abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
we present timing solutions for 12 pulsars discovered in the green bank north celestial cap 350 mhz pulsar survey, including six millisecond pulsars (msps), a double neutron star (dns) system, and a pulsar orbiting a massive white dwarf companion. timing solutions presented here include 350 and 820 mhz green bank telescope data from initial confirmation and follow-up, as well as a dedicated timing campaign spanning 1 ryr psr j1122-3546 is an isolated msp, psrs j1221-0633 and j1317-0157 are msps in black widow systems and regularly exhibit eclipses, and psrs j2022+2534 and j2039-3616 are msps that can be timed with high precision and have been included in pulsar timing array experiments seeking to detect low-frequency gravitational waves. psrs j1221-0633 and j2039-3616 have fermi large area telescope gamma-ray counterparts and also exhibit significant gamma-ray pulsations. we measure proper motions for three of the msps in this sample and estimate their space velocities, which are typical compared to those of other msps. we have detected the advance of periastron for psr j1018-1523 and therefore measure the total mass of the dns system, m tot = 2.3 ± 0.3 m ⊙. long-term pulsar timing with data spanning more than 1 yr is critical for classifying recycled pulsars, carrying out detailed astrometry studies, and shedding light on the wealth of information in these systems post-discovery. | the green bank north celestial cap survey. vii. 12 new pulsar timing solutions |
we report the discovery of absorption features in the x-ray spectrum of the transient x-ray pulsar gro j2058+42. the features are detected around ∼10, ∼20, and ∼30 kev in both nustar observations carried out during the source type ii outburst in spring 2019. the most intriguing property is that the deficit of photons around these energies is registered only in the narrow phase interval covering around 10% of the pulsar spin period. we interpret these absorption lines as a cyclotron resonant scattering line (fundamental) and two higher harmonics. the measured energy allow us to estimate the magnetic field strength of the neutron star as ∼1012 g. | discovery of a pulse-phase-transient cyclotron line in the x-ray pulsar gro j2058+42 |
we report the discovery of diffuse x-ray emission around the supernova remnant (snr) g106.3+2.7, which is associated with ver j2227+608 and hawc j2227+610 and is known as a candidate for a pev cosmic-ray accelerator (pevatron). we analyze observational data of suzaku around the snr and the adjacent pulsar psr j2229+6114. we find diffuse x-ray emission that is represented by either thermal or nonthermal processes. however, the metal abundance for the thermal emission is <0.13 z⊙, which may be too small in the milky way and suggests that the emission is nonthermal. the intensity of the diffuse emission increases toward psr j2229+6114 in the same way as radio emission, and it is in contrast with gamma-ray emission concentrated on a molecular cloud. the x-ray photon index does not change with the distance from the pulsar and it indicates that radiative cooling is ineffective and particle diffusion is not extremely slow. the x-ray and radio emissions seem to be of leptonic origin and the parent electrons may originate from the pulsar. the gamma-ray emission appears to be of hadronic origin because of its spatial distribution. the parent protons may be tightly confined in the cloud separately from the diffusing electrons. | x-ray emission from the pevatron-candidate supernova remnant g106.3+2.7 |
recently, the high altitude water cherenkov (hawc) collaboration reported the discovery of a tev halo around the geminga pulsar. the tev emission is believed to originate from the inverse compton scattering of pulsar-injected electrons/positrons off cosmic microwave background photons. during this time, these electrons should inevitably radiate x-ray photons via synchrotron radiation, providing a useful constraint on the magnetic field in the tev halo. in this work, we analyze the data of xmm-newton and chandra, and obtain an upper limit for the diffuse x-ray flux in a 600″ region around the geminga pulsar, which is at a level of ≲ {10}-14 {erg} {cm}}-2 {{{s}}}-1. by numerically modeling both the x-ray and tev observations assuming the isotropic diffusion of injected electrons/positrons, we find that the magnetic field inside the tev halo is required to be <1 μg, which is significantly weaker than the typical magnetic field in the interstellar medium. the weak magnetic field together with the small diffusion coefficient inferred from the hawc observation implies that the bohm limit of particle diffusion may probably have been achieved in the tev halo. we also discuss alternative possibilities for the weak x-ray emission, such as the hadronic origin of the tev emission or a specific magnetic field topology, in which a weak magnetic field and a very small diffusion coefficient might be avoided. | constraining the magnetic field in the tev halo of geminga with x-ray observations |
we investigate the aperiodic variability for a relatively large sample of accreting neutron stars and intermediate polars, focusing on the properties of the characteristic break commonly observed in power spectra of accreting objects. in particular, we investigate the relation of the break frequency and the magnetic field strength, both of which are connected to the size of the magnetosphere. we find that for the majority of objects in our sample the measured break frequency values indeed agree with estimated inner radii of the accretion disc, which allows to use observed break frequencies to independently assess the magnetic field strength and structure in accreting compact objects. as a special case, we focus on hercules x-1 which is a persistent, medium-luminosity x-ray pulsar accreting from its low-mass companion. in the literature, it has been suggested that the complex pulse profiles, the spin-up behaviour and the luminosity-correlation of the cyclotron energy seen in her x-1 can be explained with a complex magnetic field structure of the neutron star. here, we connect the measured break frequency to the magnetospheric radius and show that the magnetic field strength derived assuming a dipole configuration is nearly an order of magnitude smaller than the magnetic field strength corresponding to the cyclotron energy. accordingly, this discrepancy can be explained with the magnetic field having strong multipole components. the multipolar structure would also increase the accreting area on the neutron star surface, explaining why the critical luminosity for accretion column formation is puzzlingly high in this source. | constraints on the magnetic field structure in accreting compact objects from aperiodic variability |
the opening of the gravitational wave window by ground-based laser interferometers has made possible many new tests of gravity, including the first constraints on polarization. it is hoped that, within the next decade, pulsar timing will extend the window by making the first detections in the nanohertz frequency regime. pulsar timing offers several advantages over ground-based interferometers for constraining the polarization of gravitational waves due to the many projections of the polarization pattern provided by the different lines of sight to the pulsars, and the enhanced response to longitudinal polarizations. here, we show that existing results from pulsar timing arrays can be used to place stringent limits on the energy density of longitudinal stochastic gravitational waves. however, unambiguously distinguishing these modes from noise will be very difficult due to the large variances in the pulsar-pulsar correlation patterns. existing upper limits on the power spectrum of pulsar timing residuals imply that the amplitude of vector longitudinal (vl) and scalar longitudinal (sl) modes at frequencies of 1/year are constrained, avl<4 ×10-16 and asl<4 ×10-17, while the bounds on the energy density for a scale invariant cosmological background are ωvlh2<4 ×10-11 and ωslh2<3 ×10-13. | constraining alternative theories of gravity using pulsar timing arrays |
observations by the high altitude water cherenkov (hawc) observatory indicate that many young pulsars (including geminga and monogem) are surrounded by spatially extended, multi-tev emitting regions. it is not currently known, however, whether tev emission is also produced by recycled, millisecond pulsars (msps). in this study, we perform a stacked analysis of 24 msps within hawc's field of-view, finding between 2.6 -3.1 σ evidence that these sources are, in fact, surrounded by tev halos. the efficiency with which these msps produce tev halos is similar to that exhibited by young pulsars. this result suggests that several dozen msps will ultimately be detectable by hawc, including many "invisible" pulsars without radio beams oriented in our direction. the tev halos of unresolved msps could also dominate the tev-scale diffuse emission observed at high galactic latitudes. we also discuss the possibility that tev and radio observations could be used to constrain the population of msps that is present in the inner milky way, thereby providing us with a new way to test the hypothesis that msps are responsible for the galactic center gev excess. | millisecond pulsars, tev halos, and implications for the galactic center gamma-ray excess |
we study the influence of strong magnetic fields in hybrid stars, composed by hadrons and a pure quark matter core, and analyse their structure and stability as well as some possible evolution channels due to the magnetic field decay. using an ad hoc parametrization of the magnetic field strength and taking into account landau-quantization effects in matter, we calculate hybrid magnetized equations of state and some associated quantities, such as particle abundances and matter magnetization, for different sets of parameters and different magnetic field strengths. moreover, we compute the magnetized stable stellar configurations, the mass versus radius and the gravitational mass versus central energy density relationships, the gravitational mass versus baryon mass diagram, and the tidal deformability. our results are in agreement with both, the ∼ 2 m_⊙ pulsars and the data obtained from gw170817. in addition, we study the stability of stellar configurations assuming that slow and rapid phase transitions occur at the sharp hadron-quark interface. we find that, unlike in the rapid transition scenario, where ∂m/∂ɛc < 0 is a sufficient condition for instability, in the slow transition scenario there exists a connected extended stable branch beyond the maximum mass star, for which ∂m/∂ɛc < 0. finally, analysing the gravitational mass versus baryon mass relationship, we have calculated the energy released in transitions between stable stellar configurations. we find that the inclusion of the magnetic field and the existence of new stable branches allows the possibility of new channels of transitions that fulfil the energy requirements to explain gamma-ray bursts. | magnetized hybrid stars: effects of slow and rapid phase transitions at the quark-hadron interface |
this chapter discusses the implications of x-ray binaries on our knowledge of type ibc and type ii supernovae. x-ray binaries contain accreting neutron stars and stellar-mass black holes which are the end points of massive star evolution. studying these remnants thus provides clues to understanding the evolutionary processes that lead to their formation. we focus here on the distributions of dynamical masses, space velocities, and chemical anomalies of their companion stars. these three observational features provide unique information on the physics of core collapse and supernovae explosions within interacting binary systems. there is suggestive evidence for a gap between ≈ 2 and 5 m⊙ in the observed mass distribution. this might be related to the physics of the supernova explosions although selections effects and possible systematics may be important. the difference between neutron star mass measurements in low-mass x-ray binaries (lmxbs) and pulsar masses in high-mass x-ray binaries (hmxbs) reflects their different accretion histories, with the latter presenting values close to birth masses. on the other hand, black holes in lmxbs appear to be limited to ≲ 12 m⊙ because of strong mass loss during the wind wolf-rayet phase. detailed studies of a limited sample of black hole x-ray binaries suggest that the more massive black holes have a lower space velocity, which could be explained if they formed through direct collapse. conversely, the formation of low-mass black holes through a supernova explosion implies that large escape velocities are possible through ensuing natal and/or blaauw kicks. finally, chemical abundance studies of the companion stars in seven x-ray binaries indicate they are metal rich (all except gro j1655-40) and possess large peculiar abundances of α-elements. comparison with supernova models is, however, not straightforward given current uncertainties in model parameters such as mixing. | x-ray binaries |
in the last 20 years our understanding of the millisecond pulsar population changed dramatically. thanks to the large effective area and good time resolution of the nasa x-ray observatory rossi x-ray timing explorer, we discovered that neutron stars in low mass x-ray binaries (lmxbs) spins at frequencies between 200 and 750 hz, and indirectly confirmed the recycling scenario, according to which neutron stars are spun up to millisecond periods during the lmxb-phase. in the meantime, the continuous discovery of rotation-powered millisecond pulsars in binary systems in the radio and gamma-ray band (mainly with the fermi large area telescope) allowed us to classify these sources into two "spiders" populations, depending on the mass of their companion stars: black widow pulsars, with very low-mass companion stars, and redbacks, with larger mass companion stars possibly filling their roche lobes without accretion of matter onto the neutron star. it was soon regained that millisecond pulsars in short orbital period lmxbs are the progenitors of the spider populations of rotation-powered millisecond pulsars, although a direct link between accretion-powered and rotation-powered millisecond pulsars was still missing. in 2013 the esa x-ray observatory xmm-newton spotted the x-ray outburst of a new accreting millisecond pulsar (igr j18245-2452) in a source that was previously classified as a radio millisecond pulsar, probably of the redback type. follow up observations of the source when it went back to x-ray quiescence showed that it was able to swing between accretion-powered to rotation-powered pulsations in a relatively short timescale (few days), promoting this source as the direct link between the lmxb and the radio millisecond pulsar phases. following discoveries showed that there exists a bunch of sources which alternates x-ray activity phases, showing x-ray coherent pulsations, to radio-loud phases, showing radio pulsations, establishing a new class of millisecond pulsars, the so-called transitional millisecond pulsars. in this review we describe these exciting discoveries and the properties of accreting and transitional millisecond pulsars, highlighting what we know and what we have still to learn about in order to fully understand the (sometime puzzling) behaviour of these systems and their evolutive connection. | accreting pulsars: mixing-up accretion phases in transitional systems |
the fermi large area telescope has provided the most detailed view towards the galactic centre (gc) in high-energy gamma-rays. besides the interstellar emission and point source contributions, the data suggest a residual diffuse gamma-ray excess. the similarity of its spatial distribution with the expected profile of dark matter has led to claims that this may be evidence for dark matter particle annihilation. here, we investigate an alternative explanation that the signal originates from millisecond pulsars (msps) formed in dense globular clusters and deposited at the gc as a consequence of cluster inspiral and tidal disruption. we use a semi-analytical model to calculate the formation, migration, and disruption of globular clusters in the galaxy. our model reproduces the mass of the nuclear star cluster and the present-day radial and mass distribution of globular clusters. for the first time, we calculate the evolution of msps from disrupted globular clusters throughout the age of the galaxy and consistently include the effect of the msp spin-down due to magnetic-dipole braking. the final gamma-ray amplitude and spatial distribution are in good agreement with the fermi observations and provide a natural astrophysical explanation for the gc excess. | disrupted globular clusters and the gamma-ray excess in the galactic centre |
we report the discovery of psr j2251-3711, a radio pulsar with a spin period of 12.1 s, the second longest currently known. its timing parameters imply a characteristic age of 15 myr, a surface magnetic field of 1.3 × 1013 g, and a spin-down luminosity of 2.9 × 1029 erg s-1. its dispersion measure of 12.12(1) pc cm-3 leads to distance estimates of 0.5 and 1.3 kpc according to the ne2001 and ymw16 galactic free electron density models, respectively. some of its single pulses show an uninterrupted 180-deg sweep of the phase-resolved polarization position angle, with an s-shape reminiscent of the rotating vector model prediction. however, the fact that this sweep occurs at different phases from one pulse to another is remarkable and without straightforward explanation. although psr j2251-3711 lies in the region of the $p-\dot{p}$ parameter space occupied by the x-ray isolated neutron stars (xins), there is no evidence for an x-ray counterpart in our swift xrt observation; this places a 99 per cent-confidence upper bound on its unabsorbed bolometric thermal luminosity of $1.1 \times 10^{31}~(d / 1~\mathrm{kpc})^2~\mathrm{erg\, s}^{-1}$ for an assumed temperature of 85 ev, where d is the distance to the pulsar. further observations are needed to determine whether it is a rotation-powered pulsar with a true age of at least several myr, or a much younger object such as an xins or a recently cooled magnetar. extreme specimens like psr j2251-3711 help bridge populations in the so-called neutron star zoo in an attempt to understand their origins and evolution. | the survey for pulsars and extragalactic radio bursts - iv. discovery and polarimetry of a 12.1-s radio pulsar |
low-frequency gravitational-wave experiments require the highest timing precision from an array of the most stable millisecond pulsars. several known sources of noise on short timescales in single radio pulsar observations are well described by a simple model of three components: template fitting from a finite signal-to-noise ratio, pulse phase/amplitude jitter from single-pulse stochasticity, and scintillation errors from short-timescale interstellar scattering variations. currently template-fitting errors dominate, but as radio telescopes push toward higher signal-to-noise ratios, jitter becomes the next dominant term for most millisecond pulsars. understanding the statistics of jitter becomes crucial for properly characterizing arrival time uncertainties. we characterize the radio frequency dependence of jitter using data on 48 pulsars in the north american nanohertz observatory for gravitational waves timing program. we detect significant jitter in 43 of the pulsars and test several functional forms for its frequency dependence; we find significant frequency dependence for 30 pulsars. we find moderate correlations of rms jitter with pulse width (r = 0.62) and number of profile components (r = 0.40) the single-pulse rms jitter is typically ≈1% of pulse phase. the average frequency dependence for all pulsars using a power-law model has index -0.42. we investigate the jitter variations for the interpulse of psr b1937+21 and find no significant deviations from the main pulse rms jitter. we also test the time variation of jitter in two pulsars and find that systematics likely bias the results for high-precision pulsars. pulsar timing array analyses must properly model jitter as a significant component of the noise within the detector. | the nanograv 12.5 yr data set: the frequency dependence of pulse jitter in precision millisecond pulsars |
we report on a series of spectroscopic observations of psr j1311-3430, an extreme black-widow gamma-ray pulsar with a helium-star companion. in a previous study we estimated the neutron star mass as {{m}ns}=2.68+/- 0.14 {{m}⊙ } (statistical error), based on limited spectroscopy and a basic (direct heating) light-curve model; however, much larger model-dependent systematics dominate the mass uncertainty. our new spectroscopy reveals a range of complex source behavior. the variable he i companion wind emission lines can dominate broadband photometry, especially in red filters or near minimum brightness, and the wind flux should complete companion evaporation in a spin-down time. the heated companion face also undergoes dramatic flares, reaching ∼40,000 k over ∼20% of the star; this is likely powered by a magnetic field generated in the companion. the companion center-of-light radial velocity is now well measured with {{k}col}=615.4+/- 5.1 km s-1. we detect non-sinusoidal velocity components due to the heated face flux distribution. using our spectra to excise flares and wind lines, we generate substantially improved light curves for companion continuum fitting. we show that the inferred inclination and neutron star mass, however, remain sensitive to the poorly constrained heating pattern. the neutron star’s mass, {{m}ns}, is likely less than the direct heating value and could range as low as 1.8 m⊙for extreme equatorial heating concentration. while we cannot yet pin down {{m}ns}, our data imply that an intrabinary shock reprocesses the pulsar emission and heats the companion. improved spectra and, especially, models that include such shock heating are needed for precise parameter measurement. | a spectroscopic study of the extreme black widow psr j1311-3430 |
black-holes are known to span at least 9 orders of magnitude in mass: from the stellar-mass objects observed by the laser interferometer gravitational-wave observatory scientific collaboration and virgo collaboration, to supermassive black-holes like the one observed by the event horizon telescope at the heart of m87. regardless of the mass scale, all of these objects are expected to form binaries and eventually emit observable gravitational radiation, with more massive objects emitting at ever lower gravitational-wave frequencies. we present the tool, gwent, for modeling the sensitivities of current and future generations of gravitational wave detectors across the entire gravitational-wave spectrum of coalescing black-hole binaries (bhbs). we provide methods to generate sensitivity curves for pulsar timing arrays (ptas) using a novel realistic pta sensitivity curve generator (hazboun, romano and smith 2019 phys. rev. d 100 104028), space-based interferometers using adaptive models that can represent a wide range of proposed detector designs (amaro-seoane et al 2017 arxiv:1702.00786), and ground-based interferometers using realistic noise models that can reproduce current (abbott et al 2016 phys. rev. lett. 116 061102), second, and third generation designs (hild et al 2011 class. quantum grav. 28 094013), as well as novel variations of the essential design parameters. to model the signal from bhbs at any mass scale, we use phenomenological waveforms capable of modeling the inspiral, merger, and ringdown for sources with varying mass ratios and spins (khan et al 2016 phys. rev. d 93 044007; husa et al 2016 phys. rev. d 93 044006). using this adaptable framework, we produce signal-to-noise ratios (snr) for the combination of any modeled parameter, associated with either the detector or the source. by allowing variation across each detector and source parameter, we can pinpoint the most important factors to determining the optimal performance for particular instrument designs. the adaptability of our detector and signal models can easily be extended to new detector designs and other models of gravitational wave signals. | sensitivity of present and future detectors across the black-hole binary gravitational wave spectrum |
we have conducted the meterwavelength single-pulse polarimetric emission survey to study the radio emission properties of normal pulsars. a total of 123 pulsars with periods between 0.1 and 8.5 s were observed in the survey at two different frequencies: 105 profiles at 333 mhz, 118 profiles at 618 mhz, and 100 pulsars at both. in this work we concentrate primarily on the time-averaged properties of the pulsar emission. the measured widths of the pulsar profiles in our sample usually exhibit the radius-to-frequency mapping. we validate the existence of lower bounds for the distribution of profile widths with pulsar period (p), which is seen for multiple definitions of the width, namely, a lower boundary line (lbl) at 2.°7p-0.5 with width measured at 50% level of profile peak, an lbl at 5.°7 p-0.5 for 10% level of peak, and an lbl at 6.°3p-0.5 for width defined as 5σ above the baseline level. in addition, we have measured the degree of linear polarization in the average profile of pulsars and confirmed their dependence on pulsar spin-down energy loss (\dot{e}). the single-pulse polarization data show interesting trends, with the polarization position angle (ppa) distribution exhibiting the simple rotating vector model for high-\dot{e} pulsars, while the ppa becomes more complex for medium- and low-\dot{e} pulsars. the single-pulse total intensity data are useful for studying a number of emission properties from pulsars like subpulse drifting, nulling, and mode changing, which are being explored in separate works. | meterwavelength single-pulse polarimetric emission survey |
the detection of a stochastic gravitational-wave signal from the superposition of many inspiraling supermassive black holes with pulsar timing arrays (ptas) is likely to occur within the next decade. with this detection will come the opportunity to learn about the processes that drive black-hole-binary systems toward merger through their effects on the gravitational-wave spectrum. we use bayesian methods to investigate the extent to which effects other than gravitational-wave emission can be distinguished using pta observations. we show that, even in the absence of a detection, it is possible to place interesting constraints on these dynamical effects for conservative predictions of the population of tightly bound supermassive-black-hole binaries. for instance, if we assume a relatively weak signal consistent with a low number of bound binaries and a low black-hole-mass to galaxy-mass correlation, we still find that a nondetection by a simulated array, with a sensitivity that should be reached in practice within a few years, disfavors gravitational-wave-dominated evolution with an odds ratio of ∼30 ∶1 . such a finding would suggest either that all existing astrophysical models for the population of tightly bound binaries are overly optimistic, or else that some dynamical effect other than gravitational-wave emission is actually dominating binary evolution even at the relatively high frequencies/small orbital separations probed by ptas. | constraining the solution to the last parsec problem with pulsar timing |
we investigate compact objects formed by dark matter admixed with ordinary matter made of neutron-star matter and white-dwarf material. we consider non-self annihilating dark matter with an equation of state given by an interacting fermi gas. we find new stable solutions, dark compact planets, with earth-like masses and radii from a few km to few hundred km for weakly interacting dark matter which are stabilized by the mutual presence of dark matter and compact star matter. for the strongly interacting dark matter case, we obtain dark compact planets with jupiter-like masses and radii of few hundred km. these objects could be detected by observing exoplanets with unusually small radii. moreover, we find that the recently observed 2 m⊙ pulsars set limits on the amount of dark matter inside neutron stars which is, at most, 1 0-6 m⊙ . | dark compact planets |
understanding the average motion of a multitude of superfluid vortices in the interior of a neutron star is a key ingredient for most theories of pulsar glitches. in this paper, we propose a kinetic approach to compute the mutual friction force that is responsible for the momentum exchange between the normal and superfluid components in a neutron star, where the mutual friction is extracted from a suitable average over the motion of many vortex lines. as a first step towards a better modelling of the repinning and depinning processes of many vortex lines in a neutron star, we consider here only straight and non-interacting vortices: we adopt a minimal model for the dynamics of an ensemble of point vortices in two dimensions immersed in a non-homogeneous medium that acts as a pinning landscape. since the degree of disorder in the inner crust or outer core of a neutron star is unknown, we compare the two possible scenarios of periodic and disordered pinscapes. this approach allows us to extract the mutual friction between the superfluid and the normal component in the star when, in addition to the usual magnus and drag forces acting on vortex lines, also a pinning force is at work. the effect of disorder on the depinning transition is also discussed. | superfluid vortex-mediated mutual friction in non-homogeneous neutron star interiors |
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 the mass accretion rate. additionally, we find that the long-term evolution of the pulsar spin frequency shows evidence for a modulation at the earth's orbital period, allowing for pulsar timing based astrometry of this accreting millisecond pulsar. | timing the pulsations of the accreting millisecond pulsar sax j1808.4-3658 during its 2019 outburst |
we present the spin frequency and profile evolution of the radio pulsar j1119 - 6127 following magnetar-like x-ray bursts from the system in 2016 july. using data from the parkes radio telescope, we observe a smooth and fast spin-down process subsequent to the x-ray bursts resulting in a net change in the pulsar rotational frequency of δν ≈ -4 × 10-4 hz. during the transition, a net spin-down rate increase of δ \dot{ν }≈ -1× 10^{-10} hz s-1 is observed, followed by a return of \dot{ν } to its original value. in addition, the radio pulsations disappeared after the x-ray bursts and reappeared about two weeks later with the flux density at 1.4 ghz increased by a factor of 5. the flux density then decreased and undershot the normal flux density followed by a slow recovery back to normal. the pulsar's integrated profile underwent dramatic and short-term changes in total intensity, polarization, and position angle. despite the complex evolution, we observe correlations between the spin-down rate, pulse profile shape, and radio flux density. strong single pulses have been detected after the x-ray bursts with their energy distributions evolving with time. the peculiar but smooth spin frequency evolution of psr j1119-6127 accompanied by systematic pulse profile and flux density changes are most likely to be a result of either reconfiguration of the surface magnetic fields or particle winds triggered by the x-ray bursts. the recovery of spin-down rate and pulse profile to normal provides us the best case to study the connection between high magnetic-field pulsars and magnetars. | peculiar spin frequency and radio profile evolution of psr j1119-6127 following magnetar-like x-ray bursts |
understanding the evolution of the angle χ between a magnetar's rotation and magnetic axes sheds light on the star's birth properties. this evolution is coupled with that of the stellar rotation ω, and depends on the competing effects of internal viscous dissipation and external torques. we study this coupled evolution for a model magnetar with a strong internal toroidal field, extending previous work by modelling - for the first time in this context - the strong protomagnetar wind acting shortly after birth. we also account for the effect of buoyancy forces on viscous dissipation at late times. typically, we find that χ → 90° shortly after birth, then decreases towards 0° over hundreds of years. from observational indications that magnetars typically have small χ, we infer that these stars are subject to a stronger average exterior torque than radio pulsars, and that they were born spinning faster than ∼100-300 hz. our results allow us to make quantitative predictions for the gravitational and electromagnetic signals from a newborn rotating magnetar. we also comment briefly on the possible connection with periodic fast radio burst sources. | magnetar birth: rotation rates and gravitational-wave emission |
neutron stars are known to show accelerated spin-up of their rotational frequency called a glitch. highly magnetized rotating neutron stars (pulsars) are frequently observed by radio telescopes (and in other frequencies), where the glitch is observed as irregular arrival times of pulses which are otherwise very regular. a glitch in an isolated neutron star can excite the fundamental (f )-mode oscillations which can lead to gravitational wave generation. this gravitational wave signal associated with stellar fluid oscillations has a damping time of 10-200 ms and occurs at the frequency range between 2.2-2.8 khz for the equation of state and mass range considered in this work, which is within the detectable range of the current generation of ground-based detectors. electromagnetic observations of pulsars (and hence pulsar glitches) require the pulsar to be oriented so that the jet is pointed toward the detector, but this is not a requirement for gravitational wave emission which is more isotropic and not jetlike. hence, gravitational wave observations have the potential to uncover nearby neutron stars where the jet is not pointed towards the earth. in this work, we study the prospects of finding glitching neutron stars using a generic all-sky search for short-duration gravitational wave transients. the analysis covers the high-frequency range from 1-4 khz of ligo-virgo detectors for signals up to a few seconds. we set upper limits for the third observing run of the ligo-virgo detectors and present the prospects for upcoming observing runs of ligo, virgo, kagra, and ligo india. we find the detectable glitch size will be around 10-5 hz for the fifth observing run for pulsars with spin frequencies and distances comparable to the vela pulsar. we also present the prospects of localizing the direction in the sky of these sources with gravitational waves alone, which can facilitate electromagnetic follow-up. we find that for the five detector configuration, the localization capability for a glitch size of 10-5 hz is around 132 deg2 at 1 σ confidence for 50% of events with distance and spin frequency as that of vela. | prospects for detecting and localizing short-duration transient gravitational waves from glitching neutron stars without electromagnetic counterparts |
we study the redshift-space fluctuations induced by a stochastic gravitational wave background (sgwb) via the sachs-wolfe effect. the redshift-space fluctuations can be encapsulated in a line-of-sight integral that is useful for studying the imprint of short-wavelength gravitational waves on the cosmic microwave background (cmb) anisotropy. we thus derive constraints on the sgwb from small-scale cmb anisotropy measurements. our results reproduce the constraint on the short-wavelength sgwb, previously derived from the planck and bicep/keck array cmb data with a cmb boltzmann numerical code. furthermore, we improve the constraint and extend it to shorter wavelengths by using the cmb measurements made by the atacama cosmology telescope and the south pole telescope. also, the integral provides us with a precise redshift fluctuation correlation between a pair of pulsars in pulsar timing measurements, which conveniently incorporates the effect of the pulsar term into a small-angle correlation. we further discuss the observation of pulsar pairs in globular clusters to look for this small-angle correlation. | redshift-space fluctuations in stochastic gravitational wave background |
hawc j1826-128 is one of the brightest galactic tev γ-ray sources detected by the high altitude water cherenkov (hawc) observatory, with photon energies extending up to nearly ~100 tev. this hawc source spatially coincides with the h.e.s.s. tev source hess j1826-130 and the "eel" pulsar wind nebula (pwn), which is associated with the gev pulsar psr j1826-1256. in the x-ray band, chandra and xmm-newton revealed that the eel pwn is composed of both a compact nebula (~15″) and diffuse x-ray emission (~6' × 2') extending away from the pulsar. our nustar observation detected hard x-ray emission from the compact pwn up to ~20 kev and evidence of the synchrotron burn-off effect. in addition to the spatial coincidence between hess j1826-130 and the diffuse x-ray pwn, our multiwavelength spectral energy distribution (sed) analysis using x-ray and γ-ray data establishes a leptonic origin of the tev emission associated with the eel pwn. furthermore, our evolutionary pwn sed model suggests (1) a low pwn b-field of ~1 μg, (2) a significantly younger pulsar age (t ~ 5.7 kyr) than the characteristic age (τ = 14.4 kyr), and (3) a maximum electron energy of ${e}_{\max }=2$ pev. the low b-field, as well as the putative supersonic motion of the pulsar, may account for the asymmetric morphology of the diffuse x-ray emission. our results suggest that the eel pwn may be a leptonic pevatron particle accelerator powered by the ~6 kyr old pulsar psr j1826-1256 with a spin-down power of 3.6 × 1036 erg s-1. | the eel pulsar wind nebula: a pevatron-candidate origin for hawc j1826-128 and hess j1826-130 |
we report four new pulsars discovered in the core-collapsed globular cluster (gc) ngc 6624 by the trapum large survey project with the meerkat telescope. all of the new pulsars found are isolated. psr j1823-3021i and psr j1823-3021k are millisecond pulsars with period of respectively 4.319 and 2.768 ms. psr j1823-3021j is mildly recycled with a period of 20.899 ms, and psr j1823-3022 is a long period pulsar with a period of 2.497 s. the pulsars j1823-3021i, j1823-3021j, and j1823-3021k have position and dispersion measure (dm) compatible with being members of the gc and are therefore associated with ngc 6624. pulsar j1823-3022 is the only pulsar bright enough to be re-detected in archival observations of the cluster. this allowed the determination of a timing solution that spans over two decades. it is not possible at the moment to claim the association of pulsar j1823-3022 with the gc given the long period and large offset in position (~3 arcmin) and dm (with a fractional difference of 11 percent compared the average of the pulsars in ngc 6624). the discoveries made use of the beamforming capability of the trapum backend to generate multiple beams in the same field of view which allows sensitive searches to be performed over a few half-light radii from the cluster centre and can simultaneously localize the discoveries. the discoveries reflect the properties expected for pulsars in core-collapsed gcs. | four pulsar discoveries in ngc 6624 by trapum using meerkat |
we perform three-dimensional (3d) hydrodynamical simulations of new-born neutron stars (nss) colliding with main-sequence binary companions after a supernova explosion. based on those hydrodynamical models, we construct a semi-analytical formula that describes the drag force inside stars with steep density gradients. we then compute the outcome of ns-companion collisions over a wide range of parameters using the semi-analytical formula. depending on the direction and magnitude of the natal kick, we find that the collision may lead to various outcomes. for relatively fast kicks and high impact parameters, the ns may penetrate the companion star envelope without merging. by allowing the ns to plunge through their companions, the companion can be accelerated to have runaway velocities up to ~10 per cent above the theoretical upper limit considered in classical binary disruption scenarios. the ns can capture and carry away up to a few per cent of the companion envelope as it escapes, which may form pulsar planets or cause outflows through accretion to heat the ejecta from inside and power the supernova light curve. for lower impact parameters, the ns will directly merge with the companion and form a thorne-żytkow object. in intermediate cases, the ns penetrates the companion envelope several times before merging, possibly causing multiple bumps in the supernova light curve like in sn2015bn and sn2019stc. | neutron stars colliding with binary companions: formation of hypervelocity stars, pulsar planets, bumpy superluminous supernovae and thorne-żytkow objects |
pulsar timing offers an independent avenue to test general relativity and alternative gravity theories. this requires an understanding of how metric polarizations beyond the familiar transverse tensor ones imprint as a stochastic gravitational wave background and correlate the arrival time of radio pulses from a pair of millisecond pulsars. in this work, we focus on an isotropic stochastic gravitational wave background and present a straightforward, self-contained formalism for obtaining the power spectrum and the overlap reduction function, the relevant physical observable in a pulsar timing array, for generic gravitational degrees of freedom featuring both transverse and longitudinal modes off the light cone. we additionally highlight our consideration of finite pulsar distances, which we find significant in two ways: first, making all the modes well defined, and second, keeping the small-scale power that is contained by pulsars of subdegree separations in the sky. we discuss this for tensor, vector, and scalar polarizations, for each one focusing on the angular power spectrum and the overlap reduction function for an isotropic stochastic gravitational wave background. our results pave the road for an efficient numerical method for examining the gravitational wave-induced spatial correlations across millisecond pulsars in a pulsar timing array. | stochastic gravitational wave background phenomenology in a pulsar timing array |
we report results on the timing analysis of the 2020 giant outburst of 1a 0535+262, using broadband data from insight-hxmt. the analysis of the pulse profile evolution from the subcritical-luminosity to the supercritical-luminosity regime is presented for the first time. we found that the observed pulse profile exhibits a complex dependence on both energy and luminosity. a dip structure at the energy of the cyclotron resonant scattering features is found for the first time in the pulse fraction-energy relation of 1a 0535+262, when the outburst evolves in a luminosity range from 4.8 × 1037 to 1.0 × 1038 erg s-1. the observed structure is luminosity dependent and appears around the source critical luminosity (~6.7 × 1037 erg s-1). | timing properties of the x-ray accreting pulsar 1a 0535+262 studied with insight-hxmt |
we present 22 new (+3 confirmed) cataclysmic variables (cvs) in the non-core-collapsed globular cluster 47 tucanae (47 tuc). the total number of cvs in the cluster is now 43, the largest sample in any globular cluster so far. for the identifications we used near-ultraviolet (nuv) and optical images from the hubble space telescope, in combination with x-ray results from the chandra x-ray observatory. this allowed us to build the deepest nuv cv luminosity function of the cluster to date. we found that the cvs in 47 tuc are more concentrated towards the cluster centre than the main-sequence turn-off stars. we compared our results to the cv populations of the core-collapsed globular clusters ngc 6397 and ngc 6752. we found that 47 tuc has fewer bright cvs per unit mass than those two other clusters. that suggests that dynamical interactions in core-collapsed clusters play a major role creating new cvs. in 47 tuc, the cv population is probably dominated by primordial and old dynamically formed systems. we estimated that the cvs in 47 tuc have total masses of ∼1.4 m⊙. we also found that the x-ray luminosity function of the cvs in the three clusters is bimodal. additionally, we discuss a possible double degenerate system and an intriguing/unclassified object. finally, we present four systems that could be millisecond pulsar companions given their x-ray and nuv/optical colours. for one of them we present very strong evidence for being an ablated companion. the other three could be co or he white dwarfs. | new cataclysmic variables and other exotic binaries in the globular cluster 47 tucanae* |
we present results from observations of the galactic center magnetar, psr j1745-2900, at 2.3 and 8.4 ghz with the nasa deep space network 70 m antenna, dss-43. we study the magnetar’s radio profile shape, flux density, radio spectrum, and single pulse behavior over a ∼1 year period between mjds 57233 and 57621. in particular, the magnetar exhibits a significantly negative average spectral index of < α > =-1.86+/- 0.02 when the 8.4 ghz profile is single-peaked, which flattens considerably when the profile is double-peaked. we have carried out an analysis of single pulses at 8.4 ghz on mjd 57479 and find that giant pulses and pulses with multiple emission components are emitted during a significant number of rotations. the resulting single pulse flux density distribution is incompatible with a log-normal distribution. the typical pulse width of the components is ∼1.8 ms, and the prevailing delay time between successive components is ∼7.7 ms. many of the single pulse emission components show significant frequency structure over bandwidths of ∼100 mhz, which we believe is the first observation of such behavior from a radio magnetar. we report a characteristic single pulse broadening timescale of < {τ }d> =6.9+/- 0.2 {ms} at 8.4 ghz. we find that the pulse broadening is highly variable between emission components and cannot be explained by a thin scattering screen at distances ≳ 1 kpc. we discuss possible intrinsic and extrinsic mechanisms for the magnetar’s emission and compare our results to other magnetars, high magnetic field pulsars, and fast radio bursts. | pulse morphology of the galactic center magnetar psr j1745-2900 |
searching for gravitational waves in pulsar timing array data is computationally intensive. the data is unevenly sampled, and the noise is heteroscedastic, necessitating the use of a time-domain likelihood function with attendant expensive matrix operations. the computational cost is exacerbated when searching for individual supermassive black hole binaries, which have a large parameter space due to the additional pulsar distance, phase offset and noise model parameters needed for each pulsar. we introduce a new formulation of the likelihood function which can be used to make the bayesian analysis significantly faster. we divide the parameters into projection and shape parameters. we then accelerate the exploration of the projection parameters by more than four orders of magnitude by precomputing the expensive inner products for each set of shape parameters. the projection parameters include nuisance parameters such as the gravitational wave phase offset at each pulsar. in the new scheme, these troublesome nuisance parameters are efficiently marginalized over using multiple-try markov chain monte carlo sampling as part of a metropolis-within-gibbs scheme. the acceleration provided by our method will become increasingly important as pulsar timing datasets rapidly grow. our method also makes sophisticated analyses more tractable, such as searches for multiple binaries, or binaries with non-negligible eccentricities. | fast bayesian analysis of individual binaries in pulsar timing array data |
many short gamma-ray bursts (grbs) originate from binary neutron star mergers, and there are several theories that predict the production of coherent, prompt radio signals either prior, during, or shortly following the merger, as well as persistent pulsar-like emission from the spin-down of a magnetar remnant. here we present a low frequency (170-200 mhz) search for coherent radio emission associated with nine short grbs detected by the swift and/or fermi satellites using the murchison widefield array (mwa) rapid-response observing mode. the mwa began observing these events within 30-60 s of their high-energy detection, enabling us to capture any dispersion delayed signals emitted by short grbs for a typical range of redshifts. we conducted transient searches at the grb positions on timescales of 5 s, 30 s, and 2 min, resulting in the most constraining flux density limits on any associated transient of 0.42, 0.29, and 0.084 jy, respectively. we also searched for dispersed signals at a temporal and spectral resolution of 0.5 s and 1.28 mhz, but none were detected. however, the fluence limit of 80-100 jy ms derived for grb 190627a is the most stringent to date for a short grb. assuming the formation of a stable magnetar for this grb, we compared the fluence and persistent emission limits to short grb coherent emission models, placing constraints on key parameters including the radio emission efficiency of the nearly merged neutron stars ( $ɛ_r\lesssim10^{-4}$ ), the fraction of magnetic energy in the grb jet ( $ɛ_b\lesssim2×10^{-4}$ ), and the radio emission efficiency of the magnetar remnant ( $ɛ_r\lesssim10^{-3}$ ). comparing the limits derived for our full grb sample (along with those in the literature) to the same emission models, we demonstrate that our fluence limits only place weak constraints on the prompt emission predicted from the interaction between the relativistic grb jet and the interstellar medium for a subset of magnetar parameters. however, the 30-min flux density limits were sensitive enough to theoretically detect the persistent radio emission from magnetar remnants up to a redshift of $z∼0.6$ . our non-detection of this emission could imply that some grbs in the sample were not genuinely short or did not result from a binary neutron star merger, the grbs were at high redshifts, these mergers formed atypical magnetars, the radiation beams of the magnetar remnants were pointing away from earth, or the majority did not form magnetars but rather collapse directly into black holes. | early-time searches for coherent radio emission from short grbs with the murchison widefield array |
we describe the design of a gravitational wave timing array, a novel scheme that can be used to search for low-frequency gravitational waves by monitoring continuous gravitational waves at higher frequencies. we show that observations of gravitational waves produced by galactic binaries using a space-based detector like lisa provide sensitivity in the nanohertz to microhertz band. while the expected sensitivity is several magnitudes worse than what can be achieved by pulsar timing arrays, it supplements other recent proposals for gravitational wave searches in the microhertz regime. this regime is below the frequencies to which lisa is directly sensitive, and above the frequency range generally targeted by pulsar timing array searches. the low-frequency extension of sensitivity does not require any experimental design change to space-based gravitational wave detectors, and can be achieved with the data products that would already be collected by them. | gravitational wave timing array |
the state of supranuclear matter in compact stars remains puzzling, and it is argued that pulsars could be strangeon stars. what would happen if binary strangeon stars merge? this kind of merger could result in the formation of a hyper-massive strangeon star, accompanied by bursts of gravitational waves and electromagnetic radiation (and even a strangeon kilonova explained in the paper). the tidal polarizability of binary strangeon stars is different from that of binary neutron stars, because a strangeon star is self-bound on the surface by the fundamental strong force while a neutron star by the gravity, and their equations of state are different. our calculation shows that the tidal polarizability of merging binary strangeon stars is favored by gw170817. three kinds of kilonovae (i.e., of neutron, quark and strangeon) are discussed, and the light curve of the kilonova at 2017 gfo following gw170817 could be explained by considering the decaying strangeon nuggets and remnant star spin-down. additionally, the energy ejected to the fireball around the nascent remnant strangeon star, being manifested as a gamma-ray burst, is calculated. it is found that, after a prompt burst, an x-ray plateau could follow in a timescale of 102 - 103 s. certainly, the results could be tested also by further observational synergies between gravitational wave detectors (e.g., advanced ligo) and x-ray telescopes (e.g., the chinese hxmt satellite and extp mission), and especially if the detected gravitational wave form is checked by peculiar equations of state provided by the numerical relativistical simulation. | merging strangeon stars |
in this work we introduce a novel approach to the pulsar classification problem in time-domain radio astronomy using a born machine, often referred to as a quantum neural network. using a single-qubit architecture, we show that the pulsar classification problem maps well to the bloch sphere and that comparable accuracies to more classical machine learning approaches are achievable. we introduce a novel single-qubit encoding for the pulsar data used in this work and show that this performs comparably to a multi-qubit qaoa encoding. | quantum machine learning for radio astronomy |
globular clusters (gcs) are the ideal environment for the formation of neutron stars (nss) and millisecond pulsars (msps). nss origin and evolution provide a useful information on stellar dynamics and evolution in star clusters. nss are among the most interesting astrophysical objects, being precursors of several high-energy phenomena such as gravitational waves and gamma-ray bursts. due to a large velocity kick that they receive at birth, most of the nss escape the local field, affecting the evolution and dynamics of their parent cluster. in this paper, we study the origin and dynamical evolution of nss within gcs with different initial masses, metallicities, and primordial binary fractions. we find that the radial profile of nss is shaped by the black hole (bh) content of the cluster, which partially quenches the ns segregation until most of the bhs are ejected from the system. independently on the cluster mass and initial configuration, the nss map the average stellar population, as their average radial distance is {≈ } 60-80 {{ per cent}} of the cluster half-mass radius. finally, by assuming a recycling fraction of frec = 0.1 and an average msp gamma-ray emission of lγ = 2 × 1033 erg s-1, we show that the typical gamma-ray emission from our gcs agrees with observations and supports the msp origin of the gamma-ray excess signal observed by the fermi-lat telescope in the galactic centre. | neutron stars and millisecond pulsars in star clusters: implications for the diffuse gamma-radiation from the galactic centre |
the repeating frb 121102, the only fast radio burst (frb) with an accurately determined position, is associated with a variable persistent radio source. i suggest that an frb originates in the accretion disc funnels of black holes. narrowly collimated radiation is emitted along the wandering instantaneous angular momentum axis of accreted matter. this emission is observed as a fast radio burst when it sweeps across the direction to the observer. in this model, in contrast to neutron star (pulsar, rrat or sgr) models, repeating frbs do not have underlying periodicity and are co-located with persistent radio sources resulting from their off-axis emission. the model is analogous, on smaller spatial, lower mass and accretion rate and shorter temporal scales, to an active galactic nucleus (agn), with frb corresponding to blazars in which the jets point towards us. the small inferred black hole masses imply that frbs are not associated with galactic nuclei. | frb as products of accretion disc funnels |
we consider the acceleration of leptons up to gev-tev energies in the bow shock wind nebula of psr j0437-4715 and their subsequent diffusion through the interstellar magnetic fields. the leptons accelerated at the pulsar wind termination surface are injected into re-acceleration in colliding shock flows. modeled spectra of synchrotron emission from the accelerated electrons and positrons are consistent with the far-ultraviolet and x-ray observations of the nebula carried out with the hubble space telescope and chandra x-ray observatory. these observations are employed to constrain the absolute fluxes of relativistic leptons, which are escaping from the nebula and eventually reaching the solar system after energy-dependent diffusion through the local interstellar medium accompanied by synchrotron and compton losses. it is shown that accelerated leptons from the nebula of psr j0437-4715 can be responsible both for the enhancement of the positron fraction above a few gev detected by pamela and ams-02 spectrometers and for the tev range lepton fluxes observed with h.e.s.s., veritas, fermi, calet, and dampe. | gev-tev cosmic-ray leptons in the solar system from the bow shock wind nebula of the nearest millisecond pulsar j0437-4715 |
force-free electrodynamics (ffe) is a closed set of equations for the electromagnetic field of a magnetically dominated plasma. there are strong arguments for the existence of force-free plasmas near pulsars and active black holes, but ffe alone cannot account for the observational signatures, such as coherent radio emission and relativistic jets and winds. we reformulate ffe as the effective field theory of a cold string fluid and initiate a systematic study of corrections in a derivative expansion. at leading order the effective theory is equivalent to (generalized) ffe, with the strings comprised by magnetic field line world sheets. higher-order corrections generically give rise to nonzero accelerating electric fields (e .b ≠0 ). we discuss potential observable consequences and comment on an intriguing numerical coincidence. | effective field theory of force-free electrodynamics |
in this paper, we estimate the sensitivity of gravitational wave (gw) detection for future chinese pulsar timing array (pta) projects. the calculation of sensitivity is based on the well-known crámer-rao bound idea. the red noise and dispersion measure (dm) variation noise has be included in the modeling. we demonstrate that the future chinese telescope can be very valuable for future pta experiments and gw detection efforts. | prospects of gravitational wave detection using pulsar timing array for chinese future telescopes |
neutron stars are fascinating astrophysical objects immersed in strong gravitational and electromagnetic fields, at the edge of our current theories. these stars manifest themselves mostly as pulsars, emitting a timely very stable and regular electromagnetic signal. even though discovered almost fifty years ago, they still remain mysterious compact stellar objects. in this review, we summarize the most fundamental theoretical aspects of neutron star magnetospheres and winds. the main competing models explaining their radiative properties like multi-wavelength pulse shapes and spectra and the underlying physical processes such as pair creation and radiation mechanisms are scrutinized. a global but still rather qualitative picture slowly emerges thanks to recent advances in numerical simulations on the largest scales. however considerations about pulsar magnetospheres remain speculative. for instance, the exact composition of the magnetospheric plasma is not yet known. is it solely filled with a mixture of \pm $]]> leptons or does it contain a non-negligible fraction of protons and/or ions? is it almost entirely filled or mostly empty except for some small anecdotal plasma filled regions? answers to these questions will strongly direct the description of the magnetosphere to seemingly contradictory results leading sometimes to inconsistencies. nevertheless, accounts are given as to the latest developments in the theory of pulsar magnetospheres and winds, the existence of a possible electrosphere and physical insight obtained from related observational signatures of multi-wavelength pulsed emission. | theory of pulsar magnetosphere and wind |
a detailed analysis of nulling was conducted for the pulsars studied in the meterwavelength single-pulse polarimetric emission survey. we characterized nulling in 36 pulsars including 17 pulsars where the phenomenon was reported for the first time. the most dominant nulls lasted for a short duration, less than five periods. longer duration nulls extending to hundreds of periods were also seen in some cases. a careful analysis showed the presence of periodicities in the transition from the null to the burst states in 11 pulsars. in our earlier work, fluctuation spectrum analysis showed multiple periodicities in 6 of these 11 pulsars. we demonstrate that the longer periodicity in each case was associated with nulling. the shorter periodicities usually originate from subpulse drifting. the nulling periodicities were more aligned with the periodic amplitude modulation, indicating a possible common origin for both. the most prevalent nulls last for a single period and can be potentially explained using random variations affecting the plasma processes in the pulsar magnetosphere. on the other hand, longer-duration nulls require changes in the pair-production processes, which need an external triggering mechanism for the changes. the presence of periodic nulling puts an added constraint on the triggering mechanism, which also needs to be periodic. | meterwavelength single-pulse polarimetric emission survey. iii. the phenomenon of nulling in pulsars |
we investigate the possible scenario of deconfinement of hyperon rich hadronic matter to quark matter at high densities and the resulting hybrid star (hs) properties are analyzed. in the relativistic mean-field framework, we construct the equation of state (eos) of hadronic matter using the effective chiral model while the pure quark matter is described using the mit bag model. we revisit the hyperon puzzle and analyze the possibility of hadron-quark phase transition with proper choice of the bag constant. in static condition the maximum mass of the resultant hss are in good agreement with the recent observational bounds on the same from high mass pulsars such as psr j1614-2230 and psr j0348+0432. on invoking the phenomenon of phase transition, the radius of canonical mass (r1.4) and value of r1.6 predicted by the model lie within the range prescribed from binary neutron star merger detected by the ligo-virgo collaboration in 2017. the surface redshift obtained for the hss also satisfy the constraints from pulsars rx j0 720.4-3125 and 1e 1 207.4-5209. it is worth noting that unlike several other works, we add no modifications to the original form of the bag model to satisfy these recent observational and empirical constraints on ns properties. we also discuss the rotational aspects of the hss by calculating the properties like rotational mass, radius, energy density, moment of inertia at different angular velocities. the maximum bound on rotational frequency from the rapidly rotating pulsars like psr b1937+21 and psr j1748-2446ad are satisfied with the hs configuration. we also test the universality of our hybrid eos in terms of normalized moment of inertia. | effects of hadron-quark phase transition on properties of neutron stars |
the temporal stability of millisecond pulsars is remarkable, rivaling even some terrestrial atomic clocks at long timescales. using this property, we show that millisecond pulsars distributed in the galactic neighborhood form an ensemble of accelerometers from which we can directly extract the local galactic acceleration. from pulsar spin period measurements, we demonstrate acceleration sensitivity with about 1 σ precision using 117 pulsars. we also present a complementary analysis using orbital periods of 13 binary pulsar systems that eliminates the systematics associated with pulsar braking and results in a local acceleration of (1.7 ±0.5 ) ×10-10 m/s 2 in good agreement with expectations. this work is a first step toward dynamically measuring acceleration gradients that will eventually inform us about the dark matter density distribution in the milky way galaxy. | milky way accelerometry via millisecond pulsar timing |
in this paper, we consider the mimetic gravitational theory to derive a novel category of anisotropic star models. to end and to put the resulting differential equations into a closed system, the form of the metric potential grr as used by tolman is assumed, as well as a linear form of the equation of state. the resulting energy momentum components, energy density, and radial and tangential pressures contain five constants: three of these are determined through the junction condition, matching the interior with the exterior schwarzschild solution; the fourth is constrained by the vanishing of the radial pressure on the boundary; and the fifth is constrained by a real compact star. the physical acceptability of our model is tested using the data of the pulsar 4u 1820-30. the stability of this model is evaluated using the tolman-oppenheimer-volkoff equation and the adiabatic index, and it is shown to be stable. finally, our model is challenged with other compact stars, demonstrating that it is consistent with those stars. | anisotropic compact stars in the mimetic gravitational theory |
here we present stringent low-frequency (185 mhz) limits on coherent radio emission associated with a short-duration gamma-ray burst (sgrb). our observations of the short gamma-ray burst (grb) 180805a were taken with the upgraded murchison widefield array (mwa) rapid-response system, which triggered within 20s of receiving the transient alert from the swift burst alert telescope, corresponding to 83.7 s post-burst. the sgrb was observed for a total of 30 min, resulting in a $3σ$ persistent flux density upper limit of 40.2 mjy beam-1. transient searches were conducted at the swift position of this grb on 0.5 s, 5 s, 30 s and 2 min timescales, resulting in $3σ$ limits of 570-1 830, 270-630, 200-420, and 100-200 mjy beam-1, respectively. we also performed a dedispersion search for prompt signals at the position of the sgrb with a temporal and spectral resolution of 0.5 s and 1.28 mhz, respectively, resulting in a $6σ$ fluence upper-limit range from 570 jy ms at dm $=3 000$ pc cm-3 ( $z∼ 2.5$ ) to 1 750 jy ms at dm $=200$ pc cm-3 ( $z∼ 0.1)$ , corresponding to the known redshift range of sgrbs. we compare the fluence prompt emission limit and the persistent upper limit to sgrb coherent emission models assuming the merger resulted in a stable magnetar remnant. our observations were not sensitive enough to detect prompt emission associated with the alignment of magnetic fields of a binary neutron star just prior to the merger, from the interaction between the relativistic jet and the interstellar medium (ism) or persistent pulsar-like emission from the spin-down of the magnetar. however, in the case of a more powerful sgrb (a gamma-ray fluence an order of magnitude higher than grb 180805a and/or a brighter x-ray counterpart), our mwa observations may be sensitive enough to detect coherent radio emission from the jet-ism interaction and/or the magnetar remnant. finally, we demonstrate that of all current low- frequency radio telescopes, only the mwa has the sensitivity and response times capable of probing prompt emission models associated with the initial sgrb merger event. | murchison widefield array rapid-response observations of the short grb 180805a |
context. accreting highly magnetized pulsars in binary systems are among the brightest x-ray emitters in our galaxy. although a number of high-quality broad-band (0.1-100 kev) x-ray observations are available, the spectral energy distribution of these sources is usually investigated by adopting pure phenomenological models rather than models linked to the physics of accretion.aims: in this paper, a detailed spectral study of the x-ray emission recorded from the high-mass x-ray binary pulsars cen x-3, 4u 0115+63, and her x-1 is carried out by using bepposax and joined suzaku +nustar data, together with an advanced version of the compmag model, which provides a physical description of the high-energy emission from accreting pulsars, including the thermal and bulk comptonization of cyclotron and bremsstrahlung seed photons along the neutron star accretion column.methods: the compmag model is based on an iterative method for solving second-order partial differential equations, whose convergence algorithm has been improved and consolidated during the preparation of this paper.results: our analysis shows that the broad-band x-ray continuum of all considered sources can be self-consistently described by the compmag model. the cyclotron absorption features (not included in the model) can be accounted for by using gaussian components. from the fits of the compmag model to the data we inferred the physical properties of the accretion columns in all sources, finding values reasonably close to those theoretically expected according to our current understanding of accretion in highly magnetized neutron stars.conclusions: the updated version of the compmag model has been tailored to the physical processes that are known to occur in the columns of highly magnetized accreting neutron stars and it can thus provide a better understanding of the high-energy radiation from these sources. the availability of broad-band high-quality x-ray data, such as those provided by bepposax in the past and currently from nustar and other facilities, is crucial to fully exploit the potentialities of the model. the advent of the astro-h mission, endowed with an unprecedented combination of high sensitivity and x-ray broad-band coverage, provides good perspectives to improve our understanding of accretion onto highly magnetized neutron stars through physical models like the one adopted here. | a new model for the x-ray continuum of the magnetized accreting pulsars |
the recent discovery of a population of eccentric (e ∼ 0.1) millisecond pulsar (msp) binaries with low-mass white dwarf companions in the galactic field represents a challenge to evolutionary models that explain msp formation as recycling: all such models predict that the orbits become highly circularized during a long period of accretion. the members of this new population exhibit remarkably similar properties (orbital periods, eccentricities, companion masses, spin periods), and several models have been put forward that suggest a common formation channel. in this work, we present the results of an extensive timing campaign focusing on one member of this new population, psr j1946+3417. through the measurement of both the advance of periastron and the shapiro delay for this system, we determine the mass of the pulsar, mass of the companion and the inclination of the orbit to be 1.828(22) m⊙, 0.2656(19) m⊙ and 76.4 ± 0.6 degrees, respectively, under the assumption that general relativity is the true description of gravity. notably, this is the third highest mass measured for any pulsar. using these masses and the astrometric properties of psr j1946+3417, we examine three proposed formation channels for eccentric msp binaries. while our results are consistent with circumbinary disc-driven eccentricity growth or neutron star to strange star phase transition, we rule out rotationally delayed accretion-induced collapse as the mechanism responsible for the configuration of the psr j1946+3417 system. | a massive millisecond pulsar in an eccentric binary |
we report on timing, flux density, and polarimetric observations of the transient magnetar and 5.54 s radio pulsar xte j1810-197 using the green bank, nançay, and parkes radio telescopes beginning in early 2006, until its sudden disappearance as a radio source in late 2008. repeated observations through 2016 have not detected radio pulsations again. the torque on the neutron star, as inferred from its rotation frequency derivative \dot{ν }, decreased in an unsteady manner by a factor of three in the first year of radio monitoring, until approximately mid-2007. by contrast, during its final year as a detectable radio source, the torque decreased steadily by only 9%. the period-averaged flux density, after decreasing by a factor of 20 during the first 10 months of radio monitoring, remained relatively steady in the next 22 months, at an average of 0.7 ± 0.3 mjy at 1.4 ghz, while still showing day-to-day fluctuations by factors of a few. there is evidence that during this last phase of radio activity the magnetar had a steep radio spectrum, in contrast to earlier flat-spectrum behavior. no secular decrease presaged its radio demise. during this time, the pulse profile continued to display large variations; polarimetry, including of a new profile component, indicates that the magnetic geometry remained consistent with that of earlier times. we supplement these results with x-ray timing of the pulsar from its outburst in 2003 up to 2014. for the first 4 years, xte j1810-197 experienced non-monotonic excursions in frequency derivative by at least a factor of eight. but since 2007, its \dot{ν } has remained relatively stable near its minimum observed value. the only apparent event in the x-ray record that is possibly contemporaneous with the radio shutdown is a decrease of ≈20% in the hot-spot flux in 2008-2009, to a stable, minimum value. however, the permanence of the high-amplitude, thermal x-ray pulse, even after the (unexplained) radio demise, implies continuing magnetar activity. | radio disappearance of the magnetar xte j1810-197 and continued x-ray timing |
faraday rotation occurs along every line of sight in the galaxy; rotation measure (rm) synthesis allows a 3d representation of the interstellar magnetic field. this study uses data from the global magneto-ionic medium survey, a combination of single-antenna spectro-polarimetric studies, including northern sky data from the dominion radio astrophysical observatory (drao) 26 m telescope (1270-1750 mhz) and southern sky data from the parkes 64 m telescope (300-480 mhz). from the synthesized faraday spectral cubes we compute the zeroth, first, and second moments to find the total polarized emission, mean rm, and rm width of the polarized emission. from drao first moments we find a weak vertical field directed from galactic north to south, but parkes data reveal fields directed toward the sun at high latitudes in both hemispheres: the two surveys clearly sample different volumes. drao second moments show feature widths in faraday spectra increasing with decreasing positive latitudes, implying that longer lines of sight encounter more faraday rotating medium, but this is not seen at negative latitudes. parkes data show the opposite: at positive latitudes the second moment decreases with decreasing latitude, but not at negative latitudes. comparing first moments with rms of pulsars and extragalactic sources and a study of depolarization together confirm that the drao survey samples to larger distances than the parkes data. emission regions in the drao survey are typically 700-1000 pc away, slightly beyond the scale height of the magneto-ionic medium; emission detected in the parkes survey is entirely within the magneto-ionic disk, less than 500 pc away. | the galactic magneto-ionic medium survey: moments of the faraday spectra |
we describe psr j1926-0652, a pulsar recently discovered with the five-hundred-meter aperture spherical radio telescope (fast). using sensitive single-pulse detections from fast and long-term timing observations from the parkes 64 m radio telescope, we probed phenomena on both long and short timescales. the fast observations covered a wide frequency range from 270 to 800 mhz, enabling individual pulses to be studied in detail. the pulsar exhibits at least four profile components, short-term nulling lasting from 4 to 450 pulses, complex subpulse drifting behaviors and intermittency on scales of tens of minutes. while the average band spacing p 3 is relatively constant across different bursts and components, significant variations in the separation of adjacent bands are seen, especially near the beginning and end of a burst. band shapes and slopes are quite variable, especially for the trailing components and for the shorter bursts. we show that for each burst the last detectable pulse prior to emission ceasing has different properties compared to other pulses. these complexities pose challenges for the classic carousel-type models. | psr j1926-0652: a pulsar with interesting emission properties discovered at fast |
perpendicular relativistic (γ0= 10) shocks in magnetized pair plasmas are investigated using two-dimensional particle-in-cell simulations. a systematic survey, from unmagnetized to strongly magnetized shocks, is presented accurately capturing the transition from weibel-mediated to magnetic-reflection-shaped shocks. this transition is found to occur for upstream flow magnetizations 10-3 < σ < 10-2 at which a strong perpendicular net current is observed in the precursor, driving the so-called current-filamentation instability. the global structure of the shock and shock formation time are discussed. the magnetohydrodynamics shock jump conditions are found in good agreement with the numerical results, except for 10-4 < σ < 10-2 where a deviation up to 10 per cent is observed. the particle precursor length converges towards the larmor radius of particles injected in the upstream magnetic field at intermediate magnetizations. for σ > 10-2, it leaves place to a purely electromagnetic precursor following from the strong emission of electromagnetic waves at the shock front. particle acceleration is found to be efficient in weakly magnetized perpendicular shocks in agreement with previous works, and is fully suppressed for σ > 10-2. diffusive shock acceleration is observed only in weakly magnetized shocks, while a dominant contribution of shock drift acceleration is evidenced at intermediate magnetizations. the spatial diffusion coefficients are extracted from the simulations allowing for a deeper insight into the self-consistent particle kinematics and scale with the square of the particle energy in weakly magnetized shocks. these results have implications for particle acceleration in the internal shocks of active galactic nucleus jets and in the termination shocks of pulsar wind nebulae. | perpendicular relativistic shocks in magnetized pair plasma |
accreting pulsars power relativistic jets and display a complex spin phenomenology. these behaviours may be closely related to the large-scale configuration of the star's magnetic field, shaped by its interaction with the surrounding accretion disc. here, we present the first relativistic simulations of the interaction of a pulsar magnetosphere with an accretion flow. our axisymmetric simulations treat the magnetospheric, or coronal, regions using a resistive extension of force-free electrodynamics. the magnetic field is also evolved inside the disc, which is a defined volume with a specified velocity field and conductivity profile, found using an α-disc model. we study a range of disc α-parameters, thicknesses, magnetic prandtl numbers and inner truncation radii. we find that a large fraction of the magnetic flux in the pulsar's closed zone is opened by the intrusion of the disc, leading to an enhancement of the power extracted by the pulsar wind and the spin-down torque applied to the pulsar. in our simulations, most of the spin-down contribution to the stellar torque acts on open field lines. the efficiency of field-line opening is high in the simulations' long-term quasi-steady states, which implies that a millisecond pulsar's electromagnetic wind could be strong enough to power the observed neutron-star radio jets, and may significantly affect the pulsar's spin evolution. | simulations of the magnetospheres of accreting millisecond pulsars |
the detection of the unusually heavy binary neutron star merger gw190425 marked a stark contrast to the mass distribution from known galactic pulsars in double neutron star binaries and gravitational-wave source gw170817. we suggest here a formation channel for heavy binary neutron stars and light black hole-neutron star binaries in which massive helium stars, which had their hydrogen envelope removed during a common-envelope phase, remain compact and avoid mass transfer onto the neutron star companion, possibly avoiding pulsar recycling. we present three-dimensional simulations of the supernova explosion of the massive stripped helium star and follow the mass fallback evolution and the subsequent accretion onto the neutron star companion. we find that fallback leads to significant mass growth in the newly formed neutron star. this can explain the formation of heavy binary neutron star systems such as gw190425, as well as predict the assembly of light black hole-neutron star systems such as gw200115. this formation avenue is consistent with the observed mass-eccentricity correlation of binary neutron stars in the milky way. finally, avoiding mass transfer suggests an unusually long spin-period population of pulsar binaries in our galaxy. | fallback supernova assembly of heavy binary neutron stars and light black hole-neutron star pairs and the common stellar ancestry of gw190425 and gw200115 |
psr j1829+2456 is a radio pulsar in a relativistic binary system with another neutron star. it has a rotational period of 41 ms and a mildly eccentric (e = 0.14) 28 h orbit. we have continued its observations with the arecibo radio telescope and have now measured the individual neutron star masses of this system: the pulsar and companion masses are $1.306\, \pm \, 0.007\, \mathrm{m}_{\odot}$ and $1.299\, \pm \, 0.007\, \mathrm{m}_{\odot}$ ($2\sigma - 95{{\ \rm per\ cent}}$ confidence, unless stated otherwise), respectively. we have also measured the proper motion for this system and used it to estimate a space velocity of $49^{+77}_{-30}$$\, \mathrm{km}\, \mathrm{s}^{-1}$ with respect to the local standard of rest. the relatively low values for companion mass, space velocity, and orbital eccentricity in this system make it similar to other double neutron star systems in which the second-formed neutron star is thought to have formed in a low-kick, low mass-loss, symmetric supernova. | precise mass measurements for the double neutron star system j1829+2456 |
pulsars in the galactic centre promise to enable unparalleled tests of gravity theories and black hole physics and to serve as probes of the stellar formation history and evolution and the interstellar medium in the complex central region of the milky way. the community has surveyed the innermost region of the galaxy for decades without detecting a population of pulsars, which is puzzling. a strong scattering of the pulsed signals in this particular direction has been argued to be a potential reason for the non-detections. scattering has a strong inverse dependence on observing frequency, therefore an effective way to alleviate its effect is to use higher frequencies in a survey for pulsars in the galactic centre, in particular, close to the supermassive black hole sagittarius a*. we present the first pulsar survey at short millimetre wavelengths, using several frequency bands between 84 and 156 ghz (λ = 3.5-1.92 mm), targeted to the galactic centre. the observations were made with the institut de radioastronomie millimétrique 30m telescope in 28 epochs between 2016 december and 2018 may. this survey is the first that is essentially unaffected by scattering and therefore unbiased in population coverage, including fast-spinning pulsars that might be out of reach of lower-frequency galactic centre surveys. we discovered no new pulsars and relate this result mainly to the decreased flux density of pulsars at high frequencies, combined with our current sensitivity. however, we demonstrate that surveys at these extremely high radio frequencies are capable of discovering new pulsars, analyse their sensitivity limits with respect to a simulated galactic centre pulsar population, and discuss the main challenges and possible improvements for similar surveys in the future. | searching for pulsars in the galactic centre at 3 and 2 mm |
context. during its performance verification phase, the soft x-ray instrument erosita on board the spektrum-roentgen-gamma (srg) spacecraft observed large regions in the magellanic clouds in which almost 40 known high-mass x-ray binaries (hmxbs, including candidates) are located.aims: we looked for new hmxbs in the erosita data, searched for pulsations in hmxb candidates, and investigated the long-term behaviour of the full sample using archival x-ray and optical data.methods: for sufficiently bright sources, we performed a detailed spectral and temporal analysis of their erosita data. a source detection analysis of the erosita images in different energy bands provided count rates and upper limits for the remaining sources.results: we report the discovery of a new be/x-ray binary in the large magellanic cloud. the transient srget j052829.5-690345 was detected with a 0.2-8.0 kev luminosity of~1035 erg s−1. it exhibits a hard x-ray spectrum, typical for this class of hmxbs. the ogle i-band light curve of the v~15.7mag counterpart shows large variations up to 0.75 mag, which occur with a quasi-period of~511 days. the erosita observations of the small magellanic cloud covered 16 be/x-ray binary pulsars, 5 of which were bright enough for an accurate determination of their current pulse period. the pulse periods for sxp 726 and sxp 1323 measured from erosita data are~800 s and~1006 s, respectively, which is very different from their discovery periods. including archival xmm-newton observations, we update the spin-period history of the two long-period pulsars, which have shown nearly linear trends in their period evolution for more than 15 yr. the corresponding average spin-down rate for sxp 726 is 4.3 s yr−1, while sxp 1323 has a spin-up rate of -23.2 s yr−1. we discuss the spin evolution of the two pulsars in the framework of quasi-spherical accretion. | erosita calibration and performance verification phase: high-mass x-ray binaries in the magellanic clouds |
subpulse drifting in pulsar radio emission is considered to be one of the most promising phenomena for uncovering the underlying physical processes. here, we present a detailed study of such a phenomenon in observations of psr j1822-2256, made using the upgraded giant meterwave radio telescope (ugmrt). observations were made simultaneously using the band 3 (300-500 mhz) and band 4 (550-750 mhz) receivers of the ugmrt. the pulsar is known to exhibit subpulse drifting, mode changing, and nulling. our observations reveal four distinct subpulse drifting modes of emission (a, b, c, and d) for this pulsar, with the drift periodicities of 17.9p1, 5.8p1, 8p1, and 14.1p1, respectively (where p1 is the pulsar rotation period), two of which exhibit some new features that were not reported in the previous studies. we also investigate the possible spark configuration, characterized by the number of sparks (n) in the carousel patterns of these four drift modes, and our analysis suggests two representative solutions for the number of sparks for a carousel rotation period, p4, which lies in the range of 13-16. the large frequency coverage of our data (300-750 mhz) is also leveraged to explore the frequency dependence of single-pulse characteristics of the pulsar emission, particularly the frequency-dependent subpulse behaviour and the emission heights for the observed drift modes. our analysis suggests a clear modal dependence of inferred emission heights. we discuss the implications for the pulsar emission mechanism and its relation to the proposed spark configuration. | revisiting the subpulse drifting phenomenon in psr j1822-2256: drift modes, sparks, and emission heights |
we study the observation of polarized stochastic gravitational-wave background (sgwb) in pulsar-timing-array experiments. the time residual for an observed pulsar is formulated as a line-of-sight integral that incorporates the effects of the pulsar term, from which we construct the correlation function of the time residual between a pair of pulsars in terms of the overlap reduction functions (orfs) for the sgwb intensity and polarization anisotropies. our formulation provides a numerical scheme for computing the orfs for high multipole moments, and the lowest-moment orfs for the sgwb linear polarization are worked out for the first time. | observation of a polarized stochastic gravitational-wave background in pulsar-timing-array experiments |
we report the discovery of psr j1555-2908, a 1.79 ms radio and gamma-ray pulsar in a 5.6 hr binary system with a minimum companion mass of 0.052 m ⊙. this fast and energetic ( $\dot{e}=3\times {10}^{35}$ erg s-1) millisecond pulsar was first detected as a gamma-ray point source in fermi large area telescope (lat) sky survey observations. guided by a steep-spectrum radio point source in the fermi error region, we performed a search at 820 mhz with the green bank telescope that first discovered the pulsations. the initial radio pulse timing observations provided enough information to seed a search for gamma-ray pulsations in the lat data, from which we derive a timing solution valid for the full fermi mission. in addition to the discovery and timing of radio and gamma-ray pulsations, we searched for x-ray pulsations using nicer but no significant pulsations were detected. we also obtained time-series r-band photometry that indicates strong heating of the companion star by the pulsar wind. material blown off the heated companion eclipses the 820 mhz radio pulse during inferior conjunction of the companion for ≈10% of the orbit, which is twice the angle subtended by its roche lobe in an edge-on system. | discovery, timing, and multiwavelength observations of the black widow millisecond pulsar psr j1555-2908 |
we investigate the anisotropies of the stochastic gravitational-wave background (sgwb) produced by cosmic strings associated with the spontaneous u(1) symmetry breaking of grand unified theory, which happens at the onset of inflation. the string network evolution is determined by primordial fluctuations and never reaches the scaling regime. the string loops are inhomogeneously distributed in large scale regions, resulting in large anisotropies in the sgwb. we find that the angular power spectrum of sgwb anisotropies depends on frequency, which is testable in multiband observations of gws. in particular, gws from the cosmic strings can appropriately interpret the common-spectrum process reported by nanograv collaboration, and the angular power spectrum in the nanohertz band, $\mathtt{l}(\mathtt{l}+1)c_{\mathtt{l}}=5.6\times 10^{-2}$ at large scales, is expected to be detectable by pulsar timing array experiments in the near future. | a new picture of cosmic string evolution and anisotropic stochastic gravitational-wave background |
the curvature radiation is applied to the explanation of the circular polarization of fast radio bursts (frbs). significant circular polarization is reported in both apparently non-repeating and repeating frbs. curvature radiation can produce significant circular polarization at the wing of the radiation beam. in the curvature radiation scenario, in order to see significant circular polarization in frbs, (1) more energetic bursts, (2) bursts with electrons having higher lorentz factor, and (3) a slowly rotating neutron star at the center are required. different rotational period of the central neutron star may explain why some frbs have high circular polarization, while others do not. considering possible difference in refractive index for the parallel and perpendicular components of electric field, the position angle may change rapidly over the narrow pulse window of the radiation beam. the position angle swing in frbs may also be explained by this non-geometric origin, besides that of the rotating vector model. | circular polarization of fast radio bursts in the curvature radiation scenario |
in this paper, we introduce the post-minkowskian approximation of energy-momentum-squared gravity (emsg). this approximation is used to study the gravitational energy flux in the context of emsg. as an application of our results, we investigate the emsg effect on the first time derivative of the orbital period of the binary pulsars. utilizing this post-keplerian parameter, the free parameter of the emsg theory, f0' , is estimated for six known binary pulsars. taking the binaries that have the most accurate observations, it turns out that -6 ×10-37 m s2 kg-1<f0'<+10-36 m s2 kg-1 . this bound is in agreement with the precedent studies. | constraining energy-momentum-squared gravity by binary pulsar observations |
we present a global kinetic plasma simulation of an axisymmetric pulsar magnetosphere with self-consistent e ± pair production. we use the particle-in-cell method and log-spherical coordinates with a grid size 4096 × 4096. this allows us to achieve a high voltage induced by the pulsar rotation and investigate pair creation in a young pulsar far from the death line. we find the following: (1) the energy release and e ± creation are strongly concentrated in the thin, y-shaped current sheet, with a peak localized in a small volume at the y-point. (2) the y-point is shifted inward from the light cylinder by ~15% and "breathes" with a small amplitude. (3) the dense e ± cloud at the y-point is in ultrarelativistic rotation, which we call superrotation, because it exceeds corotation with the star. the cloud receives angular momentum flowing from the star along the poloidal magnetic field lines. (4) gamma-ray emission peaks at the y-point and is collimated in the azimuthal direction, tangent to the y-point circle. (5) the separatrix current sheet between the closed magnetosphere and the open magnetic field lines is sustained by the electron backflow from the y-point cloud. its thickness is self-regulated to marginal charge starvation. (6) only a small fraction of dissipation occurs in the separatrix inward of the y-point. a much higher power is released in the equatorial plane, including the y-point where the created dense e ± plasma is spun up and intermittently ejected through the nozzle between the two open magnetic fluxes. | axisymmetric pulsar magnetosphere revisited |
fermi science tools is a suite of tools for the analysis of both the large-area telescope (lat) and the gamma-ray burst monitor (gbm) data, including point source analysis for generating maps, spectra, and light curves, pulsar timing analysis, and source identification. | fermitools: fermi science tools |
context. as the importance of gravitational wave (gw) astrophysics increases rapidly, astronomers interested in gws who are not experts in this field sometimes need to get a quick idea of what gw sources can be detected by certain detectors, and the accuracy of the measured parameters.aims: the gw-toolbox is a set of easy-to-use, flexible tools to simulate observations of the gw universe with different detectors, including ground-based interferometers (advanced ligo, advanced virgo, kagra, einstein telescope, cosmic explorer, and also customised interferometers), space-borne interferometers (lisa and a customised design), and pulsar timing arrays mimicking the current working arrays (epta, ppta, nanograv, ipta) and future ones. we include a broad range of sources, such as mergers of stellar-mass compact objects, namely black holes, neutron stars, and black hole-neutron star binaries, supermassive black hole binary mergers and inspirals, galactic double white dwarfs in ultra-compact orbit, extreme-mass-ratio inspirals, and stochastic gw backgrounds.methods: we collected methods to simulate source populations and determine their detectability with various detectors. our aim is to provide a comprehensive description of the methodology and functionality of the gw-toolbox.results: the gw-toolbox produces results that are consistent with previous findings in the literature, and the tools can be accessed via a website interface or as a python package. in the future, this package will be upgraded with more functions. gw-universe.org https://bitbucket.org/radboudradiolab/gwtoolbox | the gravitational wave universe toolbox. a software package to simulate observations of the gravitational wave universe with different detectors |
several conjectures have been put forward to explain rotating radio transients (rrats), the newest subclass of neutron stars, and their connections to other radio pulsars. this work discusses these conjectures in the context of the characteristic properties of the rrat population. contrary to expectations, it is seen that: (a) the rrat population is statistically un-correlated with the nulling pulsars and (b) the rrat phenomenon is unlikely to be related to old age or death-line proximity. it is perhaps more likely that the special emission property of rrats is a signature of them being later evolutionary phases of other types of neutron stars which may have resulted in restructuring their magnetic fields. | radio pulsar sub-populations (ii): the mysterious rrats |
anaeromyxobacter is globally distributed in soil environments, especially predominant in paddy soils. current studies based on environmental dna/rna analyses frequently detect gene fragments encoding nitrogenase of anaeromyxobacter from various soil environments. although the importance of anaeromyxobacter as a diazotroph in nature has been suggested by culture-independent studies, there has been no solid evidence and validation from genomic and culture-based analyses that anaeromyxobacter fixes nitrogen. this study demonstrates that anaeromyxobacter harboring nitrogenase genes exhibits diazotrophic ability; moreover, n 2 -dependent growth was demonstrated in vitro and in the soil environment. our findings indicate that nitrogen fixation is important for anaeromyxobacter to survive under nitrogen-deficient environments and provide a novel insight into the environmental function of anaeromyxobacter , which is a common bacterium in soils. abstract biological nitrogen fixation is an essential reaction in a major pathway for supplying nitrogen to terrestrial environments. previous culture-independent analyses based on soil dna/rna/protein sequencing could globally detect the nitrogenase genes/proteins of anaeromyxobacter (in the class deltaproteobacteria ), commonly distributed in soil environments and predominant in paddy soils; this suggests the importance of anaeromyxobacter in nitrogen fixation in soil environments. however, direct experimental evidence is lacking; there has been no research on the genetic background and ability of anaeromyxobacter to fix nitrogen. therefore, we verified the diazotrophy of anaeromyxobacter based on both genomic and culture-dependent analyses using anaeromyxobacter sp. strains psr-1 and red267 isolated from soils. based on the comparison of nif gene clusters, strains psr-1 and red267 as well as strains fw109-5, k, and diazotrophic geobacter and pelobacter in the class deltaproteobacteria contain the minimum set of genes for nitrogenase ( nifbhdken ). these results imply that anaeromyxobacter species have the ability to fix nitrogen. in fact, anaeromyxobacter psr-1 and red267 exhibited n 2 -dependent growth and acetylene reduction activity (ara) in vitro . transcriptional activity of the nif gene was also detected when both strains were cultured with n 2 gas as a sole nitrogen source, indicating that anaeromyxobacter can fix and assimilate n 2 gas by nitrogenase. in addition, psr-1- or red267-inoculated soil showed ara activity and the growth of the inoculated strains on the basis of rna-based analysis, demonstrating that anaeromyxobacter can fix nitrogen in the paddy soil environment. our study provides novel insights into the pivotal environmental function, i.e., nitrogen fixation, of anaeromyxobacter , which is a common soil bacterium. importance anaeromyxobacter is globally distributed in soil environments, especially predominant in paddy soils. current studies based on environmental dna/rna analyses frequently detect gene fragments encoding nitrogenase of anaeromyxobacter from various soil environments. although the importance of anaeromyxobacter as a diazotroph in nature has been suggested by culture-independent studies, there has been no solid evidence and validation from genomic and culture-based analyses that anaeromyxobacter fixes nitrogen. this study demonstrates that anaeromyxobacter harboring nitrogenase genes exhibits diazotrophic ability; moreover, n 2 -dependent growth was demonstrated in vitro and in the soil environment. our findings indicate that nitrogen fixation is important for anaeromyxobacter to survive under nitrogen-deficient environments and provide a novel insight into the environmental function of anaeromyxobacter , which is a common bacterium in soils. | diazotrophic anaeromyxobacter isolates from soils |
we investigate the properties of asymmetric quark matter and strange quark matter in the framework of the su(3) nambu-jona-lasinio (njl) model with two types of vector interactions: (1) the flavor-dependent repulsion among different flavors of quarks with the coupling constant gv , and (2) the universal repulsion and the vector-isovector interaction among different flavors of quarks with the coupling constants gv and gi v. using these two types of vector interactions in the njl model, we study the quark symmetry energy in asymmetric quark matter, the constituent quark mass, the quark fraction, the equation of state in strange quark matter, the maximum mass of a quark star, and the properties of the qcd phase diagram. we find that including the two types of vector interactions in the su(3) njl model can significantly influence the quark matter symmetry energy as well as the properties of strange quark matter and quark stars. in particular, our results indicate that we can describe psr j 1614 -2230 and psr j 0348 +0432 as quark stars by considering the universal repulsion and the vector-isovector interaction among quark matter in the su(3) njl model. | quark matter in an su(3) nambu-jona-lasinio model with two types of vector interactions |
it has been recently claimed by two different groups that the spectral modulation observed in gamma rays from galactic pulsars and supernova remnants can be due to conversion of photons into ultra-light axion-like-particles (alps) in large-scale galactic magnetic fields. while we show the required best-fit photon-alp coupling, $g_{a\gamma} \sim 2 \times 10^{-10}$ gev${}^{-1}$, to be consistent with constraints from observations of photon-alps mixing in vacuum, this is in conflict with other bounds, specifically from the cast solar axion limit, from the helium-burning lifetime in globular clusters, and from the non-observations of gamma rays in coincidence with sn 1987a. in order to reconcile these different results, we propose that environmental effects in matter would suppress the alp production in dense astrophysical plasma, allowing to relax previous bounds and make them compatible with photon-alp conversions in the low-density galactic medium. if this explanation is correct, the claimed alp signal would be on the reach of next-generations laboratory experiments such as alps ii. | reconciling hints on axion-like-particles from high-energy gamma rays with stellar bounds |
black widows are close binary systems in which a millisecond pulsar is orbited by a companion, a few per cent the mass of the sun. it has been suggested that the pulsar's rotationally powered γ-ray luminosity gradually evaporates the companion, eventually leaving behind an isolated millisecond pulsar. the evaporation efficiency is determined by the temperature tch ∝ f2/3 to which the outflow is heated by the flux f on a dynamical time-scale. evaporation is most efficient for companions that fill their roche lobes. in this case, the outflow is dominated by a cap around the l1 point with an angle θg ∼ (tch/tg)1/2, and the evaporation time is tevap = 0.46(tch/tg)-2 gyr, where tg > tch is the companion's virial temperature. we apply our model to the observed black widow population, which has increased substantially over the last decade, considering each system's orbital period, companion mass, and pulsar spin-down power. while the original black widow (psr b1957+20) evaporates its companion on a few gyr time-scale, direct evaporation on its own is too weak to explain the overall population. we propose instead that the evaporative wind couples to the companion's magnetic field, removes angular momentum from the binary, and maintains stable roche lobe overflow. while a stronger wind carries more mass, it also reduces the alfvén radius, making this indirect magnetic braking mechanism less dependent on the flux $t_{\rm mag}\propto t_{\rm evap}^{1/3}$ . this reduces the scatter in evolution times of observed systems, thus better explaining the combined black widow and isolated millisecond pulsar populations. | black widow evolution: magnetic braking by an ablated wind |
dm_phase maximizes the coherent power of a radio signal instead of its intensity to calculate the best dispersion measure (dm) for a burst such as those emitted by pulsars and fast radio bursts (frbs). it is robust to complex burst structures and interference, thus mitigating the limitations of traditional methods that search for the best dm value of a source by maximizing the signal-to-noise ratio (s/n) of the detected signal. | dm_phase: algorithm for correcting dispersion of radio signals |
with the largest dish five-hundred-meter aperture spherical radio telescope (fast), both the mean and single pulses of psr b2016+28, especially including the single-pulse structure, are investigated in detail in this study. the mean pulse profiles at different frequencies can be well fitted in a conal model, and the peak separation of intensity-dependent pulse profiles increases with intensity. the integrated pulses are obviously frequency dependent (pulse width decreases by 20% as frequency increases from 300 to 750 mhz), but the structure of single pulses changes slightly (the corresponding correlation scale decreases by only 1%). this disparity between mean and single pulses provides independent evidence for the existence of the rs-type vacuum inner gap, indicating a strong bond between particles on the pulsar surface. diffused drifting sub-pulses are analyzed. the results show that the modulation period along pulse series ( p 3) is positively correlated to the separation between two adjacent sub-pulses ( p 2). this correlation may hint a rough surface on the pulsar, eventually resulting in the irregular drift of sparks. all the observational results may have significant implications in the dynamics of pulsar magnetosphere and are discussed extensively in this paper. | the radiation structure of psr b2016+28 observed with fast |
we report on the results of a 4 year timing campaign of psr j2222-0137, a 2.44 day binary pulsar with a massive white dwarf (wd) companion, with the nançay, effelsberg, and lovell radio telescopes. using the shapiro delay for this system, we find a pulsar mass mp= 1.76 ± 0.06 m ⊙ and a wd mass mc= 1.293 ± 0.025 m ⊙. we also measure the rate of advance of periastron for this system, which is marginally consistent with the general relativity prediction for these masses. the short lifetime of the massive wd progenitor star led to a rapid x-ray binary phase with little (< 10-2 m ⊙) mass accretion onto the neutron star; hence, the current pulsar mass is, within uncertainties, its birth mass, which is the largest measured to date. we discuss the discrepancy with previous mass measurements for this system; we conclude that the measurements presented here are likely to be more accurate. finally, we highlight the usefulness of this system for testing alternative theories of gravity by tightly constraining the presence of dipolar radiation. this is of particular importance for certain aspects of strong-field gravity, like spontaneous scalarization, since the mass of psr j2222-0137 puts that system into a poorly tested parameter range. | a massive-born neutron star with a massive white dwarf companion |
repeating and apparently non-repeating fast radio bursts (frbs) differ by orders of magnitude in duty factors, energy, and rotation measure. extensive monitoring of apparently non-repeating frb has failed to find any repetitions. this suggests that the two types differ qualitatively, rather than in repetition rate, and are produced by distinct kinds of sources. the absence of periodicity in repeating frb argues that they are not produced by neutron stars. they may originate in dilute relativistic jets produced by low luminosity black hole accretion. non-repeating frb may be produced by catastrophic events such as the collapse of an accreting magnetic neutron star to a black hole or of an accreting magnetic white dwarf to a neutron star, during which a disappearing magnetic moment radiates dipole radiation that accelerates electrons in nearby matter. if they are emitted by collimated beams of relativistic particles or charge `bunches' with lorentz factor γ, their radiation is collimated into a solid angle ∼γ-2 sterad, reducing the energy requirement. if powered by magnetic reconnection, a pulse of length δt may draw on the magnetic energy in a volume ∼γ4(cδt)3, although only a fraction ∼1/γ2 of this may be dissipated without decollimation. | fast radio burst energetics and sources |
we perform 2.5d axisymmetric simulations of the pulsar magnetosphere (aligned dipole rotator) using the charge conservative, relativistic, electromagnetic particle in cell code picsar. particle in cell codes are a powerful tool to use for studying the pulsar magnetosphere, because they can handle the force-free and vacuum limits and provide a self-consistent treatment of magnetic reconnection. in the limit of dense plasma throughout the magnetosphere, our solutions are everywhere in the force-free regime except for dissipative regions at the polar caps, in the current layers, and at the y-point. these dissipative regions arise self-consistently, since we do not have any explicit dissipation in the code. a minimum of ≈15-20 per cent of the electromagnetic spin-down luminosity is transferred to the particles inside 5 light cylinder radii. however, the particles can carry as much as ≳ 50 per cent of the spin-down luminosity if there is insufficient plasma in the outer magnetosphere to screen the component of electric field parallel to the magnetic field. in reality, the component of the spin-down luminosity carried by the particles could be radiated as gamma-rays, but high-frequency synchrotron emission would need to be implemented as a sub-grid process in our simulations and is not present for the current suite of runs. the value of the spin-down luminosity in our simulations is within ≈10 per cent of the force-free value, and the structure of the electromagnetic fields in the magnetosphere is on the whole consistent with the force-free model. | dissipation, energy transfer, and spin-down luminosity in 2.5d pic simulations of the pulsar magnetosphere |
the paucity of observed supermassive black hole binaries (smbhbs) may imply that the gravitational wave background (gwb) from this population is anisotropic, rendering existing analyses suboptimal. we present the first constraints on the angular distribution of a nanohertz stochastic gwb from circular, inspiral-driven smbhbs using the 2015 european pulsar timing array data. our analysis of the gwb in the ∼2 - 90 nhz band shows consistency with isotropy, with the strain amplitude in l >0 spherical harmonic multipoles ≲40 % of the monopole value. we expect that these more general techniques will become standard tools to probe the angular distribution of source populations. | limits on anisotropy in the nanohertz stochastic gravitational wave background |
we present the first sub-arcminute images of the galactic center above 10 kev, obtained with nustar. nustar resolves the hard x-ray source igr j17456-2901 into non-thermal x-ray filaments, molecular clouds, point sources, and a previously unknown central component of hard x-ray emission (chxe). nustar detects four non-thermal x-ray filaments, extending the detection of their power-law spectra with γ ∼ 1.3-2.3 up to ∼50 kev. a morphological and spectral study of the filaments suggests that their origin may be heterogeneous, where previous studies suggested a common origin in young pulsar wind nebulae (pwne). nustar detects non-thermal x-ray continuum emission spatially correlated with the 6.4 kev fe kα fluorescence line emission associated with two sgr a molecular clouds: mc1 and the bridge. broadband x-ray spectral analysis with a monte-carlo based x-ray reflection model self-consistently determined their intrinsic column density (∼1023 cm-2), primary x-ray spectra (power-laws with γ ∼ 2) and set a lower limit of the x-ray luminosity of sgr a* flare illuminating the sgr a clouds to lx ≳ 1038 erg s-1. above ∼20 kev, hard x-ray emission in the central 10 pc region around sgr a* consists of the candidate pwn g359.95-0.04 and the chxe, possibly resulting from an unresolved population of massive cvs with white dwarf masses mwd ∼ 0.9 m⊙. spectral energy distribution analysis suggests that g359.95-0.04 is likely the hard x-ray counterpart of the ultra-high gamma-ray source hess j1745-290, strongly favoring a leptonic origin of the gc tev emission. | nustar hard x-ray survey of the galactic center region i: hard x-ray morphology and spectroscopy of the diffuse emission |
> we review our high-time-resolution radio observations of the crab pulsar and compare our data to a variety of models for the emission physics. the main pulse and the low frequency interpulse come from regions somewhere in the high-altitude emission zones (caustics) that also produce pulsed x-ray and -ray emission. although no emission model can fully explain these two components, the most likely models suggest they arise from a combination of beam-driven instabilities, coherent charge bunching and strong electromagnetic turbulence. because the radio power fluctuates on a wide range of time scales, we know the emission zones are patchy and dynamic. it is tempting to invoke unsteady pair creation in high-altitude gaps as the source of the variability, but current pair cascade models cannot explain the densities required by any of the likely models. it is harder to account for the mysterious high frequency interpulse. we understand neither its origin within the magnetosphere nor the striking emission bands in its dynamic spectrum. the most promising models are based on analogies with solar zebra bands, but they require unusual plasma structures which are not part of our standard picture of the magnetosphere. we argue that radio observations can reveal much about the upper magnetosphere, but work is required before the models can address all of the data. | radio emission physics in the crab pulsar |
relic gravitational waves (rgws) generated in the early universe form a stochastic gw background, which can be directly probed by measuring the timing residuals of millisecond pulsars. in this paper, we investigate the constraints on the rgws and on the inflationary parameters by the observations of current and potential future pulsar timing arrays. in particular, we focus on effects of various cosmic phase transitions (e.g., e+e- annihilation, qcd transition, and supersymmetry breaking) and relativistic free-streaming gases (neutrinos and dark fluids) in the general scenario of the early universe, which have been neglected in the previous works. we find that the phase transitions can significantly damp the rgws in the sensitive frequency range of pulsar timing arrays, and the upper limits of the tensor-to-scalar ratio r increase by a factor ∼2 for both current and future observations. however, the effects of free-steaming neutrinos and dark fluids are all too small to be detected. meanwhile, we find that, if the effective equation of state w in the early universe is larger than 1 /3 , i.e., deviating from the standard hot big bang scenario, the detection of rgws by pulsar timing arrays becomes much more promising. | detecting relic gravitational waves by pulsar timing arrays: effects of cosmic phase transitions and relativistic free-streaming gases |
we report the discovery of two long-term intermittent radio pulsars in the ongoing pulsar arecibo l-band feed array survey. following discovery with the arecibo telescope, extended observations of these pulsars over several years at jodrell bank observatory have revealed the details of their rotation and radiation properties. psrs j1910+0517 and j1929+1357 show long-term extreme bimodal intermittency, switching between active (on) and inactive (off) emission states and indicating the presence of a large, hitherto unrecognized underlying population of such objects. for psr j1929+1357, the initial duty cycle was fon = 0.008, but two years later, this changed quite abruptly to fon = 0.16. this is the first time that a significant evolution in the activity of an intermittent pulsar has been seen, and we show that the spin-down rate of the pulsar is proportional to the activity. the spin-down rate of psr j1929+1357 is increased by a factor of 1.8 when it is in active mode, similar to the increase seen in the other three known long-term intermittent pulsars. these discoveries increase the number of known pulsars displaying long-term intermittency to five. these five objects display a remarkably narrow range of spin-down power (\dot{e} ∼ {10}32 {erg} {{{s}}}-1) and accelerating potential above their polar caps. if confirmed by further discoveries, this trend might be important for understanding the physical mechanisms that cause intermittency. | two long-term intermittent pulsars discovered in the palfa survey |
we combined chandra acis observations of the globular cluster 47 tucanae (47 tuc) from 2000, 2002 and 2014-2015 to create a deeper x-ray source list, and study some of the faint radio millisecond pulsars (msps) present in this cluster. we have detected 370 x-ray sources within the half-mass radius (2.79 arcsec) of the cluster, 81 of which are newly identified, by including new data and using improved source detection techniques. the majority of the newly identified sources are in the crowded core region, indicating cluster membership. we associate five of the new x-ray sources with chromospherically active by dra or w uma variables identified by albrow et al. we present alternative positions derived from two methods, centroiding and image reconstruction, for faint, crowded sources. we are able to extract x-ray spectra of the recently discovered msps 47 tuc aa, 47 tuc ab, the newly timed msp 47 tuc z, and the newly resolved msps 47 tuc s and 47 tuc f. generally, they are well fitted by blackbody or neutron star atmosphere models, with temperatures, luminosities and emitting radii similar to those of other known msps in 47 tuc, though 47 tuc aa and 47 tuc ab reach lower x-ray luminosities. we limit x-ray emission from the full surface of the rapidly spinning (542 hz) msp 47 tuc aa, and use this limit to put an upper bound for amplitude of r-mode oscillations in this pulsar as α < 2.5 × 10-9 and constrain the shape of the r-mode instability window. | chandra studies of the globular cluster 47 tucanae: a deeper x-ray source catalogue, five new x-ray counterparts to millisecond radio pulsars, and new constraints to r-mode instability window |
braking index measurements of young radio pulsars are all smaller than the value expected for spin-down by magnetic dipole braking. we investigate magnetic field evolution in the neutron star crust due to hall drift as an explanation for observed braking indices. using numerical simulations and a semi-analytic model, we show that an ≈1014 g quadrupolar toroidal field in the neutron star crust at birth leads to growth of the dipole moment at a rate large enough to agree with measured braking indices. a key factor is the density at which the crust yields to magnetic stresses that build up during the evolution, which sets a characteristic minimum hall time-scale. the observed braking indices of pulsars with inferred dipole fields of ≲ 1013 g can be explained in this picture, although with a significant octupole component needed in some cases. for the stronger field pulsars, those with bd ≳ 1013 g, we find that the magnetic stresses in the crust exceed the maximum shear stress before the pulsar reaches its current age, likely quenching the hall effect. this may have implications for the magnetar activity seen in the high magnetic field radio pulsar psr j1846-0258. observations of braking indices may therefore be a new piece of evidence that neutron stars contain subsurface toroidal fields that are significantly stronger than the dipole field, and may indicate that the hall effect is important in a wider range of neutron stars than previously thought. | hall drift and the braking indices of young pulsars |
an exact solution of two singularities in the teleparallel equivalent to general relativity theory has been obtained. a holographic visualization of the binary black holes (bbhs) space-time, due to the non vanishing torsion scalar field, has been given. the acceleration tensor of bbhs space-time has been calculated. the results identify the repulsive gravity zones of the bbhs field. the total conserved quantities of the bbhs has been evaluated. possible gravitational radiation emission by the system has been calculated without assuming a weak field initial data. | exact teleparallel gravity of binary black holes |
we have discovered 21 rotating radio transients (rrats) in data from the green bank telescope (gbt) 350 mhz drift-scan and the green bank north celestial cap pulsar surveys using a new candidate sifting algorithm. rrats are pulsars with sporadic emission that are detected through their bright single pulses rather than fourier domain searches. we have developed rrattrap, a single-pulse sifting algorithm that can be integrated into pulsar survey data analysis pipelines in order to find rrats and fast radio bursts. we have conducted follow-up observations of our newly discovered sources at several radio frequencies using the gbt and low frequency array, yielding improved positions and measurements of their periods, dispersion measures (dms), and burst rates, as well as phase-coherent timing solutions for four of them. the new rrats have dms ranging from 15 to 97 {pc} {{cm}}-3, periods of 240 ms to 3.4 s, and estimated burst rates of 20 to 400 pulses hr-1 at 350 mhz. we use this new sample of rrats to perform statistical comparisons between rrats and canonical pulsars in order to shed light on the relationship between the two populations. we find that the dm and spatial distributions of the rrats agree with those of the pulsars found in the same survey. we find evidence that slower pulsars (i.e., p\gt 200 ms) are preferentially more likely to emit bright single pulses than are faster pulsars (p\lt 200 ms), although this conclusion is tentative. our results are consistent with the proposed link between rrats, transient pulsars, and canonical pulsars as sources in various parts of the pulse activity spectrum. | discovery and follow-up of rotating radio transients with the green bank and lofar telescopes |
due to observational challenges, our knowledge of low-level accretion flows around neutron stars is limited. we present nustar, swift and chandra observations of the low-mass x-ray binary igr j17062-6143, which has been persistently accreting at ≃0.1 per cent of the eddington limit since 2006. our simultaneous nustar/swift observations show that the 0.5-79 kev spectrum can be described by a combination of a power law with a photon index of γ ≃ 2, a blackbody with a temperature of ktbb ≃ 0.5 kev (presumably arising from the neutron star surface) and disc reflection. modelling the reflection spectrum suggests that the inner accretion disc was located at rin ≳ 100 gm/c2 (≳225 km) from the neutron star. the apparent truncation may be due to evaporation of the inner disc into a radiatively-inefficient accretion flow, or due to the pressure of the neutron star magnetic field. our chandra gratings data reveal possible narrow emission lines near 1 kev that can be modelled as reflection or collisionally ionized gas, and possible low-energy absorption features that could point to the presence of an outflow. we consider a scenario in which this neutron star has been able to sustain its low accretion rate through magnetic inhibition of the accretion flow, which gives some constraints on its magnetic field strength and spin period. in this configuration, igr j17062-6143 could exhibit a strong radio jet as well as a (propeller-driven) wind-like outflow. | an in-depth study of a neutron star accreting at low eddington rate: on the possibility of a truncated disc and an outflow |
we present a comprehensive discussion about the origin of the features in the leptonic component of the cosmic-ray spectrum. working in the framework of a up-to-date cr transport scenario tuned on the most recent ams-02 and voyager data, we show that the prominent features recently found in the positron and in the all-electron spectra by several experiments are compatible with a scenario in which pulsar wind nebulae (pwne) are the dominant sources of the positron flux, and nearby supernova remnants (snrs) shape the high-energy peak of the electron spectrum. in particular we argue that the drop-off in positron spectrum found by ams-02 at ~ 300 gev can be explained—under different assumptions—in terms of a prominent pwn that provides the bulk of the observed positrons in the ~ 100 gev domain, on top of the contribution from a large number of older objects. finally, we turn our attention to the spectral softening at ~ 1 tev in the all-lepton spectrum, recently reported by several experiments, showing that it requires the presence of a nearby supernova remnant at its final stage. | features in cosmic-ray lepton data unveil the properties of nearby cosmic accelerators |
the dark matter particle explorer (dampe) is a satellite-borne, high-energy particle and -ray detector, which is dedicated to indirectly detecting particle dark matter and studying high-energy astrophysics. the first results about precise measurement of the cosmic ray electron plus positron spectrum between 25 gev and 4.6 tev were published recently. the dampe spectrum reveals an interesting spectral softening arount 0:9 tev and a tentative peak around 1:4 tev. these results have inspired extensive discussion. the detector of dampe, the data analysis, and the first results are introduced. in particular, the physical interpretations of the dampe data are reviewed. | dark matter particle explorer observations of high-energy cosmic ray electrons plus positrons and their physical implications |
we search for far-infrared counterparts of known supernova remnants (snrs) in the galactic plane (10° < |l| < 60°) at 70-500 μm using the herschel infrared galactic plane survey (hi-gal). of 71 sources studied, we find that 29 (41 per cent) snrs have a clear fir detection of dust emission associated with the snr. dust from 8 of these is in the central region, and 4 indicate pulsar wind nebulae (pwne) heated ejecta dust. a further 23 have dust emission in the outer shell structures which is potentially related to swept-up material. many galactic sne have dust signatures but we are biased towards detecting ejecta dust in young remnants and those with a heating source (shock or pwn). we estimate the dust temperature and mass contained within three pwne, g11.2-0.3, g21.5-0.9, and g29.7-0.3, using modified blackbody fits. to more rigorously analyse the dust properties at various temperatures and dust emissivity index β, we use point process mapping (ppmap). we find significant quantities of cool dust (at 20-40 k) with dust masses of md = 0.34 ± 0.14 m⊙, md = 0.29 ± 0.08 m⊙, and md = 0.51 ± 0.13 m⊙ for g11.2-0.3, g21.5-0.9, and g29.7-0.3, respectively. we derive the dust emissivity index for the pwn ejecta dust in g21.5-0.3 to be β = 1.4 ± 0.5 compared to dust in the surrounding medium where β = 1.8 ± 0.1. | a catalogue of galactic supernova remnants in the far-infrared: revealing ejecta dust in pulsar wind nebulae |
during the spin-up phase of a large pulsar glitch - a sudden decrease of the rotational period of a neutron star - the angular velocity of the star may overshoot, namely reach values greater than that observed for the new post-glitch equilibrium. these transient phenomena are expected on the basis of theoretical models for pulsar internal dynamics, and their observation has the potential to provide an important diagnostic for glitch modelling. in this article, we present a simple criterion to assess the presence of an overshoot, based on the minimal analytical model that is able to reproduce an overshooting spin-up. we employed it to fit the data of the 2016 glitch of the vela pulsar, obtaining estimates of the fractional moments of inertia of the internal superfluid components involved in the glitch, of the rise and decay timescales of the overshoot, and of the mutual friction parameters between the superfluid components and the normal one. we studied the cases with and without strong entrainment in the crust: in the former, we found an indication of a large inner core strongly coupled to the observable component, and of a reservoir of angular momentum extending into the core to densities below nuclear saturation; while in the latter, a large reservoir extending above nuclear saturation and a standard normal component without inner core were found. | core and crust contributions in overshooting glitches: the vela pulsar 2016 glitch |
due to their high magnetic fields and plasma densities, pulsars provide excellent laboratories for tests of beyond standard model (bsm) physics. when axions or axion-like particles (alps) approach closely enough to pulsars, they can be resonantly converted to photons, yielding dramatic electromagnetic signals. we discuss the possibility of detecting such signals from bound configurations of axions, colliding with pulsar magnetospheres. we find that all but the densest axion stars, oscillons, are tidally destroyed well before resonant conversion can take place. oscillons can be efficiently converted to photons, leading to bright, ephemeral radio flashes. observation of the galactic bulge using existing (very large array and lofar) and forthcoming (square kilometer array) radio missions has the potential to detect such events for axion masses in the range ma in [0.1 μev, 30 μev], even if oscillons make up a negligible fraction of dark matter. | resonant conversion of dark matter oscillons in pulsar magnetospheres |
cyclotron resonance scattering features observed in the spectra of some x-ray pulsars show significant changes of the line centroid energy with the pulsar luminosity. whereas for bright sources above the so-called critical luminosity, these variations are established to be connected with the appearance of the high-accretion column above the neutron star surface, at low, sub-critical luminosities the nature of the variations (but with the opposite sign) has not been discussed widely. we argue here that the cyclotron line is formed when the radiation from a hotspot propagates through the plasma falling with a mildly relativistic velocity on to the neutron star surface. the position of the cyclotron resonance is determined by the doppler effect. the change of the cyclotron line position in the spectrum with luminosity is caused by variations of the velocity profile in the line-forming region affected by the radiation pressure force. the presented model has several characteristic features: (i) the line centroid energy is positively correlated with the luminosity; (ii) the line width is positively correlated with the luminosity as well; (iii) the position and the width of the cyclotron absorption line are variable over the pulse phase; (iv) the line has a more complicated shape than widely used lorentzian or gaussian profiles; (v) the phase-resolved cyclotron line centroid energy and the width are negatively and positively correlated with the pulse intensity, respectively. the predictions of the proposed theory are compared with the variations of the cyclotron line parameters in the x-ray pulsar gx 304-1 over a wide range of sub-critical luminosities as seen by the integral observatory. | positive correlation between the cyclotron line energy and luminosity in sub-critical x-ray pulsars: doppler effect in the accretion channel |
we present a new class of solutions to the einstein's field equations corresponding to a static spherically symmetric anisotropic system by generalizing the ansatz of finch and skea [class. quantum grav. 6:467, 1989] for the gravitational potential grr . the anisotropic stellar model previously studied by sharma and ratanpal [int. j. mod. phys. d 13:1350074, 2013] is a sub-class of the solutions provided here. based on physical requirements, regularity conditions and stability, we prescribe bounds on the model parameters. by systematically fixing values of the model parameters within the prescribed bound, we demonstrate that our model is compatible with the observed masses and radii of a wide variety of compact stars like 4u 1820-30, psr j1903+327, 4u 1608-52, vela x-1, psr j1614-2230, sax j1808.4-3658 and her x-1. | modified finch and skea stellar model compatible with observational data |
it is difficult to discover pulsars via their gamma-ray emission because current instruments typically detect fewer than one photon per million rotations. this creates a significant computing challenge for isolated pulsars, where the typical parameter search space spans wide ranges in four dimensions. it is even more demanding when the pulsar is in a binary system, where the orbital motion introduces several additional unknown parameters. building on earlier work by pletsch & clark, we present optimal methods for such searches. these can also incorporate external constraints on the parameter space to be searched, for example, from optical observations of a presumed binary companion. the solution has two parts. the first is the construction of optimal search grids in parameter space via a parameter space metric, for initial semicoherent searches and subsequent fully coherent follow-ups. the second is a method to demodulate and detect the periodic pulsations. these methods have different sensitivity properties than traditional radio searches for binary pulsars and might unveil new populations of pulsars. | exploiting orbital constraints from optical data to detect binary gamma-ray pulsars |
we model millisecond pulsar winds colliding with radiatively driven companion winds in black widow and redback systems. for the redbacks, the geometry of this intrabinary shock (ibs) is quite sensitive to the expected equatorial concentration in the pulsar outflow. we thus analytically extend ibs thin-shock models to ∼ {\sin }2nθ pulsar winds. we compute the synchrotron emission from such shocks, including the buildup and cooling of the particle population as it accelerates along the ibs. for reasonable parameters, this ibs flux dominates the binary emission in the x-ray band. the modeling shows subtle variation in spectrum across the ibs peak, accessible to sensitive x-ray studies. as example applications, we fit archival cxo/xmm data from the black widow pulsar j1959+2048 and the redback psr j2339-0533, finding that the model reproduces well the orbital light-curve profiles and energy spectra. the results show a very hard injected electron spectrum, indicating likely dominance by reconnection. the light-curve fitting is sensitive to the geometric parameters, including the very important orbital inclination i. coupled with optical fits of the companion star, such ibs x-ray light-curve modeling can strongly constrain the binary geometry and the energetics of the millisecond pulsar wind. | the synchrotron emission pattern of intrabinary shocks |
motivated by the neutron lifetime puzzle, it is proposed that neutrons may decay into new states yet to be observed. we review the neutron star constraints on dark fermions carrying unit baryon number with masses around 939 mev, and discuss the interaction strengths required for the new particle. the possibility of neutrons decaying into three dark fermions is investigated. while up to six flavors of dark quarks with masses around 313 mev can be compatible with massive pulsars, any such exotic states lighter than about 270 mev are excluded by the existence of low-mass neutron stars around ∼1.2m⊙. light dark quarks in the allowed mass range may form a halo surrounding normal neutron stars. we discuss the potential observable signatures of the halo during binary neutron star mergers. | neutron star constraints on neutron dark decays |
the exploration of the lunar south polar region and the ground truthing of polar volatiles is one of the top priorities for several space agencies and private partners. here we use moon mineralogy mapper surficial water ice detections to investigate the location of water-ice-bearing permanently shaded regions (psrs) near the south pole. we extract a variety of parameters such as their temperature regime, slope, hydrogen content, number of ice detections, depth stability for water ice and dry ice, and mobility aspects. we identify 169 water-ice-bearing psrs and use their characteristics to identify sites that allow us to access the highest abundances of volatiles, sites that can be visited to characterize the lateral or vertical distribution of volatiles (water ice and dry ice), and sites that allow for the fastest recovery of a scientifically interesting sample. collectively, 37 psrs are identified as sites of interest, including 11 that would address more than one mission objective and may be, for that reason, higher-priority targets of exploration. these psrs are found in shoemaker, faustini, cabeus, malapert, nobile, sverdrup, wiechert j, and haworth craters, as well as three unnamed craters (psrs 57, 120, and 89). these sites are all located within 6° of the south pole. we present case studies for a relatively short traverse mission (20-50 km) to psr 89, a medium-length traverse (∼100 km) to sverdrup 1, and a longer traverse (∼300 km) to cabeus that can serve as a guide in planning upcoming exploration missions. | framework for coordinated efforts in the exploration of volatiles in the south polar region of the moon |
we discuss the unique spin evolution of the young x-ray pulsar psr j0537-6910, a system in which the regular spin down is interrupted by glitches every few months. drawing on the complete timing data from the rossi x-ray timing explorer (from 1999 to 2011), we argue that a trend in the interglitch behavior points to an effective braking index close to n = 7, which is much larger than expected. this value is interesting because it would accord with the neutron star spinning down due to gravitational waves from an unstable r-mode. we discuss to what extent this, admittedly speculative, scenario may be consistent and if the associated gravitational-wave signal would be within reach of ground-based detectors. our estimates suggest that one may, indeed, be able to use future observations to test the idea. further precision timing would help to enhance the achievable sensitivity, and we advocate a joint observing campaign between the neutron star interior composition explorer and the ligo-virgo network. | the enigmatic spin evolution of psr j0537-6910: r-modes, gravitational waves, and the case for continued timing |
context. globular clusters (gcs) contain a unique pulsar population, with many exotic systems that can form only in their dense stellar environments. such systems are potentially very interesting for new tests of gravity theories and neutron-star mass measurements.aims: the leap in sensitivity of the upgraded giant metrewave radio telescope (ugmrt) in india, especially at low radio frequencies (< 1 ghz), motivated a new search for radio pulsars in a group of eight southern gcs. we aim to image these clusters in order to have independent measurements of the radio fluxes of known pulsars and the identification of bright radio sources that could be pulsars missed by pulsation search pipelines due to their inherent limitations.methods: the observations were conducted at 650 mhz (band 4 receivers) on terzan 5, ngc 6441, ngc 6440, and ngc 6544, and at 400 mhz (band 3 receivers) on ngc 6652, ngc 6539, ngc 1851, and m 30. segmented acceleration and jerk searches were performed on the data. simultaneously, we obtained interferometric data on these clusters, which were later converted into radio images.results: we discovered psr j1835−3259b, a 1.83-ms pulsar in ngc 6652; this is in a near-circular wide orbit of 28.7-h with an unidentified low-mass (∼0.2 m⊙) companion, likely a helium white dwarf. we derived a ten-year timing solution for this system. we also present measurements of scattering, flux densities, and spectral indices for some of the previously known pulsars in these gcs.conclusions: a significant fraction of the pulsars in these clusters have steep spectral indices. additionally, we detected eight radio point sources not associated with any known pulsar positions in the radio images. there are four newly identified sources, three in ngc 6652 and one in ngc 6539, as well as one previously identified source in ngc 1851, ngc 6440, ngc 6544, and terzan 5. surprisingly, our images show that our newly discovered pulsar, psr j1835−3259b, is the brightest pulsar in all gcs we have imaged; like other pulsars with broad profiles (terzan 5 c and o), its flux density in the radio images is much larger than in its pulsations. this indicates that their pulsed emission is only a fraction of their total emission. the detection of radio sources outside the core radii but well within the tidal radii of these clusters show that future gc surveys should complement the search analysis by using the imaging capability of interferometers, and preferentially synthesise large number of search beams in order to obtain a larger field of view. | upgraded gmrt survey for pulsars in globular clusters. i. discovery of a millisecond binary pulsar in ngc 6652 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.