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Thermonuclear (type-I) bursts exhibit properties that depend both on the local surface conditions of the neutron stars on which they ignite, as well as the physical parameters of the host binary system. However, constraining the system parameters requires a comprehensive method to compare the observed bursts to simulations. We have further developed the beansp code for this purpose and analysed the bursts observed from IGR J17498 |$-$| 2921, a 401-Hz accretion-powered pulsar, discovered during it's 2011 outburst. We find good agreement with a model having H-deficient fuel with |$X=0.15\pm 0.4$|⁠ , and CNO metallicity |$Z=0.0014^{+0.0004}_{-0.0003}$|⁠ , about a tenth of the solar value. The model has the system at a distance of |$5.7^{+0.6}_{-0.5}$|  kpc, with a massive (⁠|${\approx} 2\ \mathrm{ M}_\odot$|⁠) neutron star and a likely inclination of |$60^\circ$|⁠. We also re-analysed the data from the 2002 outburst of the accretion-powered millisecond pulsar SAX J1808.4 |$-$| 3658. For that system we find a substantially closer distance than previously inferred, at |$2.7\pm 0.3$|  kpc, likely driven by a larger degree of burst emission anisotropy. The other system parameters are largely consistent with the previous analysis. We briefly discuss the implications for the evolution of these two systems. [ABSTRACT FROM AUTHOR]

A pulsar's pulse profile gets broadened at low frequencies due to dispersion along the line of sight or due to multipath propagation. The dynamic nature of the interstellar medium makes both of these effects time-dependent and introduces slowly varying time delays in the measured times-of-arrival similar to those introduced by passing gravitational waves. In this article, we present an improved method to correct for such delays by obtaining unbiased dispersion measure (DM) measurements by using low-frequency estimates of the scattering parameters. We evaluate this method by comparing the obtained DM estimates with those, where scatter-broadening is ignored using simulated data. A bias is seen in the estimated DMs for simulated data with pulse-broadening with a larger variability for a data set with a variable frequency scaling index, |$\alpha$|⁠ , as compared to that assuming a Kolmogorov turbulence. Application of the proposed method removes this bias robustly for data with band averaged signal-to-noise ratio larger than 100. We report the measurements of the scatter-broadening time and |$\alpha$| from analysis of PSR J1643 |$-$| 1224, observed with upgraded Giant Metrewave Radio Telescope as part of the Indian Pulsar Timing Array experiment. These scattering parameters were found to vary with epoch and |$\alpha$| was different from that expected for Kolmogorov turbulence. Finally, we present the DM time-series after application of this technique to PSR J1643 |$-$| 1224. [ABSTRACT FROM AUTHOR]

We present evidence for |$\gamma$| -ray emission from a stacked population of 39 high-latitude globular clusters (GCs) not detected in the Fermi Point Source Catalogue, likely attributable to populations of millisecond pulsars within them. In this work, we use 13 yr of data collected by the Large Area Telescope aboard the Fermi Gamma-Ray Space Telescope to search for a cumulative signal from undetected GCs and compared them to control fields (CFs), selected to match the celestial distribution of the target clusters so as to distinguish the |$\gamma$| -ray signal from background emission. The joint likelihood distribution of the GCs has a significant separation (⁠|$\sim 4\sigma$|⁠) from that of the CFs. We also investigate correlations between detected cluster luminosities and other cluster properties such as distance, the number of millisecond pulsars associated with each cluster, and stellar encounter rate but find no significant relationships. [ABSTRACT FROM AUTHOR]

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. ASKAP J175534.9 |$-$| 252749.1 does not appear to repeat, with only a single intense two-minute |$\sim$| 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. [ABSTRACT FROM AUTHOR]

A neutron star (NS) accreting matter from a companion star in a low-mass X-ray binary (LMXB) system can spin up to become a millisecond pulsar (MSP). Properties of many such MSP systems are known, which is excellent for probing fundamental aspects of NS physics when modelled using the theoretical computation of NS LMXB evolution. Here, we systematically compute the long-term evolution of NS, binary, and companion parameters for NS LMXBs using the stellar evolution code mesa. We consider the baryonic to gravitational mass conversion to calculate the NS mass evolution and show its cruciality for the realistic computation of some parameters. With computations using many combinations of parameter values, we find the general nature of the complex NS spin frequency (⁠|$\nu$|⁠) evolution, which depends on various parameters, including accretion rate, fractional mass-loss from the system, and companion star magnetic braking. Further, we utilize our results to precisely match some main observed parameters, such as |$\nu$|⁠ , orbital period (⁠|$P_{\rm orb}$|⁠), etc. of four accreting millisecond X-ray pulsars (AMXPs). By providing the |$\nu$|⁠ , |$P_{\rm orb}$|⁠ , and the companion mass spaces for NS LMXB evolution, we indicate the distribution and plausible evolution of a few other AMXPs. We also discuss the current challenges in explaining the parameters of AMXP sources with brown dwarf companions and indicate the importance of modelling the transient accretion in LMXBs as a possible solution. [ABSTRACT FROM AUTHOR]

Magnetar-like activity has been observed in a large variety of neutron stars. PSR J1846−0258 is a young 327 ms radio-quiet pulsar with a large rotational power (∼8 × 1036 erg s−1), and resides at the center of the supernova remnant Kes 75. It is one of the rare examples of a high-magnetic-field pulsar showing characteristics both of magnetars and radio pulsars, and can thus provide important clues on the differences in the emission mechanisms between these two classes. In 2006, PSR J1846−0258 was detected to undergo an outburst for the first time, accompanied by a large flux increase, millisecond X-ray bursts, significant spectral changes, and a large timing glitch. In the period between 2020 May and June, after 14 yr of quiescent stable emission, the source underwent a second magnetar-like outburst, which was followed up with several observations by Neutron Star Interior Composition Explorer, XMM-Newton, NuSTAR, and Swift. In this work, we report on the long-term timing and X-ray spectral properties of the source following the 2020 outburst, and place upper limits on any source activity at radio wavelengths. We demonstrate that the pulsed flux increased by a factor >6 during the outburst, followed by nontrivial variability in the spin-down rate. Our timing analysis shows that the spin frequency and its derivative are clearly affected by magnetospheric activity due to the outburst. We find hints for an oscillation in the frequency derivative with a timescale of 50–60 days, recovering later on to stable quiescence. [ABSTRACT FROM AUTHOR]

The Dark Matter Particle Explorer (DAMPE) is a cosmic-ray detector as well as a pair-converting γ -ray telescope. The effective area, reflecting the geometrical cross-section area, the γ -ray conversion probability, and the photon selection efficiency, is important in γ -ray analyses. In this work, we find a significant time variation in the effective area, as large as ∼−4% yr−1 at 2 GeV for the high-energy trigger. We derive the data-based correction factors to the effective areas and apply corrections to both the effective areas and the exposure maps. The calibrated exposure can be ∼12% smaller than the Monte Carlo one on average at 2 GeV. The calibration is further verified using the observation of the Vela pulsar, showing the spectral parameters with the correction are more consistent with those in the Fermi-LAT catalog than the ones without correction. All the corrections are now implemented in the latest version of the DAMPE γ -ray analysis toolkit DmpST. [ABSTRACT FROM AUTHOR]

We present the first Chandra X-ray Observatory (CXO) catalog of "pulsar X-ray filaments," or "misaligned outflows." These are linear, synchrotron-radiating features powered by ultrarelativistic electrons and positrons that escape from bow shock pulsars. The filaments are misaligned with the (large) pulsar velocity, distinguishing them from the pulsar wind nebula (PWN) trail, which is also often visible in CXO ACIS images. Spectral fits and morphological properties are extracted for five secure filaments and three candidates using a uniform method. We present a search of archival CXO data for linear diffuse features; the known examples are recovered and a few additional weak candidates are identified. We also report on a snapshot CXO ACIS survey of pulsars with properties similar to the filament producers, finding no new filaments but some diffuse emission, including one PWN trail. Finally, we provide an updated model for the pulsar properties required to create filaments in light of these new observations. [ABSTRACT FROM AUTHOR]

Stochastic and secular variations in the spin frequency |$\nu$| of a rotation-powered pulsar complicate the interpretation of the measured braking index, n , in terms of a power-law spin-down torque |$\propto \nu ^{n_{\rm pl}}$|⁠. Both categories of variation can lead to anomalous braking indices, with |$\vert n \vert = \vert \nu \ddot{\nu } / \dot{\nu }^2 \vert \gg 1$|⁠ , where the overdot symbolizes a derivative with respect to time. Here, we quantify the combined effect of stochastic and secular deviations from pure power-law spin-down on measurements of n. Through analytical calculations, Monte Carlo simulations involving synthetic data, and modern Bayesian timing techniques, it is shown that the variance of n satisfies the predictive, falsifiable formula |$\langle n^{2} \rangle = (n_{\rm pl}+\dot{K}_{\rm dim})^{2}+\sigma _{\rm dim}^{2}$|⁠ , where |$\dot{K}_{\rm dim}$| is inversely proportional to the time-scale |$\tau _K$| over which the proportionality constant of the power-law spin-down torque varies, |$\sigma _{\rm dim}$| is proportional to the timing noise amplitude and inversely proportional to the square root of the total observing time, and the average is over an ensemble of random realizations of the timing noise process. The anomalous regime |$\langle n^2 \rangle \gg 1$| occurs for |$\dot{K}_{\rm dim} \gg 1$|⁠ , |$\sigma _{\rm dim} \gg 1$|⁠ , or both. The sign of n depends in part on the sign of |$\dot{K}_{\rm dim}$|⁠ , so it is possible to measure unequal numbers of positive and negative n values in a large sample of pulsars. The distinguishable impact of stochastic and secular anomalies on phase residuals is quantified to prepare for extending the analysis of synthetic data to real pulsars. [ABSTRACT FROM AUTHOR]

Using observational data obtained with the Five-hundred-meter Aperture Spherical radio Telescope, we succeeded in identifying subcomponents of different pulse profile components of PSR B1822−09 by the phase-to-phase cross correlations between intensity sequences of single pulses. The determined number of the subcomponents and edges of the subcomponents are consistent with the results of Gaussian fitting on the mean pulse profiles of PSR B1822−09. According to the results, the main pulse (MP) in both the radio burst mode (B mode) and the radio-quiet mode (Q mode), the precursor (PC), and the interpulse (IP) of PSR B1822−09 are all composed of three subcomponents. The correlation coefficients between intensity sequences at different pulse phases reveal a positive correlation between the subcomponent C8 of the MP and C3 of the IP in the Q mode, and a positive correlation between C5 of the PC and C2 of the IP during the switching process from the B mode to the Q mode. These complex correlations present a challenge for the existing scenarios that describe relations between different pulse profile components. We proposed a hypothesis that different subcomponents correspond to different subpatches on the pulsar surface, and emissions from a subpatch reveal responses of the subpatch to some variations like the voltage in the magnetosphere. Therefore, correlations between different subcomponents depend on the responses of the subpatches to the variations. [ABSTRACT FROM AUTHOR]

The Be/X-ray binary pulsar RX J0440.9+4431 went through a giant outburst in December 2022 with a peak flux of |$\sim$| 2.3 Crab in 15–50 keV. We studied the broad-band timing and spectral properties of RX J0440.9+4431 using four AstroSat observations, where the source transited between subcritical and supercritical accretion regimes. Pulsations were detected significantly above 100 keV. The pulse profiles were found to be highly luminosity- and energy-dependent. A significant evolution in the pulse profile shape near the peak of the outburst indicates a possible change in the accretion mode and beaming patterns of RX J0440.9+4431. The rms pulsed fraction was luminosity- and energy-dependent, with a concave-like feature around 20–30 keV. The depth of this feature varied with luminosity, indicating changes in the accretion column height and proportion of reflected photons. The broad-band continuum spectra were best fitted with a two-component Comptonization model with a blackbody component or a two-blackbody component model with a thermal Comptonization component. A quasi-periodic oscillation (QPO) at 60 mHz was detected at a luminosity of |$2.6 \times 10^{37}$|  erg s |$^{-1}$|⁠ , which evolved into 42 mHz at |$1.5 \times 10^{37}$|  erg s |$^{-1}$|⁠. The QPO rms were found to be energy dependent with an overall increasing trend with energy. For the first time, we found the QPO frequency varying with photon energy in an X-ray pulsar, which poses a challenge in explaining the QPO with current models such as the Keplarian and beat frequency model. Hence, more physically motivated models are required to understand the physical mechanism behind the mHz QPOs. [ABSTRACT FROM AUTHOR]

This work presents the first-ever broadband (0.7–25.0 keV) timing and spectral analysis of Be-HMXB 2S 1417–624 during its 2021 outburst. Using AstroSat observations, coherent pulsations at ∼ 17.36633 s (MJD 59239.082) were detected in 0.7–7.0 keV SXT and 3.0–25.0 keV LAXPC data. The pulse profile was dual peaked at all energies, with the relative intensity of the main peak increasing with energy. The peaks in the SXT profiles were broad and comprised of several mini-structures. The LAXPC profiles were relatively smooth and had higher pulsed fractions, which increased with energy. The SXT + LAXPC simultaneous energy spectrum is well described by an absorbed power-law with exponential cut-off, a ∼ 1.6 keV black body component, and a 6.47 keV emission line. A model comprising of an absorbed power law with high energy cut-off plus a partial covering absorber and Gaussian emission line fits the spectrum quite well. These results have been compared with timing and spectral features during the previous outbursts of this transient pulsar. [ABSTRACT FROM AUTHOR]

Recycled millisecond pulsars are susceptible to starquakes as they are continuously accreting matter from their binary companion. A starquake happens when the rotational frequency of the star crosses its breaking frequency. In this study, we perform a model analysis of an accreting neutron star suffering a starquake. We analyse two models: a spherical star with accreting mountains and a deformed star with accreting mountains. We find that as the star crosses the breaking frequency and suffers a starquake, there is a sudden change in the continuous gravitational wave signal arriving from it. The amplitude of the gravitational wave signal increases suddenly both for the spherical and deformed star. For the spherical star, the accreting matter entirely dictates the amplitude of the gravitational wave. For the deformed star, both the accreting matter and the deformation from spherical symmetry play a significant role in determining the amplitude of the gravitational wave signal. This sudden change in the continuous gravitational wave signal in recycled millisecond pulsars can be a unique signature for such pulsars undergoing a starquake. [ABSTRACT FROM AUTHOR]

Recent radio surveys have revealed pulsars with dispersion and scattering delays induced by ionized gas that are larger than the rest of the observed pulsar population, in some cases with electron column densities (or dispersion measures, DMs) larger than the maximum predictions of Galactic electron density models. By cross-matching the observed pulsar population against H ii region catalogs, we show that the majority of pulsars with DM > 600 pc cm−3 and scattering delays τ (1 GHz) > 10 ms lie behind H ii regions, and that H ii region intersections may be relevant to as much as a third of the observed pulsar population. The fraction of the full pulsar population with sightlines intersecting H ii regions is likely larger. Accounting for H ii regions resolves apparent discrepancies where Galactic electron density models place high-DM pulsars beyond the Galactic disk. By comparing emission measures inferred from recombination line observations to pulsar DMs, we show that H ii regions can contribute tens to hundreds of parsecs per cubic centimeter in electron column density along a pulsar line of sight. We find that nearly all pulsars with significant excess (and deficit) scattering from the mean τ –DM relation are spatially coincident with known discrete ionized gas structures, including H ii regions. Accounting for H ii regions is critical to the interpretation of radio dispersion and scattering measurements as electron density tracers, both in the Milky Way and in other galaxies. [ABSTRACT FROM AUTHOR]

In light of NANOGrav data, we provide for the first time possible observational signatures of Superstring theory. First, we work with inflection-point inflationary potentials naturally realized within Wess–Zumino-type no-scale Supergravity, which give rise to the formation of microscopic primordial black holes (PBHs) triggering an early matter-dominated era (eMD) and evaporating before big bang nucleosynthesis (BBN). Remarkably, we obtain an abundant production of primordial gravitational waves (PGW) at the frequency ranges of nHz, Hz and kHz and in strong agreement with pulsar time array (PTA) gravitational wave (GW) data. This PGW background could serve as a compelling observational signature for the presence of quantum gravity via no-scale Supergravity. [ABSTRACT FROM AUTHOR]

There is growing interest in the overlap reduction function in pulsar timing array observations as a probe of modified gravity. However, current approximations to the Hellings–Downs curve for subluminal gravitational wave propagation, say v < 1 , diverge at small angular pulsar separation. In this paper, we find that the overlap reduction function for the v < 1 case is sensitive to finite distance effects. First, we show that finite distance effects introduce an effective cut-off in the spherical harmonics decomposition at ℓ ∼ 1 - v 2 k L , where ℓ is the multipole number, k the wavenumber of the gravitational wave and L the distance to the pulsars. Then, we find that the overlap reduction function in the small angle limit approaches a value given by π k L v 2 (1 - v 2) 2 times a normalization factor, exactly matching the value for the autocorrelation recently derived. Although we focus on the v < 1 case, our formulation is valid for any value of v. [ABSTRACT FROM AUTHOR]

This paper is designed for heavy pulsars coming from the Neutron Star Interior Composition Explorer. The research model is describe by Einstein field equations for anisotropic fluid configuration with spherical symmetry. As per present perceptiveness, modified non-linear Van der Waals equation of state is used to relate physical variables. The continuity of inner and outer matter is obtained by comparing inner spacetime to outer Schwarzschild metric. The physical viability of this model is evaluated and further it is compared with observational data of pulsars PSR J0348+0432, PSR J0740+6620 and PSR J0030+0451. The model fulfils all physical and mathematical characteristics of the dense structure studies. It offers the factual proofs carried by evolution of celestial configurations. The working model presented here is physically viable and shows stable behaviour. [ABSTRACT FROM AUTHOR]

Andreev–Bashkin entrainment makes the hydrodynamics of the binary superfluid solution particularly interesting. We investigate stability and motion of quantum vortices in such system. [ABSTRACT FROM AUTHOR]

A small number of pulsars are known to emit giant pulses (GPs), single pulses much brighter than average. Among these is PSR J0534+2200, also known as the Crab pulsar, a young pulsar with high GP rates. Long-term monitoring of the Crab pulsar presents an excellent opportunity to perform statistical studies of its GPs and the processes affecting them, potentially providing insight into the behavior of other neutron stars that emit bright single pulses. Here, we present an analysis of a set of 24,985 Crab GPs obtained from 88 hr of daily observations at a center frequency of 1.55 GHz by the 20 m telescope at the Green Bank Observatory, spread over 461 days. We study the effects of refractive scintillation at higher frequencies than previous studies and compare methods of correcting for this effect. We also search for deterministic patterns seen in other single-pulse sources, possible periodicities seen in several rotating radio transients and fast radio bursts, and clustering of GPs like that seen in the repeating fast radio burst FRB 121102. [ABSTRACT FROM AUTHOR]

Massive data shoving can reach the greatest throughput, which is necessary for distributed streaming storage to function at its best. The comparison of the distributed streaming storage systems Pulsar and Pravega for a given number of producers and data packet size is covered in detail in this study. This analysis' benchmark tool accommodates several producers and consumers. When connection pooling is enabled and 0.5 million records are thrust at a 10 Mbps data rate, both streaming storages are assessed for latency percentile comparison. A novel idea called sbk-charts is introduced in the current study, which can create practical charts from CSV files. Multiple CSV files can be joined by sbk-charts to construct a single combined xlsx file with helpful charts. The outcomes of the experiment are then evaluated for performance comparison in a number of dimensions. [ABSTRACT FROM AUTHOR]

As the number of spacecraft heading beyond Earth's orbit increased in recent years, autonomous navigation solutions have become increasingly important. One such solution is pulsar-based navigation. The availability of pulsar signals for simulations and HIL testing is essential for the development of pulsar-based navigation. This study proposes a method to develop a surrogate model of pulsar signals based on radio pulsar observations. The selection of suitable pulsars for the radio telescope is discussed, and a series of observations are conducted. The collected data are processed using the PRESTO software, and the pulsar parameters for the model are derived. Unlike current pulsar signal models, the proposed model anticipates pulsar signal parameters to change over time. It can provide dynamic input parameters for known synthetic pulsar signal generators, resulting in a more realistic signal. [ABSTRACT FROM AUTHOR]

In this paper, a class of anisotropic compact stars is analyzed in Heintzmann geometry. The Einstein field equations (EFEs) have been solved to obtain the stellar model in presence of pressure anisotropy. We have considered the g t t metric component as proposed by Heintzmann, and by solving the EFEs, the g r r metric component is evaluated in the presence of pressure anisotropy. It is noted that for an isotropic star (α = 0), the maximum mass lies within the range 1.87–3.04 M ⊙ for radii ranging between 8–13 km. For anisotropic compact stars, the maximum mass increases with α and lies within the range 1.99–3.23 M ⊙ for anisotropy parameter α = 0. 5. The physical viability of the model is examined by applying our model to study the properties of a few known compact objects. All the stability conditions are fulfilled in the proposed model. It is also interesting to note that the maximum mass calculated from our model from geometrical consideration and solving the TOV equation is approximately equal, and the radii predicted from the present model comply with the estimated radius from observations of recently observed pulsars and lighter compact objects of GW events such as GW 190814 and GW 170817. [ABSTRACT FROM AUTHOR]

CXOU J110926.4−650224 is a candidate transitional millisecond pulsar (tMSP) with X-ray and radio emission properties reminiscent of those observed in confirmed tMSPs in their X-ray 'subluminous' disc state. We present the results of observing campaigns that, for the first time, characterise the optical and near-infrared variability of this source and establish a connection with the mode-switching phenomenon observed in X-rays. The optical emission exhibited flickering activity, frequent dipping episodes where it appeared redder, and a multi-peaked flare where it was bluer. The variability pattern was strongly correlated with that of the X-ray emission. Each dip matched an X-ray low-mode episode, indicating that a significant portion of the optical emission originates from nearly the same region as the X-ray emission. The near-infrared emission also displayed remarkable variability, including a dip of 20 min in length during which it nearly vanished. Time-resolved optical spectroscopic observations reveal significant changes in the properties of emission lines from the disc and help infer the spectral type of the companion star to be between K0 and K5. We compare the properties of CXOU J110926.4−650224 with those of other tMSPs in the X-ray subluminous disc state and discuss our findings within the context of a recently proposed scenario that explains the phenomenology exhibited by the prototypical tMSP PSR J1023+0038. [ABSTRACT FROM AUTHOR]

Context. Two millisecond pulsars, PSR J1513−2550 and PSR J2017−1614, with spin periods of about 2.1 and 2.3 ms were recently discovered in the radio and γ-rays and classified as black widow pulsars in tight binary stellar systems with orbital periods of about 4.3 and 2.3 h. Aims. Our goals are to reveal the fundamental parameters of both systems and their binary components using multi-wavelength observations. Methods. We carried out the first time-series multi-band optical photometry of the objects with the 2.1-m telescope of the Observatorio Astronómico Nacional San Pedro Mártir, the 6.5-m Magellan-1 telescope, and the 10.4-m Gran Telescopio Canarias. To derive the parameters of both systems, we fitted the obtained light curves with a model assuming heating of the companion by the pulsar. We also analysed archival X-ray data obtained with the XMM-Newton observatory. Results. For the first time, we firmly identified J1513−2550 in the optical and both pulsars in X-rays. The optical light curves of both systems have a single peak per orbital period with a peak-to-peak amplitude of ≳2 magnitudes. The J2017−1614 light curves are symmetric, while J1513−2550 demonstrates strong asymmetry whose nature remains unclear. Conclusions. We constrained the orbital inclinations, pulsar masses, companion temperatures and masses, and the distances to both systems. We also conclude that J2017−1614 may contain a massive neutron star of 2.4 ± 0.6 M⊙. The X-ray spectra of both sources can be fitted by power laws with parameters typical of black widow systems. [ABSTRACT FROM AUTHOR]

We present a comparative analysis of photometric observations of the cataclysmic variable TT Ari in its bright state obtained by the TESS orbital observatory in 2021 and 2023 and by ground-based amateur telescopes in 2022. The light curves from 2021 and 2022 are dominated by modulations with a period slightly shorter than the orbital one (negative superhumps), 0.13292 and 0.13273 d, respectively. From the data obtained in 2023, we see much stronger modulations appearing on a much longer timescale of a few days with an amplitude of up to 0.5 mag, compared to 0.2 mag in 2021. We also find the negative superhump variability with the period of 0.1338 d in the 2023 observations, but the significance of these negative superhumps is much lower than in the previous seasons. We detect less significant additional modulations with a period exceeding the orbital one (positive superhumps) in the observations from 2021 and 2022. Their periods are 0.15106 and 0.1523 d, respectively. We also find a previously unnoticed periodic signal corresponding to the orbital period of 0.13755 d in the TESS observations in 2021. Theoretical models of tidal precession of an elliptical disk predict a decrease in the precession period (and an increase in the period of the positive superhumps) with increasing disk radius, which is consistent with the observed photometric behavior of the system. This enables us to estimate the mass ratio q of the components in TT Ari to be in the range of 0.24–0.29. The tilted disk precession model predicts a period of nodal precession whose value is in general agreement with observations. [ABSTRACT FROM AUTHOR]

Ultra-light dark matter perturbs the orbital motion of binary pulsars, in particular by causing peculiar time variations of a binary's orbital parameters, which then induce variations in the pulses' times of arrival. Binary pulsars have therefore been shown to be promising detectors of ultra-light dark matter. To date, the sensitivity of binary pulsars to ultra-light dark matter has only been studied for dark matter masses in a narrow resonance band around a multiple of the binary pulsar orbital frequency. In this study we devise a two-step, bayesian method that enables us to compute semi-analytically the sensitivity for all masses, also away from the resonance, and to combine several observed binaries into one global sensitivity curve. We then apply our method to the case of a universal, linearly-coupled, scalar ultra-light dark matter. We find that with next-generation radio observatories the sensitivity to the ultra-light dark matter coupling will surpass that of Solar-System constraints for a decade in mass around m ∼ 10−21 eV, even beyond resonance [ABSTRACT FROM AUTHOR]

Context. Large thermal variations have been observed in neutron stars that typically are not aligned with density gradients. Such terms may activate the Biermann battery effect, leading to thermoelectric interactions and to the generation of electromotive force. Aims. We aim to identify the possible impact of a temperature anisotropy on the crust of a neutron star can have in the evolution of its magnetic field, through the thermoelectric terms. Methods. We considered a neutron star crust with large temperature gradients, associated with long-lived hot spots, described by a localized Gaussian-type function. We simulated the interplay between the battery term and the Hall and Ohmic evolution numerically for axisymmetric systems. Results. The results indicate that for crust temperatures of ∼109 K the toroidal field can be amplified up to ∼1014 − 1015 G near the points of maximum temperature gradients, and it locally changes the architecture of the poloidal field lines. For internal crustal temperatures of ∼108 K, the temperature gradient generates fields that are lower by about two orders of magnitude. In these cases, saturation is achieved after some hundred thousand years, after which the battery and Ohmic dissipation balance each other, whereas the Hall drift contributes comparatively little to the final field strength, but it can affect its structure. Conclusions. We conclude that the thermoelectric effect can impact the overall magnetic field evolution, provided that the thermal gradient is maintained for a sufficiently long time. Neutron stars endowned with moderate-strength magnetic fields may be affected by the thermoelectric effect if the hotspots survive for timescales of a few kiloyears. [ABSTRACT FROM AUTHOR]

Context. The existence of a population of millisecond pulsars in the Galactic bulge is supported, along with other evidence, by the Fermi GeV excess, an anomalous γ-ray emission detected almost 15 years ago in the direction of the Galactic center. However, radio surveys searching for pulsations have not yet revealed bulge millisecond pulsars. Aims. Identifying promising bulge millisecond pulsar candidates is key to motivating pointed radio pulsation searches. Candidates are often selected among steep-spectrum or polarized radio sources, but multiwavelength information can also be exploited: The aim of this work is to pinpoint strong candidates among the yet unidentified X-ray sources. Methods. We investigated the multiwavelength counterparts of sources detected by the Chandra X-ray observatory that have spectral properties expected for millisecond pulsars in the Galactic bulge. We considered that ultraviolet, optical, and strong infrared counterparts indicate that an X-ray source is not a bulge pulsar, while a radio or a faint infrared counterpart makes it a promising candidate. Results. We identify a large population of more than a thousand X-ray sources without optical, ultraviolet, or strong infrared counterparts. Among them, five are seen for the first time in unpublished radio imaging data from the Very Large Array. We provide the list of promising candidates, for most of which follow-up pulsation searches are ongoing. [ABSTRACT FROM AUTHOR]

Transitional millisecond pulsars (tMSPs) represent a dynamic category of celestial sources that establish a crucial connection between low-mass X-ray binaries and millisecond radio pulsars. These systems exhibit transitions from rotation-powered states to accretion-powered ones and vice versa, highlighting the tight evolutionary link expected by the so-called recycling scenario. In their active phase, these sources manifest two distinct emission modes named high and low, occasionally punctuated by sporadic flares. Here, we present high-time-resolution spectroscopic observations of the binary tMSP J1023+0038, in the sub-luminous disc state. This is the first short-timescale (∼1 min) optical spectroscopic campaign ever conducted on a tMSP. The campaign was carried out over the night of June 10, 2021 using the Gran Telescopio Canarias. The optical continuum shows erratic variability, without clear evidence of high and low modes or of orbital modulation. Besides, the analysis of these high-temporal-cadence spectroscopic observations reveals, for the first time, evidence for a significant (up to a factor of ∼2) variability in the emission line properties (equivalent width and full width half maximum) over a timescale of minutes. Intriguingly, the variability episodes observed in the optical continuum and in the emission line properties seem uncorrelated, making their origin unclear. [ABSTRACT FROM AUTHOR]

We present the results of a search for continuous gravitational wave signals (CGWs) in the second data release (DR2) of the European Pulsar Timing Array (EPTA) Collaboration. The most significant candidate event from this search has a gravitational wave frequency of 4–5 nHz. Such a signal could be generated by a supermassive black hole binary (SMBHB) in the local Universe. We present the results of a follow-up analysis of this candidate using both Bayesian and frequentist methods. The Bayesian analysis gives a Bayes factor of 4 in favour of the presence of the CGW over a common uncorrelated noise process. In contrast, the frequentist analysis estimates the p-value of the candidate to be < 1%, also assuming the presence of common uncorrelated red noise. However, comparing a model that includes both a CGW and a gravitational wave background (GWB) to a GWB only, the Bayes factor in favour of the CGW model is only 0.7. Therefore, we cannot conclusively determine the origin of the observed feature, nor can we rule it out as a CGW source. We present results of simulations that demonstrate that data containing a weak gravitational wave background can be misinterpreted as data including a CGW and vice versa, providing two plausible explanations for the EPTA DR2 data. Further investigations combining data from all PTA collaborations will be needed to reveal the true origin of this feature. [ABSTRACT FROM AUTHOR]

Aims. Global particle-in-cell (PIC) simulations of pulsar magnetospheres are performed with volume-, surface-, and pair-production-based plasma injection schemes to systematically investigate the transition between electrosphere and force-free pulsar magnetospheric regimes. Methods. We present a new extension of the PIC code OSIRIS that can be used to model pulsar magnetospheres with a two-dimensional axisymmetric spherical grid. The subalgorithms of the code and thorough benchmarks are presented in detail, including a new first-order current deposition scheme that conserves charge to machine precision. Results. We show that all plasma injection schemes produce a range of magnetospheric regimes. Active solutions can be obtained with surface and volume injection schemes when using artificially large plasma-injection rates, and with pair-production-based plasma injection for sufficiently large separation between kinematic and pair-production energy scales. [ABSTRACT FROM AUTHOR]

We answer frequently asked questions (FAQs) about the Hellings and Downs correlation curve—the 'smoking-gun' signature that pulsar timing arrays (PTAs) have detected gravitational waves (GWs). Many of these questions arise from inadvertently applying intuition about the effects of GWs on LIGO-like detectors to the case of pulsar timing, where not all of it applies. This is because Earth-based detectors, like LIGO and Virgo, have arms that are short (km scale) compared to the wavelengths of the GWs that they detect ( ≈ 10 2 –104 km). In contrast, PTAs respond to GWs whose wavelengths (tens of light-years) are much shorter than their arms (a typical PTA pulsar is hundreds to thousands of light-years from Earth). To demonstrate this, we calculate the time delay induced by a passing GW along an Earth-pulsar baseline (a 'one-arm, one-way' detector) and compare it in the 'short-arm' (LIGO-like) and 'long-arm' (PTA) limits. This provides qualitative and quantitative answers to many questions about the Hellings and Downs curve. The resulting FAQ sheet should help in understanding the 'evidence for GWs' recently announced by several PTA collaborations. [ABSTRACT FROM AUTHOR]

Recently a data set containing linear and circular polarisation information of a collection of six hundred pulsars has been released. The operative radio wavelength for the same was 21 cm. Pulsars radio emission process is modelled either with synchroton/superconducting self-Compton route or with curvature radiation route. These theories fall short of accounting for the circular polarisation observed, as they are predisposed towards producing, solely, linear polarisation. Here we invoke (pseudo)scalars and their interaction with photons mediated by colossal magnetic fields of pulsars, to account for the circular part of polarisation data. This enables us to estimate the pseudoscalar parameters such as its coupling to photons and its mass in conjunction as product. To obtain these values separately, we turn our attention to recent observation on 47 pulsars, whose absolute polarisation position angles have been made available. Except, a third of the latter set, the rest of it overlaps with the expansive former data set on polarisation type and degree. This helps us figure out, both the pseudoscalar parameters individually, that we report here. [ABSTRACT FROM AUTHOR]

This article provides a first-hand account of the 1982 Arecibo observations that led to the discovery of PSR B1937+21, the first-known millisecond pulsar. [ABSTRACT FROM AUTHOR]

It has now been just over four decades since the first discovery of a millisecond spin period pulsar (MSP), B1937+21, by Don Backer and collaborators in late 1982. This finding of an entirely new class of astronomical object revolutionized pulsar astronomy and provided inspiration for novel scientific investigation for decades to come, continuing to the current day and beyond. Here we review the events leading to the discovery, based on archival material, personal correspondence, and first-hand accounts of several of the participants. We also briefly review the enormous impact that MSPs have had on physics and astronomy by highlighting major MSP-related science of the past 40 years. [ABSTRACT FROM AUTHOR]

Millisecond pulsars, like pulsars, have led to major advances in many areas of astronomy and physics. The discovery in 2023 of a cosmological gravitational wave (GW) stochastic background using millisecond pulsar timing arrays has focused attention on the importance of millisecond pulsars, to both multi-messenger astronomy and cosmology, and for identifying the origin of the GW stochastic background, which is hypothesized to be due to supermassive black hole binaries (SMBHBs). Unlike pulsars, however, for which the details of the discovery are well-known, those of millisecond pulsars are not well known. In particular, the details of the first crucial step in the discovery of millisecond pulsars, namely the discovery of interplanetary scintillation (IPS) in the radio source 4C 21.53, are known only to the author. This paper presents a first-hand account of this crucial first step, which resulted ultimately in the discovery of millisecond pulses from this object. A brief description of interplanetary and interstellar scintillation and scattering is given in the Appendix. [ABSTRACT FROM AUTHOR]

Abstract The discovery of the first pulsar in a binary star system, the Hulse–Taylor pulsar, 50 years ago opened up an entirely new field of experimental gravity. For the first time it was possible to investigate strong-field and radiative aspects of the gravitational interaction. Continued observations of the Hulse–Taylor pulsar eventually led, among other confirmations of the predictions of general relativity (GR), to the first evidence for the reality of gravitational waves. In the meantime, many more radio pulsars have been discovered that are suitable for testing GR and its alternatives. One particularly remarkable binary system is the Double Pulsar, which has far surpassed the Hulse–Taylor pulsar in several respects. In addition, binary pulsar-white dwarf systems have been shown to be particularly suitable for testing alternative gravitational theories, as they often predict strong dipolar gravitational radiation for such asymmetric systems. A rather unique pulsar laboratory is the pulsar in a hierarchical stellar triple, that led to by far the most precise confirmation of the strong-field version of the universality of free fall. Using radio pulsars, it could be shown that additional aspects of the Strong Equivalence Principle apply to the dynamics of strongly self-gravitating bodies, like the local position and local Lorentz invariance of the gravitational interaction. So far, GR has passed all pulsar tests with flying colours, while at the same time many alternative gravity theories have either been strongly constrained or even falsified. New telescopes, instrumentation, timing and search algorithms promise a significant improvement of the existing tests and the discovery of (qualitatively) new, more relativistic binary systems.

Pulsars often display systematic variations in the position and/or intensity of the subpulses, the components that comprise each single pulse. Although the drift of these subpulses was observed in the early years of pulsar research, and their potential for understanding the elusive emission mechanism was quickly recognized, there is still no consensus on the cause of the drift. We explore the electrodynamics of two recently proposed or refined drift models: one where plasma lags behind corotation, connecting the drift with the rotational pole; and another where plasma drifts around the electric potential extremum of the polar cap. Generally, these are different locations, resulting in different drift behaviours, that can be tested with observations. In this study, however, we specifically examine these models in the axisymmetric case, where the physics is well understood. This approach seems counter-intuitive as both models then predict similar large-scale plasma drift. However, it allows us to show, by studying conditions within the sparks for both models, that the lagging behind corotation model is inconsistent with Faraday's law. The modified carousel (MC) model, where plasma drifts around the electric potential extremum, not only aligns with Faraday's law, but also provides a future direction for developing a comprehensive model of plasma generation in the polar cap region. Unlike previous models, which considered the drift only inside the discharging regions, the MC model reveals that the electric field between the discharges is not completely screened, and plasma drifts there – a paradigm shift for the drifting subpulse phenomenon. [ABSTRACT FROM AUTHOR]

A number of pulsar timing arrays have recently reported preliminary evidence for the existence of a nanohertz frequency gravitational wave background. These analyses rely on noise analyses, which are inherently complex due to the many astrophysical and instrumental factors. We investigate whether realistic systematic errors, stemming from misspecified noise models that fail to capture salient features of the pulsar timing noise, could bias the evidence for gravitational waves. We consider two plausible forms of misspecification: small instrumental pulse arrival time offsets and radio-frequency-dependent time-correlated noise. Using simulated data, we calculate the distribution of the commonly used optimal statistic with no signal present and using plausibly misspecified noise models. By comparing the optimal statistic distribution with the distribution created using "quasi-resampling" techniques (such as sky scrambles and phase shifts), we endeavour to determine the extent to which plausible misspecification might lead to a false positive. The results are reassuring: we find that quasi-resampling techniques tend to underestimate the significance of pure-noise data sets. We conclude that recent reported evidence for a nanohertz gravitational wave background is likely robust to the most obvious sources of systematic errors; if anything, the significance of the signal is potentially underestimated. [ABSTRACT FROM AUTHOR]

Glitching pulsars are expected to be important sources of gravitational waves (GWs). In this paper, we explore six different models that propose the emission of transient continuous waves, lasting days to months, coincident with glitches. The maximal GW energy is calculated for each model, which is then used to determine whether associated GWs could be detectable with LIGO-Virgo-KAGRA's O4 detectors. We provide an analytical approximation to calculate the signal-to-noise ratio (SNR) which includes information about the source's sky position, improving on previous estimates that assume isotropic or sky and orientation averaged sensitivities. By analysing the entire glitching population, we find that certain models predict detectable signals in O4, whereas others do not. We also rank glitching pulsars by SNR, based on archival data, and we find that for all models, the Vela pulsar (PSR J0835 |$-$| 4510) would provide the strongest signal. Moreover, PSR J0537 |$-$| 6910 is not expected to yield a detectable signal in O4, but will start becoming relevant for next-generation detectors. Our analysis also extends to the entire pulsar population, regardless of whether they have glitched, and we provide a list of pulsars that would present a significant signal, if they were to glitch. Finally, we apply our analysis to the 2024 April Vela glitch and find that a signal should be detectable under certain models. The non-detection of a supposedly detectable signal would provide an efficiency factor that quantifies a model's contribution to GW emission, eventually leading to a differentiation of models and independent constraints on physical parameters. [ABSTRACT FROM AUTHOR]

We use data from the MeerTime project on the MeerKAT telescope to ask whether the radio emission properties of millisecond pulsars (MSPs) and slowly rotating, younger pulsars (SPs) are similar or different. We show that the flux density spectra of both populations are similarly steep, and the widths of MSP profiles obey the same dependence on the rotational period as slow pulsars. We also show that the polarization of MSPs has similar properties to slow pulsars. The commonly used pseudo-luminosity of pulsars, defined as the product of the flux density and the distance squared, is not appropriate for drawing conclusions about the relative intrinsic radio luminosity of SPs and MSPs. We show that it is possible to scale the pseudo-luminosity to account for the pulse duty cycle and the solid angle of the radio beam, in such a way that MSPs and SPs do not show clear differences in intrinsic luminosity. The data therefore support common emission physics between the two populations in spite of orders of magnitude difference in their period derivatives and inferred, surface, dipole magnetic field strengths. [ABSTRACT FROM AUTHOR]

The detection of the nano-Hz gravitational-wave background (GWB) is one of the main targets of Pulsar timing arrays (PTAs). The detection can be achieved via searching for a common signal with quadrapolar correlation between pulsar pairs. Errors in the Solar-System ephemeris (SSE) can induce dipolar correlations in PTA data, which may affect the results of GWB searches, especially when the data quality is not high enough to constrain the correlation pattern. We investigate the effect of unmodelled SSE errors on GWB searches with PTAs, using simulations with properties based on the European Pulsar Timing Array data set. When the GWB signal is strong, SSE errors have little effect on the GWB search results, including parameter inference and model selection. When the GWB signal is weak, SSE errors can lead to overestimation of the GWB amplitude. However, model comparison would show strong support for dipolar correction, which implies the source of the common signal to be SSE-related and helps avoid its misidentification as a GWB signal. This indicates that SSE error is unlikely to be the main source of the common signal detected recently with real PTA data. We also use simulations to test the ability of the SSE model LINIMOSS in absorbing SSE-error signals and leaving the GWB signal intact. We show that marginalizing LINIMOSS planetary parameters with infinite priors is good at absorbing SSE errors, but may also lead to improper absorption of a GWB signal. Caution is therefore required when setting appropriate limits on the priors of SSE parameters. [ABSTRACT FROM AUTHOR]

It is believed that the core of a neutron star can be host to various novel phases of matter, from nucleon superfluid phase to exotic high baryon density quantum chromodynamics (QCD) phases. Different observational signals for such phase transitions have been discussed in the literature. Here, we point out a unique phenomenon associated with phase transition to a superfluid phase, which may be the nucleon superfluid phase or a phase like the colour-flavour locked phase, allowing for superfluid vortices. In any superfluid phase transition, a random network of vortices forms via the so-called Kibble–Zurek mechanism, which eventually mostly decays away, finally leaving primarily vortices arising from the initial angular momentum of the core. This transient, random vortex network can have a non-zero net angular momentum for the superfluid component, which will generally be oriented in an arbitrary direction. This is in contrast to the final vortices, which arise from initial rotation and hence have the initial angular momentum of the neutron star. The angular momentum of the random vortex network is balanced by an equal and opposite angular momentum in the normal fluid due to the conservation of angular momentum, thereby imparting an arbitrarily oriented angular momentum component to the outer shell of the neutron star. This will affect the pulse timing and pulse profile of a pulsar. These changes in the pulses will decay away in a characteristic manner that this as the random vortex network decays, obeying specific scaling laws leading to universal features for the detection of superfluid transitions occurring in a pulsar core. [ABSTRACT FROM AUTHOR]

Variations in the radiation intensity of pulsar B0950+08 from 2014 to 2022 with scales from minutes to years were analyzed. The observations were obtained in daily survey using the Large Phased Array (LPA) radio telescope. The high variability of radiation is shown both from pulse to pulse and on scales greater than 3 min. The average value of the estimated amplitude of these variations in 3.2 min is 25 Jy, the modulation index is unity. The average relative amplitude of the interpulse (IP) is of the main pulse. In individual pulses, the amplitude of the interpulse may exceed the amplitude of the main pulse (MP), but this is a rare event. Radiation is observed in almost the entire period of the pulsar. For the first time, the relative amplitude of radiation between the main pulse and the interpulse (radiation bridge) was measured. When averaging for ~10 h, it varies from 0.8 to 1.31% with an average value of . A high correlation between MP and IP amplitude variations both when averaging profiles over 3.2 min and when averaging over years was found. This correlation is due to refractive interstellar scintillation. The frequency scale of IP diffraction interstellar scintillation was measured for the first time, and that the spectral shapes for IP and MP were shown to be well correlated and have the same frequency scale. There are strong variations in the frequency scale of scintillation from session to session (time interval from one day) on scales of 200–800 kHz. The refractive scale of scintillation of 1–2 days was determined. A modulation of radiation with a characteristic scale of ~130 days, which, apparently, is also associated with refractive scintillation, was found. [ABSTRACT FROM AUTHOR]

Pulsars are believed to be one of the most important celestial objects in the universe. The emission mechanism of pulsars is still a big paradox for physicists, as no completely acceptable theory can reach a suitable consensus with observation. Some complicated coherent plasma processes and acceleration-based mechanisms in the pulsar magnetosphere generate a powerful radio beam. There have been dedicated theories such as the geometrical and relativistic phase shift (RPS) methods. The relativistic phase shift method is owing to the combined effects of aberration-retardation (A/R) and polar cap current effect (PCC), etc., and by implementing this method, we make quantitative inspections to deduce the emission altitude of the pulsar's radio emission components. Here, we have shown the estimation of the emission height of pulsar PSR B2111+46 for both core and conal components at 925 MHz, 1.25 GHz, 1.65 GHz, and 4.85 GHz. Moreover, we have estimated the foot point, normalized with the last open field line constant, corresponding to pulse edges at multiple bands. Current analysis of the paper shows that at least for PSR B2111+46, the full polar cap is not sensitive to radio emission for most of the cases in the given stretch of radio frequency. [ABSTRACT FROM AUTHOR]

In this paper, we report the detailed observation of the drift subpulse behavior of PSR J1514–4834 at a central frequency of 1369 MHz using the Parkes 64-m radio telescope. We have found that individual pulses of this pulsar exhibit distinct modulation behaviors for different profile components. The leading and middle components display periodic amplitude modulation with a period of P 3 = 37.5 ± 0.8 P , and a drifting sub-pulse phenomenon is detected in the phase region of trailing component with the measured drifting periods P 2 = 7.0 ± 0.4 P and P 3 = 37.5 ± 0.8 P . Additionally, it was observed that the leading and trailing components of the pulsar have a clear correlation, the middle and trailing components have a clear anti-correlation, and there is no apparent correlation between the leading and middle components. Moreover, this pulsar deviates from the range of most amplitude-modulated pulsars in the E ˙ − P 3 diagram, but it still falls within the category of subpulse drifting. PSR J1514–4834 exhibits periodic emission modulation and sub-pulse drifting simultaneously in different profile components, which is difficult to understand with the traditional carousel model. Our observational results will provide new observation evidence for theoretical studies of single-pulse emission mechanisms in pulsars. [ABSTRACT FROM AUTHOR]

Following a brief introduction to pulsars and how to intercept radio-frequency transmissions from them, this article describes the design and results of an amateur project aimed at detecting and validating the strongest pulsar in the northern celestial hemisphere, with only a modest back-garden radio telescope. Techniques are described to improve verification confidence for weak, low signal-to-noise ratio observations by closer tracking of pulsar pulse train properties and also to identify the strongest pulsar scintillation sequence in the recorded observation data. The methods are illustrated based on an observation of pulsar 80329+54. [ABSTRACT FROM AUTHOR]

Millisecond pulsars (MSPs) are a kind of radio pulsars with short spin periods, playing a key role in many aspects of stellar astrophysics. In recent years, some more MSPs with wide orbits (⁠|$\gt 30\, \rm d$|⁠) have been discovered, but their origin is still highly unclear. In this work, according to an adiabatic power-law assumption for the mass-transfer process, we carried out a large number of complete binary evolution computations for the formation of MSPs with wide orbits through the iron core-collapse supernova (CCSN) channel, in which a neutron star originating from a CCSN accretes matter from a red-giant star and spun up to millisecond periods. We found that this channel can form the observed MSPs with wide orbits in the range of |$30\!-\!1200\, {\rm d}$|⁠ , in which the white dwarf (WD) companions have masses in the range of |$0.28\!-\!0.55\, \rm M_{\odot }$|⁠. We also found that almost all the observed MSPs can be reproduced by this channel in the WD companion mass versus orbital period diagram. We estimate that the Galactic numbers of the resulting MSPs from the CCSN channel are in the range of |$\sim 4.8\!-\!8.5\times 10^{5}$|⁠. Compared with the accretion-induced collapse channel, the CCSN channel provides a main way to produce MSPs with wide orbits. [ABSTRACT FROM AUTHOR]

Radiation from X-ray pulsars (XRPs) was expected to be strongly linearly polarized owing to a large difference in their ordinary and extraordinary mode opacities. The launch of IXPE allowed us to check this prediction. IXPE observed a dozen X-ray pulsars, discovering pulse-phase dependent variation of the polarization degree (PD) and polarization angle (PA). Although the PD showed rather erratic profiles resembling flux pulse dependence, the PA in most cases showed smooth variations consistent with the rotating vector model (RVM), which can be interpreted as a combined effect of vacuum birefringence and dipole magnetic field structure at a polarization-limiting (adiabatic) radius. Application of the RVM allowed us to determine XRP geometry and to confirm the free precession of the NS in Her X-1. Deviations from RVM in two bright transients led to the discovery of an unpulsed polarized emission likely produced by scattering off the accretion disk wind. [ABSTRACT FROM AUTHOR]