Simon Johnston

Glitch-associated profile variations provide unique insights into the coupling between the neutron star interior and its magnetosphere. PSR J1740−3015, a pulsar with one of the highest known glitch rates (37 detected glitches), has no prior reports of such radiative variations. Using ∼14 yr of archival data from the Parkes 64 m radio telescope, we present the first detection of glitch-related profile evolution in this source, focusing on two well-characterized events: Glitches 9 (MJD 57468.59(40)) and 10 (MJD 58232.4(4)). These two glitches exhibit diverse yet interconnected profile behaviors: Glitch 9 shows a significant relative enhancement of the trailing component, a transitional profile state during its ∼430 day recovery period, and persistent increasing of the 20% pulse width ( W ₂₀ ) postrecovery; Glitch 10 displays a distinctive two-stage evolution: gradual narrowing to a stable narrow state (〈 W ₂₀ 〉 ≈ 3 . ° 916 ± 0 . ° 047) that persists for ∼90(8) days—decoupled from its ∼71 day intrinsic recovery timescale—before abruptly reverting to the preglitch wide state. This work identifies PSR J1740−3015 as only the second pulsar confirmed to host transitional radiative states during postglitch recovery, expanding the observational sample of glitch–magnetosphere coupling phenomena and providing new constraints on the interaction between neutron star internal dynamics and external radiative properties.

We present the Thousand Pulsar Array (TPA) single-pulse data set, obtained with the MeerKAT radio telescope and comprising time-series observations of 1192 pulsars, typically containing ~1000 consecutive pulses per source. We describe the MeerTime Single Pulse software pipeline which calibrates the data and automatically excises interference signals to produce data products suitable for typical single-pulse studies. To demonstrate the capabilities of the dataset, we carry out a population-level study of phase-averaged single-pulse energy distributions and nulling behaviour. Pulse energy distributions are modelled within a Bayesian framework choosing from a range of intrinsic energy distributions, and including an explicit nulling fraction. We find that approximately half of the pulsars require multi-component intrinsic energy distributions, while the remainder are consistent with single-component models. Nulling is detected or constrained for most pulsars in the sample, and both the occurrence and inferred nulling fraction show systematic variation across the P–$\dot{P}$ diagram. In particular, nulling fractions increase with spin period and exhibit only a weak dependence on period derivative. We also examine trends in the preferred forms of pulse energy distributions as a function of spin-down luminosity, finding modest evidence for population-level evolution. Estimates of single-pulse luminosities indicate that individual pulses can exceed the long-term average luminosity by large factors, particularly for low-$\dot{E}$ pulsars. These results characterise the statistical properties of single-pulse emission across a large pulsar sample and highlight the limitations of phase-averaged energy distributions for capturing the full complexity of pulsar emission variability.

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.

It has been proposed that radio pulsars can be distinguished from other point-like radio sources in continuum images by their unique interstellar scintillation signatures. Using data from the Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) survey, we conducted a pilot survey of radio pulsars at high Galactic latitude regions via the variance imaging method. Out of approximately 59,800 compact radio sources detected in a ~480 square degree survey area, we identified 20 highly variable sources. Among them, 9 are known pulsars, 1 is a known radio star, 1 is an ultra-long period source, 3 are radio star candidates, and the remaining 6 are pulsar candidates. Notably, we discovered two strongly scintillating pulsars: one with a period of 85.707 ms and a dispersion measure (DM) of 19.4 pc/cm^3, and another with a period of 5.492 ms and a DM of 29.5 pc/cm^3. In addition, a third pulsar was discovered in the variance images, with a period of 14.82 ms and a DM of 39.0 pc/cm^3. This source shows a steep radio spectrum and a high degree of circular polarisation. These results underscore the strong potential of variance imaging for pulsar detection in full EMU and future radio continuum surveys planned with Square Kilometre Array (SKA).

Fast radio bursts (FRBs) are energetic, short-duration radio pulses of unclear origin. To explore effective survey strategies for detecting FRBs from nearby globular clusters (GCs), we investigate the burst energy distribution, which has a strong influence on the detection rate. We reanalyze FRBs and pulsars exhibiting broad energy distributions by fitting their high-energy tails with power-law models. Two cosmological repeating FRBs (FRB 20201124A and FRB 20220912A), one nearby FRB (FRB 20200120E), and two pulsars (RRATs J1846−0257 and J1854+0306) exhibit power-law indices of α ≳ −1, suggesting that their bright pulses contribute significantly to the total radio pulse energy. The brightest bursts from these sources can be fitted with a power-law model (α _Bri = −0.26 ± 0.05), suggesting that an extremely flat index is required to naturally derive high-luminosity FRBs from low-luminosity sources. We present detailed survey strategies for FAST, MeerKAT, and Parkes cryoPAF in the search for FRBs in nearby GCs using different power-law indices, recommending targets for observation. We suggest that combining observations with FAST (∼3 hr) and Parkes cryoPAF (10−20 hr) is practicable for discovering new FRBs in nearby GCs.

We discovered four millisecond pulsars (MSPs) in searches of 80 γ-ray sources conducted from 2015 to 2017 with the Murriyang radio telescope of the Parkes Observatory. We provide an overview of the survey and focus on the results of a follow-up pulsar timing campaign. Using Fermi Large Area Telescope data, we have detected γ-ray pulsations from all four pulsars, and by combining radio and γ-ray data, we obtain improved timing solutions. We also provide flux density distributions for the radio pulsars and flux-calibrated and phase-aligned radio and γ-ray pulse profiles. Some of the pulsars may be suitable for radio pulsar timing array experiments. PSR J0646–5455, PSR J1803–4719, and PSR J2045–6837 are in typical, nearly circular white dwarf binaries with residual eccentricities proportional to their binary periods. PSR J1833–3840 is a black widow pulsar with the longest known period, P _b = 0.9 day, and a very soft radio spectrum. PSR J0646–5455 has a strong, Vela-like γ-ray pulse profile and is suitable for inclusion in the γ-ray pulsar timing array. Despite this, it is possibly one of the lowest-efficiency γ-ray MSPs known. Indeed, all four new γ-ray MSPs have lower-than-average efficiency, a potential indication of bias in earlier searches. Finally, we retrospectively evaluate the efficiency of this survey: while only four new MSPs were directly discovered, subsequent campaigns have found pulsars in a further 19 of our targets, an excellent 30% efficiency.

Measuring the magnetic field of the Milky Way reveals the structure and evolution of the Galaxy. Pulsar rotation measures (RMs) provide a means to probe this Galactic magnetic field (GMF) in three dimensions. We use the largest single-origin data set of pulsar measurements, from the MeerKAT Thousand-Pulsar-Array, to map out GMF components parallel to pulsar lines of sight. We also present these measurements for easy integration into the consolidated RM catalogue, RMTable. Focusing on the Galactic disc, we investigate competing theories of how the GMF relates to the spiral arms, comparing our observational map with five analytic models of magnetic field structure. We also analyse RMs to extragalactic radio sources, to help build-up a three-dimensional picture of the magnetic structure of the Galaxy. In particular, our large number of measurements allows us to investigate differing magnetic field behaviour in the upper and lower halves of the Galactic plane. We find that the GMF is best explained as following the spiral arms in a roughly bisymmetric structure, with antisymmetric parity with respect to the Galactic plane. This picture is complicated by variations in parity on different spiral arms, and the parity change location appears to be shifted by a distance of 0.15 kpc perpendicular to the Galactic plane. This indicates a complex relationship between the large-scale distributions of matter and magnetic fields in our Galaxy. Future pulsar discoveries will help reveal the origins of this relationship with greater precision, as well as probing the locations of local magnetic field inhomogenities.

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, Δτ _int = Δτ ₀(ΔL)^(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 (>10¹⁷ 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.