While the temporal variations of the spectropolarimetric nature of pulsars remain unexplored, this investigation offers significant potential for uncovering key insights into pulsar emission mechanisms, magnetic field geometry, and propagation effects within the magnetosphere. We developed a package for investigating time-varying spectral behavior for full Stokes parameters and demonstrate it on a millisecond pulsar (MSP), J2144−5237, in a binary system (orbital period ∼10 days) using the Parkes Ultra-Wideband Low receiver. In this study we report rotation measure variation with orbital phase. We find that the temporal variations in the spectra of Stokes I , Q , and V are generally correlated throughout the orbit, while Stokes U exhibits intervals of both correlation and anticorrelation with Stokes I , depending on the orbital phase. We also provide a Poincaré sphere representation of the polarization properties of J2144−5237, demonstrating a systematic temporal change of Poincaré sphere location for the main component with orbital phase. To our knowledge, this is the first investigation of the time-varying properties of the spectropolarimetric nature of any pulsars or MSPs. Extending this study to probe the spectrotemporal nature of full Stokes data on a larger sample of MSPs or pulsars has the potential to provide vital information on emission mechanisms inside the magnetosphere, interstellar propagation effects, and binary interactions.

The measured braking index, n = vv/v(2), of a rotation-powered pulsar with spin frequency v (where an overdot symbolizes a time derivative) and braking torque Kv(npl), features secular and stochastic anomalies arising from K not equal 0 and random torque noise respectively. Previous studies quantified the variance (n(2)) = (n(pl)+K-dim)(2)(+) sigma(2)(dim), where the secular anomaly, K(di)m, is inversely proportional to the characteristic time-scale T-x over which K varies; the stochastic anomaly sigma(2)(dim) =sigma(2)(v)v(2)y(v)(-2)(-4) (-1)(T)(obs) is a function of the timing noise amplitude sigma(v), a damping time-scale y(-1) (v)and the total observing time Tobs; and the average is taken over an ensemble of random realizations of the noise process. Here, we use a hierarchical Bayesian scheme, based on the formula for (n(2)), to infer the population-level distribution of n(pt) + K-dim for a sample of 68 young radio pulsars, observed for greater than or similar to 10 yr with Murriyang, the 64-m Parkes radio telescope. Upon assuming that the Apt + K-dim values are drawn from a population-level Gaussian, N(mu(rho iota), sigma(rho iota)), the Bayesian scheme returns the mean u(pt) = 9.953(-5.26)(+5.58) and standard deviation sigma(rho iota) = 10.89(+5.14) (-3.)69. At a per-pulsar level it returns posterior medians satisfying-13.86pl+Kdim <= 30.38. The secular anomaly dominates the stochastic anomaly, with posterior medians satisfying |n(pi) + K-dim| >=sigma(dim) in 10 out of 68 objects. The inference results imply that some mechanism other than electromagnetic or gravitational radiation reaction with overline K = 0 operates in at least 66 out of 68 analysed pulsars, in line with previous observational studies. The results are also consistent with t(k)<= v/|v|(,)with implications for the physical mechanism causing K not equal 0.

Millisecond pulsars (MSPs) are powerful probes of globular clusters (GCs), tracing stellar evolution, cluster dynamics, and the local gravitational potential. We investigate the MSP population in GC Omega Centauri. We perform Fourier-domain acceleration and jerk searches on MeerKAT observations, and carry out pulsar timing using MeerKAT and Parkes Murriyang data spanning 2021-2025. We fold Fermi LAT and NICER photons using updated radio ephemerides to search for high-energy pulsations. We discover a new isolated MSP, PSR J1326-4728S (hereafter S), with a spin period of 4.538 ms and a dispersion measure of 96.24 cm^3pc. We update the orbital parameters of all known binary systems, with those of I, N, and Q differing significantly from previous estimates, and obtain new timing solutions for G, H, and K. Pulsars B, G, H, K, and L exhibit black widow-like properties, I, N and Q are found in wider binaries, with N and Q having >0.2 M_⊙ companions, and N showing a significant orbital eccentricity (e=0.093). Significant spin period derivatives are measured for eight pulsars and interpreted as arising from the cluster gravitational potential. No pulsed high-energy emission is detected from individual pulsars. The inferred line-of-sight accelerations are consistent with a King-model gravitational potential. While our measurements are insensitive to an intermediate-mass black hole with mass 10^3-10^4 M_⊙, they place an upper limit of <10^5 M_⊙ at 90

A striking aspect of the radio profiles of many millisecond pulsars (MSPs) is that they consist of components separated from each other by regions lacking in emission. We devise a technique for determining 'disjoint' from 'contiguous' components and show that 39 per cent of MSPs have disjoint components as opposed to only 3 per cent of the slow pulsar population. We surmize that the pulsars with these disjoint components show evidence for both emission above the polar cap and from the current sheet beyond the light cylinder (LC), colocated with gamma-ray emission. For some of the radio MSPs only the LC emission is being observed. It is our contention that almost all of the current population of gamma-ray MSPs show evidence for colocated radio emission. A simple geometric explanation allows the presence (or not) of LC emission and the relationship (or not) between the gamma-ray and radio profiles to be determined. The LC components have frequently very high polarization and typically flat position-angle traverses thus helping to explain the difficulties in determining the geometry of MSPs. In cases where the geometry can be determined the values broadly align with expectations. In this picture, the number of potentially detectable radio MSPs is higher than previously thought, although the actual detectability of LC components depends on their luminosity function. A mechanism is required to produce coherent radio emission far from the stellar surface. These ideas have implications for our understanding of the populations of radio-loud and radio-quiet rotation-powered millisecond pulsars, and may have implications for the long-term timing stability of some of these sources.

Abridged. The measured braking index, n=ν/^2, of a rotation-powered pulsar with spin frequency ν and braking torque K ν^n_ pl, features secular and stochastic anomalies arising from K̇≠ 0 and random torque noise respectively. Previous studies quantified the variance ⟨ n^2⟩ = (n_ pl+K̇_ dim)^2+σ_ dim^2, where the secular anomaly, K̇_ dim, is inversely proportional to the characteristic time-scale τ_K over which K varies; the stochastic anomaly, σ_ dim^2 = σ_^2ν^2γ_^-2^-4T_ obs^-1, is a function of the timing noise amplitude σ_, a damping time-scale γ_^-1 and the total observing time T_ obs; and the average is taken over an ensemble of random realizations of the noise process. Here, we use a hierarchical Bayesian scheme, based on the formula for ⟨ n^2⟩, to infer the population-level distribution of n_ pl+K̇_ dim for a sample of 68 young radio pulsars, observed for ≳ 10 years with Murriyang, the 64-m Parkes radio telescope. Upon assuming that the n_ pl+K̇_ dim values are drawn from a population-level Gaussian, N(μ_ pl, σ_ pl), the Bayesian scheme returns the mean μ_ pl = 9.95^+5.58_-5.26 and standard deviation σ_ pl=10.89^+5.14_-3.69. At a per-pulsar level it returns posterior medians satisfying -13.86 ≤ n_ pl+K̇_ dim≤ 30.38. The secular anomaly dominates the stochastic anomaly, with posterior medians satisfying |n_ pl + K̇_ dim| ≥ σ_ dim in 10 out of 68 objects.

We investigated H i absorption toward a single pulsar, PSR J1644−4559, and its variability over timescales from days to years, using Murriyang, CSIRO’s Parkes Radio Telescope. Our 19 epochs of spectral observations, spanning 1.2 yr with intervals as short as 1 day, provide the most comprehensive cadence coverage for monitoring H i absorption to date. We identified two significant detections of tiny-scale atomic structure (TSAS) with spatial scales ranging from a lower limit of ∼11 au to an upper limit of 165 au, both exhibiting integrated signal-to-noise ratios exceeding 5.0. We find a relationship between linear size and optical depth variation in the cold neutral medium (CNM) component hosting the TSAS, described by a power-law relationship, Δ τ _int = Δ τ _0 (Δ L ) ^( ^α ^−2)/2 , with α = 4.1 ± 0.4. This is the first observational evidence explicitly connecting TSAS to turbulence in CNM. This power-law index is significantly steeper than previously reported values for the CNM, where α ranges from 2.3 to 2.9, but similar to those observed in the warm ionized gas. Additionally, we observe no significant variation in α across the entire range of spatial scales traced in our study, indicating that turbulence may be cascading down and dissipating at smaller scales. While there is no precise proper-motion measurement for this pulsar, our estimates for the turbulence dissipation in the CNM place the lower and upper limits at less than 0.03 au and 0.4 au, respectively.

This paper presents a comprehensive study of the eclipse properties of the spider millisecond pulsar (MSP) J1908+2105, using wide-band observations from the uGMRT and Parkes UWL. For the first time, we observed that this pulsar exhibits extended eclipses up to 4 GHz, the highest frequency band of the Parkes Ultra-Wideband, making it one of only three MSPs known to have such high-frequency eclipses. This study reveals synchrotron absorption as the primary eclipse mechanism for J1908+2105. We present modeling of synchrotron optical depth with various possible combinations of the parameters to explain the observed eclipsing in this as well as other spider MSPs. Observed eclipses at unusually high frequencies for J1908+2105 significantly aided in constraining the magnetic field and electron column density in the eclipse medium while modeling the synchrotron optical depth. Combining our findings with data from other MSPs in the literature, for the first time we note that a higher cutoff frequency of eclipsing, particularly above 1 GHz, is consistently associated with a higher electron column density (>10 ^17 cm ^−2 ) in the eclipse medium. Additionally, we present the first evidence of lensing effects near eclipse boundaries in this MSP, leading to significant magnification of radio emissions. The orbital-phase-resolved polarization analysis presented in this paper further indicates variation in rotation measure and consequently stronger magnetic fields in the eclipse region.

The HTRU-S Low Latitude survey data within 1 degrees of the Galactic Centre (GC) were searched for pulsars using the Fast Folding Algorithm (FFA). Unlike traditional Fast Fourier Transform (FFT) pipelines, the FFA optimally folds the data for all possible periods over a given range, which is particularly advantageous for pulsars with low-duty cycles. For the first time, a search over acceleration was included in the FFA to improve its sensitivity to binary pulsars. The steps in dispersion measure (DM) and acceleration were optimized, resulting in a reduction of the number of trials by 86 percent. This was achieved over a search period range from 0.6 to 432-s, i.e. 10 percent of the observation time (4320s), with a maximum DM of 4000pccm(-3) and an acceleration range of +/- 128ms(-2). The search resulted in the re-detections of four known pulsars, including a pulsar that was missed in the previous FFT processing of this survey. This result indicates that the FFA pipeline is more sensitive than the FFT pipeline used in the previous processing of the survey within our parameter range. Additionally, we discovered a 1.89-s pulsar, PSR J1746-2829, with a large DM, located 0.5 from the GC. Follow-up observations revealed that this pulsar has a relatively flat spectrum (alpha = -0.9 +/- 0.1) and has a period derivative of similar to 1.3 x 10(-12)ss(-1), implying a surface magnetic field of similar to 5.2 x 10(13)G and a characteristic age of similar to 23000yr. While the period, spectral index, and surface magnetic field strength are similar to many radio magnetars, other characteristics such as high linear polarization are absent.

ABSTRACT A number of pulsars are known to have profile evolution on time-scales of months, often correlated with spin-down rate changes. Here, we present the first result from 3 yr of monitoring observations from MeerKAT as part of the Thousand Pulsar Array programme. This programme obtains high-fidelity pulse profiles for ∼ 500 pulsars, which enabled the detection of subtle changes in seven sources not previously known to exhibit long-term profile evolution. A 2D Gaussian convolution is used to highlight correlated emission variability in both the pulse phase and observing epoch direction. Simulations show that for one additional source the observed profile variability is likely to originate from stochastic single-pulse shape variability (jitter). We find that it is common for long-term profile variability to be associated with changes in polarization fractions, but not with polarization position angle (PA) changes. PA changes are expected if emission height changes or precession is responsible for the profile variability. PSR J1741−3927 is the only pulsar in our sample that shows correlated PA variability, and this is associated with orthogonal polarization mode activity. For the six other pulsars limits on possible emission height changes and impact angle changes are derived. These limits are consistent with the small changes in the total intensity profile shape. None of the sources show detectable spin-down variability correlated with the emission changes, which are thought to be driven by magnetospheric current fluctuations. Therefore, the absence of correlated spin-down rate variability allows upper limits to be placed on changes in the magnetospheric charge density.

The S-shaped swing of the linear polarization position angle (PPA) observed in many pulsars can be interpreted by the rotating vector model (RVM). However, efforts to fit the RVM for a large sample of pulsars observed with the MeerKAT telescope as a part of the Thousand-Pulsar-Array (TPA) programme, only succeeded for about half the cases. High time-resolution studies suggest that the failed cases arise due to the presence of orthogonal polarization modes, or highly disordered distribution of PPA points. One such example is PSR~J1645-0317. Recently it has been shown that the RVM can be recovered in this pulsar by using only time samples which are greater than 80% linearly polarized. In this work we test this novel approach on the brightest 249 pulsars from the TPA sample, of which 177 yield sufficient highly polarized samples to be amenable to our method. Remarkably, only 9 of these pulsars (5%) now fail to fit the RVM as opposed to 59% from the original analysis. This result favours the paradigm that the underlying mechanism is coherent curvature radiation.

This study presents an orbital-phase-dependent analysis of three black widow spider millisecond pulsars (BW MSPs), aiming to investigate the magnetic field within the eclipse environment. The ultrawide-bandwidth low-frequency receiver of the Parkes Murriyang radio telescope is utilized for full polarization observations covering frequencies from 704−4032 MHz. Depolarization of pulsed emission is observed during the eclipse phase of three BW MSPs, namely PSR J0024−7204J, PSR J1431−4715, and PSR J1959+2048, consistent with previous studies of other BW MSPs. We estimated orbital-phase-dependent rotation measure values for these MSPs. The wide bandwidth observations also provided constraints on the eclipse cutoff frequency for these BW MSPs. For PSR J0024−7204J, we report temporal variation of the eclipse cutoff frequency coupled with changes in the electron column density within the eclipse medium across six observed eclipses. Moreover, the eclipse cutoff frequency for PSR J1431−4715 is determined to be 1251 ± 80 MHz, leading to the conclusion that synchrotron absorption is the primary mechanism responsible for the eclipsing. Additionally, for PSR J1959+2048, the estimated cutoff frequency exceeded 1400 MHz, consistent with previous studies. With this investigation, we have doubled the sample size of BW MSPs with orbital-phase-resolved studies, allowing a better probe of the eclipse environment.

The Galactic center is host to a population of extraordinary radio filaments, thin linear structures that trace out magnetic field lines running perpendicular to the Galactic plane. Using Murriyang, the 64 m Parkes radio telescope, we conducted a search for pulsars centered on the position of a compact source in the filament G359.0−0.2. We discovered a millisecond pulsar (MSP), PSR J1744−2946, with a period P = 8.4 ms, that is bound in a 4.8 hr circular orbit around an M c > 0.05 M ⊙ companion. The pulsar dispersion measure of 673.7 ± 0.1 pc cm −3 and Faraday rotation measure of 3011 ± 3 rad m −2 are the largest of any known MSP. Its radio pulses are moderately scattered due to multipath propagation through the interstellar medium, with a scattering timescale of 0.87 ± 0.08 ms at 2.6 GHz. Using MeerKAT, we localized the pulsar to a point source embedded in a low-luminosity radio filament, the “Sunfish”, that is unrelated to G359.0−0.2. Our discovery of the first MSP within 1° of the Galactic center hints at a large population of these objects detectable via high-frequency surveys. The association with a filament points to pulsars as the energy source responsible for illuminating the Galactic center radio filaments.

Radio emission from magnetars provides a unique probe of the relativistic, magnetized plasma within the near-field environment of these ultra-magnetic neutron stars. The transmitted waves can undergo birefringent and dispersive propagation effects that result in frequency-dependent conversions of linear to circularly polarized radiation and vice-versa, thus necessitating classification when relating the measured polarization to the intrinsic properties of neutron star and fast radio burst (FRB) emission sites. We report the detection of such behavior in 0.7-4 GHz observations of the P = 5.54 s radio magnetar XTE J1810$-$197 following its 2018 outburst. The phenomenon is restricted to a narrow range of pulse phase centered around the magnetic meridian. Its temporal evolution is closely coupled to large-scale variations in magnetic topology that originate from either plastic motion of an active region on the magnetar surface or free precession of the neutron star crust. Our model of the effect deviates from simple theoretical expectations for radio waves propagating through a magnetized plasma. Birefringent self-coupling between the transmitted wave modes, line-of-sight variations in the magnetic field direction and differences in particle charge or energy distributions above the magnetic pole are explored as possible explanations. We discuss potential links between the immediate magneto-ionic environments of magnetars and those of FRB progenitors.

The double pulsar system, PSR J0737−3039A/B, consists of two neutron stars bound together in a highly relativistic orbit that is viewed nearly edge-on from the Earth. This alignment results in brief radio eclipses of the fast-rotating pulsar A when it passes behind the toroidal magnetosphere of the slow-rotating pulsar B. The morphology of these eclipses is strongly dependent on the geometric orientation and rotation phase of pulsar B, and their time evolution can be used to constrain the geodetic precession rate of the pulsar. We demonstrate a Bayesian inference framework for modelling high-sensitivity eclipse light curves obtained with MeerKAT between 2019 and 2023. Using a hierarchical inference approach, we obtained a precession rate of Ω SO B = 5.16° −0.34° +0.32° yr −1 (68% confidence intervals) for pulsar B, consistent with predictions from general relativity to a relative uncertainty of 6.5%. This updated measurement provides a 6.1% test of relativistic spin-orbit coupling in the strong-field regime. We show that a simultaneous fit to all of our observed eclipses can in principle return a ∼1.5% test of spin-orbit coupling. However, systematic effects introduced by the current geometric orientation of pulsar B along with inconsistencies between the observed and predicted eclipse light curves result in difficult to quantify uncertainties when using this approach. Assuming the validity of general relativity, we definitively show that the spin axis of pulsar B is misaligned from the total angular momentum vector by 40.6° ±0.1° and that the orbit of the system is inclined by approximately 90.5° from the direction of our line of sight. Our measured geometry for pulsar B suggests the largely empty emission cone contains an elongated horseshoe-shaped beam centred on the magnetic axis, and that it may not be re-detected as a radio pulsar until early 2035.

We report the radio and high-energy properties of a new outburst from the radio-loud magnetar 1E 1547.0−5408. Following the detection of a short burst from the source with Swift-BAT on 2022 April 7, observations by NICER detected an increased flux peaking at (6.0 ± 0.4) × 10 −11 erg s −1 cm −2 in the soft X-ray band, falling to a baseline level of 1.7 × 10 −11 erg s −1 cm −2 over a 17 day period. Joint spectroscopic measurements by NICER and NuSTAR indicated no change in the hard nonthermal tail despite the prominent increase in soft X-rays. Observations at radio wavelengths with Murriyang, the 64 m Parkes radio telescope, revealed that the persistent radio emission from the magnetar disappeared at least 22 days prior to the initial Swift-BAT detection and was redetected two weeks later. Such behavior is unprecedented in a radio-loud magnetar, and may point to an unnoticed slow rise in the high-energy activity prior to the detected short bursts. Finally, our combined radio and X-ray timing revealed the outburst coincided with a spin-up glitch, where the spin frequency and spin-down rate increased by 0.2 ± 0.1 μ Hz and (−2.4 ± 0.1) × 10 −12 s −2 , respectively. A linear increase in the spin-down rate of (−2.0 ± 0.1) × 10 −19 s −3 was also observed over 147 days of postoutburst timing. Our results suggest that the outburst may have been associated with a reconfiguration of the quasi-polar field lines, likely signaling a changing twist, accompanied by spatially broader heating of the surface and a brief quenching of the radio signal, yet without any measurable impact on the hard X-ray properties.

In spite of the rich phenomenology of the polarization properties of radio pulsars, the rotating vector model (RVM) created 50 years ago remains the best method to determine the beam geometry of a pulsar. We apply the RVM to a sample of 854 radio pulsars observed with the MeerKAT telescope in order to draw conclusions about the population of pulsars as a whole. The main results are that (i) the geometrical interpretation of the position angle traverse is valid in the majority of the population, (ii) the pulsars for which the RVM fails tend to have a high fraction of circular polarization compared to linear polarization, (iii) emission heights obtained through both geometrical and relativistic methods show that the majority of pulsars must have emission heights less than 1000 km independent of spin period, (iv) orthogonal mode jumps are seen in the position angle traverse in about one third of the population. All these results are weakly dependent on the pulsar spin-down energy.

We present the largest single survey to date of average profiles of radio pulsars, observed and processed using the same telescope and data reduction software. Specifically, we present measurements for 1170 pulsars, observed by the Thousand Pulsar Array (TPA) programme at the 64-dish SARAO MeerKAT radio telescope, in a frequency band from 856 to 1712 MHz. We provide rotation measures (RM), dispersion measures, flux densities and polarization properties. The catalogue includes 254 new RMs that substantially increase the total number of known pulsar RMs. Our integration times typically span over 1000 individual rotations per source. We show that the radio (pseudo)luminosity has a strong, shallow dependence on the spin-down energy, proportional to $\dot{E}^{0.15\pm0.04}$, that contradicts some previous proposals of population synthesis studies. In addition, we find a significant correlation between the steepness of the observed flux density spectra and $\dot{E}$, and correlations of the fractional linear polarization with $\dot{E}$, the spectral index, and the pulse width, which we discuss in the context of what is known about pulsar radio emission and how pulsars evolve with time. On the whole, we do not see significant correlations with the estimated surface magnetic field strength, and the correlations with $\dot{E}$ are much stronger than those with the characteristic age. This finding lends support to the suggestion that magnetic dipole braking may not be the dominant factor for the evolution of pulsar rotation over the lifetimes of pulsars. A public data release of the high-fidelity time-averaged pulse profiles in full polarization accompanies our catalogue.

ABSTRACT We report on the subpulse modulation properties of 1198 pulsars using the Thousand-Pulsar-Array programme on MeerKAT. About 35 per cent of the analysed pulsars exhibit drifting subpulses that are more pronounced towards the death line, consistent with previous studies. We estimate that this common phenomenon is detectable in 60 per cent of the overall pulsar population if high-quality data were available for all. This large study reveals the evolution of drifting subpulses across the pulsar population in unprecedented detail. In particular, we find that the modulation period P3 follows a V-shaped evolution with respect to the characteristic age τc, such that the smallest P3 values, corresponding to the Nyquist period P3 ≃ 2, are found at τc ≃ 107.5 yr. The V-shaped evolution can be interpreted and reproduced if young pulsars possess aliased fast intrinsic P3, which monotonically increase, ultimately achieving a slow unaliased P3. Enhancement of irregularities in intrinsic subpulse modulation by aliasing in small-τc pulsars would explain their observed less well defined P3’s and weaker spectral features. Modelling these results as rotating subbeams, their circulation must slow down as the pulsar evolves. This is the opposite to that expected if circulation is driven by $\boldsymbol{E}\times \boldsymbol{B}$ drift. This can be resolved if the observed P3 periodicity is due to a beat between an $\boldsymbol{E}\times \boldsymbol{B}$ system and the pulsar period. As a by-product, we identified the correct periods and spin-down rates for 12 pulsars, for which harmonically related values were reported in the literature.

We describe IXPE polarization observations of the pulsar wind nebula (PWN) MSH 15-5(2), the "Cosmic Hand." We find X-ray polarization across the PWN, with B-field vectors generally aligned with filamentary X-ray structures. High-significance polarization is seen in arcs surrounding the pulsar and toward the end of the "jet," with polarization degree PD > 70%, thus approaching the maximum allowed synchrotron value. In contrast, the base of the jet has lower polarization, indicating a complex magnetic field at significant angle to the jet axis. We also detect significant polarization from PSR B1509-58 itself. Although only the central pulse phase bin of the pulse has high individual significance, flanking bins provide lower-significance detections and, in conjunction with the X-ray image and radio polarization, can be used to constrain rotating vector model solutions for the pulsar geometry.