Preprint of a chapter of the book 'Millisecond Pulsars', of the Astrophysics and Space Science Library (ASSL) 2021 series edited by Sudip Bhattacharyya, Alessandro Papitto and Dipankar Bhattacharya
Neutron Stars are among the most exotic objects in the Universe. A neutron star, with a mass of 1.4-2 Solar masses within a radius of about 10-15 km, is the most compact stable configuration of matter in which degeneracy pressure can still balance gravity, since further compression would lead to gravitational collapse and formation of a black hole. As gravity is extreme, rotation is extreme: neutron stars are the fastest rotating stars known, with periods as short as a millisecond. The presence of a magnetic field not aligned with the rotation axis of the star is the origin of pulsating emission from these sources, which for this reason are dubbed pulsars. The discovery in 1998 of the first Accreting Millisecond X-ray Pulsar, started an exciting season of continuing discoveries. In the last 20 years, thanks to the extraordinary performance of astronomical detectors in the radio, optical, X-ray, and Gamma-ray bands, astrophysicists had the opportunity to thoroughly investigate the so-called Recycling Scenario: the evolutionary path leading to the formation of a Millisecond-spinning Pulsar. In this chapter we review the general properties of Accreting Millisecond X-ray Pulsars, which provide the first evidence that neutron stars are spun up to millisecond periods by accretion of matter and angular momentum from a (low-mass) companion star. We describe the general characteristics of this class of systems with particular attention to their spin and orbital parameters, their short-term and long-term evolution, as well as the information that can be drawn from their X-ray spectra.
186 binary pulsars are shown in the magnetic field versus spin period (B-P) dia- gram, and their relations to the millisecond pulsars can be clearly seen. We declaim a minimum accretion rate for the millisecond pulsar formation both from the observation and theory. If the accretion rate is lower than the minimum accretion rate, the pulsar in binary system will not become a millisecond pulsar after the evolution.
In this review paper we explain the following gamma-ray emission features from the millisecond pulsars. (1)Why is the dipolar field of millisecond pulsars so weak but the magnetic pair creation process may still be able to control the size of the outergap? (2)A sub-GeV pulse component could occur in the vicinity of the radio pulse of millisecond pulsars. (3)Orbital modulated gamma-rays should exist in the black widow systems for large viewing angle.
We construct a relativistic model for the newly discovered millisecond pulsar PSR J0514 - 4002A located in the globular cluster NGC 1851 (A. Ridolfi, P.C.C. Freire, Y. Gupta, S.M. Ransom, MNRAS 490, 3860 (2019)) by using Tolman VII spacetime. We have obtained central density ($ρ_{0}$), central pressure ($p_{0}$), probable radius, compactness ($u$) and surface redshift ($Z_{s}$) of the above mentioned newly discovered millisecond pulsar, which is very much consistent with reported data. Equation of State (EoS) of the millisecond pulsar has comes out as stiff in nature which is physically accept…
Rotation-powered millisecond radio pulsars have been spun up to their present spin period by a $10^8$ - $10^9$ yr long X-ray-bright phase of accretion of matter and angular momentum in a low-to-intermediate mass binary system. Recently, the discovery of transitional pulsars that alternate cyclically between accretion and rotation-powered states on time scales of a few years or shorter, has demonstrated this evolutionary scenario. Here, we present a thorough statistical analysis of the spin distributions of the various classes of millisecond pulsars to assess the evolution of their spin period …
This chapter provides a phenomenological appraisal of the high-energy emission of millisecond pulsars. We comment on some of their properties as a population, as well as consider the especial cases of transitional pulsars, other redbacks, and black widow systems.
A simple and natural explanation for the minimum period of millisecond pulsars follows from a correlation between the accretion rate and the frozen surface dipole magnetic field resulting from Ohmic diffusion through the neutron star crust in initial stages of accretion in low mass X-ray binaries.
R-modes can generate strong magnetic fields in the core of accreting millisecond neutron stars (NSs). The diffusion of these fields outside the core causes the growth of the external magnetic field and thus it affects the evolution of the spin down rates $\dot{P}$ of the millisecond pulsars (MSPs). The diffusion of the internal magnetic field provides a new evolutionary path for the MSPs. This scenario could explain the large $\dot{P}$ of the pulsars J1823-3021A and J1824-2452A.
Based on MAGIC observations from June and July 2007, we present upper limits to the E>140 GeV emission from the globular cluster M13. Those limits allow us to constrain the population of millisecond pulsars within M13 and to test models for acceleration of leptons inside their magnetospheres and/or surrounding. We conclude that in M13 either millisecond pulsars are fewer than expected or they accelerate leptons less efficiently than predicted.
Millisecond pulsars in tight binaries have recently opened new challenges in our understanding of physical processes governing the evolution of binaries and the interaction between astrophysical plasma and electromagnetic fields. Transitional systems that showed changes from rotation-powered to accretion powered states and vice versa have bridged the populations of radio and accreting millisecond pulsars, eventually demonstrating the tight evolutionary link envisaged by the recycling scenario. A decade of discoveries and theoretical efforts have just grasped the complex phenomenology of transi…
The heating associated with the deposition of $γ$-rays in an accretion disk is proposed as a mechanism to facilitate the transformation of a low mass X-ray binary to the radio millisecond pulsar phase. The $γ$-ray emission produced in the outer gap accelerator in the pulsar magnetosphere likely irradiates the surrounding disk, resulting in its heating and to the possible escape of matter from the system. We apply the model to PSR J1023+0038, which has recently been discovered as a newly born rotation powered millisecond pulsar. The predicted $γ$-ray luminosity $\sim 6 \times 10^{34}~\mathrm{er…
Transitional millisecond pulsars (tMSPs), which are systems that harbor a pulsar in the throes of the recycling process, have emerged as a new source class since the discovery of the first such system a decade ago. These systems switch between accretion-powered low-mass X-ray binary (LMXB) and rotation-powered radio millisecond pulsar (RMSP) states, and provide exciting avenues to understand the physical processes that spin-up neutron stars to millisecond periods. During the last decade, three tMSPs, as well as a candidate source, have been extensively probed using systematic, multi-wavelength…
Redback millisecond pulsars (hereafter redbacks) are a sub-population of eclipsing millisecond pulsars in close binaries. The formation processes of these systems are not clear. The three pulsars showing transitions between rotation- and accretion-powered states belong to both redbacks and transient low-mass X-ray binaries (LMXBs), suggesting a possible evolutionary link between the them. Through binary evolution calculations, we show that the accretion disks in almost all LMXBs are subject to the thermal-viscous instability during certain evolutionary stages, and the parameter space for the d…
Millisecond x-ray pulsars have weak magnetic dipole moments of $\sim 10^{16}$\,T\,m$^3$ compared to ordinary X-ray pulsars with dipole moments of $10^{20}$\,T\,m$^3$. For this reason a surrounding accretion disc can extend closer to the neutron star, and thus reach a higher temperature, at which the opacity is dominated by electron scattering and radiation pressure is strong. We compute the self-similar structure of such a geometrically thin axisymmetric accretion disc with an internal dynamo. Such models produce significantly stronger torques on the neutron star than models without dynamos, a…
More than four decades after the discovery of pulsars, the composition of matter at their cores is still a mystery. This white paper summarizes how recent high-precision measurements of millisecond pulsar masses have introduced new experimental constraints on the properties of super-dense matter, and how continued timing of intriguing new objects, coupled with radio telescope surveys to discover more pulsars, might introduce significantly more stringent constraints.
The multi-wavelength pulsed emission from young pulsars and millisecond pulsars can be well modeled with the single-pole 3-dimension annular gap and core gap model. To distinguish our single magnetic pole model from two-pole models (e.g. outer gap model and two-pole caustic model), the convincing values of the magnetic inclination angle and the viewing angle will play a key role.
We have used LOFAR to perform targeted millisecond pulsar surveys of Fermi gamma-ray sources. Operating at a center frequency of 135 MHz, the surveys use a novel semi-coherent dedispersion approach where coherently dedispersed trials at coarsely separated dispersion measures are incoherently dedispersed at finer steps. Three millisecond pulsars have been discovered as part of these surveys. We describe the LOFAR surveys and the properties of the newly discovered pulsars.
Resluts of 3D numerical simulations in the framework of pair starved polar cap model (PSPC) for millisecond pulsars are presented. In the investigated PSPC model electric field structure highly depends on the pulsar inclination which is clearly visible in the computed spectra of electrons escaping pulsar magnetosphere which become bimodal with the increasing inclination. This is an important result for modelling very high energy radiation from globular clusters where currently the standard power law or monoenergetic electron distributions are used.
Observations by the Fermi Large Area Telescope of gamma-ray millisecond pulsar light curves imply copious pair production in their magnetospheres, and not exclusively in those of younger pulsars. Such pair cascades may be a primary source of Galactic electrons and positrons, contributing to the observed enhancement in positron flux above ~10 GeV. Fermi has also uncovered many new millisecond pulsars, impacting Galactic stellar population models. We investigate the contribution of Galactic millisecond pulsars to the flux of terrestrial cosmic-ray electrons and positrons. Our population synthesi…
We summarize the state of the art and future directions in using millisecond radio pulsars to test gravitation and measure intrinsic, fundamental parameters of the pulsar systems. As discussed below, such measurements continue to yield high-impact constraints on viable nuclear processes that govern the theoretically-elusive interior of neutron stars, and place the most stringent limits on the validity of general relativity in extreme environments. Ongoing and planned pulsar-timing measurements provide the greatest opportunities for measurements of compact-object masses and new general-relativi…
Transitional millisecond pulsars are accreting millisecond pulsars that switch between accreting X-ray binary and millisecond radio pulsar states. Only a handful of these objects have been identified so far. Terzan 5 CX1 is a variable hard X-ray source in the globular cluster Terzan 5. In this paper, we identify a radio counterpart to CX1 in deep Very Large Array radio continuum data. Chandra observations over the last fourteen years indicate that CX1 shows two brightness states: in 2003 and 2016 the source was the brightest X-ray source in the cluster (at L$_X \sim 10^{33}$ erg s$^{-1}$), whi…
We have systematically studied the X-ray emission properties of globular cluster millisecond pulsars in order to evaluate their spectral properties and luminosities in a uniform way. Cross-correlating the radio timing positions of the cluster pulsars with the high resolution Chandra images revealed 31 X-ray counterparts identified in nine different globular cluster systems, including those in 47 Tuc. Timing analysis has been performed for all sources corresponding to the temporal resolution available in the archival Chandra data. Making use of unpublished data on M28, M4 and NGC 6752 allowed u…
Pulsed high energy radiation from pulsars is not yet completely understood. In this paper, we use the 3D self-consistent annular gap model to study light curves for both young and millisecond pulsars observed by the Fermi Gamma-ray Space Telescope. The annular gap can generate high energy emission for short-period pulsars. The annular gap regions are so large that they have enough electric potential drop to accelerate charged particles to produce gamma-ray photons. For young pulsars, the emission region is from the neutron star surface to about half of the light cylinder radius, and the peak e…
We investigate the spin dynamics of a millisecond pulsar (MSP) in compact orbit around a Kerr-like massive black hole with an general mass quadrupole. We use the Mathisson-Papetrou-Dixon formulation to compute the orbital and spin evolution of the MSP, accounting for the non-linear interaction of the pulsar's energy-momentum tensor on the background spacetime metric. We investigate how the MSP spin and BH quadrupole moment manifest in the pulsar spin-orbital dynamics. We discuss the astrophysical observational implications of these spin and orbital dynamics on the timing of a radio pulsar in a…
In this paper we present a coherent timing analysis of the 401 Hz pulsations of the accreting millisecond X-ray pulsar SAX J1808.4-3658 during its 2019 outburst. Using observations collected with the Neutron Star Interior Composition Explorer (NICER), we establish the pulsar spin frequency and orbital phase during its latest epoch. We find that the 2019 outburst shows a pronounced evolution in pulse phase over the course of the outburst. These phase shifts are found to correlate with the source flux, and are interpreted in terms of hot-spot drift on the stellar surface, driven by changes in th…
The recycling model suggested that low-mass X-ray binaries (LMXBs) could evolve into binary millisecond pulsars (BMSPs). In this work, we attempt to investigate the progenitor properties of BMSPs formed by the recycling evolutionary channel, and if sub-millisecond pulsars can be produced by this channel. Using Eggleton's stellar evolution code, considering that the dead pulsars can be spun up to a short spin period by the accreting material and angular momentum from the donor star, we have calculated the evolution of close binaries consisting of a neutron star and a low-mass main-sequence dono…
Millisecond radio pulsars have long been proposed to form from a spin-up recycling process in a binary system. In this paper we demonstrate that the accretion-induced field-decay and spin-up model for recycled pulsars can indeed produce those millisecond pulsars with relatively weak magnetic fields of $10^8-10^9$ G and short spin periods of a few milliseconds. Our results also suggest that the value of the currently observed highest spin frequency of millisecond pulsars may simply be constrained by the amount of mass available for accretion.
We modelled the radio and gamma-ray light curves of millisecond pulsars using outer gap, two-pole caustic, low-altitude slot gap, and pair-starved polar cap geometric models, combined with a semi-empirical conal radio model. We find that no model fits all cases, with the outer gap and two-pole caustic models providing best fits for comparable numbers of millisecond pulsar light curves. We find a broad distribution of best-fit inclination angles as well as a clustering at large observer angles. The outer gap model furthermore seems to require relatively larger inclination angles, while the two-…
Rotation-powered "recycled" millisecond pulsars are a variety of rapidly-spinning neutron stars that typically show thermal X-ray radiation due to the heated surface of their magnetic polar caps. Detailed numerical modeling of the rotation-induced thermal X-ray pulsations observed from recycled millisecond pulsars, including all relevant relativistic and stellar atmospheric effects, has been identified as a promising approach towards an astrophysical determination of the true neutron star mass-radius relation, and by extension the state of cold matter at densities exceeding those of atomic nuc…
In millisecond pulsars the existence of the Coriolis force allows the development of the so-called Rossby oscillations (r-modes) which are know to be unstable to emission of gravitational waves. These instabilities are mainly damped by the viscosity of the star or by the existence of a strong magnetic field. A fraction of the observed millisecond pulsars are known to be inside Low Mass X-ray Binaries (LMXBs), systems in which a neutron star (or a black hole) is accreting from a donor whose mass is smaller than 1 $M_\odot$. Here we show that the r-mode instabilities can generate strong toroidal…
Weakly magnetic, millisecond spinning neutron stars attain their very fast rotation through a 1E8-1E9 yr long phase during which they undergo disk-accretion of matter from a low mass companion star. They can be detected as accretion-powered millisecond X-ray pulsars if towards the end of this phase their magnetic field is still strong enough to channel the accreting matter towards the magnetic poles. When mass transfer is much reduced or ceases altogether, pulsed emission generated by particle acceleration in the magnetosphere and powered by the rotation of the neutron star is observed, prefer…
We report the discovery of burst oscillations from the intermittent accretion-powered millisecond pulsar (AMP) HETE J1900.1-2455, with a frequency approximately 1 Hz below the known spin frequency. The burst oscillation properties are far more similar to those of the non-AMPs and Aql X-1 (an intermittent AMP with a far lower duty cycle), than those of the AMPs SAX J1808.4-3658 and XTE J1814-338. We discuss the implications for models of the burst oscillation and intermittency mechanisms.
We present Keck spectroscopic measurements of the millisecond pulsar binary J2215+5135. These data indicate a neutron-star (NS) mass M_NS=1.6Mo, much less than previously estimated. The pulsar heats the companion face to T_D~9000K; the large heating efficiency may be mediated by the intrabinary shock dominating the X-ray light curve. At the best-fit inclination i=88.8deg, the pulsar should be eclipsed. We find weak evidence for such eclipses in the pulsed gamma-rays; an improved radio ephemeris allows use of up to 5 times more Fermi-LAT gamma-ray photons for a definitive test of this picture. …
The Galactic population of rotation-powered (aka radio) millisecond pulsars (MSPs) exhibits diverse X-ray properties. Energetic MSPs show pulsed non-thermal radiation from their magnetospheres. Eclipsing binary MSPs predominantly have X-ray emission from a pulsar wind driven intra-binary shock. Typical radio MSPs emit X-rays from their heated magnetic polar caps. These thermally emitting MSPs offer the opportunity to place interesting constraints on the long sought after dense matter equation of state, making them important targets of investigation of the recently deployed Neutron Star Interio…
Observations of short-duration gamma-ray bursts and their afterglows show that a good fraction (perhaps $\gtrsim50\%$) of binary neutron star mergers lead to strongly magnetized, rapidly rotating pulsars (including millisecond magnetars), no matter whether the pulsar remnants are short- or long-lived. Such compact objects are very likely to have significant radial oscillations and high interior temperatures, as indicated in recent numerical simulations. In this paper, we have investigated rotation-induced gravitational radiation from possibly existing, radially oscillating pulsars after binary…
We report on the discovery of three new millisecond pulsars (namely J1748-2446aj, J1748-2446ak and J1748-2446al) in the inner regions of the dense stellar system Terzan 5. These pulsars have been discovered thanks to a method, alternative to the classical search routines, that exploited the large set of archival observations of Terzan 5 acquired with the Green Bank Telescope over 5 years (from 2010 to 2015). This technique allowed the analysis of stacked power spectra obtained by combining ~206 hours of observation. J1748-2446aj has a spin period of ~2.96 ms, J1748-2446ak of ~1.89 ms (thus it …
Significant gamma-ray pulsations have been detected from ~40 millisecond pulsars (MSPs) using 3 years of sky-survey data from the Fermi LAT and radio timing solutions from across the globe. We have fit the radio and gamma-ray pulse profiles of these MSPs using geometric versions of slot gap and outer gap gamma-ray emission models and radio cone and core models. For MSPs with radio and gamma-ray peaks aligned in phase we also explore low-altitude slot gap gamma-ray models and caustic radio models. The best-fit parameters provide constraints on the viewing geometries and emission sites. While th…
The maximum mass of a neutron star has important implications across multiple research fields, including astrophysics, nuclear physics and gravitational wave astronomy. Compact binary millisecond pulsars (with orbital periods shorter than about a day) are a rapidly-growing pulsar population, and provide a good opportunity to search for the most massive neutron stars. Applying a new method to measure the velocity of both sides of the companion star, we previously found that the compact binary millisecond pulsar PSR J2215+5135 hosts one of the most massive neutron stars known to date, with a mas…
We present a summary of gamma-ray millisecond pulsar (MSP) observations with the Fermi Large Area Telescope. The radio and gamma-ray light curves of these MSPs have been modeled in the framework of the retarded vacuum dipole magnetic field. Likelihood fitting of the radio and gamma-ray light curves with geometric emission models allows us to give model-dependent confidence contours for the viewing geometry in these systems which are complementary to those from polarization measurements.
Millisecond pulsars are rapidly rotating neutron stars where general relativity plays a strong role in the propagation of light from the neutron star to observer. The observed X-ray pulse shapes carry information on the mass, radius and surface shape of the neutron star. Comparison of theoretical calculations of pulse shapes with observed pulse shapes can give useful constraints on neutron star properties. Then comparison with calculated properties giving an assumed equation of state (EOS) can confirm or rule out the assumed EOS.
We consider the evolution of millisecond radio pulsars in binary systems with a main-sequence or evolved stellar companion. Evolution of non-accreting binary systems with "eclipsing" milisecond pulsars was described by Kluźniak, Czerny & Ray (1992) who predicted that systems like the one containing the Terzan 5 PSR 1744-24A will in the future become accreting low mass X-ray binaries (LMXBs), while PSR 1957+20 may evaporate its companion. The model presented in the current paper gives similar results for these two objects and allows to obtain diverse evolutionary tracks of millisecond pulsars w…
We report on gamma-ray orbital modulation of the transitioning millisecond pulsar binary XSS J12270-4859 detected in the Fermi Large Area Telescope (LAT) data. We use long-term optical data taken with the XMM-Newton Optical Monitor and the Swift UltraViolet Optical Telescope to inspect radio timing solutions that are limited to relatively short time intervals, and find that extrapolation of the solutions aligns well the phasing of the optical data over 15 years. The Fermi-LAT data folded on the timing solutions exhibit significant modulation (p = 5x10^-6) with a gamma-ray minimum at the inferi…
We present X-ray observations of the "redback" eclipsing radio millisecond pulsar and candidate radio pulsar/X-ray binary transition object PSR J1723-2837. The X-ray emission from the system is predominantly non-thermal and exhibits pronounced variability as a function of orbital phase, with a factor of ~2 reduction in brightness around superior conjunction. Such temporal behavior appears to be a defining characteristic of this variety of peculiar millisecond pulsar binaries and is likely caused by a partial geometric occultation by the main-sequence-like companion of a shock within the binary…
This paper investigates the progenitors of Millisecond Pulsars (MSPs) with a distribution of long orbital periods (P_orb > 2 d), to show the link between white dwarf (WD) binaries and long orbits for some binary MSPs through the Accretion Induced Collapse (AIC) of a WD. For this purpose, a model is presented to turn binary MSPs into wide binaries and highly circular orbits (e < 0.1) through the asymmetric kick imparted to the pulsar during the AIC process, which may indicate a sizeable kick velocity along the rotation of the proto-neutron star. The results show the effects of shock wave, bindi…
Fermi has detected over 200 pulsars above 100 MeV. In a previous work, using 3 years of LAT data (1FHL catalog) we reported that 28 of these pulsars show emission above 10 GeV; only three of these, however, were millisecond pulsars (MSPs). The recently-released Third Catalog of Hard Fermi-LAT Sources (3FHL) contains over 1500 sources showing emission above 10 GeV, 17 of which are associated with gamma-ray MSPs. Using three times as much data as in our previous study (1FHL), we report on a systematic analysis of these pulsars to determine the highest energy (pulsed) emission fromMSPs and discus…
We present a study of the observational properties of Millisecond Pulsars (MSPs) by way of their magnetic fields, spin periods and masses. These measurements are derived through the scenario of Accretion Induced Collapse (AIC) of white dwarfs (WDs) in stellar binary systems, in order to provide a greater understanding of the characteristics of MSP populations. In addition, we demonstrate a strong evolutionary connection between neutron stars and WDs with binary companions from a stellar binary evolution perspective via the AIC process.
Fermi Large Area Telescope (LAT) has recently detected 8 gamma-ray millisecond pulsars (MSPs), providing an unprecedented opportunity to probe the magnetospheres of these low-spin-down pulsars. We performed 3D emission modeling, including various Special Relativistic effects, in the context of pair-starved polar cap (PSPC), slot gap (SG), and outer gap (OG) pulsar models. Most of the light curves are best fit by SG and OG models, surprisingly indicating the presence of narrow accelerating gaps limited by robust pair production. All model fits imply high-altitude emission, and we observe exclus…
Binary radio pulsars are generally believed to have been spun up to millisecond periods (i.e. recycling) via mass accretion from their donor stars, and they are the descendants of neutron star low-mass X-ray binaries. However, some studies indicate that the formation of pulsars from the accretion-induced collapse (AIC) of accreting white dwarfs (WDs) cannot be excluded. In this work, we use a population synthesis code to examine if the AIC channel can produce eccentric binary millisecond pulsars (BMSPs) in the Galaxy. Our simulated results indicate that, only when the natal MSPs receive a rela…
We present flux density measurements and pulse profiles for the millisecond pulsar PSR J2145-0750 spanning 37 to 81 MHz using data obtained from the first station of the Long Wavelength Array. These measurements represent the lowest frequency detection of pulsed emission from a millisecond pulsar to date. We find that the pulse profile is similar to that observed at 102 MHz. We also find that the flux density spectrum between ~40 MHz to 5 GHz is suggestive of a break and may be better fit by a model that includes spectral curvature with a rollover around 730 MHz rather than a single power law.
We perform MHD simulations of a thin resistive and viscous accretion disk around a neutron star with the surface dipolar magnetic field of 10$^8$ Gauss. The system evolution is followed during the interval of 500 millisecond pulsar rotations. Matter is accreted through a stable accretion column from the disk onto the star. We also show propagation of the stellar wind through the corona. Analysis of the mass accretion flux and torques on the star shows that the disk reaches the quasi-stationary state.
Among the current sample of over 2000 radio pulsars known primarily in the disk of our Galaxy, millisecond pulsars now number almost 200. Due to the phenomenal success of blind surveys of the Galactic field, and targeted searches of Fermi gamma-ray sources, for the first time in over a decade, Galactic millisecond pulsars now outnumber their counterparts in globular clusters! In this paper, I briefly review earlier results from studies of the Galactic millisecond pulsar population and present new constraints based on a sample of 60 millisecond pulsars discovered by 20 cm Parkes multibeam surve…
We present timing observations of four millisecond pulsars discovered in the Parkes 20-cm multibeam pulsar survey of the Galactic plane. PSRs J1552-4937 and J1843-1448 are isolated objects with spin periods of 6.28 and 5.47 ms respectively. PSR J1727-2946 is in a 40-day binary orbit and has a spin period of 27 ms. The 4.43-ms pulsar J1813-2621 is in a circular 8.16-day binary orbit around a low-mass companion star with a minimum companion mass of 0.2 solar masses. Combining these results with detections from five other Parkes multibeam surveys, gives a well-defined sample of 56 pulsars with sp…
It is believed that millisecond pulsars attain their fast spins by accreting matter and angular momentum from companion stars. Theoretical modelling of the accretion process suggests a spin-up line in the period-period derivative ($P$-$\dot{P}$) diagram of millisecond pulsars, which plays an important role in population studies of radio millisecond pulsars and accreting neutron stars in X-ray binaries. Here we present observational evidence for such a spin-up line using a sample of 143 radio pulsars with $P$ < 30 ms. We also find that PSRs~J1823$-$3021A and J1824$-$2452A, located near the clas…
Using our previously derived simple analytic expression for the bolometric light curves of supernovae, we demonstrate that the collision of the fast debris of ordinary supernova explosions with relatively slow-moving shells from pre-supernova eruptions can produce the observed bolometric light curves of superluminous supernovae (SLSNe) of all types. These include both, those which can be explained as powered by spinning-down millisecond magnetars and those which cannot. That and the observed close similarity between the bolometric light-curves of SLSNe and ordinary interacting SNe suggest that…
Millisecond pulsars are old neutron stars that have been spun up to high rotational frequencies via accretion of mass from a binary companion star. An important issue for understanding the physics of the early spin evolution of millisecond pulsars is the impact of the expanding magnetosphere during the terminal stages of the mass-transfer process. Here I report binary stellar evolution calculations that show that the braking torque acting on a neutron star, when the companion star decouples from its Roche-lobe, is able to dissipate >50% of the rotational energy of the pulsar. This effect may e…
We consider the currently observed spin distributions of various types of neutron stars, including isolated and binary radio millisecond pulsars in the Galactic plane and globular cluster system as well as neutron stars in low-mass X-ray binary systems where the spin rate is known either through coherent pulsations or burst oscillations. We find that the spin distributions of isolated and binary radio millisecond pulsars are statistically different, at least for those residing in globular clusters, with the binary pulsars being on average faster spinning. This result is likely to hold despite …
Nuclear-powered X-ray millisecond pulsars are the third type of millisecond pulsars, which are powered by thermonuclear fusion processes. The corresponding brightness oscillations, known as burst oscillations, are observed during some thermonuclear X-ray bursts, when the burning and cooling accreted matter gives rise to an azimuthally asymmetric brightness pattern on the surface of the spinning neutron star. Apart from providing neutron star spin rates, this X-ray timing feature can be a useful tool to probe the fundamental physics of neutron star interior and surface. This chapter presents an…
