We report the detection of a glitch in the millisecond pulsar (MSP) PSR J0900-3144, which is included in the European, MeerKAT, and Parkes pulsar timing array (PTA) experiments. The data set combines observations from the MeerKAT, Nanc,ay, Lovell, and Murriyang telescopes, spanning a total baseline of approximately 14 yr. The glitch occurred on MJD 59942(17), with a measured fractional spin frequency step of Av(g) /v = 1 . 15(13) x 10(-12). This event represents the third glitch detected in an MSP, following those in PSRs B1821-24A and J0613-0200. Although smaller in amplitude than the previous two, the glitch in PSR J0900-3144 is of a comparable order of magnitude. The updated MSP glitch rate is 2 . 5(1) x 10(-3 )glitches per pulsar per year, which suggests it is likely that current PTAs will detect another MSP glitch within 5 yr. Using simulations, we demonstrate that such small glitches can go undetected, especially in short data sets such as those from new PTAs, and can bias the inferred achromatic noise model parameters, potentially leading to the down-weighting of the pulsar in gravitational wave background searches.

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.

Located at the centres of supernova remnants, central compact objects (CCOs) are among the most puzzling neutron stars. CCOs are bright in thermal X-rays, yet have evaded detection by major radio telescopes for decades, giving rise to the view that they are intrinsically radio-quiet and possess exceptionally weak magnetic fields. Here we show that the prototypical young CCO 1E 1207.4-5209 is in fact a faint radio pulsar rotating at the 0.4-s X-ray period. Analysis of its polarization indicates that the radio beam intersects our line of sight near the magnetic pole, affirming that its radio faintness is intrinsic. Once its supernova remnant dissipates, this source would be misidentified as an apparently gigayear-old pulsar. The CCO's low radio flux density may explain why many supernova remnants lack detectable radio pulsars and suggests a hidden population of young, slowly rotating neutron stars.

Magnetars are isolated neutron stars with exceptionally strong surface fields exceeding 1014 G (ref. 1). Their bright X-ray emission probes physical regimes in which quantum electrodynamics (QED) influences radiation propagation2-4. Strong magnetic fields induce polarization-dependent refractive indices in the vacuum5,6; such vacuum birefringence remains a long-standing but unconfirmed prediction of QED. Here we report phase- and energy-resolved polarization measurements of the radio-emitting magnetar 1E 1547.0-5408 obtained by coordinating X-ray and radio observations from the Imaging X-ray Polarimetry Explorer, the Neutron Star Interior Composition Explorer and the Parkes/Murriyang Observatory. We detect large polarization degrees (PDs) in the thermally dominant soft X-ray band, reaching phase-averaged values of 65% at 2 keV before substantially decreasing between 2 keV and 4 keV. At certain rotational phases, the 2-3 keV PD rises to nearly 80% while remaining high (≳40%) throughout the radio beam crossing. The phase-dependent X-ray and radio polarization angles are both consistent with the rotating vector model, suggesting that the emission geometries track the large-scale magnetic field of the star. Collectively, these characteristics challenge standard surface emission models using non-refractive propagation of light to infinity. Vacuum-birefringence-governed magnetospheric propagation can naturally explain the X-ray polarization signals. Our results represent a marked advance in probing this hallmark prediction of QED, opening a new cosmic window into superstrong-field quantum physics, thereby motivating further observational and theoretical studies concentrating on this domain.

Radio-loud magnetars are well known for exhibiting radiative behaviors that are seldom seen among the wider pulsar population. Yet one form of emission that remains elusive among pulsars and magnetars is narrowband bursts of radio waves. Such emission is a hallmark of repeating sources of fast radio bursts (FRBs), intense radio flashes that originate from distant galaxies. Here, we report the detection of 84 narrowband radio bursts during observations of the magnetar 1E 1547.0-5408 by the Murriyang telescope. They were confined to a transient profile component that appeared between 2009 February 23 to 25, one month after its 2009 outburst. Their appearance coincided with both dramatic changes in the magnetar line-of-sight magnetic-field geometry, and an emergent pulsed hard X-ray component detected by the Rossi X-ray Timing Explorer. The leading edge of the hard X-ray emission was phase-aligned with the narrowband component. This may indicate the bursts originated from pair cascades along closed field lines, though open-field line emission remains valid. Our characterization of the bursts suggests they may represent a low-energy analogue of the repeating FRB mechanism, further linking FRB progenitors to young, highly magnetized neutron stars.

Pulsar timing is used for a variety of applications including tests of fundamental physics, probing the structure of neutron stars, and detecting nanohertz gravitational waves. Development of robust methods and generation of high-quality timing data is therefore of utmost importance. In this paper, we present a new technique for creating high-fidelity templates that can be used to measure the pulse times of arrival with significantly increased precision compared to existing methods. Our framework makes use of all available polarimetric information to generate frequency-dependent models of pulse-shape evolution of all four Stokes parameters. We apply this method to millisecond pulsars observed by the Parkes Pulsar Timing Array and show that it results in timing measurement uncertainties reduced up to $\sim$20-30 per cent. We also present, for the first time, phase- and frequency-resolved polarimetric measurements of millisecond pulsars observed with the Parkes Murriyang ultra-wide-bandwdith low receiver. The data, plots, and codes underlying this analysis are made publicly available.

Fast radio bursts (FRBs) are bright, energetic, radio pulses of extragalactic origin. A dichotomy has emerged in the population: some produce repeat bursts, while the majority do not. Most repeating sources only show rare repetitions, and none have been studied extensively over the wide bandwidths necessary to disentangle the physical processes that produce emission from distortions to bursts caused by intervening ionised gas. Here we present radio observations of the most active repeating source, FRB 20240114A. Using an ultrawideband receiving system, we have detected 5526 repetitions, revealing an extreme spectral and temporal variability in the burst emission. The bursts exhibit longer-term broadband variations in central emission frequency over multiple months, and narrowband bursts that have correlations in central frequencies on time scales of milliseconds to minutes. The spectral and temporal properties are consistent with the source undergoing magnification by foreground plasma lenses, potentially embedded in a turbulent circumsource medium. This extreme example highlights the role of plasma lenses in the observed properties of burst emission and can explain the diversity in activity and energetics of the entire FRB population.

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.

Pulsars are often lauded for their (relative) rotational and radio emission stability over long time scales. However, long-term observing programmes are identifying an increasing number of pulsars that deviate from this preconceived notion. Using Gaussian process regression and Bayesian inference techniques, we investigated the emission and rotational stability of 259 isolated radio pulsars that have been monitored using Murriyang, the Parkes 64 m radio telescope, over the past three decades. We found that 238 pulsars display significant variability in their spin-down rates, 52 of which also exhibit changes in profile shape. Including 23 known state-switching pulsars, this represents the largest catalogue of variable pulsars identified to date and indicates that these behaviours are ubiquitous among the wider population. The intensity of spin-down fluctuations positively scales with increasing pulsar spin-down rate, with only a marginal dependence on spin-frequency. This may have substantial implications for ongoing searches for gravitational waves in the ensemble timing of millisecond pulsars. We also discuss challenges in explaining the physical origins of quasi-periodic and transient profile/spin-down variations detected among a subset of our pulsars.

Continuous gravitational waves (CWs) emission from neutron stars carries information about their internal structure and equation of state, and it can provide tests of General Relativity. We present a search for CWs from a set of 45 known pulsars in the first part of the fourth LIGO--Virgo--KAGRA observing run, known as O4a. We conducted a targeted search for each pulsar using three independent analysis methods considering the single-harmonic and the dual-harmonic emission models. We find no evidence of a CW signal in O4a data for both models and set upper limits on the signal amplitude and on the ellipticity, which quantifies the asymmetry in the neutron star mass distribution. For the single-harmonic emission model, 29 targets have the upper limit on the amplitude below the theoretical spin-down limit. The lowest upper limit on the amplitude is $6.4\!\times\!10^{-27}$ for the young energetic pulsar J0537-6910, while the lowest constraint on the ellipticity is $8.8\!\times\!10^{-9}$ for the bright nearby millisecond pulsar J0437-4715. Additionally, for a subset of 16 targets we performed a narrowband search that is more robust regarding the emission model, with no evidence of a signal. We also found no evidence of non-standard polarizations as predicted by the Brans-Dicke theory.

The millisecond pulsar PSR J1713+0747 is a high-priority target for pulsar timing array experiments due to its long-term timing stability, and bright, narrow pulse profile. In April 2021, PSR J1713+0747 underwent a significant profile change event, observed by several telescopes worldwide. Using the broad bandwidth and polarimetric fidelity of the Ultra-Wideband Low-frequency receiver on Murriyang, CSIRO's Parkes radio telescope, we investigated the long-term spectro-polarimetric behaviour of this profile change in detail. We highlight the broad-bandwidth nature of the event, which exhibits frequency dependence that is inconsistent with cold-plasma propagation effects. We also find that spectral and temporal variations are stronger in one of the orthogonal polarisation modes than the other and observe mild variations (similar to 3 - 5 sigma significance) in circular polarisation above 1 400 MHz following the event. However, the linear polarisation position angle remained remarkably stable in the profile leading edge throughout the event. With over three years of data post-event, we find that the profile has not yet recovered back to its original state, indicating a long-term asymptotic recovery, or a potential reconfiguration of the pulsar's magnetic field. These findings favour a magnetospheric origin of the profile change event over a line-of-sight propagation effect in the interstellar medium.

Matter inside neutron stars is compressed to densities several times greater than nuclear saturation density, while maintaining low temperatures and large asymmetries between neutrons and protons. Neutron stars, therefore, provide a unique laboratory for testing physics in environments that cannot be recreated on Earth. To uncover the highly uncertain nature of cold, ultra-dense matter, discovering and monitoring pulsars is essential, and SKA will play a crucial role in this endeavour. In this paper, we will present the current state-of-the-art in dense matter physics and dense matter superfluidity, and discuss recent advances in measuring global neutron star properties (masses, moments of inertia, and maximum rotation frequencies) as well as non-global observables (pulsar glitches and free precession). We will specifically highlight how radio observations of isolated neutron stars and those in binaries---such as those performed with SKA in the near future---inform our understanding of ultra-dense physics and address in detail how SKA's unprecedented sensitivity, large-scale survey and sub-arraying capabilities will enable novel dense matter constraints. We will also address the potential impact of dark matter and modified gravity models on these constraints and emphasise the role of synergies between SKA and other facilities, specifically X-ray telescopes and next-generation gravitational wave observatories.

Long-period radio transients are a new class of astronomical objects characterized by prolonged periods ranging from 18 min to 54 min. They exhibit highly polarized, coherent, beamed radio emission lasting only 10–100 s. The intrinsic nature of these objects is subject to speculation, with highly magnetized white dwarfs and neutron stars being the prevailing candidates. Here we present ASKAP J183950.5−075635.0, boasting the longest known period of this class at 6.45 h. It exhibits emission characteristics of an ordered dipolar magnetic field, with pulsar-like bright main pulses and weaker interpulses offset by about half a period that are indicative of an oblique or orthogonal rotator. This phenomenon, observed in a long-period radio transient, confirms that the radio emission originates from both magnetic poles and that the observed period corresponds to the rotation period. The spectroscopic and polarimetric properties of ASKAP J183950.5−075635.0 are consistent with a neutron star origin, and this object is a crucial piece of evidence in our understanding of long-period radio sources and their links to neutron stars. Coherent radio emission with a long (nearly 6.5 h) period has been detected from both magnetic poles of a rotating compact object, offering insights into the evolution and emission mechanism of compact radio transients.

There has been a rapid increase in the known fast radio burst (FRB) population, yet the progenitor(s) of these events have remained an enigma. A small number of FRBs have displayed some level of quasi-periodicity in their burst profile, which can be used to constrain their plausible progenitors. However, these studies suffer from the lack of polarization data which can greatly assist in constraining possible FRB progenitors and environments. Here, we report on the detection and characterisation of FRB 20230708A by the Australian Square Kilometre Array Pathfinder (ASKAP), a burst which displays a rich temporal and polarimetric morphology. We model the burst time series to test for the presence of periodicity, scattering and scintillation. We find a potential period of T = 7.267 ms within the burst, but with a low statistical significance of 1.77 sigma. Additionally, we model the burst's time- and frequency-dependent polarization to search for the presence of (relativistic and non-relativistic) propagation effects. We find no evidence to suggest that the high circular polarization seen in FRB 20230708A is generated by Faraday conversion. The majority of the properties of FRB 20230708A are broadly consistent with a (non-millisecond) magnetar model in which the quasi-periodic morphology results from microstructure in the beamed emission, but other explanations are not excluded.

Recently, a class of long-period radio transients (LPTs) has been discovered, exhibiting emission thousands of times longer than radio pulsars1-5. These findings, enabled by advances in wide-field radio surveys, challenge existing models of rotationally powered pulsars. Proposed models include highly magnetized neutron stars6, white-dwarf pulsars7 and white-dwarf binary systems with low-mass companions8. Although some models predict X-ray emission6,9, no LPTs have been detected in X-rays despite extensive searches1-5,10. Here we report the discovery of an extremely bright LPT (10-20 Jy in radio), ASKAP J1832-0911, which has coincident radio and X-ray emission, both with a 44.2-minute period. Its correlated and highly variable X-ray and radio luminosities, combined with other observational properties, are unlike any known Galactic object. The source could be an old magnetar or an ultra-magnetized white dwarf; however, both interpretations present theoretical challenges. This X-ray detection from an LPT reveals that these objects are more energetic than previously thought and establishes a class of hour-scale periodic X-ray transients with a luminosity of about 1033 erg s-1 linked to exceptionally bright coherent radio emission.

PSR B1259-63 is a gamma-ray binary system with a 48 ms radio pulsar orbiting around an O9.5Ve star, LS 2883, in a highly eccentric ~3.4 yr long orbit. Close to the periastron the system is detected from radio up to the TeV energies due to the interaction of LS 2883 and pulsar's outflows. The observations of last 4 periastra passages taken in 2010-2021 demonstrate periastron to periastron variability at all wavelength, probably linked to the state of the decretion disk. In this paper we present the results of our optical, radio and X-ray observational campaigns on PSR B1259-63 performed in 2024 accompanied with the analysis of the publicly available GeV FERMI/LAT data. We show that this periastron passage was characterised by the early flaring of X-rays before the periastron passage and GeV emission after the periastron passage, which can be explained by a larger size of the decretion disk as supported by the optical observations. The structure of the GeV flare is also in agreement with the disruption of the large dense disk. The possible X-ray/radio correlation was observed only during the post-periastron rise of X-ray and radio emission.

PSR J1227-6208 is a 34.53-ms recycled pulsar with a massive companion. This system has long been suspected to belong to the emerging class of massive recycled pulsar-ONeMg white dwarf systems such as PSR J2222-0137, PSR J1528-3146, and J1439-5501. Here, we present an updated emission and timing analysis with more than 11 years of combined Parkes and MeerKAT data, including 19 hours of high-frequency data from the newly installed MeerKAT S-band receivers. We measure a scattering timescale of 1.22 ms at 1 GHz with a flat scattering index of 3.33 < beta < 3.62, and a mean flux density of 0.53 - 0.62 mJy at 1 GHz with a steep spectral index of 2.06 < alpha < 2.35. Around 15% of the emission is linearly and circularly polarised, but the polarisation angle does not follow the rotating vector model. Thanks to the sensitivity of MeerKAT, we successfully measure a rate of periastron advance of omega 7 = 0.0171(11) deg yr(-1), and a Shapiro delay with an orthometric amplitude of h(3) = 3.6 +/- 0.5 mu s and an orthometric ratio of sigma = 0.85 +/- 0.05. The main source of uncertainty in our timing analysis is chromatic correlated dispersion measure noise, which we model as a power law in the Fourier space thanks to the large frequency coverage provided by the Parkes UWL receiver. Assuming general relativity and accounting for the measurements across all the implemented timing noise models, the total mass, companion mass, pulsar mass, and inclination angle are constrained at 2.3 < M-t/M-circle dot < 3.2, 1.21 < M-c/M-circle dot < 1.47, 1.16 < M-p/M-circle dot < 1.69, and 77.5 < i/deg < 80.3. We also constrain the longitude of ascending node to either Omega(a) = 266 +/- 78 deg or Omega(a) = 86 +/- 78 deg. We argue against a neutron star nature of the companion based on the very low orbital eccentric of the system (e = 1.15 x 10(-3)), and instead classify the companion of PSR J1227-6208 as a rare, massive ONeMg white dwarf close to the Chandrasekhar limit.

Several sources of repeating coherent bursts of radio emission with periods of many minutes have now been reported in the literature. These 'ultralong period' (ULP) sources have no clear multiwavelength counterparts and challenge canonical pulsar emission models, leading to debate regarding their nature. In this work, we report the discovery of a bright, highly polarized burst of radio emission at low Galactic latitude as part of a wide-field survey for transient and variable radio sources. ASKAPJ175534.9-252749.1 does not appear to repeat, with only a single intense two-minute <^> 200-mJy burst detected from 60 h of observations. The burst morphology and polarization properties are comparable to those of classical pulsars but the duration is more than one hundred times longer, analogous to ULPs. Combined with the existing ULP population, this suggests that these sources have a strong Galactic latitude dependence and hints at an unexplored population of transient and variable radio sources in the thin disc of the Milky Way. The resemblance of this burst with both ULPs and pulsars calls for a unified coherent emission model for objects with spin periods from milliseconds to tens of minutes. However, whether or not these are all neutron stars or have the same underlying power source remains open for debate.

Fast Radio Bursts (FRBs) are short-timescale transients of extragalactic origin. The number of detected FRBs has grown dramatically since their serendipitous discovery from archival data. Some FRBs have also been seen to repeat. The polarimetric properties of repeating FRBs show diverse behaviour and, at times, extreme polarimetric morphology, suggesting a complex magneto-ionic circumburst environment for this class of FRB. The polarimetric properties such as circular polarisation behaviour of FRBs are crucial for understanding their surrounding magnetic-ionic environment. The circular polarisation previously observed in some of the repeating FRB sources has been attributed to propagation effects such as generalised Faraday rotation (GFR), where conversion from linear to circular polarisation occurs due to the non-circular modes of transmission in relativistic plasma. The discovery burst from the repeating FRB$~$20180301A showed significant frequency-dependent circular polarisation behaviour, which was initially speculated to be instrumental due to a sidelobe detection. Here we revisit the properties given the subsequent interferometric localisation of the burst, which indicates that the burst was detected in the primary beam of the Parkes/Murriyang 20-cm multibeam receiver. We develop a Bayesian Stokes-Q, U, and V fit method to model the GFR effect, which is independent of the total polarised flux parameter. Using the GFR model we show that the rotation measure (RM) estimated is two orders of magnitude smaller and opposite sign ($\sim$28 rad$\,$m$^{-2}$) than the previously reported value. We interpret the implication of the circular polarisation on its local magnetic environment and reinterpret its long-term temporal evolution in RM.

In addition to being the most magnetic objects in the known Universe, magnetars are the only objects observed to generate fast-radio-burst-like emissions. The formation mechanism of magnetars is still highly debated and may potentially be probed with the magnetar velocity distribution. We carried out a 3 yr long astrometric campaign on Swift J1818.0-1607, the fastest-spinning magnetar, using the Very Long Baseline Array. After applying the phase-calibrating 1D interpolation strategy, we obtained a small proper motion of 8.5 mas yr(-1) mag and a parallax of 0.12 +/- 0.02 mas (uncertainties at 1 sigma confidence throughout the Letter) for Swift J1818.0-1607. The latter is the second magnetar parallax and is among the smallest neutron star parallaxes ever determined. From the parallax, we derived the distance 9.4(-1.6)(+2.0) kpc, which locates Swift J1818.0-1607 at the far side of the Galactic central region. Combined with the distance, the small proper motion leads to a transverse peculiar velocity v(perpendicular to )= 48(-16)(+50) km s(-1)-a new lower limit to magnetar v(perpendicular to). Incorporating previous v perpendicular to estimates of seven other magnetars, we acquired v perpendicular to = 149(-68)(+132) km s(-1) for the sample of astrometrically studied magnetars, corresponding to the three-dimensional space velocity similar to 190(-87)(+168) km s(-1), smaller than the average level of young pulsars. Additionally, we found that the magnetar velocity sample does not follow the unimodal young pulsar velocity distribution reported by Hobbs et al. at >2 sigma confidence, while loosely agreeing with more recent bimodal young pulsar velocity distributions derived from relatively small samples of quality astrometric determinations.