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we examine the cosmological and astrophysical signatures of a "dark baryon," a neutral fermion that mixes with the neutron. as the mixing is through a higher-dimensional operator at the quark level, production of the dark baryon at high energies is enhanced so that its abundance in the early universe may be significant. treating its initial abundance as a free parameter, we derive new, powerful limits on the properties of the dark baryon. primordial nucleosynthesis and the cosmic microwave background provide strong constraints due to the interconversion of neutrons to dark baryons through their induced transition dipole, and due to late decays of the dark baryon. additionally, neutrons in a neutron star could decay slowly to dark baryons, providing a novel source of heat that is constrained by measurements of pulsar temperatures. taking all the constraints into account, we identify parameter space where the dark baryon can be a viable dark matter candidate and discuss promising avenues for probing it. | cosmological and astrophysical probes of dark baryons |
the spacetime surrounding compact objects such as neutron stars and black holes provides an excellent place to study gravity in the strong, nonlinear, dynamical regime. here, the effects of strong curvature can leave their imprint on observables which we may use to study gravity. recently, nicer provided a mass and radius measurement of an isolated neutron star using x-rays, while ligo/virgo measured the tidal deformability of neutron stars through gravitational waves. these measurements can be used to test the relation between the tidal deformability and compactness of neutron stars that are known to be universal in general relativity. here, we take (shift-symmetric) scalar-gauss-bonnet gravity (motivated by a low-energy effective theory of a string theory) as an example and study whether one can apply the nicer and ligo/virgo measurements to the universal relation to test the theory. to do so, this paper is mostly devoted on theoretically constructing tidally deformed neutron star solutions in this theory perturbatively and calculate the tidal deformability for the first time. we find that the relation between the tidal deformability and compactness remains to be mostly universal for a fixed dimensionless coupling constant of the theory though the relation is different from the one in general relativity. we also present a universal relation between the tidal deformability of one neutron star and the compactness for another neutron star that can be directly applied to observations by ligo/virgo and nicer. for the equations of state considered in this paper, it is still inconclusive whether one can place a meaningful bounds on scalar gauss-bonnet gravity with the new universal relations. however, we found a new bound from the mass measurement of the pulsar j 0740 +6620 that is comparable to other existing bounds from black hole observations. | tidal deformabilities of neutron stars in scalar-gauss-bonnet gravity and their applications to multimessenger tests of gravity |
background: we analyze several constraints on the nuclear equation of state (eos) currently available from neutron star (ns) observations and laboratory experiments and study the existence of possible correlations among properties of nuclear matter at saturation density with ns observables. methods: we use a set of different models that include several phenomenological eoss based on skyrme and relativistic mean field models as well as microscopic calculations based on different many-body approaches, i.e., the (dirac–)brueckner–hartree–fock theories, quantum monte carlo techniques, and the variational method. results: we find that almost all the models considered are compatible with the laboratory constraints of the nuclear matter properties as well as with the largest ns mass observed up to now, 2.14‑0.09+0.10m⊙ for the object psr j0740+6620, and with the upper limit of the maximum mass of about 2.3–2.5m⊙ deduced from the analysis of the gw170817 ns merger event. conclusion: our study shows that whereas no correlation exists between the tidal deformability and the value of the nuclear symmetry energy at saturation for any value of the ns mass, very weak correlations seem to exist with the derivative of the nuclear symmetry energy and with the nuclear incompressibility. | a modern view of the equation of state in nuclear and neutron star matter |
a first-order mev-scale cosmological phase transition (pt) can generate a peak in the power spectrum of stochastic gravitational wave background around nanohertz frequencies. with the recent international pulsar timing array data release two covering nanohertz frequencies, we search for such a phase transition signal. for the standard 4-parameter pt model, we obtain the pt temperature $t_\star\in$ [66 mev, 30 gev], which indicates that dark or qcd phase transitions occurring below 66 mev have been ruled out at $2\,\sigma$ confidence level. this constraint is much tighter than $t_\star\sim$ [1 mev, 100 gev] from nanograv. we also give much tighter $2\,\sigma$ bounds on the pt duration $h_\star/\beta>0.1$, strength $\alpha_\star>0.39$ and friction $\eta<2.74$ than nanograv. for the first time, we find a positive correlation between $\mathrm{log}_{10}t_\star$ and $\mathrm{log}_{10}h_\star/\beta$ implying that pt temperature increases with increasing bubble nucleation rate. to avoid large theoretical uncertainties in calculating pt spectrum, we make bubble spectral shape parameters $a$, $b$, $c$ and four pt parameters free together, and confront this model with data. we find that pulsar timing is very sensitive to the parameter $a$, and give the first clear constraint $a=1.27_{-0.54}^{+0.71}$ at $1\,\sigma$ confidence level. | squeezing cosmological phase transitions with international pulsar timing array |
we study the asymptotically flat spacetime in chern-simons modified gravity and then gravitational memory effects are considered in this work. if the chern-simons scalar does not directly couple with the ordinary matter fields, there are also displacement, spin, and center-of-mass memory effects as in general relativity. this is because the term of the action that violates the parity invariance is linear in the scalar field but quadratic in the curvature tensor. this results in the parity violation occurring at the higher orders in the inverse luminosity radius. although there exists the chern-simons scalar field, interferometers, pulsar timing arrays, and the gaia mission are incapable of detecting its polarization, so the scalar field does not induce any new memory effects that can be detected by interferometers or pulsar timing arrays. the asymptotic symmetry group is also the extended bondi-metzner-sachs group. the constraints on the memory effects excited by the tensor modes are obtained as well. | asymptotic analysis of chern-simons modified gravity and its memory effects |
this manuscript investigates the compact stars solutions in the background of observational data (radii and mass) by employing the karmarkar condition under the f(g , t) modified gravity for an anisotropic source of fluid. for this study, we have assumed a specific model for grr metric potential function, which has fulfilled the karmarkar condition. this assuming model helps to calculate another metric function gtt by using the karmarkar condition scenario. further, this study deals to discuss the necessary physically properties by using the observational data for 4u 1538-52, lmc x-4, and psr j1614-2230 models with three different values of parameter β. it is depicted from this current study; the calculated solutions are physically acceptable with best degree of accuracy. all the physically necessary relevant parameters and properties compact stars are presented graphically. it is noticed during this study the parameter β, has some importance and considerable role for these calculated solutions. in the end, it is concluded that our obtained solutions are physically arguable with well-behaved nature for f(g , t) modified gravity for these discussed compact stars. | realistic solutions of fluid spheres in f(g , t) gravity under karmarkar condition |
for decades, observations of faraday rotation have provided unique insights into the plasma density and magnetic field structure of the solar wind. faraday rotation (fr) is the rotation of the plane of polarization when linearly polarized radiation propagates through a magnetized plasma, such as the solar corona, coronal mass ejection (cme), or stream interaction region. fr measurements are very versatile: they provide a deeper understanding of the large-scale coronal magnetic field over a range of heliocentric distances (especially ≈1.5 to 20 r⊙) not typically accessible to in situ spacecraft observations; detection of small-timescale variations in fr can provide information on magnetic field fluctuations and magnetohydrodynamic wave activity; and measurement of differential fr can be used to detect electric currents. fr depends on the integrated product of the plasma density and the magnetic field component along the line of sight to the observer; historically, models have been used to distinguish between their contributions to fr. in the last two decades, though, new methods have been developed to complement fr observations with independent measurements of the plasma density based on the choice of background radio source: calculation of the dispersion measure (pulsars), measurement of thomson scattering brightness (radio galaxies), and application of radio ranging and apparent-doppler tracking (spacecraft). new methods and new technology now make it possible for fr observations of solar wind structures to return not only the magnitude of the magnetic field, but also the full vector orientation. in the case of a cme, discerning the internal magnetic flux rope structure is critical for space weather applications. | modern faraday rotation studies to probe the solar wind |
we reconsider the problem of the hyperon puzzle and its suggested solution by quark deconfinement within the two-phase approach to hybrid compact stars with recently obtained hadronic and quark matter equations of state. for the hadronic phase we employ the hypernuclear equation of state from the lowest order constrained variational method and the quark matter phase is described by a sufficiently stiff equation of state based on a color superconducting nonlocal nambu-jona-lasinio model with constant (model nlnjla) and with density-dependent (model nlnjlb) parameters. we study the model dependence of the phase transition obtained by a maxwell construction. our study confirms that also with the present set of equations of state quark deconfinement presents a viable solution of the hyperon puzzle even for the new constraint on the lower limit of the maximum mass from psr j 0740 +6620 . in this work we provide with model nlnjlb for the first time a hybrid star eos with an intermediate hypernuclear matter phase between the nuclear and color superconducting quark matter phases, for which the maximum mass of the compact star reaches 2.2 m⊙ , in accordance with most recent constraints. in model nlnjla such a phase cannot be realized because the phase transition onset is at low densities, before the hyperon threshold density is passed. we discuss possible consequences of the hybrid equation of state for the deconfinement phase transition in symmetric matter as it will be probed in future heavy-ion collisions at the gsi facility for antiproton and ion research, the nuclotron-based ion collider facility, and corresponding energy scan programs at the cern large hadron collider and the bnl relativistic heavy ion collider. | first-order phase transition from hypernuclear matter to deconfined quark matter obeying new constraints from compact star observations |
pulsar wind nebulae, blazars, gamma ray bursts and magnetars all contain regions where the electromagnetic energy density greatly exceeds the plasma energy density. these sources exhibit dramatic flaring activity where the electromagnetic energy distributed over large volumes, appears to be converted efficiently into high energy particles and γ -rays. we call this general process magnetoluminescence. global requirements on the underlying, extreme particle acceleration processes are described and the likely importance of relativistic beaming in enhancing the observed radiation from a flare is emphasized. recent research on fluid descriptions of unstable electromagnetic configurations are summarized and progress on the associated kinetic simulations that are needed to account for the acceleration and radiation is discussed. future observational, simulation and experimental opportunities are briefly summarized. | magnetoluminescence |
in this work we explore the evolution of magnetic fields inside strongly magnetized neutron stars in axisymmetry. we model numerically the coupled field evolution in the core and the crust. our code models the hall drift and ohmic effects in the crust, the back-reaction on the field from magnetically induced elastic deformation of the crust, the magnetic twist exchange between the crust and the core, and the drift of superconducting flux tubes inside the core. the correct hydromagnetic equilibrium is enforced in the core. we find that (i) the hall attractor found by gourgouliatos and cumming in the crust exists also for configurations when the b-field penetrates into the core. however, the evolution time-scale for the core-penetrating fields is dramatically different from that of the fields confined to the crust. (ii) the combination of jones' flux tube drift and ohmic dissipation in the crust can deplete the pulsar magnetic fields on the time-scale of 150 myr if the crust is hot (t ∼ 2 × 108 k), but acts on much slower time-scales for cold neutron stars, such as recycled pulsars (∼1.8 gyr, depending on impurity levels). (iii) the outward motion of superfluid vortices during the rapid spin-down of a young highly magnetized pulsar can result in a partial expulsion of flux from the core when b ≲ 1013 g. however for b ≳ 2 × 1013 g, the combination of a stronger magnetic field and a longer spin period implies that the core field cannot be expelled. | magnetic field evolution of neutron stars - i. basic formalism, numerical techniques and first results |
we apply collisionless particle-in-cell simulations of relativistic pair plasmas to explore whether driven turbulence is a viable high-energy astrophysical particle accelerator. we characterize nonthermal particle distributions for varying system sizes up to l/2πρe0 = 163, where l/2π is the driving scale and ρe0 is the initial characteristic larmor radius. we show that turbulent particle acceleration produces power-law energy distributions that, when compared at a fixed number of large-scale dynamical times, slowly steepen with increasing system size. we demonstrate, however, that convergence is obtained by comparing the distributions at different times that increase with system size (approximately logarithmically). we suggest that the system-size dependence arises from the time required for particles to reach the highest accessible energies via fermi acceleration. the converged power-law index of the energy distribution, α ≈ 3.0 for magnetization σ = 3/8, makes turbulence a possible explanation for nonthermal spectra observed in systems such as the crab nebula. | system-size convergence of nonthermal particle acceleration in relativistic plasma turbulence |
popular models of repeating fast radio bursts (frbs; and perhaps of all frbs) involve neutron stars because of their high rotational or magnetostatic energy densities. these models take one of two forms: giant but rare pulsar-like pulses like those of rotating radio transients, and outbursts like those of soft gamma repeaters. here i collate the evidence, recently strengthened, against these models, including the absence of galactic micro-frbs, and attribute the 16 d periodicity of frb 180916.j0158+65 to the precession of a jet produced by a massive black hole's accretion disc. | are fast radio bursts made by neutron stars? |
we present global fits of an effective field theory description of real, and complex scalar dark matter candidates. we simultaneously take into account all possible dimension 6 operators consisting of dark matter bilinears and gauge invariant combinations of quark and gluon fields. we derive constraints on the free model parameters for both the real (five parameters) and complex (seven) scalar dark matter models obtained by combining planck data on the cosmic microwave background, direct detection limits from lux, and indirect detection limits from the fermi large area telescope. we find that for real scalars indirect dark matter searches disfavour a dark matter particle mass below 100 gev. for the complex scalar dark matter particle current data have a limited impact due to the presence of operators that lead to p-wave annihilation, and also do not contribute to the spin-independent scattering cross-section. although current data are not informative enough to strongly constrain the theory parameter space, we demonstrate the power of our formalism to reconstruct the theoretical parameters compatible with an actual dark matter detection, by assuming that the excess of gamma rays observed by the fermi large area telescope towards the galactic centre is entirely due to dark matter annihilations. please note that the excess can very well be due to astrophysical sources such as millisecond pulsars. we find that scalar dark matter interacting via effective field theory operators can in principle explain the galactic centre excess, but that such interpretation is in strong tension with the non-detection of gamma rays from dwarf galaxies in the real scalar case. in the complex scalar case there is enough freedom to relieve the tension. | effective field theory of dark matter: a global analysis |
we present techniques developed to calibrate and correct murchison widefield array low-frequency (72-300 mhz) radio observations for polarimetry. the extremely wide field-of-view, excellent instantaneous (u, v)-coverage and sensitivity to degree-scale structure that the murchison widefield array provides enable instrumental calibration, removal of instrumental artefacts, and correction for ionospheric faraday rotation through imaging techniques. with the demonstrated polarimetric capabilities of the murchison widefield array, we discuss future directions for polarimetric science at low frequencies to answer outstanding questions relating to polarised source counts, source depolarisation, pulsar science, low-mass stars, exoplanets, the nature of the interstellar and intergalactic media, and the solar environment. | the challenges of low-frequency radio polarimetry: lessons from the murchison widefield array |
we describe directed searches for continuous gravitational waves (gws) in data from the sixth laser interferometer gravitational-wave observatory (ligo) science data run. the targets were nine young supernova remnants not associated with pulsars; eight of the remnants are associated with non-pulsing suspected neutron stars. one target's parameters are uncertain enough to warrant two searches, for a total of 10. each search covered a broad band of frequencies and first and second frequency derivatives for a fixed sky direction. the searches coherently integrated data from the two ligo interferometers over time spans from 5.3-25.3 days using the matched-filtering {f}-statistic. we found no evidence of gw signals. we set 95% confidence upper limits as strong (low) as 4 × 10-25 on intrinsic strain, 2 × 10-7 on fiducial ellipticity, and 4 × 10-5 on r-mode amplitude. these beat the indirect limits from energy conservation and are within the range of theoretical predictions for neutron-star ellipticities and r-mode amplitudes. | searches for continuous gravitational waves from nine young supernova remnants |
context. lofar offers the unique capability of observing pulsars across the 10-240 mhz frequency range with a fractional bandwidth of roughly 50%. this spectral range is well suited for studying the frequency evolution of pulse profile morphology caused by both intrinsic and extrinsic effects such as changing emission altitude in the pulsar magnetosphere or scatter broadening by the interstellar medium, respectively.aims: the magnitude of most of these effects increases rapidly towards low frequencies. lofar can thus address a number of open questions about the nature of radio pulsar emission and its propagation through the interstellar medium.methods: we present the average pulse profiles of 100 pulsars observed in the two lofar frequency bands: high band (120-167 mhz, 100 profiles) and low band (15-62 mhz, 26 profiles). we compare them with westerbork synthesis radio telescope (wsrt) and lovell telescope observations at higher frequencies (350 and 1400 mhz) to study the profile evolution. the profiles were aligned in absolute phase by folding with a new set of timing solutions from the lovell telescope, which we present along with precise dispersion measures obtained with lofar.results: we find that the profile evolution with decreasing radio frequency does not follow a specific trend; depending on the geometry of the pulsar, new components can enter into or be hidden from view. nonetheless, in general our observations confirm the widening of pulsar profiles at low frequencies, as expected from radius-to-frequency mapping or birefringence theories. we offer this catalogue of low-frequency pulsar profiles in a user friendly way via the epn database of pulsar profiles, http://www.epta.eu.org/epndb/ | wide-band, low-frequency pulse profiles of 100 radio pulsars with lofar |
context. many energetic supernovae (sne) are thought to be powered by the rotational energy of a highly magnetized, rapidly rotating neutron star. the emission from the associated luminous pulsar wind nebula (pwn) can photoionize the sn ejecta, leading to a nebular spectrum of the ejecta with signatures that might reveal the pwn. sn 2012au is hypothesized to be one such sn.aims: we investigate the impact of different ejecta and pwn parameters on the sn nebular spectrum, and test whether any photoionization models are consistent with sn 2012au. we study how constraints from the nebular phase can be linked into modeling of the diffusion phase and the radio emission of the magnetar.methods: we present a suite of late-time (1-6 yr) spectral simulations of sn ejecta powered by an inner pwn. over a large grid of one-zone models, we study the behavior of the physical state and line emission of the sn as the pwn luminosity (lpwn), the injected spectral energy distribution (sed) temperature (tpwn), the ejecta mass (mej), and the composition (pure o or realistic) vary. we discuss the resulting emission in the context of the observed behavior of sn 2012au, a strong candidate for a pwn-powered sn. we used optical light-curve models and broadband pwn models to predict possible radio emission from sn 2012au.results: the sn nebular spectrum varies as tpwn varies because the ejecta become less ionized as tpwn increases. ejecta models with low mass and high pwn power obtain runaway ionization for o i, and in extreme cases, also o ii, causing a sharp decrease in their ion fraction over a small change in the parameter space. certain models can reproduce the oxygen line luminosities of sn 2012au reasonably well at individual epochs, but we find no model that fits over the whole time evolution. this is likely due to uncertainties and simplifications in the model setup. using our derived constraints from the nebular phase, we predict that the magnetar powering sn 2012au had an initial rotation period ~15 ms, and it is expected to be a strong radio source (f > 100 μjy) for decades. | toward nebular spectral modeling of magnetar-powered supernovae |
pulsars have been identified as good candidates for the acceleration of cosmic rays, up to ultra-high energies. however, a precise description of the acceleration processes at play is still to be established. using 2d particle-in-cell simulations, we study proton acceleration in axisymmetric pulsar magnetospheres. protons and electrons are extracted from the neutron star surface by the strong electric field induced by the rotation of the star, and electrons and positrons are produced in the magnetosphere through pair production process. as pair production has a crucial impact on electromagnetic fields, on gaps and thus on particle acceleration, we study its influence on the maximum energy and luminosity of protons escaping the magnetosphere. protons are accelerated and escape in all our simulations. however, the acceleration sites are different for the protons and the pairs. as shown in previous studies, pairs are accelerated to their highest energies at the y-point and in the equatorial current sheet, where magnetic reconnection plays an important role. in contrast, protons gain most of their kinetic energy below the light-cylinder radius within the separatrix current layers, but they are not confined within the equatorial current sheet. their maximum lorentz factors can reach 15% to 75% of the maximum lorentz factor obtained by acceleration through the full vacuum potential drop from pole to equator, and increase with decreasing pair production. their luminosity can reach 0.2% to 4% of the theoretical spin down luminosity of an aligned pulsar, and the minimum luminosity is obtained at the transition between the force-free and electrosphere regimes. these estimates support that millisecond pulsars could accelerate cosmic rays up to pev energies and that new born millisecond pulsars could accelerate cosmic rays up to ultra-high energies. | proton acceleration in pulsar magnetospheres |
the north american nanohertz observatory for gravitational waves (nanograv) collaboration has recently reported strong evidence for a stochastic process affecting the 12.5 yr dataset of pulsar timing residuals. we show that the signal can be interpreted in terms of a stochastic gravitational wave background emitted from a network of axionic strings in the early universe. the spontaneous breaking of the peccei-quinn symmetry originate the axionic string network and the qcd axion, the dark matter particle in the model. we explore a nonstandard cosmological model driven by an exotic scalar field ϕ which evolves under the influence of a self-interacting potential; the axion field starts to oscillate during the modified cosmology, and provides the dark matter observed. for an equation of state wϕ<1 /3 , the qcd axion mass is smaller than expected in the standard cosmology and the gw spectrum from axionic strings is larger. we assess the parameter space of the model which is consistent with the nanograv-12.5 yr detection, which can be explained within 95% limit by a qcd axion field evolving in a dust-like scenario, as well as within 68% limit in a cosmology with wϕ<0 . | qcd axion and gravitational waves in light of nanograv results |
we explore the potential of pulsar timing arrays (ptas) such as nanograv, epta, and ppta to detect the stochastic gravitational wave background in theories of massive gravity. in general relativity, the function describing the dependence of the correlation between the arrival times of signals from two pulsars on the angle between them is known as the hellings-downs curve. we compute the analogous overlap reduction function for massive gravity, including the additional polarization states and the correction due to the mass of the graviton, and compare the result with the hellings-downs curve. the primary result is a complete analytical form for the analog hellings-downs curve, providing a starting point for future numerical studies aimed at a detailed comparison between pta data and the predictions of massive gravity. we study both the massless limit and the stationary limit as checks on our calculation, and discuss how our formalism also allows us to study the impact of massive spin-2 dark matter candidates on data from ptas. | detecting the stochastic gravitational wave background from massive gravity with pulsar timing arrays |
after large galaxies merge, their central supermassive black holes are expected to form binary systems. their orbital motion should generate a gravitational wave background (gwb) at nanohertz frequencies. searches for this background use pulsar timing arrays, which perform long-term monitoring of millisecond pulsars at radio wavelengths. we used 12.5 years of fermi large area telescope data to form a gamma-ray pulsar timing array. results from 35 bright gamma-ray pulsars place a 95% credible limit on the gwb characteristic strain of 1.0 × 10−14 at a frequency of 1 year–1. the sensitivity is expected to scale with tobs, the observing time span, as tobs−13/6. this direct measurement provides an independent probe of the gwb while offering a check on radio noise models. | a gamma-ray pulsar timing array constrains the nanohertz gravitational wave background |
observations of optical and near-infrared counterparts of binary neutron star mergers not only enrich our knowledge about the abundance of heavy elements in the universe and help reveal the remnant object just after the merger, which is generally known, but can also effectively constrain the dense properties of the nuclear matter and the equation of state (eos) in the interior of the merging stars. following the relativistic mean-field description of nuclear matter, we perform a bayesian inference of the eos and the properties of the nuclear matter using the first multi-messenger event gw170817/at2017gfo, together with the nicer mass-radius measurements of pulsars. the kilonova is described by a radiation-transfer model with the dynamical ejecta, and light curves connect with the eos through the quasi-universal relations between the properties of the ejecta (the ejected mass, velocity, opacity, or electron fraction) and binary parameters (the mass ratio and reduced tidal deformability). it is found that the posterior distributions of the reduced tidal deformability from the at2017gfo analysis display a bimodal structure, with the first peak enhanced by the gw170817 data, leading to slightly softened posterior eoss, while the second peak cannot be achieved by a nuclear eos with saturation properties in their empirical ranges. the inclusion of nicer data results in a stiffened eos posterior because of the massive pulsar psr j0740+6620. we provide the results at nuclear saturation density for the nuclear incompressibility, the symmetry energy, and its slope, as well as the nucleon effective mass, from our analysis of the observational data. | a bayesian inference of a relativistic mean-field model of neutron star matter from observations of nicer and gw170817/at2017gfo |
we analysed the thermal emission from the entire surface of the millisecond pulsar psr j0437-4715 observed in the ultraviolet and soft x-ray bands. for this, we calculated non-magnetized, partially ionized atmosphere models of hydrogen, helium, and iron compositions and included plasma frequency effects that may affect the emergent spectrum. this is particularly true for the coldest atmospheres composed of iron (up to a few per cent changes in the soft x-ray flux). employing a markov chain monte carlo method, we found that the spectral fits favour a hydrogen atmosphere, disfavour a helium composition, and rule out iron atmosphere and blackbody models. by using a gaussian prior on the dust extinction, based on the latest 3d map of galactic dust, and accounting for the presence of hot polar caps found in the previous work, we found that the hydrogen atmosphere model results in a well-constrained neutron star radius {r_ns}= 13.6^{+0.9}_{-0.8}{ km} and bulk surface temperature t_eff^{∞}=(2.3± 0.1){× 105}{ k}. this relatively large radius favours a stiff equation of state and disfavours a strange quark composition inside neutron stars. | neutron star radius measurement from the ultraviolet and soft x-ray thermal emission of psr j0437-4715 |
neutron stars (ns)s are astrophysical objects with strong gravitational and electromagnetic fields. since there are several effects on radiation processes around the star, it is impossible to consider whole effects all together. one way to study the processes is by considering them one by one as a toy model. in this paper, we have investigated the effects of spacetime deformation on the surface magnetic field of the slowly rotating neutron star and its plasma magnetospheric processes, such as the plasma magnetosphere formation around the star. at first, the approximate vacuum solutions of the maxwell equations for the electromagnetic fields of a magnetized neutron star in a slowly rotating deformed spacetime metric have been obtained. it has been shown that the positive deformation parameter leads to an increase in the value of the (surface) magnetic field at the near zone of the neutron star, while the effect of the negative deformation parameter is vice versa. we have also considered the electric field of the slowly rotating neutron star in the spacetime. in the slow rotation approximation, we have studied the particle acceleration in the polar cap zone, considering the effect of deformation of spacetime on the γ-lorentz factor of a relativistic charged particle. it is shown that in the case of the positive deformation, an additional gravity occurs around the ns. the effects of spacetime deformation on magneto-dipolar radiation of radio pulsars and polar cap size have also been studied and shown that negative deformation of spacetime increased the radiation luminosity and as positive deformation increases, the luminosity decreases. size of polar cap region of a neutron star, where magnetic field lines open, increases with increasing the value of the deformation parameter 𝜖. moreover, we have studied the influence of the spacetime deformation on the death line for radio pulsar, which separates the region in p-p˙ (b - p) diagram, where the pulsar can or cannot radiate in radio band (create pair production) through inverse compton scattering (ics). it is shown that the negative (positive) deformation shifts upward (downward) the death line, which means that even a small negative (positive) deformation of spacetime may cause to be radio-quite (be radio load) the radio pulsar which is lying on the death line (in p-p˙ diagram) in the gr frame with its corresponding parameters. | particle acceleration and electromagnetic field of deformed neutron stars |
the particle-in-cell (pic) method has been developed by oscar buneman, charles birdsall, roger w. hockney, and john dawson in the 1950s and, with the advances of computing power, has been further developed for several fields such as astrophysical, magnetospheric as well as solar plasmas and recently also for atmospheric and laser-plasma physics. currently more than 15 semi-public pic codes are available which we discuss in this review. its applications have grown extensively with increasing computing power available on high performance computing facilities around the world. these systems allow the study of various topics of astrophysical plasmas, such as magnetic reconnection, pulsars and black hole magnetosphere, non-relativistic and relativistic shocks, relativistic jets, and laser-plasma physics. we review a plethora of astrophysical phenomena such as relativistic jets, instabilities, magnetic reconnection, pulsars, as well as pic simulations of laser-plasma physics (until 2021) emphasizing the physics involved in the simulations. finally, we give an outlook of the future simulations of jets associated to neutron stars, black holes and their merging and discuss the future of pic simulations in the light of petascale and exascale computing. | pic methods in astrophysics: simulations of relativistic jets and kinetic physics in astrophysical systems |
high time resolution and accuracy are of critical importance in the studies of timing analysis and time delay localization of gamma-ray bursts (grbs), soft gamma-ray repeaters (sgrs) and pulsars. the gravitational wave high-energy electromagnetic counterpart all-sky monitor (gecam) consisting of two micro-satellites, gecam-a and gecam-b, launched on 2020 december 10, is aimed at monitoring and locating x-ray and grbs all over the sky. to achieve its scientific goals, gecam is designed to have the highest time resolution (0.1 $\mu {\rm s}$) among all grb detectors ever flown. here, we make a comprehensive time calibration campaign including both on-ground and on-orbit tests to derive not only the relative time accuracy of gecam satellites and detectors, but also the absolute time accuracy of gecam-b. using the on-ground calibration with a $\rm ^{22}na$ radioactive source, we find that the relative time accuracy between gecam-a and gecam-b is about 0.15 $\mu {\rm s}$ (1σ). to measure the relative time accuracy between all detectors of a single gecam satellite, cosmic-ray events detected on orbit are utilized since they could produce many secondary particles simultaneously record by multiple detectors. we find that the relative time accuracy among all detectors onboard gecam-b is about 0.12 $\mu {\rm s}$ (1σ). finally, we use the novel li-ccf method to perform the absolute time calibration with crab pulsar and sgr j1935+2154, both of which were jointly observed by gecam-b and fermi/gbm, and obtain that the time difference between gecam-b and fermi/gbm is 3.06 ± 6.04 $\mu {\rm s}$ (1σ). | on-ground and on-orbit time calibrations of gecam |
in the present paper, we investigate the dynamics of magnetized particles around magnetically and electrically reissner-nordström (rn) black hole. the main idea of the work is to distinguish the effects of electric and magnetic charges of the rn black hole and spin of the rotating kerr black hole through the dynamics of the magnetized particles. in this study, we have treated a magnetized neutron star as a magnetized test particle, in particular, the magnetar sgr (psr) j1745-2900 orbiting around the supermassive black hole sagittarius a* (smbh sgra*) with the magnetic interaction parameter b =0.716 and the parameter β =10.2 . the comparison of the effects of the magnetic and electric charges, and magnetic interaction parameters on the dynamics of the magnetar modeled as a magnetized particle near the smbh sgr a* has shown that the magnetic charge of the rn black hole can mimic the spin parameter of a rotating kerr black hole up to a /m ≃0.82 . the external magnetic field can mimic the magnetic charge of the rn black hole up to qm/m =0.4465 . we have shown that the electric charge of the rn black hole can mimic the black hole magnetic charge up to qm/m =0.5482 and the magnetic field interaction with the magnetized particle acts against the increase of the mimicking value of the black hole spin parameter. the studies may be helpful to explain the observability of radio pulsars around the smbh sgra* system and taking it as a real astrophysical laboratory to get more precise constraints on the central black hole and dominated parameters of the alternate gravity. finally, we have investigated the effects of magnetic and electric charge of the rn black hole in the center-of-mass energy of head-on collisions of magnetized particles with neutral, electrically charged, and magnetized particles. both electric and magnetic charges of the rn black hole would lead to an increase in the center of the mass-energy of the collisions. | distinguishing magnetically and electrically charged reissner-nordström black holes by magnetized particle motion |
initial distributions of pulsar periods and magnetic fields are essential components of multiple modern astrophysical models. not enough work has been done to properly constrain these distributions using direct measurements. here, we aim to fill this gap by rigorously analysing the properties of young neutron stars (nss) associated to supernova remnants (snrs). in order to perform this task, we compile a catalogue of 56 nss uniquely paired to snrs with known age estimate. further, we analyse this catalogue using multiple statistical techniques. we found that distribution of magnetic fields and periods for radio pulsars are both well described using the lognormal distribution. the mean magnetic field is log10[b/g] = 12.44 and standard deviation is σb = 0.44. magnetars and central compact objects do not follow the same distribution. the mean initial period is $\log _{10} p_0 [p / \mathrm{s}] = -1.04_{-0.2}^{+0.15}$ and standard deviation is $\sigma _{\rm p} = 0.53_{-0.08}^{+0.12}$. we show that the normal distribution does not describe the initial periods of nss sufficiently well. parameters of the initial period distribution are not sensitive to the exact value of the braking index. | initial periods and magnetic fields of neutron stars |
discoveries of rotating radio transients and fast radio bursts (frbs) in pulsar surveys suggest that more of such transient sources await discovery in archival data sets. here we report on a single-pulse search for dispersed radio bursts over a wide range of galactic latitudes (|b| < 60°) in data previously searched for periodic sources by burgay et al. we re-detected 20 of the 42 pulsars reported by burgay et al. and one rotating radio transient reported by burke-spolaor. no frbs were discovered in this survey. taking into account this result, and other recent surveys at parkes, we corrected for detection sensitivities based on the search software used in the analyses and the different back-ends used in these surveys and find that the all-sky frb event rate for sources with a fluence above 4.0 jy ms at 1.4 ghz to be r = 4.4^{+5.2}_{-3.1} × 10^3 frbs d-1 sky-1, where the uncertainties represent a 99 per cent confidence interval. while this rate is lower than inferred from previous studies, as we demonstrate, this combined event rate is consistent with the results of all systematic frb searches at parkes to date and does not require the need to postulate a dearth of frbs at intermediate latitudes. | a search for rotating radio transients and fast radio bursts in the parkes high-latitude pulsar survey |
the dark matter particle explorer, a space-based high precision cosmic-ray detector, has just reported the new measurement of the total electron plus positron energy spectrum up to 4.6 tev. a notable feature in the spectrum is the spectral break at ∼0.9 tev, with the spectral index softening from -3.1 to -3.9. such a feature is very similar to the knee at the cosmic nuclei energy spectrum. in this work, we propose that the knee-like feature can be explained naturally by assuming that the electrons are accelerated at the supernova remnants (snrs) and released when the snrs die out with lifetimes around 105 years. the cut-off energy of those electrons have already decreased to several tev due to radiative cooling, which may induce the observed tev spectral break. another possibility is that the break is induced by a single nearby old snr. such a scenario may bring a large electron flux anisotropy that may be observable by the future detectors. we also show that a minor part of electrons escaping during the acceleration in young and nearby snrs is able to contribute to a several tev or higher energy region of the spectrum. | explanation of the knee-like feature in the dampe cosmic {e}^{-}+{e}^{+} energy spectrum |
the neutron star interior composition explorer (nicer) has extensively monitored the 2019 august outburst of the 401 hz millisecond x-ray pulsar sax j1808.4-3658. in this letter, we report on the detection of a bright helium-fueled type i x-ray burst. with a bolometric peak flux of (2.3 ± 0.1) × 10-7 erg s-1 cm-2, this was the brightest x-ray burst among all bursting sources observed with nicer to date. the burst shows a remarkable two-stage evolution in flux, emission lines at 1.0 and 6.7 kev, and burst oscillations at the known pulsar spin frequency, with ≈4% fractional sinusoidal amplitude. we interpret the burst flux evolution as the detection of the local eddington limits associated with the hydrogen and helium layers of the neutron star envelope. the emission lines are likely associated with fe, due to reprocessing of the burst emission in the accretion disk. | a nicer thermonuclear burst from the millisecond x-ray pulsar sax j1808.4-3658 |
plasma energization through magnetic reconnection in the magnetically dominated regime featured by low plasma beta ( β = 8 π n k t 0 / b 2 ≪ 1 ) and/or high magnetization ( σ = b 2 / ( 4 π n m c 2 ) ≫ 1 ) is important in a series of astrophysical systems such as solar flares, pulsar wind nebula, and relativistic jets from black holes. in this paper, we review the recent progress on kinetic simulations of this process and further discuss plasma dynamics and particle acceleration in a low-β reconnection layer that consists of electron-positron pairs. we also examine the effect of different initial thermal temperatures on the resulting particle energy spectra. while earlier papers have concluded that the spectral index is smaller for higher σ, our simulations show that the spectral index approaches p = 1 for sufficiently low plasma β, even if σ ∼ 1 . since this predicted spectral index in the idealized limit is harder than most observations, it is important to consider effects that can lead to a softer spectrum such as open boundary simulations. we also remark that the effects of three-dimensional reconnection physics and turbulence on reconnection need to be addressed in the future. | particle acceleration during magnetic reconnection in a low-beta pair plasma |
motivated by the recent discoveries that six ultraluminous x-ray sources (ulxs) are powered by highly super-eddington x-ray pulsars, we searched for additional pulsating ulx (pulx) candidates by identifying sources that exhibit long-term flux variability of at least an order of magnitude (a common feature seen in the six known pulxs, which may potentially be related to transitions to the propeller regime). expanding on previous studies, we used the available fluxes from xmm-newton, swift, and chandra, along with carefully computed upper limits in cases of a non-detection, to construct long-term light curves for a sample of 296 ulxs selected from the xmm-newton archive. among these 296, we find 25 sources showing flux variability larger than a factor of 10, of which 17 show some evidence for (or are at least consistent with) exhibiting bimodal flux distributions, as would be expected for sources undergoing propeller transitions. these sources are excellent candidates for continued monitoring programs to further test for this behaviour. there are three sources in our final sample with fluxes similar to ngc 5907 ulx1, currently the faintest known pulx, which would also be good targets for deeper observations with current facilities to search for pulsations. for the rest of the pulx candidates identified here, the next generation of x-ray telescopes (such as athena) may be required to determine their nature owing to their lower peak fluxes. | the hunt for pulsating ultraluminous x-ray sources |
we perform a bayesian analysis of neutrons star moment of inertia by utilizing the available gravitational-wave data from ligo/virgo (gw170817 and gw190425) and mass-radius measurements from the neutron star interior composition explorer (psr j0030+0415 and psr j0740 + 6620), incorporating the possible phase transition in the pulsar inner core. we find that the moment of inertia of pulsar a in the double pulsar binary j0737-3039 is $\sim 1.30\times 10^{45}\, {\rm g\, cm^2}$, which only slightly depends on the employed hadronic equation of states. we also demonstrate how a moment of inertia measurement would improve our knowledge of the equation of state and the mass-radius relation for neutron stars and discuss whether a quark deconfinement phase transition is supported by the available data and forthcoming data that could be consistent with this hypothesis. we find that if pulsar a is a quark star, its moment of inertia is a large value of $\sim 1.55\times 10^{45}\, {\rm g\, cm^2}$ suggesting the possibility of distinguishing it from (hybrid-)neutron stars with measurements of psr j0737-3039a moment of inertia. we finally demonstrate the moment-of-inertia-compactness universal relations and provide analytical fits for both (hybrid-)neutron star and quark star results based on our analysis. | on the moment of inertia of psr j0737-3039 a from ligo/virgo and nicer |
aims: we report on the measurement and investigation of pulsed high-energy γ-ray emission from the vela pulsar, psr b0833-45, based on observations with the largest telescope of h.e.s.s., ct5, in monoscopic mode, and on data obtained with the fermi-lat.methods: data from 40.3 h of observations carried out with the h.e.s.s. ii array from 2013 to 2015 have been used. a dedicated very low-threshold event reconstruction and analysis pipeline was developed to achieve the lowest possible energy threshold. eight years of fermi-lat data were analysed and also used as reference to validate the ct5 telescope response model and analysis methods.results: a pulsed γ-ray signal at a significance level of more than 15σ is detected from the p2 peak of the vela pulsar light curve. of a total of 15 835 events, more than 6000 lie at an energy below 20 gev, implying a significant overlap between h.e.s.s. ii-ct5 and the fermi-lat. while the investigation of the pulsar light curve with the lat confirms characteristics previously known up to 20 gev in the tens of gev energy range, ct5 data show a change in the pulse morphology of p2, i.e. an extreme sharpening of its trailing edge, together with the possible onset of a new component at 3.4σ significance level. assuming a power-law model for the p2 spectrum, an excellent agreement is found for the photon indices (γ ≃ 4.1) obtained with the two telescopes above 10 gev and an upper bound of 8% is derived on the relative offset between their energy scales. using data from both instruments, it is shown however that the spectrum of p2 in the 10-100 gev has a pronounced curvature; this is a confirmation of the sub-exponential cut-off form found at lower energies with the lat. this is further supported by weak evidence of an emission above 100 gev obtained with ct5. in contrast, converging indications are found from both ct5 and lat data for the emergence of a hard component above 50 gev in the leading wing (lw2) of p2, which possibly extends beyond 100 gev.conclusions: the detection demonstrates the performance and understanding of ct5 from 100 gev down to the sub-20 gev domain, i.e. unprecedented low energy for ground-based γ-ray astronomy. the extreme sharpening of the trailing edge of the p2 peak found in the h.e.s.s. ii light curve of the vela pulsar and the possible extension beyond 100 gev of at least one of its features, lw2, provide further constraints to models of γ-ray emission from pulsars. | first ground-based measurement of sub-20 gev to 100 gev γ-rays from the vela pulsar with h.e.s.s. ii |
in the present paper we derive strong constrains on scalarization in scalar-gauss-bonnet (sgb) gravity using observations of pulsars in close binary systems. since scalarized neutron stars carry a nonzero scalar change, they emit scalar dipole radiation while inspiraling which speeds up the orbital decay. the observations support the conjecture that such radiation is either absent or very small for the observed binary pulsars. using this, we determine the allowed range of parameters for sgb gravity. we also transfer the derived constraints to black holes in sgb gravity. it turns out that the maximum mass of a scalarized black hole cannot exceed roughly 10 to 20 solar masses, depending on the initial assumptions we make for the nuclear matter equations of state. the black hole scalar charge on the other hand can reach relatively large values that are potentially observable. | constraining scalarization in scalar-gauss-bonnet gravity through binary pulsars |
we study the possibility of probing new physics accounting for $(g-2)_\mu$ anomaly and gravitational waves with pulsar timing array measurements. the model we consider is either a light gauge boson or neutral scalar interacting with muons. we show that the parameter spaces of dark $u(1)$ model with kinetic mixing explaining $(g-2)_\mu$ anomaly can realize a first-order phase transition, and the yield-produced gravitational wave may address the common red noise observed in the nanograv 12.5-yr dataset. | probing new physics for $(g-2)_\\mu$ and gravitational waves |
the recent measurement by lhaaso of gamma-ray emission extending up to hundreds of tev from multiple galactic sources represents a major observational step forward in the search for the origin of the galactic cosmic rays. the burning question is if this ultra-high-energy emission is associated with the acceleration of protons and/or nuclei to pev energies, or if it can be associated with pev-electron accelerators. a strong klein-nishina suppression of inverse compton emission at these energies is unavoidable; nevertheless, we show here that inverse compton emission can provide a natural explanation for the measured emission and that an association with the established pev-electron accelerating source class of pulsar wind nebulae is also rather natural. however, a clear distinction between different models requires taking multi-wavelength data into account, having good knowledge of the local environmental conditions, and, in some cases, performing multi-source modelling. | pulsar wind nebula origin of the lhaaso-detected ultra-high energy γ-ray sources |
tev halos are regions of enhanced photon emissivity surrounding pulsars. while multiple sources have been discovered, a self-consistent explanation of their radial profile and spherically symmetric morphology remains elusive due to the difficulty in confining high-energy electrons and positrons within ∼20 pc regions of the interstellar medium. one proposed solution utilizes anisotropic diffusion to confine the electron population within a "tube" that is auspiciously oriented along the line of sight. we show that while such models may explain a unique source such as geminga, the phase space of such solutions is very small and they are unable to simultaneously explain the size and approximate radial symmetry of the tev halo population. | anisotropic diffusion cannot explain tev halo observations |
the globular cluster 47 tucanae (47 tuc) is one of the most massive star clusters in the milky way and is exceptionally rich in exotic stellar populations. for several decades it has been a favorite target of observers, and yet it is computationally very challenging to model because of its large number of stars (n ≳ 106) and high density. here we present detailed and self-consistent 47 tuc models computed with the cluster monte carlo code (cmc). the models include all relevant dynamical interactions coupled to stellar and binary evolution, and reproduce various observations, including the surface brightness and velocity dispersion profiles, pulsar accelerations, and numbers of compact objects. we show that the present properties of 47 tuc are best reproduced by adopting an initial stellar mass function that is both bottom-heavy and top-light relative to standard assumptions (as in, e.g., kroupa 2001), and an initial elson profile (elson et al. 1987) that is overfilling the cluster's tidal radius. we include new prescriptions in cmc for the formation of binaries through giant star collisions and tidal captures, and we show that these mechanisms play a crucial role in the formation of neutron star binaries and millisecond pulsars in 47 tuc; our best-fit model contains ~50 millisecond pulsars, 70% of which are formed through giant collisions and tidal captures. our models also suggest that 47 tuc presently contains up to ~200 stellar-mass black holes, ~5 binary black holes, ~15 low-mass x-ray binaries, and ~300 cataclysmic variables. | compact object modeling in the globular cluster 47 tucanae |
based on the accurately calibrated interaction fsugold, we show that including isovector-scalar δ meson and its coupling to isoscalar-scalar σ meson in the relativistic mean-field (rmf) model can soften the symmetry energy e sym(n) at intermediate densities while stiffening the e sym(n) at high densities. we find this new rmf model can be simultaneously compatible with (1) the constraints on the equation of state of symmetric nuclear matter at suprasaturation densities from flow data in heavy-ion collisions; (2) the neutron skin thickness of 208pb from the prex-ii experiment; (3) the largest mass of a neutron star (ns) reported so far from psr j0740+6620; (4) the limit of λ1.4 ≤ 580 for the dimensionless tidal deformability of the canonical 1.4 m ⊙ ns from the gravitational-wave signal gw170817; (5) the mass-radius relation of psr j0030+0451 and psr j0740+6620 measured by nicer. the new model thus removes the tension between prex-ii and gw170817 observed in the conventional rmf model. | effects of isoscalar- and isovector-scalar meson mixing on neutron star structure |
in this work, we study variations in the parabolic scintillation arcs of the binary millisecond pulsar psr j1643-1224 over five years using the large european array for pulsars (leap). the two-dimensional (2d) power spectrum of scintillation, called the secondary spectrum, often shows a parabolic distribution of power, where the arc curvature encodes the relative velocities and distances of the pulsar, ionized interstellar medium, and earth. we observe a clear parabolic scintillation arc, which varies in curvature throughout the year. the distribution of power in the secondary spectra is inconsistent with a single scattering screen, which is fully 1d or entirely isotropic. we fit the observed arc curvature variations with two models: an isotropic scattering screen and a model with two independent 1d screens. we measure the distance to the scattering screen to be in the range 114-223 pc, depending on the model, consistent with the known distance of the foreground large-diameter h ii region sh 2-27 (112 ± 17 pc), suggesting that it is the dominant source of scattering. we obtain only weak constraints on the pulsar's orbital inclination and longitude of ascending node, since the scintillation pattern is not very sensitive to the pulsar's motion and the screen is much closer to the earth than the pulsar. more measurements of this kind - where scattering screens can be associated with foreground objects - will help to inform the origins and distribution of scattering screens within our galaxy. | modelling annual scintillation arc variations in psr j1643-1224 using the large european array for pulsars |
aims: the usefulness and versatility of the psrsalsa open-source pulsar data-analysis project is demonstrated through an analysis of the radio pulsar b1839-04. this study focuses on the phenomenon of bi-drifting, an effect where the drift direction of subpulses is systematically different in different pulse profile components. bi-drifting is extremely rare in the pulsar population, and the theoretical implications are discussed after comparing b1839-04 with the only other known bi-drifter.methods: various tools in psrsalsa, including those allowing quantification of periodicities in the subpulse modulation, their flux distribution, and polarization properties, are exploited to obtain a comprehensive picture of the radio properties of psr b1839-04. in particular, the second harmonic in the fluctuation spectra of the subpulse modulation is exploited to convincingly demonstrate the existence of bi-drifting in b1839-04. bi-drifting is confirmed with a completely independent method allowing the average modulation cycle to be determined. polarization measurements were used to obtain a robust constraint on the magnetic inclination angle.results: the angle between the rotation and magnetic axis is found to be smaller than 35°. two distinct emission modes are discovered to be operating, with periodic subpulse modulation being present only during the weaker mode. despite the variability of the modulation cycle and interruption by mode-changes, the modulation pattern responsible for the bi-drifting is strictly phase locked over a timescale of years such that the variability is identical in the different components.conclusions: the phase locking implies that a single physical origin is responsible for both drift directions. phase locking is hard to explain for many models, including those specifically proposed in the literature to explain bi-drifting, and they are therefore shown to be implausible. it is argued that within the framework of circulating beamlets, bi-drifting could occur if the circulation were severely distorted, possibly by distortions in the magnetic field. a copy of the code is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/590/a109 | investigation of the bi-drifting subpulses of radio pulsar b1839-04 utilising the open-source data-analysis project psrsalsa |
the canadian hydrogen intensity mapping experiment (chime)/frb experiment has detected thousands of fast radio bursts (frbs) due to its sensitivity and wide field of view; however, its low angular resolution prevents it from localizing events to their host galaxies. very long baseline interferometry (vlbi), triggered by frb detections from chime/frb will solve the challenge of localization for non-repeating events. using a refurbished 10 m radio dish at the algonquin radio observatory located in ontario canada, we developed a testbed for a vlbi experiment with a theoretical λ/d ≲ 30 mas. we provide an overview of the 10 m system and describe its refurbishment, the data acquisition, and a procedure for fringe fitting that simultaneously estimates the geometric delay used for localization and the dispersive delay from the ionosphere. using single pulses from the crab pulsar, we validate the system and localization procedure, and analyze the clock stability between sites, which is critical for coherently delay referencing an frb event. we find a localization of ~200 mas is possible with the performance of the current system (single-baseline). furthermore, for sources with insufficient signal or restricted wideband to simultaneously measure both geometric and ionospheric delays, we show that the differential ionospheric contribution between the two sites must be measured to a precision of 1 × 10-8 pc cm-3 to provide a reasonable localization from a detection in the 400-800 mhz band. finally we show detection of an frb observed simultaneously in the chime and the algonquin 10 m telescope, the first non-repeating frb in this long baseline. this project serves as a testbed for the forthcoming chime/frb outriggers project. | localizing frbs through vlbi with the algonquin radio observatory 10 m telescope |
we consider spherical exact models for compact stars with anisotropic pressures and a conformal symmetry. the conformal symmetry condition generates an integral relationship between the gravitational potentials. we solve this condition to find a new anisotropic solution to the einstein field equations. we demonstrate that the exact solution produces a relativistic model of a compact star. the model generates stellar radii and masses consistent with psr j1614-2230, vela x1, psr j1903+327 and cen x-3. a detailed physical examination shows that the model is regular, well behaved and stable. the mass-radius limit and the surface red shift are consistent with observational constraints. | spherical conformal models for compact stars |
libstempo uses the tempo2 library (ascl:1210.015) to load a pulsar's tim/par files, providing python access to the toas, the residuals, the timing-model parameters, the fit procedure, and more. | libstempo: python wrapper for tempo2 |
evidence for the presence of extra fields during inflation may be found in the anisotropies of the scalar and tensor spectra across a vast range of scales. indeed, beyond the single-field slow-roll paradigm, a long tensor mode modulating the power spectrum can induce a sizable quadrupolar anisotropy. we investigate how these dynamics play out for the tensor two-point correlator. the resulting quadrupole stores information on squeezed tensor non-gaussianities, including those sourced by extra field content and responsible for the breaking of so-called consistency relations. we underscore the potential of anisotropies as a probe of new physics: testable at cosmic microwave background scales through the detection of b modes, they are accessible at smaller scales via pulsar timing arrays and interferometers. our findings are particularly relevant in that recent studies show a considerable suppression for tensor non-gaussianities if all modes are well inside the horizon. quadrupolar anisotropies instead probe an unsuppressed ultrasqueezed bispectrum where the long mode can be horizon size. | searching for fossil fields in the gravity sector |
while the majority of massive stars have a stellar companion, most pulsars appear to be isolated. taken at face value, this suggests that most massive binaries break apart due to strong natal kicks received in supernova explosions. however, the observed binary fraction can still be subject to strong selection effects, as monitoring of newly discovered pulsars is rarely carried out for long enough to conclusively rule out multiplicity. here, we use the second gaia data release to search for companions to 1534 rotation-powered pulsars with positions known to better than 0.5 arcsec. we find 22 matches to known pulsars, including 1 not reported elsewhere, and 8 new possible companions to young pulsars. we examine the photometric and kinematic properties of these systems and provide empirical relations for identifying gaia sources with potential millisecond pulsar companions. our results confirm that the observed multiplicity fraction is small. however, we show that the number of binaries below the sensitivity of gaia and radio timing in our sample could still be significantly higher. we constrain the binary fraction of young pulsars to be $f_{\rm young}^{\rm true}\le 5.3(8.3){{\ \rm per\ cent}}$ under realistic (conservative) assumptions for the binary properties and current sensitivity thresholds. for massive stars (≥10 m⊙) in particular, we find $f_{\rm ob}^{\rm true}\le 3.7{{\ \rm per\ cent}}$ , which sets a firm independent upper limit on the galactic neutron star merger rate, ≤7.2 × 10-4 yr-1. ongoing and future projects, such as the chime/pulsar program, meertime, hirax, and ultimately the ska, will significantly improve these constraints in the future. | gaia pulsars and where to find them |
we constrain the equation of state of quark stars within the bayesian statistical approach using the mass and radius measurements of psr j0030+0451 from nicer. three types of bag models, with and without non-zero finite quark mass and/or superfluidity, are employed for quark stars made up with self-bound strange quark matter. we find the $90{{\ \rm per\ cent}}$ posterior credible boundary around the most probable values of the quark star maximum mass is $m_{\rm tov}=2.38_{-0.23}^{+0.26}\, m_{\odot }$, within the model flexibility of the finite quark mass, the quark pairing gap, and the perturbative contribution from the one-gluon exchange. the radius of a canonical $1.4 \, m_{\odot }$ quark star is $r_{\rm 1.4}\sim 12.3\, {\rm km}$, smaller than the results based on neutron star models. | bayesian inference of quark star equation of state using the nicer psr j0030+0451 data |
events gw170817 and grb 170817a provide the best confirmation so far that compact binary mergers where at least one of the companions is a neutron star can be the progenitors of short gamma-ray bursts (sgrbs). an open question for gw170817 remains the values and impact of the initial neutron star spins. the initial spins could possibly affect the remnant black hole mass and spin, the remnant disk, and the formation and lifetime of a jet and its outgoing electromagnetic poynting luminosity. here we summarize our general relativistic magnetohydrodynamic simulations of spinning, neutron star binaries undergoing merger, and delayed collapse to a black hole. the binaries consist of two identical stars, modeled as γ =2 polytropes, in quasicircular orbit, each with spins χns=-0.053 , 0, 0.24, or 0.36. the stars are endowed initially with a dipolar magnetic field extending from the interior into the exterior, as in a radio pulsar. following the merger, the redistribution of angular momentum by magnetic braking and magnetic turbulent viscosity in the hypermassive neutron star (hmns) remnant, along with the loss of angular momentum due to gravitational radiation, induces the formation of a massive, nearly uniformly rotating inner core surrounded by a magnetized keplerian disklike envelope. the hmns eventually collapses to a black hole, with spin a /mbh≃0.78 independent of the initial spin of the neutron stars, surrounded by a magnetized accretion disk. the larger the initial neutron star spin the heavier the disk. after δ t ∼3000 m -4000 m ∼45 (mns/1.625 m⊙) ms -60 (mns/1.625 m⊙) ms following merger, a mildly relativistic jet is launched. the lifetime of the jet [δ t ∼100 (mns/1.625 m⊙) ms -140 (mns/1.625 m⊙) ms ] and its outgoing poynting luminosity [lem∼1051.5 ±1 erg /s ] are consistent with typical sgrbs, as well as with the blandford-znajek mechanism for launching jets and their associated poynting luminosities. | effects of spin on magnetized binary neutron star mergers and jet launching |
some of the most energetic pulsars exhibit rotation-modulated γ-ray emission in the 0.1-100 gev band. the luminosity of this emission is typically 0.1%-10% of the pulsar spin-down power (γ-ray efficiency), implying that a significant fraction of the available electromagnetic energy is dissipated in the magnetosphere and reradiated as high-energy photons. to investigate this phenomenon we model a pulsar magnetosphere using 3d particle-in-cell simulations with strong synchrotron cooling. we particularly focus on the dynamics of the equatorial current sheet where magnetic reconnection and energy dissipation take place. our simulations demonstrate that a fraction of the spin-down power dissipated in the magnetospheric current sheet is controlled by the rate of magnetic reconnection at microphysical plasma scales and only depends on the pulsar inclination angle. we demonstrate that the maximum energy and the distribution function of accelerated pairs is controlled by the available magnetic energy per particle near the current sheet, the magnetization parameter. the shape and the extent of the plasma distribution is imprinted in the observed synchrotron emission, in particular, in the peak and the cutoff of the observed spectrum. we study how the strength of synchrotron cooling affects the observed variety of spectral shapes. our conclusions naturally explain why pulsars with higher spin-down power have wider spectral shapes and, as a result, lower γ-ray efficiency. | magnetic energy dissipation and γ-ray emission in energetic pulsars |
the electrical asymmetry effect (eae) enables separate control of the ion flux and the mean ion energy in capacitively coupled plasmas (ccp). while a variety of plasma processing applications benefit from this, large-area, very-high-frequency ccps still suffer from lateral nonuniformities caused by electromagnetic standing wave effects (swe). many of such plasma sources are geometrically asymmetric and are operated at low pressure so that high frequency nonlinear plasma series resonance (psr) oscillations of the rf current are self-excited. these psr oscillations lead to the presence of short wavelength electromagnetic waves and a more pronounced swe. in this work, we investigate the influence of the eae on the nonlinear standing wave excitation in a geometrically asymmetric, low pressure capacitively coupled argon plasma driven by two consecutive harmonics (30 mhz and 60 mhz) with an adjustable phase shift, θ. we use a hairpin probe to determine the radial distribution of the electron density in combination with a high-frequency b-dot probe to measure the radial distribution of the harmonic magnetic field, which in turn is used to calculate the harmonic current density based on ampere's law. our experimental results show that the asymmetry of the discharge can be reduced electrically via the eae. in this way the self-excitation of high frequency psr oscillations can be attenuated. by tuning θ, it is, therefore, possible to switch on and off the nonlinear standing wave excitation caused by the psr and, accordingly, the plasma uniformity can be optimized. | suppression of nonlinear standing wave excitation via the electrical asymmetry effect |
we generate a new exact model for neutral anisotropic star using einstein field equations. in this model, we consider a quadratic equation of state (qeos) and a choice of gravitational potential which generalizes the choice formulated by pant and fuloria. we generate stellar masses consistent with previous findings which describe the astrophysical objects like psr j1614-2230, cen x-3, vela x-1 and exo 1785-248. new relativistic stellar masses and surface gravitational redshifts in acceptable ranges are also generated using our model. it is observed that the matter variables and gravitational potentials are well behaved. the model satisfies energy and stability conditions and all forces within the stellar object sum to zero. | a neutral stellar model with quadratic equation of state |
a new type of embedding class-i representing anisotropic fluid distribution is presented. the new solution is free from singularity and also satisfies all physical criteria. it also satisfies all energy conditions such as sec, wec, nec and dec. the solution so obtained is used to optimize mass and radius of some well compact stars candidates like, her x-1, sax j1808.4-3658, rx j1856.5-3754, psr j1614-2230 and psr j0348+0432. | a new analytic solution representing anisotropic stellar objects in embedding class i |
the discovery of millisecond pulsars switching between states powered either by the rotation of their magnetic field or by the accretion of matter has recently proved the tight link shared by millisecond radio pulsars and neutron stars in low-mass x-ray binaries. transitional millisecond pulsars also show an enigmatic intermediate state in which the neutron star is surrounded by an accretion disk and emits coherent x-ray pulsations, but is sub-luminous in x-rays with respect to accreting neutron stars, and is brighter in gamma-rays than millisecond pulsars in the rotation-powered state. here, we model the x-ray and gamma-ray emission observed from psr j1023+0038 in such a state based on the assumptions that most of the disk in-flow is propelled away by the rapidly rotating neutron star magnetosphere, and that electrons can be accelerated to energies of a few gev at the turbulent disk-magnetosphere boundary. we show that the synchrotron and self-synchrotron compton emission coming from such a region, together with the hard disk emission typical of low states of accreting compact objects, is able to explain the radiation observed in the x-ray and gamma-ray bands. the average emission observed from psr j1023+0038 is modeled by a disk in-flow with a rate of 1-3 × 10-11 m⊙ yr-1, truncated at a radius ranging between 30 and 45 km, compatible with the hypothesis of a propelling magnetosphere. we compare the results we obtained with models that assume that a rotation-powered pulsar is turned on, showing how the spin-down power released in similar scenarios is hardly able to account for the magnitude of the observed emission. | a propeller model for the sub-luminous state of the transitional millisecond pulsar psr j1023+0038 |
pixel super-resolution (psr) techniques have been developed to overcome the sampling limit in lensless digital holographic imaging. however, the inherent non-convexity of the psr phase retrieval problem can potentially degrade reconstruction quality by causing the iterations to tend toward a false local minimum. furthermore, the ill posedness of the up-sampling procedure renders psr algorithms highly susceptible to noise. in this letter, we propose a heuristic psr algorithm with adaptive smoothing (as-psr) to achieve high-fidelity reconstruction. by automatically adjusting the intensity constraints on the estimated field, the algorithm can effectively locate the optimal solution and converge with high reconstruction quality, pushing the resolution toward the diffraction limit. the proposed method is verified experimentally within a coherent modulation phase retrieval framework, achieving a twofold improvement in resolution. the as-psr algorithm can be further applied to other phase retrieval methods based on alternating projection. | high-fidelity pixel-super-resolved complex field reconstruction via adaptive smoothing |
as the moon migrated away from earth, it experienced a major spin axis reorientation. permanently shadowed regions (psrs), which are thought to have trapped ices and are a main focus of lunar exploration, appeared and grew after this (cassini state) transition and are often younger than their host craters. here, we calculate the lunar spin axis orientation and the extent of psrs based on recent advances for the time evolution of the earth-moon distance. the solar declination reached twice its current value 2.1 billion years (ga) ago, when the psr area was about half as large. the psr area becomes negligible beyond 3.4 ga ago. the site of an artificial impact in cabeus crater, where various volatiles have been detected, became continuously shadowed only about 0.9 ga ago, and hence, cold-trapping has continued into this relatively recent time period. overall estimates for the amount of cold-trapped ices have to be revised downward. most of the moon's permanently shadowed areas arose less than 2.2 billion years ago and some trapped ice during the recent past. | past extent of lunar permanently shadowed areas |
the sustainable development of sii (small inhabited islands) has critical impacts on human well-being and requires balancing complex multiobjectives, for which the most beneficial actions must be prioritized, with limited financial and labor support. the effect of current plans based on single-scale or single-objective assessments may be overestimated, and multiscale landscape assessments and plans offer a potential solution. this study aimed to bring more attention to sii and use landscape ecology theories and methods to develop a multiscale landscape assessment framework that integrates multiobjectives to identify priority action plans for sustainable development. this framework consists of a leha (landscape ecological health assessment) based on the psr (pressure-state-response) index system and a tlsa (tourism landscape suitability assessment) based on the ahp (analytic hierarchy process) index system at regional and unit landscape scales, respectively. and we verified it on xiaodeng island in xiamen, china, near kinmen island in taiwan province, which is a typical case of sii that are in the administrative division of "township" consisting of villages only. our framework is characterized by overall consistency, hierarchical transmission and spatial variability, which ensures the scientific and operability of plans that can meet both 'top-down' management objectives and 'bottom-up' development needs. the application in xiaodeng island confirmed its feasibility. we proposed 4 strategies and an action plan network of 12 actions with specific content, location and order based on the assessment results with the goal of mitigating climate change, particularly in marine ecosystems, and providing more sustainable development opportunities for sii residents. in the future, we need a long-term monitoring database, scenario modeling predictions and quantitative analysis of the plan effectiveness for sii; furthermore, we need to implement this framework at different landscape scales in other areas. | developing a multiscale landscape assessment framework integrating multiobjectives to identify priority action plans for sustainable development of small inhabited islands |
we study spherically symmetric magnetically charged generic singular black hole solutions of general relativity coupled to nonlinear electrodynamics. for characteristic values of the generic spacetime parameters and the parameter characterizing the ratio of the gravitational and electromagnetic forces acting on an electrically charged particle we study the circular orbits and related epicyclic motion and its frequencies. we demonstrate that the equatorial circular orbits are forbidden in such situations, but off-equatorial circular orbits are possible. we give dependence of the stable circular orbit on the spacetime parameters and intensity of the electromagnetic interaction of the charged particles with magnetically charged black holes. we study the possible resonance phenomena of the epicyclic frequencies and the orbital frequency of the electrically charged particles in order to fit the data of the twin high-frequency quasiperiodic oscillations of x rays observed in microquasars. moreover, the dynamics of magnetized particles around the magnetically charged generic black hole have also been explored and it is shown that as increasing magnetic charge and magnetic moment parameters, the innermost stable circular orbit (isco) radius decreases and disappears at some value of the magnetic moment parameter, inversely proportional to the magnetic charge of black hole. as an astrophysical application we treated the magnetar psr j1745-2900 orbiting around sagittarius (sgr) a* as a magnetized particle and showed that the magnetic charge of black hole can mimic black hole spin up to a /m =0.865694 at ν =2 , and the spin parameter can mimic the magnetic charge parameter up to q /m =0.578575 at ν =1 , providing exactly the same value of the isco radius. finally, we predict that no magnetar with the surface magnetic field of the order of 1014- 1 015 g can follow stable orbits, but it is possible to observe ordinary neutron stars as recycled radio pulsars in the close environment of sgr a*. | charged and magnetized particles motion in the field of generic singular black holes governed by general relativity coupled to nonlinear electrodynamics |
in this paper we show that the most luminous supernova discovered very recently, asassn-15lh, could have been powered by a newborn ultra-strongly magnetized pulsar, which initially rotates near the kepler limit. we find that if this pulsar is a neutron star, its rotational energy could be quickly lost as a result of gravitational-radiation-driven r-mode instability; if it is a strange quark star (sqs), however, this instability is highly suppressed due to a large bulk viscosity associated with the nonleptonic weak interaction among quarks and thus most of its rotational energy could be extracted to drive asassn-15lh. therefore, we conclude that such an ultra-energetic supernova provides a possible signature for the birth of an sqs. | the most luminous supernova asassn-15lh: signature of a newborn rapidly rotating strange quark star |
we consider a scenario with axions/axion-like particles chern-simons gravity coupling, such that gravitational waves can be produced directly from axion wave tachyonic instability in the early universe after inflation. this axion gravity term is less constrained compared to the well-searched axion photon coupling and can provide a direct and efficient production channel for gravitational waves. such stochastic gravitational waves can be detected by either space/ground-based gravitational wave detectors or pulsar timing arrays for a broad range of axion masses and decay constants. | gravitational waves from axion wave production |
timing a pulsar orbiting around sagittarius a* (sgr a*) can provide us with a unique opportunity of testing gravity theories. we investigate the detectability of a vector charge carried by the sgr a* black hole (bh) in the bumblebee gravity model with simulated future pulsar timing observations. the spacetime of a bumblebee bh introduces characteristic changes to the orbital dynamics of the pulsar and the light propagation of radio signals. assuming a timing precision of 1 ms, our simulation shows that a 5-yr observation of a pulsar with an orbital period $p_b\sim 0.5\,{\rm yr}$ and an orbital eccentricity $e\sim 0.8$ can probe a vector charge-to-mass ratio as small as $q/m\sim 10^{-3}$, which is much more stringent than the current constraint from the event horizon telescope (eht) observations, and comparable to the prospective constraint from extreme mass-ratio inspirals with the laser interferometer space antenna (lisa). | probing the vector charge of sagittarius a* with pulsar timing |
we investigate gravitational-wave backgrounds (gwbs) of primordial origin that would manifest only at ultra-high frequencies, from kilohertz to 100 gigahertz, and leave no signal at either ligo, einstein telescope, cosmic explorer, lisa, or pulsar-timing arrays. we focus on gwbs produced by cosmic strings and make predictions for the gw spectra scanning over high-energy scale (beyond $10^{10}$ gev) particle physics parameters. signals from local string networks can easily be as large as the big bang nucleosynthesis/cosmic microwave background bounds, with a characteristic strain as high as $10^{-26}$ in the 10 khz band, offering prospects to probe grand unification physics in the $10^{14}-10^{17}$ gev energy range. in comparison, gwb from axionic strings is suppressed (with maximal characteristic strain $\sim 10^{-31}$) due to the early matter era induced by the associated heavy axions. we estimate the needed reach of hypothetical futuristic gw detectors to probe such gw and, therefore, the corresponding high-energy physics processes. beyond the information of the symmetry-breaking scale, the high-frequency spectrum encodes the microscopic structure of the strings through the position of the uv cutoffs associated with cusps and/or kinks, as well as potential information about friction forces on the string. the ir slope, on the other hand, reflects the physics responsible for the decay of the string network. we discuss possible strategies for reconstructing the scalar potential, particularly the scalar self-coupling, from the measurement of the uv cutoff of the gw spectrum. | ultra-high frequency primordial gravitational waves beyond the khz: the case of cosmic strings |
we present the analysis of 200-ks nustar observation of the vela pulsar and the pulsar wind nebula (pwn). the phase-resolved spectra corresponding to the two main peaks in the folded pulse profile differ significantly. the spectrum of peak 1 is significantly harder than that of peak 2 in qualitative agreement with the earlier rxte results. however, for both spectra, the best-fit values of photon indices for the power-law (pl) fit are noticeably larger than the previously reported values. the hardest (peak 1) spectrum has a photon index of $1.10\pm0.15$ which is close to those measured for the bright inner jets of the pwn. we used the off-pulse interval to isolate pulsar emission and measure the compact pulsar wind nebula (pwn) spectrum in hard x-rays. we also measured the spectrum from the south-western (sw) region of the pwn which is resolved by nustar from the compact pwn. for both regions, we fit the nustar spectra by themselves and together with the chandra x-ray observatory spectra. we found that the compact pwn spectrum requires a more complex model than a simple pl with evidence for exponential cutoff in 50-80 kev. we do not find such evidence for the spectrum extracted from the sw pwn region, located farther from the pulsar, implying the energies over 600 tev for the pulsar wind particles. this may indicate in-situ particle acceleration in that region. | nustar observation of the vela pulsar and its nebula |
the maxi/gsc nova-alert system (negoro et al. 2016) detected an x-ray brightening from the be/x-ray binary pulsar v 0332+53 (x0331+53) on 2017 january 21 (mjd 57774). | maxi/gsc detection of the outburst onset from be/x-ray binary pulsar v 0332+53 (x0331+53) |
pulsar magnetospheres are thought to be filled with electron-positron plasma generated in pair cascades. the driving mechanism of these cascades is the emission of gamma-ray photons and their conversion into pairs via quantum electrodynamics (qed) processes. in this work, we present 2d particle-in-cell simulations of pair cascades in pulsar polar caps with realistic magnetic field geometry that include the relevant qed processes from first principles. our results show that, due to variation of magnetic field curvature across the polar cap, pair production bursts self-consistently develop an inclination with respect to the local magnetic field that favors the generation of coherent electromagnetic modes with properties consistent with pulsar radio emission. we show that this emission is peaked along the magnetic axis and close to the polar cap edge and may thus offer an explanation for the core and conal components of pulsar radio emission. | coherent emission from qed cascades in pulsar polar caps |
recently, evidence of stochastic gravitational wave background (sgwb) signals observed by pulsar timing array (pta) collaborations, has prompted investigations into their origins. we explore the compatibility of a proposed inflationary scenario, incorporating an intermediate null energy condition (nec)-violating phase, with the pta observations. the nec violation potentially amplifies the primordial tensor power spectrum, offering a promising explanation for pta observations. numerical analyses, primarily focused on nanograv's 15-year results, reveal the model's compatibility with pta data. notably, the model predicts a nearly scale-invariant gw spectrum in the mhz frequency range, which sets our scenario apart from other interpretations predicting a red primordial gw spectrum on smaller scales. | null energy condition violation during inflation and pulsar timing array observations |
pulsars are known for their exceptionally stable rotation. however, this stability can be disrupted by glitches, sudden increases in rotation frequency whose cause is poorly understood. in this study, we present some preliminary results from the pulsar monitoring campaign conducted at the iar since 2019. we present measurements from timing solution fits of the parameters of five glitches: one glitch in the vela pulsar, one in psr j0742-2822, one in psr j1740-3015, and two mini-glitches in psr j1048-5832. finally, we applied the vortex creep model to characterize the inter-glitch period of vela. however, the preliminary results yielded highly degenerate and loosely constrained parameters. | updates on the glitching pulsar monitoring campaign performed from iar |
recent detections of a low-frequency gravitational wave background (gwb) from various pulsar-timing-array (pta) observations have renewed the interest in the inspiraling supermassive black hole binaries (smbhbs), whose population is believed to be the most promising candidate of but disfavored by the observed gwb spectrum naively fitted with purely gw-driven circular binaries. including either orbital eccentricity or dark matter (dm) spike can improve the fit to the current data, but the inclusion of both can further display distinctive features detectable in future pta observations. with a typical initial eccentricity $e_0\sim\mathcal{o}(0.1)$ for the inspiraling smbhbs, even a shallow dm spike can easily drive the orbital eccentricity close to unity, leaving behind a large turnover eccentricity when gws begin to dominate the orbital circularization. in particular, the dm spike index $\gamma_\mathrm{sp}$ universally flattens the characteristic strain $h_c\sim f^{7/6-\gamma_\mathrm{sp}/3}$ in the infrared and produces a novel structure with an oscillating turnover followed by a flat dip and a bump-like peak at low, intermediate, and high frequencies, respectively. future pta detection of such characteristics would necessarily provide the smoking gun for the dm spike and even reveal the nature of dm. | distinctive gwbs from eccentric inspiraling smbh binaries with a dm spike |
general relativity has been very successful since its proposal more a century ago. however, various cosmological observations and theoretical consistency still motivate us to explore extended gravity theories. horndeski gravity stands out as one attractive theory by introducing only one scalar field. here we formulate the post-newtonian effective field theory of horndeski gravity and investigate the conservative dynamics of the inspiral compact binary systems. we calculate the leading effective lagrangian for a compact binary and obtain the periastron advance per period. in particular, we apply our analytical calculation to two binary systems, psr b 1534+12 and psr j0737-3039, and constrain the relevant model parameters. the theoretical framework can also be extended to higher order systematically. | post-newtonian binary dynamics in effective field theory of horndeski gravity |
the discovery of gravitational waves (gws) opens a new window for exploring the physics of the early universe. identifying the source of gws and their spectra today turn out to be the important tasks so as to assist the experimental detection of stochastic gws. in this paper, we investigate the oscillations of the ultralight dark photon (uldp) into gws in the dark halo. assuming dark matter is composed of the uldp and there are primordial dark magnetic fields (pdmfs) arising from the axion inflation and/or the dark phase transition, then the uldp can oscillate into the gw when it passes through an environment of pdmfs. we derive the local energy density of gws in the galaxy cluster induced by the instaneous oscillation of uldp in the pdmfs. these stochastic local gws exhibit a pulse-like spectrum, with frequency depending on the mass of the uldp, and can be detected in pulsar timing arrays (ptas) or future space-based interferometers. we also find that the low-frequency gw signal observed by the nanograv collaboration and other pta experiments can be explained by the oscillation of the uldp in the pdmfs in the early universe. | oscillations of ultralight dark photon into gravitational waves |
the recent analysis on the central compact object in the hess j1731-347 remnant suggests interestingly small values for its mass and radius. such an observation favors soft nuclear models that may be challenged by the observation of massive compact stars. in contrast, the recent prex-ii experiment, concerning the neutron skin thickness of $^{208}$pb, points towards stiff equations of state that favor larger compact star radii. in the present study, we aim to explore the compatibility between stiff hadronic equations of state (favored by prex-ii) and the hess j1731-347 remnant in the context of hybrid stars. for the construction of hybrid equations of state we use three widely employed skyrme models combined with the well-known vector mit bag model. furthermore we consider two different scenarios concerning the energy density of the bag. in the first case, that of a constant bag parameter, we find that the resulting hybrid equations of state are strongly disfavored by the observation of $\sim2 m_\odot$ pulsars. however, the introduction of a gaussian density dependence yields results that are compatible with the conservative $2 m_\odot$ constraint. the utilization of recent data based on the observation of psr j0030+0451, psr j0952-0607 and gw190814 allows for the imposition of additional constraints on the relevant parameters and the stiffness of the two phases. interestingly, we find that the derived hybrid equations of state do not satisfy the psr j0030+0451 constraints in $1\sigma$ and only marginally agree with the $2\sigma$ estimations. in addition, we estimate that the observation of massive pulsars, like psr~j0952-0607, in combination with the existence of hess j1731-347, may require a strong phase transition below $\sim 1.7n_0$. finally, we show that the supermassive compact object involved in gw190814 could potentially be explained as a rapidly rotating hybrid star. | hybrid stars in light of the hess j1731-347 remnant and the prex-ii experiment |
it has been suggested that the gev excess, observed from the region surrounding the galactic center, might originate from a population of millisecond pulsars that formed in globular clusters. with this in mind, we employ the publicly available fermi data to study the gamma-ray emission from 157 globular clusters, identifying a statistically significant signal from 25 of these sources (ten of which are not found in existing gamma-ray catalogs). we combine these observations with the predicted pulsar formation rate based on the stellar encounter rate of each globular cluster to constrain the gamma-ray luminosity function of millisecond pulsars in the milky way's globular cluster system. we find that this pulsar population exhibits a luminosity function that is quite similar to those millisecond pulsars observed in the field of the milky way (i.e. the thick disk). after pulsars are expelled from a globular cluster, however, they continue to lose rotational kinetic energy and become less luminous, causing their luminosity function to depart from the steady-state distribution. using this luminosity function and a model for the globular cluster disruption rate, we show that millisecond pulsars born in globular clusters can account for only a few percent or less of the observed gev excess. among other challenges, scenarios in which the entire gev excess is generated from such pulsars are in conflict with the observed mass of the milky way's central stellar cluster. | the gamma-ray pulsar population of globular clusters: implications for the gev excess |
we report on a comprehensive multiwavelength study of the pulsars in the globular cluster (gc) m5, including the discovery of m5g, a new compact noneclipsing "black widow" pulsar. thanks to the analysis of 34 yr of radio data taken with the five-hundred-meter aperture spherical radio telescope and arecibo telescopes, we obtained new phase-connected timing solutions for four pulsars and improved those of the other three. these have resulted in, among other things, (a) much improved proper motions for five pulsars, with transverse velocities (relative to the cluster) that are smaller than their respective escape velocities; (b) 3σ and 1.5σ detections of shapiro delays in m5f and m5d, respectively; and (c) greatly improved measurement of the periastron advance in m5b, whose value of $\dot{\omega }=0\buildrel{\circ}\over{.} 01361(6)$ implies that m5b is still likely to be a heavy ( ${m}_{p}={1.981}_{-0.088}^{+0.038}\,{m}_{\odot }$ ) neutron star. the binary pulsars m5d, m5e, and m5f are confirmed to be in low-eccentricity binary systems, the low-mass companions of which are newly identified to be he white dwarfs using hubble space telescope data. four pulsars are also found to be associated with x-ray sources. similarly to the eclipsing pulsar m5c, m5g shows little or no nonthermal x-ray emission, indicative of weak synchrotron radiation produced by intrabinary shocks. all seven pulsars known in m5 have short spin periods (<8 ms), and five are in binary systems with low orbital eccentricities. these characteristics differ from the overall gc pulsar population but confirm the expectations for the pulsar population in a cluster with a small rate of stellar encounters per binary system. | discovery and timing of millisecond pulsars in the globular cluster m5 with fast and arecibo |
the cherenkov telescope array (cta) is a next-generation ground-based observatory for gamma-ray astronomy at very high energies. the large-sized telescope prototype (lst-1) is located at the cta-north site, on the canary island of la palma. lsts are designed to provide optimal performance in the lowest part of the energy range covered by cta, down to ≃20 gev. lst-1 started performing astronomical observations in 2019 november, during its commissioning phase, and it has been taking data ever since. we present the first lst-1 observations of the crab nebula, the standard candle of very-high-energy gamma-ray astronomy, and use them, together with simulations, to assess the performance of the telescope. lst-1 has reached the expected performance during its commissioning period-only a minor adjustment of the preexisting simulations was needed to match the telescope's behavior. the energy threshold at trigger level is around 20 gev, rising to ≃30 gev after data analysis. performance parameters depend strongly on energy, and on the strength of the gamma-ray selection cuts in the analysis: angular resolution ranges from 0.°12-0.°40, and energy resolution from 15%-50%. flux sensitivity is around 1.1% of the crab nebula flux above 250 gev for a 50 hr observation (12% for 30 minutes). the spectral energy distribution (in the 0.03-30 tev range) and the light curve obtained for the crab nebula agree with previous measurements, considering statistical and systematic uncertainties. a clear periodic signal is also detected from the pulsar at the center of the nebula. | observations of the crab nebula and pulsar with the large-sized telescope prototype of the cherenkov telescope array |
cosi is a smex mission that provides a significant improvement in 0.2-5 mev sensitivity along with high-resolution spectroscopy, enabling studies of 511 kev positron annihilation emission and measurements of radioactive elements. cosi measures polarization of grbs, accreting black holes, and pulsars as well as localizing multimessenger sources. | the compton spectrometer and imager |
black hole-neutron star (bhns) mergers are one of the most promising targets for multimessenger astronomy. using general relativistic magnetohydrodynamic simulations of bhns undergoing merger we previously showed that a magnetically driven jet can be launched by the disk +spinning black hole remnant if the neutron star is endowed with a dipole magnetic field extending from the interior into the exterior as in a radio pulsar. these self-consistent studies considered a bhns system with mass ratio q =3 :1 , black hole spin a /mbh=0.75 aligned with the total orbital angular momentum, and a neutron star that is irrotational, threaded by an aligned magnetic field and modeled by an γ -law equation of state with γ =2 . here, as a crucial step in establishing bhns systems as viable progenitors of central engines that power short gamma-ray bursts (sgrbs) and thereby solidify their role as multimessenger sources, we survey different bhns configurations that differ in the spin of the bh companion (a /mbh=-0.5 , 0, 0.5, 0.75), in the mass ratio (q =3 :1 and q =5 :1 ) and in the orientation of the magnetic field (aligned and tilted by 90° with respect to the orbital angular momentum). we find that by δ t ∼3500 m -4000 m ∼88 (mns/1.4 m⊙) ms -100 (mns/1.4 m⊙) ms after the peak gravitational wave signal a magnetically driven jet is launched in the cases where the initial spin of the bh companion is a /mbh=0.5 or 0.75. the lifetime of the jets [δ t ∼0.5 (mns/1.4 m⊙) s -0.7 (mns/1.4 m⊙) s ] and their outgoing poynting luminosities [ljet∼1 051 ±1 erg /s ] are consistent with typical sgrbs, as well as with the blandford-znajek mechanism for launching jets and their associated poynting luminosities. by the time we terminate our simulations, we do not observe either an outflow or a large-scale magnetic field collimation in the other configurations we simulate. these results suggest that future multimessenger detections from bhnss are more likely produced by binaries with highly spinning bh companions and small tilt-angle magnetic fields, though other physical processes not considered here, such as neutrino annihilation, may help to power jets in general cases. | jet launching from binary black hole-neutron star mergers: dependence on black hole spin, binary mass ratio, and magnetic field orientation |
ultraluminous x-ray (ulx) pulsars are a new class of object powered by apparent super-critical accretion onto magnetized neutron stars. three sources in this class have been identified so far; m82 x-2, ngc 5907 ulx-1, and ngc 7793 p13 have been found to have two properties in common; ∼1 s spin periods, and for ngc 5907 ulx-1 and ngc 7793 p13 periodic x-ray flux modulations on timescales of ∼60-80 days. m82 x-2 resides in a crowded field that includes the ulx m82 x-1 separated from x-2 by 5″, as well as other bright point sources. a 60 day modulation has been observed from the region, but the origin has been difficult to identify; both m82 x-1 and x-2 have been suggested as the source. in this paper we present the analysis of a systematic monitoring campaign by chandra, the only x-ray telescope capable of resolving the crowded field. from a simple lomb-scargle periodogram analysis and a more sophisticated gaussian process analysis we find that only x-2 exhibits a periodic signal around 60 days, supporting previous claims that it is the origin. we also construct a phase-averaged flux profile of the modulations from higher-cadence swift/xrt data and find that the flux variations in the chandra data are fully consistent with the flux profile. since the orbit of the neutron star and its companion is known to be 2.5 days, the ∼60 day period must be super-orbital in origin. the flux of the modulations varies by a factor of ∼100 from the minimum to the maximum, with no evidence for spectral variations, making the origin difficult to explain. | a ∼60 day super-orbital period originating from the ultraluminous x-ray pulsar in m82 |
xte j1810-197 (psr j1809-1943) was the first magnetar that was found to emit transient radio emission. it has recently undergone another radio and high-energy outburst. this is only the second radio outburst that has been observed from this source. we observed j1810-197 soon after its recent radio outburst at low radio frequencies using the giant metrewave radio telescope. we present the 650 mhz flux density evolution of the source in the early phases of the outburst, and its radio spectrum down to frequencies as low as 300 mhz. the magnetar also exhibits radio emission in the form of strong, narrow bursts. we show that the bursts have a characteristic intrinsic width of the order of 0.5-0.7 ms, and discuss their properties in the context of giant pulses and giant micropulses from other pulsars. we also show that the bursts exhibit spectral structures that cannot be explained by interstellar propagation effects. these structures might indicate a phenomenological link with the repeating fast radio bursts that also show interesting, more detailed frequency structures. while the spectral structures are particularly noticeable in the early phases of the outburst, these seem to be less prominent as well as less frequent in the later phases, suggesting an evolution of the underlying cause of these spectral structures. | distinct properties of the radio burst emission from the magnetar xte j1810-197 |
we explore the possibility that the observed population of galactic hypervelocity stars (hvss) originate as runaway stars from the large magellanic cloud (lmc). pairing a binary evolution code with an n-body simulation of the interaction of the lmc with the milky way, we predict the spatial distribution and kinematics of an lmc runaway population. we find that runaway stars from the lmc can contribute galactic hvss at a rate of 3 × 10-6 yr-1. this is composed of stars at different points of stellar evolution, ranging from the main sequence to those at the tip of the asymptotic giant branch. we find that the known b-type hvss have kinematics that are consistent with an lmc origin. there is an additional population of hypervelocity white dwarfs whose progenitors were massive runaway stars. runaways that are even more massive will themselves go supernova, producing a remnant whose velocity will be modulated by a supernova kick. this latter scenario has some exotic consequences, such as pulsars and supernovae far from star-forming regions, and a small rate of microlensing from compact sources around the halo of the lmc. | hypervelocity runaways from the large magellanic cloud |
while theoretical models of dust condensation predict that most refractory elements produced in core-collapse supernovae (sne) efficiently condense into dust, a large quantity of dust has so far only been observed in sn 1987a. we present an analysis of observations from the spitzer space telescope, herschel space observatory, stratospheric observatory for infrared astronomy, and akari of the infrared shell surrounding the pulsar wind nebula in the supernova remnant g54.1+0.3. we attribute a distinctive spectral feature at 21 μm to a magnesium silicate grain species that has been invoked in modeling the ejecta-condensed dust in cas a, which exhibits the same spectral signature. if this species is responsible for producing the observed spectral feature and accounts for a significant fraction of the observed infrared continuum, we find that it would be the dominant constituent of the dust in g54.1+0.3, with possible secondary contributions from other compositions, such as carbon, silicate, or alumina grains. the total mass of sn-formed dust required by this model is at least 0.3 m ⊙. we discuss how these results may be affected by varying dust grain properties and self-consistent grain heating models. the spatial distribution of the dust mass and temperature in g54.1+0.3 confirms the scenario in which the sn-formed dust has not yet been processed by the sn reverse shock and is being heated by stars belonging to a cluster in which the sn progenitor exploded. the dust mass and composition suggest a progenitor mass of 16-27 m ⊙ and imply a high dust condensation efficiency, similar to that found for cas a and sn 1987a. the study provides another example of significant dust formation in a type iip sn explosion and sheds light on the properties of pristine sn-condensed dust. | a massive shell of supernova-formed dust in snr g54.1+0.3 |
in this study we demonstrate that general relativity predicts arrival time differences between gravitational wave (gw) and electromagnetic (em) signals caused by the wave effects in gravitational lensing. the gw signals can arrive earlier than the em signals in some cases if the gw/em signals have passed through a lens, even if both signals were emitted simultaneously by a source. gw wavelengths are much larger than em wavelengths; therefore, the propagation of the gws does not follow the laws of geometrical optics, including the shapiro time delay, if the lens mass is less than approximately 105 m⊙(f/hz)-1, where f is the gw frequency. the arrival time difference can reach ∼0.1 s (f/hz)-1 if the signals have passed by a lens of mass ∼8000 m⊙(f/hz)-1 with the impact parameter smaller than the einstein radius; therefore, it is more prominent for lower gw frequencies. for example, when a distant supermassive black hole binary (smbhb) in a galactic center is lensed by an intervening galaxy, the time lag becomes of the order of 10 days. future pulsar timing arrays including the square kilometre array and x-ray detectors may detect several time lags by measuring the orbital phase differences between the gw/em signals in the smbhbs. gravitational lensing imprints a characteristic modulation on a chirp waveform; therefore, we can deduce whether a measured arrival time lag arises from intrinsic source properties or gravitational lensing. determination of arrival time differences would be extremely useful in multimessenger observations and tests of general relativity. | arrival time differences between gravitational waves and electromagnetic signals due to gravitational lensing |
gravitational waves (gws) are a new avenue of observing our universe. so far, we have seen them in the ~10-100 hz range, and there are hints that we might soon detect them in the nanohertz regime. multiple efforts are underway to access gws across the frequency spectrum; however, parts of the frequency space are currently not covered by any planned or future observatories. photometric surveys can bridge the microhertz gap in the spectrum between lisa and pulsar timing arrays (ptas) through relative astrometric measurements. similar to pta measurements, these astrometric measurements rely on the correlated spacetime distortions produced by gravitational waves at earth, which induce coherent, apparent stellar position changes on the sky. to detect microhertz gws with an imaging survey, a combination of high relative astrometric precision, a large number of observed stars, and a high cadence of exposures are needed. roman's proposed core community survey, the galactic bulge time domain survey (rgbtds), would have all of these components. rgbtds would be sensitive to gws with frequencies ranging from $7.7\times 10^{-8}$ hz to $5.6\times 10^{-4}$ hz, which opens up a unique gw observing window for supermassive black hole binaries and their waveform evolution. we note that small changes to the survey could enhance roman's sensitivity to gws, making it possible to observe the gw background signal that ptas have recently hinted at with an snr $\sim$ 70. | gravitational wave detection with relative astrometry using roman's galactic bulge time domain survey |
the nature of gw190814's secondary component m2 of mass 2.50-2.67 m⊙ in the mass gap between the currently known maximum mass of neutron stars and the minimum mass of black holes is currently under hot debate. among the many possibilities proposed in the literature, m2 was suggested to be a superfast pulsar, while its r-mode stability against runaway gravitational radiation through the chandrasekhar-friedman-schutz mechanism is still unknown. previously, fortin et al. constructed a sample of 33 unified equations of state using the same nuclear interactions from the crust to the core consistently; from that sample we use those equations that fulfill all currently known astrophysical and nuclear physics constraints to compare the minimum frequency required for m2 to rotationally sustain a mass greater than 2.50 m⊙ with the critical frequency above which the r-mode instability occurs. we use two extreme damping models assuming that the crust is either perfectly rigid or elastic. using the stability of 19 observed low-mass x-ray binaries as an indication that the rigid crust damping of the r-mode dominates within the models studied, we find that m2 is r-mode-stable while rotating with a frequency higher than 870.2 hz (0.744 times its kepler frequency of 1169.6 hz) as long as its temperature is lower than about 3.9 × 107 k, further supporting the proposal that gw190814's secondary component is a supermassive and superfast pulsar. | r-mode stability of gw190814's secondary component as a supermassive and superfast pulsar |
we conduct searches for continuous gravitational waves from seven pulsars that have not been targeted in continuous wave searches of advanced ligo data before. we target emission at exactly twice the rotation frequency of the pulsars and in a small band around such a frequency. the former search assumes that the gravitational-wave quadrupole is changing in a phase-locked manner with the rotation of the pulsar. the latter search over a range of frequencies allows for differential rotation between the component emitting the radio signal and the component emitting the gravitational waves, for example the crust or magnetosphere versus the core. timing solutions derived from the arecibo 327 mhz drift-scan pulsar survey observations are used. no evidence of a signal is found and upper limits are set on the gravitational-wave amplitude. for one of the pulsars we probe gravitational-wave intrinsic amplitudes just a factor of 3.8 higher than the spin-down limit, assuming a canonical moment of inertia of 1038 kg m2. our tightest ellipticity constraint is 1.5 × 10-8, which is a value well within the range of what a neutron star crust could support. | new searches for continuous gravitational waves from seven fast pulsars |
we have measured the scattering time-scale, τ, and the scattering spectral index, α, for 84 single-component pulsars. observations were carried out with the meerkat telescope as part of the thousand-pulsar-array programme in the meertime project at frequencies between 0.895 and 1.670 ghz. our results give a distribution of values for α (defined in terms of τ and frequency ν as τ ∝ ν-α) for which, upon fitting a gaussian, we obtain a mean and standard deviation of <α> = 4.0 ± 0.6. this is due to our identification of possible causes of inaccurate measurement of τ, which, if not filtered out of modelling results, tend to lead to underestimation of α. the pulsars in our sample have large dispersion measures and are therefore likely to be distant. we find that a model using an isotropic scatter broadening function is consistent with the data, likely due to the averaging effect of multiple scattering screens along the line of sight. our sample of scattering parameters provides a strong data set upon which we can build to test more complex and time-dependent scattering phenomena, such as extreme scattering events. | the thousand-pulsar-array programme on meerkat - v. scattering analysis of single-component pulsars |
neutrons were discovered 90 years ago by james chadwick. the concept of neutron stars was hypothesized around that time by lev landau, walter baade, and fritz zwicky, and it was further developed by richard tolman, robert oppenheimer, george volkoff, and other physicists. neutron stars are astrophysical compact objects formed after the death of massive stars (more massive than our own sun). according to current understanding, the typical mass of neutron stars is comparable to that of the sun, while the radius is only ∼ 10 km. as its name implies, the main interior ingredients of such stars are neutrons, but they also consist of protons, electrons, muons, and presumably even more exotic particles, like hyperons, kaons, or quarks. the field of neutron stars was bolstered by the discovery of radio pulsars by jocelyn bell burnell, antony hewish, and collaborators in 1967 [1]. a famous achievement brought forth by the first binary pulsar, the so-called hulse-taylor pulsar, is the first-ever empirical proof that gravitational waves exist in our universe [2]. in 2017, the first binary neutron star merger was observed directly via gravitational waves (ripples of spacetime) and accompanied by enormous electromagnetic follow-up observations [3]. this event, known as gw170817, marked the dawn of multi-messenger astronomy and was chosen as "science's 2017 breakthrough of the year". | neutron stars as extreme laboratories for gravity tests |
we present the sarao meerkat galactic plane survey (smgps), a 1.3 ghz continuum survey of almost half of the galactic plane (251°$\le l \le$ 358°and 2°$\le l \le$ 61°at $|b| \le 1.5°$). smgps is the largest, most sensitive and highest angular resolution 1 ghz survey of the plane yet carried out, with an angular resolution of 8" and a broadband rms sensitivity of $\sim$10--20 $\mu$ jy/beam. here we describe the first publicly available data release from smgps which comprises data cubes of frequency-resolved images over 908--1656 mhz, power law fits to the images, and broadband zeroth moment integrated intensity images. a thorough assessment of the data quality and guidance for future usage of the data products are given. finally, we discuss the tremendous potential of smgps by showcasing highlights of the galactic and extragalactic science that it permits. these highlights include the discovery of a new population of non-thermal radio filaments; identification of new candidate supernova remnants, pulsar wind nebulae and planetary nebulae; improved radio/mid-ir classification of rare luminous blue variables and discovery of associated extended radio nebulae; new radio stars identified by bayesian cross-matching techniques; the realisation that many of the largest radio-quiet wise hii region candidates are not true hii regions; and a large sample of previously undiscovered background hi galaxies in the zone of avoidance. | the sarao meerkat 1.3 ghz galactic plane survey |
cosmic-ray positrons have long been considered a powerful probe of dark matter annihilation. in particular, myriad studies of the unexpected rise in the positron fraction have debated its dark matter or pulsar origins. in this paper, we instead examine the potential for extremely precise positron measurements by ams-02 to probe hard leptophilic dark matter candidates that do not have spectral features similar to the bulk of the observed positron excess. utilizing a detailed cosmic-ray propagation model that includes a primary positron flux generated by galactic pulsars in addition to a secondary component constrained by he and proton measurements, we produce a robust fit to the local positron flux and spectrum. we find no evidence for a spectral bump correlated with leptophilic dark matter, and set strong constraints on the dark matter annihilation cross-section that fall below the thermal annihilation cross-section for dark matter masses below 60 gev and 380 gev for annihilation into τ+τ- and e+e-, respectively, in our default model. | cosmic-ray positrons strongly constrain leptophilic dark matter |
in this paper, we assess different charged self-gravitating stellar models possessing anisotropic matter source in the background of $f(g,t)$ gravity. for this purpose, we choose a well-known model of this gravity, i.e., $f(g,t)=g^2+\varrho t$, where $\varrho$ stands for the coupling constant. the modified field equations are developed using mit bag model equation of state, and their solution is found with the help of tolman iv ansatz which contains three unknown constants. this solution is further exploited to examine the graphical behavior of her x-i, psr j1614-2230, 4u1820-30 and lmc x-4 celestial objects. we assume two different values of charge to figure out the pressure constituents, energy density, anisotropy and energy constraints graphically. we also discuss compactness, mass and redshift parameters. finally, we explore stability of the considered stars through two different methods. it is concluded that all the star candidates are viable as well as stable for $\mathcal{q}=0.1$. for the larger charge, the viable behavior is also observed for all stars but psr j1614-2230 shows unstable trend. | study of charged celestial objects in modified gravity |
the detection of nanohertz gravitational waves through pulsar timing arrays hinges on identifying a common stochastic process affecting all pulsars in a correlated way across the sky. in the presence of other deterministic and stochastic processes affecting the time-of-arrival of pulses, a detection claim must be accompanied by a detailed assessment of the various physical or phenomenological models used to describe the data. in this study, we propose posterior predictive checks as a model-checking tool that relies on the predictive performance of the models with regards to new data. we derive and study predictive checks based on different components of the models, namely the fourier coefficients of the stochastic process, the correlation pattern, and the timing residuals. we assess the ability of our checks to identify model misspecification in simulated datasets. we find that they can accurately flag a stochastic process spectral shape that deviates from the common power-law model as well as a stochastic process that does not display the expected angular correlation pattern. posterior predictive likelihoods derived under different assumptions about the correlation pattern can further be used to establish detection significance. in the era of nanohertz gravitational wave detection from different pulsar-timing datasets, such tests represent an essential tool in assessing data consistency and supporting astrophysical inference. | posterior predictive checking for gravitational-wave detection with pulsar timing arrays. ii. posterior predictive distributions and pseudo-bayes factors |
in this paper, we investigate the properties of anisotropic, spherically symmetric compact stars, especially, electrically charged strange stars in f(q) symmetric teleparallel gravity. those stars are hypothesized to be composed of strange quark matter, whose distribution is controlled by the mit-bag model equation of state (eos), which correlates density and pressure by incorporating the bag constant (which balances the inward-directed bag pressure). in contrast, the form of electrical charge distribution is chosen to be q (r ) =k r3 , where k is the charge intensity for exhibiting the charged nature of matter distributions. when considering this theory, the unidentified constraints are evaluated by the matching of interior spacetime with the reissner-nordström exterior geometry corresponding to tolman models. in particular, with the assumption that radial pressure at the stellar surface is vanishing, the radii of compact star candidates viz., gw190814, p s r j 0740 +6620 , and p s r j 1614 -2230 are predicted using their observed masses. the physical viability and hydrostatic equilibrium along with the dynamical stability of the resulting solution through graphical behavior of matter variables, energy constraints, modified tov equation, adiabatic index, and causality condition were also tested in order to describe the realistic models. conclusively, our findings indirectly support the existence of electrically charged super-massive pulsars in f(q) gravitational theory. | anisotropic electrically charged stars in f(q) symmetric teleparallel gravity |
the shapes of galaxies trace scalar physics in the late-universe through the large-scale gravitational potential. are they also sensitive to higher-spin physics? we present a general study into the observational consequences of vector and tensor modes in the early and late universe, through the statistics of cosmic shear and its higher-order generalization, flexion. higher-spin contributions arise from both gravitational lensing and intrinsic alignments, and we give the leading-order correlators for each (some of which have been previously derived), in addition to their flat-sky limits. in particular, we find non-trivial sourcing of shear $eb$ and $bb$ spectra, depending on the parity properties of the source. we consider two sources of vector and tensor modes: scale-invariant primordial fluctuations and cosmic strings, forecasting the detectability of each for upcoming surveys. shear is found to be a powerful probe of cosmic strings, primarily through the continual sourcing of vector modes; flexion adds little to the constraining power except on very small scales ($\ell\gtrsim 1000$), though it could be an intriguing probe of as-yet-unknown rank-three tensors or halo-scale physics. such probes could be used to constrain new physics proposed to explain recent pulsar timing array observations. | what can galaxy shapes tell us about physics beyond the standard model? |
we propose a new stellar structure of compact stars, the "cross stars" that consist of a hadronic matter core and a quark matter crust, with an inverted structure compared to the conventional hybrid stars. this distinct stellar structure naturally arises from the quark matter to hadronic matter transition associated with the chemical potential crossing, in the context of the quark matter hypothesis that either strange or up-down quark matter is the ground state of baryonic matter at low pressure. we find that the interplay between the hadronic matter and quark matter compositions of cross stars can help to reconcile the small radii constraints indicated by the ligo/virgo gw170817 event, the large radii constraints set for massive compact stars by recent nicer x-ray observations, and the recent observation of the most-massive pulsar psr j0952-0607. this leaves more space open for the equation of states of both hadronic matter and quark matter. | hybrid stars may have an inverted structure |
astrometry holds the potential for testing fundamental physics through the effects of the stochastic gravitational wave background (sgwb) in the $\sim 1-100$ nhz frequency band on precision measurements of stellar positions. such measurements are complementary to tests made possible by the detection of the sgwb using pulsar timing arrays. here, the feasibility of using astrometry for the identification of parity-violating signals within the sgwb is investigated. this is achieved by defining and quantifying a non-vanishing $eb$ correlation function within astrometric correlation functions, and investigating how one might estimate the detectability of such signals. | probing parity violation in the stochastic gravitational wave background with astrometry |
observations of accreting neutron stars (nss) with strong magnetic fields can be used not only for studying the accretion flow interaction with the ns magnetospheres, but also for understanding the physical processes inside nss and for estimating their fundamental parameters. of particular interest are (i) the interaction of a rotating ns (magnetosphere) with the infalling matter at different accretion rates, and (ii) the theory of deep crustal heating and the influence of a strong magnetic field on this process. here, we present results of the first systematic investigation of 16 x-ray pulsars with be optical companions during their quiescent states, based on data from the chandra, xmm-newton and swift observatories. the whole sample of sources can be roughly divided into two distinct groups: (i) relatively bright objects with a luminosity around ∼1034 erg s-1 and (hard) power-law spectra, and (ii) fainter ones showing thermal spectra. x-ray pulsations were detected from five objects in group (i) with quite a large pulse fraction of 50-70 per cent. the obtained results are discussed within the framework of the models describing the interaction of the infalling matter with the ns magnetic field and those describing heating and cooling in accreting nss. | the x-ray properties of be/x-ray pulsars in quiescence |
more than 100 millisecond pulsars (msps) have been discovered in radio observations of gamma-ray sources detected by the fermi large area telescope (lat), but hundreds of pulsar-like sources remain unidentified. here, we present the first results from the targeted survey of fermi-lat sources being performed by the transients and pulsars with meerkat (trapum) large survey project. we observed 79 sources identified as possible gamma-ray pulsar candidates by a random forest classification of unassociated sources from the 4fgl catalogue. each source was observed for 10 min on two separate epochs using meerkat's l-band receiver (856-1712 mhz), with typical pulsed flux density sensitivities of $\sim 100\, \mu$jy. nine new msps were discovered, eight of which are in binary systems, including two eclipsing redbacks and one system, psr j1526-2744, that appears to have a white dwarf companion in an unusually compact 5 h orbit. we obtained phase-connected timing solutions for two of these msps, enabling the detection of gamma-ray pulsations in the fermi-lat data. a follow-up search for continuous gravitational waves from psr j1526-2744 in advanced ligo data using the resulting fermi-lat timing ephemeris yielded no detection, but sets an upper limit on the neutron star ellipticity of 2.45 × 10-8. we also detected x-ray emission from the redback psr j1803-6707 in data from the first erosita all-sky survey, likely due to emission from an intrabinary shock. | the trapum l-band survey for pulsars in fermi-lat gamma-ray sources |
statistical anisotropy in the nanohertz-frequency gravitational wave background (gwb) is expected to be detected by pulsar timing arrays (ptas) in the near future. by developing a frequentist statistical framework that intrinsically restricts the gwb power to be positive, we establish scaling relations for multipole-dependent anisotropy decision thresholds that are a function of the noise properties, timing baselines, and cadences of the pulsars in a pta. we verify that (i) a larger number of pulsars, and (ii) factors that lead to lower uncertainty on spatial cross-correlation measurements between pulsars, lead to a higher overall gwb signal-to-noise ratio, and lower anisotropy decision thresholds with which to reject the null hypothesis of isotropy. using conservative simulations of realistic nanograv data sets, we predict that an anisotropic gwb with angular power cl=1 > 0.3cl=0 may be sufficient to produce tension with isotropy at the p = 3 × 10-3 (~3σ) level in near-future nanograv data with a 20 yr baseline. we present ready-to-use scaling relationships that can map these thresholds to any number of pulsars, configuration of pulsar noise properties, or sky coverage. we discuss how ptas can improve the detection prospects for anisotropy, as well as how our methods can be adapted for more versatile searches. | forecasting pulsar timing array sensitivity to anisotropy in the stochastic gravitational wave background |
we present the first large sample of scintillation arcs in millisecond pulsars (msps), analysing 12 sources observed with the large european array for pulsars (leap), and the effelsberg 100-m telescope. we estimate the delays from multipath propagation, measuring significant correlated changes in scattering time-scales over a 10 yr time span. many sources show compact concentrations of power in the secondary spectrum, which in psrs j0613-0200 and j1600-3053 can be tracked between observations, and are consistent with compact scattering at fixed angular positions. other sources such as psrs j1643-1224 and j0621+1002 show diffuse, asymmetric arcs which are likely related to phase-gradients across the scattering screen. psr b1937+21 shows at least three distinct screens which dominate at different times and evidence of varying screen axes or multiscreen interactions. we model annual and orbital arc curvature variations in psr j0613-0200, providing a measurement of the longitude of ascending node, resolving the sense of the orbital inclination, where our best-fit model is of a screen with variable axis of anisotropy over time, corresponding to changes in the scattering of the source. unmodelled variations of the screen's axis of anisotropy are likely to be a limiting factor in determining orbital parameters with scintillation, requiring careful consideration of variable screen properties, or independent very long baseline interferometry (vlbi) measurements. long-term scintillation studies such as this serve as a complementary tool to pulsar timing, to measure a source of correlated noise for pulsar timing arrays, solve pulsar orbits, and to understand the astrophysical origin of scattering screens. | variable scintillation arcs of millisecond pulsars observed with the large european array for pulsars |
we report on radio timing observations of psr j0210+5845 which reveal large deviations from typical pulsar spin-down behaviour. we interpret these deviations as being due to binary motion around the $v=13.5$ star 2mass j02105640$+$5845176, which is coincident in celestial position and distance with the pulsar. archival observations and new optical spectroscopy identify this star as a b6v star with a temperature of $t_\mathrm{eff}\approx 14\,000$k and a mass of $m_\mathrm{c}= 3.5$ to $3.8$m$_\odot$, making it the lowest mass main-sequence star known orbiting a non-recycled pulsar. we found that the timing observations constrain the binary orbit to be wide and moderately eccentric, with an orbital period of $p_\mathrm{b}=47^{+40}_{-14}$yr and eccentricity $e=0.46^{+0.10}_{-0.07}$. we predict that the next periastron passage will occur between 2030 and 2034. due to the low companion mass, we find that the probability for a system with the properties of psr j0210+5845 and its binary companion to survive the supernova is low. we show that a low velocity and fortuitously directed natal kick is required for the binary to remain bound during the supernova explosion, and argue that an electron-capture supernova is a plausible formation scenario for the pulsar. | psr j0210+5845; an ultra wide binary pulsar with a b6v main-sequence star companion |
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