use the phase coherence of the timing solution to simultaneously model the timing noise and glitches in a Bayesian framework, allowing us to select preferred models for both. We find the glitches can be described using only permanent and transient changes in spin frequency, i.e., no step changes in frequency derivative. For all of the glitches, we only need two exponentially decaying changes in spin frequency to model the transient components. In contrast to previous studies, we find that the dominant transient components decay on a common $\approx$ 1300 d time scale, and that a larger fraction ( $\gtrsim 25\%$) of glitch amplitudes are associated with these transient components. We also detect shorter-duration transient components of $\approx$ 25 d, as previously observed, but are limited in sensitivity to events with shorter durations by the cadence of our observations. The timing noise is well described by a steep power-law process that is independent of the glitches and subdominant to the glitch recovery. The braking index is constrained to be $<$ 8 with 95% confidence. This methodology can be used to robustly measure the properties of glitches and timing noise in other pulsars.

astro-ph.HE↗

arXiv2016

From Spin Noise to Systematics: Stochastic Processes in the First International Pulsar Timing Array Data Release

We analyse the stochastic properties of the 49 pulsars that comprise the first International Pulsar Timing Array (IPTA) data release. We use Bayesian methodology, performing model selection to determine the optimal description of the stochastic signals present in each pulsar. In addition to spin-noise and dispersion-measure (DM) variations, these models can include timing noise unique to a single observing system, or frequency band. We show the improved radio-frequency coverage and presence of overlapping data from different observing systems in the IPTA data set enables us to separate both system and band-dependent effects with much greater efficacy than in the individual PTA data sets. For example, we show that PSR J1643$-$1224 has, in addition to DM variations, significant band-dependent noise that is coherent between PTAs which we interpret as coming from time-variable scattering or refraction in the ionised interstellar medium. Failing to model these different contributions appropriately can dramatically alter the astrophysical interpretation of the stochastic signals observed in the residuals. In some cases, the spectral exponent of the spin noise signal can vary from 1.6 to 4 depending upon the model, which has direct implications for the long-term sensitivity of the pulsar to a stochastic gravitational-wave (GW) background. By using a more appropriate model, however, we can greatly improve a pulsar's sensitivity to GWs. For example, including system and band-dependent signals in the PSR J0437$-$4715 data set improves the upper limit on a fiducial GW background by $\sim 60\%$ compared to a model that includes DM variations and spin-noise only.

astro-ph.IM↗