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we report on a full-polarization analysis of the first 25 as yet non-repeating frbs detected at 1.4 ghz by the 110-antenna deep synoptic array (dsa-110) during commissioning observations. we present details of the data-reduction, calibration, and analysis procedures developed for this novel instrument. the data have 32 $\mu$s time resolution and sensitivity to faraday rotation measures (rms) between $\pm10^{6}$ rad m$^{-2}$. rms are detected for 20 frbs with magnitudes ranging from $4-4670$ rad m$^{-2}$. $9/25$ frbs are found to have high ($\ge 70\%$) linear-polarization fractions. the remaining frbs exhibit significant circular polarization ($3/25$), or are either partially depolarized ($8/25$) or unpolarized ($5/25$). we investigate the depolarization mechanism, disfavoring stochastic rm variations within a scattering screen as a dominant cause. polarization-state and possible rm variations are observed in the four frbs with multiple sub-components, but only one other frb shows a change in polarization state. we combine the dsa-110 sample with polarimetry of previously published frbs, and compare the polarization properties of frb sub-populations and frbs with galactic pulsars. although frbs are typically far more polarized than the average profiles of galactic pulsars, and exhibit greater spread in polarization fractions than pulsar single pulses, we find a remarkable similarity between frb polarization fractions and the youngest (characteristic ages $<10^{5}$ yr) pulsars. our results support a scenario wherein frb emission is intrinsically highly linearly polarized, and where propagation effects within progenitor magnetospheres can result in conversion to circular polarization and depolarization. young pulsar emission and magnetospheric-propagation geometries may form a useful analogy for the origin of frb polarization. | deep synoptic array science: polarimetry of 25 new fast radio bursts provides insights into their origins |
aims: taking advantage of more than 11 years of fermi-lat data, we perform a new and deep analysis of the pulsar wind nebula (pwn) hess j1825-137. combining this analysis with recent h.e.s.s. results we investigate and constrain the particle transport mechanisms at work inside the source as well as the system evolution.methods: the pwn is studied using 11.6 years of fermi-lat data between 1 gev and 1 tev. in particular, we present the results of the spectral analysis and the first energy-resolved morphological study of the pwn hess j1825-137 at gev energies, which provide new insights into the γ-ray characteristics of the nebula.results: an optimised analysis of the source returns an extended emission region larger than 2°, corresponding to an intrinsic size of about 150 pc, making hess j1825-137 the most extended γ-ray pwn currently known. the nebula presents a strong energy dependent morphology within the gev range, moving from a radius of ∼1.4° below 10 gev to a radius of ∼0.8° above 100 gev, with a shift in the centroid location.conclusions: thanks to the large extension and peculiar energy-dependent morphology, it is possible to constrain the particle transport mechanisms inside the pwn hess j1825-137. using the variation of the source extension and position, as well as the constraints on the particle transport mechanisms, we present a scheme for the possible evolution of the system. finally, we provide an estimate of the electron energy density and we discuss its nature in the pwn and tev halo-like scenario. | energy dependent morphology of the pulsar wind nebula hess j1825-137 with fermi-lat |
axions are a promising dark matter candidate that were motivated to solve the strong charge-parity problem and that may also address the cosmological matter-antimatter asymmetry. axion-photon conversion is possible in the presence of the strong magnetic fields, and the photon so produced will have energy equal to the axion mass. here we report new limits on axionic dark matter obtained from radio spectra of the galactic center magnetar psr j1745-2900. the magnetar has a magnetic field of 1.6 × 1014 g that interacts with a dark matter density 2 × 105 to 2 × 109 times greater than the local dark matter encountered by terrestrial haloscopes, depending on the galactic dark matter profile. no significant spectral features are detected across 62% of the axion mass range 4.1-165.6 μev (1-40 ghz). the interpretation of flux limits into limits on the two-photon coupling strength gaγγ depends on the magnetospheric conversion model and on the dark matter density at the galactic center. for a standard dark matter profile, we exclude axion models with gaγγ > 6-34 ×10-12 gev-1 with 95% confidence over the mass ranges 4.2-8.4, 8.9-10.0, 12.3-16.4, 18.6-26.9, 33.0-62.1, 70.1-74.3, 78.1-80.7, 105.5-109.6, 111.6-115.2, 126.0-159.3, and 162.5-165.6 μev. for the maximal dark matter cusp allowed by stellar orbits near sgr a*, these limits reduce to gaγγ > 6-34 × 10-14 gev-1, which exclude some theoretical models for masses >33 μev. limits may be improved by modeling stimulated axion conversion, by ray-tracing conversion pathways in the magnetar magnetosphere, and by obtaining deeper broad-band observations of the magnetar. | new limits on axionic dark matter from the magnetar psr j1745-2900 |
high-energy radiation from nonthermal particles accelerated in relativistic magnetic reconnection is thought to be important in many astrophysical systems, ranging from blazar jets and black hole accretion disk coronae to pulsars and magnetar flares. the presence of a substantial density of high-energy photons (>mev) in these systems can make two-photon pair production (γγ → e - e +) an additional source of plasma particles and can affect the radiative properties of these objects. we present the results of novel particle-in-cell simulations that track both the radiated synchrotron photons and the created pairs, with which we study the evolution of a two-dimensional reconnecting current sheet in pair plasma. synchrotron radiation from accelerated particles in the current sheet produces hot secondary pairs in the upstream, which are later advected into the current sheet where they are reaccelerated and produce more photons. in the optically thin regime, when most of the radiation is leaving the upstream unaffected, this process is self-regulating and depends only on the background magnetic field and the optical depth of photons to pair production. the extra plasma loading also affects the properties of reconnection. we study how the inflow of the secondary plasma, with multiplicities up to several hundred, reduces the effective magnetization of the plasma, suppressing the acceleration and thus decreasing the high-energy photon spectrum cutoff. this offers an explanation for the weak dependence of the observed gamma-ray cutoff in pulsars on the magnetic field at the light cylinder. | effects of synchrotron cooling and pair production on collisionless relativistic reconnection |
pulsar timing array experiments search for phenomena that produce angular correlations in the arrival times of signals from millisecond pulsars. the primary goal is to detect an isotropic and stochastic gravitational wave background. we use simulated data to show that this search can be affected by the presence of other spatially correlated noise, such as errors in the reference time standard, errors in the planetary ephemeris, the solar wind and instrumentation issues. all these effects can induce significant false detections of gravitational waves. we test mitigation routines to account for clock errors, ephemeris errors and the solar wind. we demonstrate that it is non-trivial to find an effective mitigation routine for the planetary ephemeris and emphasize that other spatially correlated signals may be present in the data. | a study of spatial correlations in pulsar timing array data |
a faraday rotation measure (rm) catalogue, or rm grid, is a valuable resource for the study of cosmic magnetism. using the second data release (dr2) from the lofar two-metre sky survey (lotss), we have produced a catalogue of 2461 extragalactic high-precision rm values across 5720 deg2 of sky (corresponding to a polarized source areal number density of ~0.43 deg-2). the linear polarization and rm properties were derived using rm synthesis from the stokes q and u channel images at an angular resolution of 20 arcsec across a frequency range of 120 to 168 mhz with a channel bandwidth of 97.6 khz. the fraction of total intensity sources (>1 mjy beam-1) found to be polarized was ~0.2 per cent. the median detection threshold was 0.6 mjy beam-1 (8σqu), with a median rm uncertainty of 0.06 rad m-2 (although a systematic uncertainty of up to 0.3 rad m-2 is possible, after the ionosphere rm correction). the median degree of polarization of the detected sources is 1.8 per cent, with a range of 0.05 per cent to 31 per cent. comparisons with cm-wavelength rms indicate minimal amounts of faraday complexity in the lotss detections, making them ideal sources for rm grid studies. host galaxy identifications were obtained for 88 per cent of the sources, along with redshifts for 79 per cent (both photometric and spectroscopic), with the median redshift being 0.6. the focus of the current catalogue was on reliability rather than completeness, and we expect future versions of the lotss rm grid to have a higher areal number density. in addition, 25 pulsars were identified, mainly through their high degrees of linear polarization. | the faraday rotation measure grid of the lofar two-metre sky survey: data release 2 |
we report on six new chandra observations of the geminga pulsar wind nebula (pwn). the pwn consists of three distinct elongated structures—two ≈ 0.2{d}250 pc long lateral tails and a segmented axial tail of ≈ 0.05{d}250 pc length, where {d}250=d/(250 {pc}). the photon indices of the power-law spectra of the lateral tails, {{γ }}≈ 1, are significantly harder than those of the pulsar ({{γ }}≈ 1.5) and the axial tail ({{γ }}≈ 1.6). there is no significant diffuse x-ray emission between the lateral tails—the ratio of the x-ray surface brightness between the south tail and this sky area is at least 12. the lateral tails apparently connect directly to the pulsar and show indications of moving footpoints. the axial tail comprises time-variable emission blobs. however, there is no evidence for constant or decelerated outward motion of these blobs. different physical models are consistent with the observed morphology and spectra of the geminga pwn. in one scenario, the lateral tails could represent an azimuthally asymmetric shell whose hard emission is caused by the fermi acceleration mechanism of colliding winds. in another scenario, the lateral tails could be luminous, bent polar outflows, while the blobs in the axial tail could represent a crushed torus. in a resemblance to planetary magnetotails, the blobs of the axial tail might also represent short-lived plasmoids, which are formed by magnetic field reconnection in the relativistic plasma of the pulsar wind tail. | geminga’s puzzling pulsar wind nebula |
the dense stellar environment of the galactic center has been proposed to host a large population of as-yet undetected millisecond pulsars (msps). recently, this hypothesis has found support in an analysis of gamma-rays detected using the large area telescope onboard the fermi satellite, which revealed an excess of diffuse gev photons in the inner 15 deg about the galactic center. the excess can be interpreted as the collective emission of thousands of msps in the galactic bulge, with a spherical distribution strongly peaked toward the galactic center. in order to fully establish the msp interpretation, it is essential to find corroborating evidence in multi-wavelength searches, most notably through the detection of radio pulsations from individual bulge msps. based on globular cluster observations and gamma-ray emission from the inner galaxy, we investigate the prospects for detecting msps in the galactic bulge. while previous pulsar surveys failed to identify this population, we demonstrate that upcoming large-area surveys of this region should lead to the detection of dozens of bulge msps. additionally, we show that deep targeted searches of unassociated fermi sources should be able to detect the first few msps in the bulge. the prospects for these deep searches are enhanced by a tentative gamma-ray/radio correlation that we infer from high-latitude gamma-ray msps. such detections would constitute the first clear discoveries of field msps in the galactic bulge, with far-reaching implications for gamma-ray observations, the formation history of the central milky way, and strategy optimization for future deep radio pulsar surveys. | radio detection prospects for a bulge population of millisecond pulsars as suggested by fermi-lat observations of the inner galaxy |
the determination of the polarization modes of gravitational waves (gws), and of their dispersion relations is decisive to scrutinize the viability of extended theories of gravity. a tool to investigate the polarization states of gws is the newman-penrose (np) formalism. however, if the speed of gws is smaller than the speed of light, the number of np variables is greater than the number of polarizations. to overpass this inconvenience we use the bardeen formalism to describe the six possible polarization modes of gws considering different general dispersion relations for the modes. the definition of a new gauge-invariant quantity enables an unambiguous description of the scalar longitudinal polarization mode. we apply the formalism to general relativity, scalar-tensor theories, and $f(r)$-gravity. to obtain a bridge between theory and experiment, we derive an explicit relation between a physical observable (the derivative of the frequency shift of an electromagnetic signal) with the gauge-invariant variables. from this relation, we find an analytical formula for the pulsar timing rms response to each polarization mode. to estimate the sensitivity of a single pulsar timing we focus on the case of a dispersion relation of a massive particle. the sensitivity curves of the scalar longitudinal and vector polarization modes change significantly depending on the value of the effective mass. the detection (or absence of detection) of the polarization modes using the pulsar timing technique has decisive implications for alternative theories of gravity. finally, the investigation of a cutoff frequency in the pulsar timing band can lead to a more stringent bound on the graviton mass than that presented by ground-based interferometers. | testing gravity with gauge-invariant polarization states of gravitational waves |
in this paper, we study compact binary millisecond pulsars with low- and very low-mass companion stars (spiders) in the galactic field, using data from the latest gaia data release (dr3). we infer the parallax distances of the optical counterparts to spiders, which we use to estimate optical and x-ray luminosities. we compare the parallax distances to those derived from radio pulse dispersion measures and find that they have systematically larger values, by 40 per cent on average. we also test the correlation between x-ray and spin-down luminosities, finding that most redbacks have a spin-down to x-ray luminosity conversion efficiency of ~0.1 per cent, indicating a contribution from the intrabinary shock. on the other hand, most black widows have an efficiency of ~0.01 per cent, similar to the majority of the pulsar population. finally, we find that the bolometric optical luminosity significantly correlates with the orbital period, with a large scatter due to different irradiated stellar temperatures and binary properties. we interpret this correlation as the effect of the increasing size of the roche lobe radius with the orbital period. with this newly found correlation, an estimate of the optical magnitude can be obtained from the orbital period and a distance estimate. | a gaia view of the optical and x-ray luminosities of compact binary millisecond pulsars |
in this paper, we discuss the holographic first order qcd phase transition with gluon condensate and the generation of gravitational waves (gws) from the phase transition. the first order qcd phase transition is dual to the first order hawking-page phase transition from holography. we study the first order hawking-page phase transition from the thermal dilatonic phase to the dilatonic black hole phase and find the phase transition temperature is proportional to the gluon condensate. after substituting into the phenomenological value of gluon condensate from qcd sum rules, we find tc=155.38 mev. in further research, we study the gws generated from holographic cosmic first order qcd phase transition with gluon condensate and the produced gws might be detected by the international pulsar timing array, square kilometre array and big-bang observer. moreover, the gluon condensate suppresses the energy density of total gws and peak frequency. | gravitational waves from holographic qcd phase transition with gluon condensate |
close-orbit low-mass x-ray binaries (lmxbs), radio binary millisecond pulsars (bmsps) with extremely low-mass helium white dwarfs (elm he wds) and ultra-compact x-ray binaries (ucxbs) are all part of the same evolutionary sequence. it is therefore of uttermost importance to understand how these populations evolve from one specie to another. moreover, ucxbs are important gravitational wave (gw) sources and can be detected by future space-borne gw observatories. however, the formation and evolutionary link between these three different populations of neutron star (ns) binaries are not fully understood. in particular, a peculiar fine-tuning problem has previously been demonstrated for the formation of these systems. in this investigation, we test a newly suggested magnetic braking prescription and model the formation and evolution of lmxbs. we compute a grid of binary evolution models and present the initial parameter space of the progenitor binaries which successfully evolve all the way to produce ucxbs. we find that the initial orbital period range of lmxbs, which evolve into detached ns + elm he wd binaries and later ucxbs, becomes significantly wider compared to evolution with a standard magnetic braking prescription, and thus helps to relieve the fine-tuning problem. however, we also find that formation of wide-orbit bmsps is prohibited for strong versions of this new magnetic braking prescription, which therefore calls for a revision of the prescription. finally, we present examples of the properties of ucxbs as galactic gw sources and discuss their detection by the lisa, tianqin, and taiji observatories. | formation of millisecond pulsars with helium white dwarfs, ultra-compact x-ray binaries, and gravitational wave sources |
we study the polarizations induced by the galileon as a stochastic gravitational wave background in the cross correlated power in a pulsar timing array. working within galileon gravity, we first show that the scalar gravitational wave signature of the galileon is encoded solely in its effective mass, which is controlled by the bare mass, conformal coupling, and a tadpole. then, we study the phenomenology of the galileon induced scalar polarizations and place observational constraints on these using the present nanograv data set. our results feature longitudinal spatial correlation, indicative of a 10-22 ev subluminal galileon, and show the galileon polarizations as a statistically compelling source of the observed spatial correlation across millisecond pulsars, if there is any. | looking out for the galileon in the nanohertz gravitational wave sky |
spider pulsars are neutron stars that have a companion star in a close orbit. the companion star sheds material to the neutron star, spinning it up to millisecond rotation periods, while the orbit shortens to hours. the companion is eventually ablated and destroyed by the pulsar wind and radiation1,2. spider pulsars are key for studying the evolutionary link between accreting x-ray pulsars and isolated millisecond pulsars, pulsar irradiation effects and the birth of massive neutron stars3-6. black widow pulsars in extremely compact orbits (as short as 62 minutes7) have companions with masses much smaller than 0.1 m⊙. they may have evolved from redback pulsars with companion masses of about 0.1-0.4 m⊙ and orbital periods of less than 1 day8. if this is true, then there should be a population of millisecond pulsars with moderate-mass companions and very short orbital periods9, but, hitherto, no such system was known. here we report radio observations of the binary millisecond pulsar psr j1953+1844 (m71e) that show it to have an orbital period of 53.3 minutes and a companion with a mass of around 0.07 m⊙. it is a faint x-ray source and located 2.5 arcminutes from the centre of the globular cluster m71. | a binary pulsar in a 53-minute orbit |
reliable neutron star mass measurements are key to determining the equation of state of cold nuclear matter, but such measurements are rare. black widows and redbacks are compact binaries consisting of millisecond pulsars and semi-degenerate companion stars. spectroscopy of the optically bright companions can determine their radial velocities, providing inclination-dependent pulsar mass estimates. although inclinations can be inferred from subtle features in optical light curves, such estimates may be systematically biased due to incomplete heating models and poorly understood variability. using data from the fermi large area telescope, we have searched for gamma-ray eclipses from 49 spider systems, discovering significant eclipses in 7 systems, including the prototypical black widow psr b1957+20. gamma-ray eclipses require direct occultation of the pulsar by the companion, and so the detection, or significant exclusion, of a gamma-ray eclipse strictly limits the binary inclination angle, providing new robust, model-independent pulsar mass constraints. for psr b1957+20, the eclipse implies a much lighter pulsar (1.81 ± 0.07 solar masses) than inferred from optical light curve modelling. | neutron star mass estimates from gamma-ray eclipses in spider millisecond pulsar binaries |
when galaxies merge, the supermassive black holes in their centers may form binaries and emit low-frequency gravitational radiation in the process. in this paper, we consider the galaxy 3c 66b, which was used as the target of the first multimessenger search for gravitational waves. due to the observed periodicities present in the photometric and astrometric data of the source, it has been theorized to contain a supermassive black hole binary. its apparent 1.05-year orbital period would place the gravitational-wave emission directly in the pulsar timing band. since the first pulsar timing array study of 3c 66b, revised models of the source have been published, and timing array sensitivities and techniques have improved dramatically. with these advances, we further constrain the chirp mass of the potential supermassive black hole binary in 3c 66b to less than (1.65 ± 0.02) × 109 m⊙ using data from the nanograv 11-year data set. this upper limit provides a factor of 1.6 improvement over previous limits and a factor of 4.3 over the first search done. nevertheless, the most recent orbital model for the source is still consistent with our limit from pulsar timing array data. in addition, we are able to quantify the improvement made by the inclusion of source properties gleaned from electromagnetic data over "blind" pulsar timing array searches. with these methods, it is apparent that it is not necessary to obtain exact a priori knowledge of the period of a binary to gain meaningful astrophysical inferences. | multimessenger gravitational-wave searches with pulsar timing arrays: application to 3c 66b using the nanograv 11-year data set |
in magnetized capacitively coupled radio frequency (rf) plasmas operated at low pressure, the magnetic asymmetry effect (mae) provides the opportunity to control the discharge symmetry, the dc self-bias, and the ion energy distribution functions at boundary surfaces by adjusting a magnetic field, that is oriented parallel to the electrodes, at one electrode, while leaving it constant at the opposite electrode. this effect is caused by the presence of different plasma densities in regions of different magnetic field strength. here, based on a balanced magnetron magnetic field configuration at the powered electrode, we demonstrate that the magnetic control of the plasma symmetry allows to tailor the generation of high frequency oscillations in the discharge current induced by the self-excitation of the plasma series resonance (psr) through adjusting the magnetic field adjacent to the powered electrode. experimental current measurements performed in an argon discharge at 1 pa as well as results of an equivalent circuit model show that nonlinear electron resonance heating can be switched on and off in this way. moreover, the self-excitation of the psr can be shifted in time (within the rf period) and in space (from one electrode to the other) by controlling the discharge symmetry via adjusting the magnetic field. | magnetic control of nonlinear electron resonance heating in a capacitively coupled radio frequency discharge |
binary pulsars are affected by general relativity (gr), causing the spin axis of each pulsar to precess. we present polarimetric radio observations of the pulsar psr j1906+0746 that demonstrate the validity of the geometrical model of pulsar polarization. we reconstruct the (sky-projected) polarization emission map over the pulsar’s magnetic pole and predict the disappearance of the detectable emission by 2028. two tests of gr are performed using this system, including the spin precession for strongly self-gravitating bodies. we constrain the relativistic treatment of the pulsar polarization model and measure the pulsar beaming fraction, with implications for the population of neutron stars and the expected rate of neutron star mergers. | radio emission from a pulsar’s magnetic pole revealed by general relativity |
in the framework of einstein's the theory of general relativity we present a new interior solution with a perfect fluid, this is constructed from the proposal of a gravitational redshift factor. the geometry is regular and its density and pressure are monotonic decrescent functions, furthermore the sound speed is smaller than the light speed and monotonic crescent. the solution depends on a parameter $w \in (0, 2.0375509325]$ related to the compactness of the star $u = gm/c^2 r$, the maximum value $u = 0.2660858316$ which allow to describe compact stars like quark stars or neutron stars. although there is a diversity of stars for which the model can be used, we only apply this solution to describe the interior of a neutron star psr j0348$+$0432. according to the observations, it is known that its mass $m = (2.01 \pm 0.04)m_{\odot}$ and its radius is between 12.062km and 12.957km, so the value of the compactness is in the range $u \in [0.2244845, 0.2509338]$. in addition to the decreasing behavior of the mentioned pressure and density functions, the results are consistent with the density values range typical of neutron stars and the maximal central density of the star result to be 1.283818 $\times 10^{18} kg/m^{3}$. | a perfect fluid model for compact stars |
more than 50 years after the discovery of pulsars1 and confirmation of their association with supernova explosions2-4, the origin of the initial spin and velocity of pulsars remains largely a mystery. the typical space velocities of several hundred km s−1 have been attributed to `kicks' resulting from asymmetries either in the supernova ejecta or in the neutrino emission5-7. observations have shown a strong tendency for alignment between the pulsar space velocity and the spin axis in young pulsars, but until now these comparisons have been restricted to two dimensions. here, we report evidence for three-dimensional alignment between the spin and velocity vectors, largely based on observations made with the five-hundred-meter aperture spherical radio telescope (fast) of the pulsar psr j0538+2817 and its associated supernova remnant s147. analysis of these and related observations has enabled us to determine the location of the pulsar within the supernova remnant and hence its radial velocity. current simulations of supernova explosions have difficulty producing such three-dimensional alignment7-9. our results, which depend on the unprecedented sensitivity of the observations, add another dimension to the intriguing correlation between pulsar spin-axis and birth-kick directions, thereby deepening the mysteries surrounding the birth of neutron stars. | evidence for three-dimensional spin-velocity alignment in a pulsar |
we have constructed mocassin photoionization plus dust radiative transfer models for the crab nebula core-collapse supernova (ccsn) remnant, using either smooth or clumped mass distributions, in order to determine the chemical composition and masses of the nebular gas and dust. we computed models for several different geometries suggested for the nebular matter distribution but found that the observed gas and dust spectra are relatively insensitive to these geometries, being determined mainly by the spectrum of the pulsar wind nebula which ionizes and heats the nebula. smooth distribution models are ruled out since they require 16-49 m ⊙of gas to fit the integrated optical nebular line fluxes, whereas our clumped models require 7.0 m ⊙of gas. a global gas-phase c/o ratio of 1.65 by number is derived, along with a he/h number ratio of 1.85, neither of which can be matched by current ccsn yield predictions. a carbonaceous dust composition is favored by the observed gas-phase c/o ratio: amorphous carbon clumped model fits to the crab’s herschel and spitzer infrared spectral energy distribution imply the presence of 0.18-0.27 m ⊙of dust, corresponding to a gas to dust mass ratio of 26-39. mixed dust chemistry models can also be accommodated, comprising 0.11-0.13 m ⊙of amorphous carbon and 0.39-0.47 m ⊙of silicates. power-law grain size distributions with mass distributions that are weighted toward the largest grain radii are derived, favoring their longer-term survival when they eventually interact with the interstellar medium. the total mass of gas plus dust in the crab nebula is 7.2 ± 0.5 m ⊙ , consistent with a progenitor star mass of ∼9 m ⊙ . | the dust and gas content of the crab nebula |
gravitational waves (gws) cause the apparent position of distant stars to oscillate with a characteristic pattern on the sky. astrometric measurements (e.g., those made by gaia) provide a new way to search for gws. the main difficulty facing such a search is the large size of the data set; gaia observes more than one billion stars. in this letter the problem of searching for gws from individually resolvable supermassive black hole binaries using astrometry is addressed for the first time; it is demonstrated how the data set can be compressed by a factor of more than 1 06, with a loss of sensitivity of less than 1%. this technique was successfully used to recover artificially injected gw signals from mock gaia data and to assess the gw sensitivity of gaia. throughout the letter the complementarity of gaia and pulsar timing searches for gws is highlighted. | astrometric search method for individually resolvable gravitational wave sources with gaia |
understanding the natal kicks, or birth velocities, of neutron stars is essential for understanding the evolution of massive binaries and double neutron star formation. we use maximum likelihood methods as published in verbunt et al. to analyse a new large data set of parallaxes and proper motions measured by deller et al. this sample is roughly three times larger than number of measurements available before. for both the complete sample and its younger part (spin-down ages τ < 3 myr), we find that a bimodal maxwellian distribution describes the measured parallaxes and proper motions better than a single maxwellian with probability of 99.3 and 95.0 per cent, respectively. the bimodal maxwellian distribution has three parameters: fraction of low-velocity pulsars and distribution parameters σ1 and σ2 for low- and high-velocity modes. for a complete sample, these parameters are as follows: $42_{-15}^{+17}$ per cent, $\sigma _1=128_{-18}^{+22}$ km s-1, and σ2 = 298 ± 28 km s-1. for younger pulsars, which are assumed to represent the natal kick, these parameters are as follows: $20_{-10}^{+11}$ per cent, $\sigma _1=56_{-15}^{+25}$ km s-1, and σ2 = 336 ± 45 km s-1. in the young population, 5 ± 3 per cent of pulsars have velocities less than 60 km s-1. we perform multiple monte carlo tests for the method taking into account realistic observational selection. we find that the method reliably estimates all parameters of the natal kick distribution. results of the velocity analysis are weakly sensitive to the exact values of scale lengths of the galactic pulsar distribution. | the observed velocity distribution of young pulsars - ii. analysis of complete psrπ |
aims: we aim to present a first step in developing a benchmark equation-of-state (eos) model for multi-messenger astronomy that unifies the thermodynamics of quark and hadronic degrees of freedom.methods: a lagrangian approach to the thermodynamic potential of quark-meson-nucleon matter was used. in this approach, dynamical chiral-symmetry breaking is described by the scalar mean-field dynamics coupled to quarks and nucleons and their chiral partners, whereby its restoration occurs in the hadronic phase by parity doubling, as well as in the quark phase. quark confinement was achieved by an auxiliary scalar field that parametrizes a dynamical infrared cut-off in the quark sector, serving as an ultraviolet cut-off for the nucleonic phase space. the gap equations were solved for the isospin-symmetric case, as well as for neutron star (ns) conditions. we also calculated the mass-radius (mr) relation of nss and their tidal deformability (td) parameter.results: the obtained eos is in accordance with nuclear matter properties at saturation density and with the flow constraint from heavy ion collision experiments. for isospin-asymmetric matter, a sequential occurrence of light quark flavors is obtained, allowing for a mixed phase of chirally-symmetric nucleonic matter with deconfined down quarks. the mr relations and tds for compact stars fulfill the constraints from the latest astrophysical observations for psr j0740+6620, psr j0030+0451, and the ns merger gw170817, whereby the tension between the maximum mass and compactness constraints rather uniquely fixes the model parameters. the model predicts the existence of stars with a core of chirally restored but purely hadronic (confined) matter for masses beyond 1.8 m⊙. stars with pure-quark matter cores are found to be unstable against the gravitational collapse. this instability is shifted to even higher densities if repulsive interactions between quarks are included. | toward a unified equation of state for multi-messenger astronomy |
scintillation of compact radio sources results from the interference between images caused by multipath propagation, and probes the intervening scattering plasma and the velocities of the emitting source and scattering screen. in frb20201124a, a repeating fast radio burst (frb) that entered a period of extreme activity, we obtained many burst detections in observations at the upgraded giant metrewave radio telescope (ugmrt) and the effelsberg 100-m radio telescope. bursts nearby in time show similar scintillation patterns, and we measure a scintillation time-scale of 14.3 ± 1.2 and 7 ± 2 min at effelsberg (1370 mhz) and ugmrt (650 mhz), respectively, by correlating burst pair spectra. the scintillation bandwidth scaled to 1 ghz is 0.5 ± 0.1 mhz, and the inferred scintillation velocity at effelsberg is $v_{\mathrm{iss}}\approx (59\pm 7) \sqrt{d_{\mathrm{ l}}/2\, \rm {kpc}}~{\rm km~s}^{-1}$, higher than earth's velocity for any screen beyond a lens distance of $d_{\mathrm{ l}} \gtrsim 400\,$ pc. from the measured scintillation bandwidth, frb20201124a has comparatively lower scattering than nearby pulsars, and is underscattered by a factor of ~30 or ~1200 compared to the ne2001 and ymw16 model predictions, respectively. this underscattering together with the measured scintillation velocity is consistent with a scattering screen more nearby the earth at $d_{\mathrm{ l}} \sim 400\,$ pc, rather than at 2 kpc spiral arm that ne2001 predicts to be the dominant source of scattering. with future measurements, the distance, geometry, and velocity of the scattering screen could be obtained through modelling of the annual variation in viss, or through interstation time delays or interferometric observations. scintillation/scattering measurements of frbs could help improve galactic electron density models, particularly in the galactic halo or at high galactic latitudes. | scintillation time-scale measurement of the highly active frb20201124a |
the historic first detection of the binary neutron star merger gw170817 by the ligo-virgo collaboration has set a limit on the gravitational deformability of neutron stars. in contrast, radio observations of psr j 0740 +6620 find a very massive neutron star. tension between the small deformability and the large maximum mass may suggest that the pressure rises rapidly with density and thus the speed of sound in dense matter is likely a large fraction of the speed of light. we use these observations and simple constant sound-speed model equations of state to set a lower bound on the maximum speed of sound in neutron stars. if the tidal deformability of a 1.4 m⊙ neutron star is less than 600, as is suggested by subsequent analyses of gw170817, then we find that the sound speed in the cores of neutron stars is likely larger than the conformal limit of c /√{3 } . implications of this for our understanding of both hadronic and quark-gluon descriptions of dense matter are discussed. | large sound speed in dense matter and the deformability of neutron stars |
galactic double neutron star systems have a tight mass distribution around ∼1.35m⊙, but the mass distribution of all known pulsars is broader (tauris et al. 2017). here we reconstruct the alsing et al. (2018), antoniadis et al. (2016) bimodal mass distribution of pulsars observed in binary systems, incorporating data from observations of j0740+6620 which were not available at the time of those works. because j0740+6620 is an outlier in the mass distribution with non-negligible uncertainty in its mass measurement, its mass receives a large correction from the population, becoming ${m}_{{\rm{j}}0740+6620}={2.03}_{-0.08}^{+0.10}\,{m}_{\odot }$ (median and 68% ci). stochastic samples from our population model, including population-informed pulsar mass estimates, are available at https://github.com/farr/alsingnsmassreplication and archived at farr & chatziioannou (2020). | a population-informed mass estimate for pulsar j0740+6620 |
fast radio bursts (frbs) are millisecond-duration signals that are highly dispersed at distant galaxies. however, the physical origin of frbs is still unknown. coherent curvature emission by bunches, e.g., powered by starquakes, has already been proposed for repeating frbs. it has the nature of understanding narrowband radiation exhibiting time-frequency drifting. recently, a highly active frb source, i.e., frb 20201124a, was reported to enter a newly active episode and emit at least some highly circular-polarized bursts. in this study, we revisit the polarized frb emission, particularly investigating the production mechanisms of a highly circular polarization (cp) by deriving the intrinsic mechanism and propagative effect. the intrinsic mechanisms of invoking charged bunches are approached with radiative coherence. consequently, a highly cp could naturally be explained by the coherent summation of outcome waves, generated or scattered by bunches, with different phases and electric vectors. different kinds of evolutionary trajectories are found on the poincaré sphere for the bunch-coherent polarization, and this behavior could be tested through future observations. cyclotron resonance can result in the absorption of r-mode photons at a low altitude region of the magnetosphere, and an frb should then be emitted from a high-altitude region if the waves have strong linear polarization. circularly polarized components could be produced from faraday conversion exhibiting a λ3-oscillation, but the average cp fraction depends only on the income wave, indicating a possibility of a highly circular-polarized income wave. the analysis could be welcome if extremely high (e.g., almost 100%) cp from repeating frbs is detected in the future. finally, the production of a bulk of energetic bunches in the pulsar-like magnetosphere is discussed, which is relevant to the nature of the frb central engine. | repeating fast radio bursts: coherent circular polarization by bunches |
wetlands are impacted by economic and political initiatives, and research on their ecosystem health is attracting increasing public attention. it is crucial that management decisions for wetland ecosystems quantify the whole ecosystem health status. in this paper, we aimed to precisely assess the ecosystem health for jiaozhou bay wetlands in shandong province, china in 2015. we selected 27 ecological, social, and economic indicators to establish the "pressure-state-response" (psr) model, then used the methods of analytic hierarchy process (ahp) and fuzzy comprehensive evaluation (fce) to calculate the weights for each indicator and acquire the health scores. our result demonstrated that, overall, the ecosystem health score was 0.5390, which indicated that jiaozhou bay was in ⅲ sub-healthy status. health scores for "pressure," "state," and "response" were 0.4544, 0.5091, and 0.6220, respectively, which indicated that the three layers were in ⅲ sub-healthy, ⅲ sub-healthy, and ⅱ generally healthy statuses, respectively. the wetland ecosystem health assessment can improve research and monitoring for the ecological resources, and provide a scientific basis for wetland planning and restoration, which further guarantees the sustainable utilization of wetland ecosystems. | ecosystem health assessment: a psr analysis combining ahp and fce methods for jiaozhou bay, china1 |
we examine the capability of pulsar timing arrays (ptas) to detect very small-scale clumps of dark matter (dm), which are a natural outcome of the standard cold dark matter (cdm) paradigm. a clump streaming near the earth or a pulsar induces an impulsive acceleration to encode residuals on pulsar timing data. we show that, assuming the standard abundance of dm clumps predicted by the cdm model, small-scale dm clumps with masses from $\sim 10^{-11} m_\odot$ to $\sim 10^{-8} \ m_\odot$ can be detectable by a pta observation for a few decades with ${\cal o}(100)$ of pulsars with a timing noise of ${\cal o}(10)$ ns located at $\gtrsim 3$ kpc away from the galactic center, as long as these mass scales are larger than the cutoff scale of the halo mass function that is determined by the particle nature of dm. our result suggests that ptas can provide a unique opportunity for testing one of the most fundamental predictions of the cdm paradigm. in addition, the detections and non-detections can constrain the cutoff mass scale inherent to the dm model. | detectability of small-scale dark matter clumps with pulsar timing arrays |
upcoming fast radio burst (frb) surveys will search ∼103 beams on the sky with a very high duty cycle, generating large numbers of single-pulse candidates. the abundance of false positives presents an intractable problem if candidates are to be inspected by eye, making it a good application for artificial intelligence (ai). we apply deep learning to single-pulse classification and develop a hierarchical framework for ranking events by their probability of being astrophysical transients. we construct a treelike deep neural network that takes multiple or individual data products as input (e.g., dynamic spectra and multibeam information) and trains on them simultaneously. we have built training and test sets using false-positive triggers from real telescopes, simulated frbs, and pulsar single pulses. training the network was independently done for both the chime pathfinder and apertif. high accuracy and recall can be achieved with a labeled training set of a few thousand events. even with high triggering rates, classification can be done very quickly on graphical processing units, which is essential for selective voltage dumps or real-time voevents. we investigate whether dedispersion back ends could be replaced by a real-time dnn classifier. it is shown that a single forward propagation through a moderate convolutional network could be faster than brute-force dedispersion, but the low signal-to-noise per pixel makes such a classifier suboptimal for this problem. real-time automated classification will prove useful for bright, unexpected signals, both now and when searchable parameter spaces outgrow our ability to manually inspect data, such as for the ska and ngvla. | applying deep learning to fast radio burst classification |
we study electron-positron pair production in polar caps of energetic pulsars to determine the maximum multiplicity of pair plasma a pulsar can produce under the most favorable conditions. this paper complements and updates our study of pair cascades presented in timokhin & harding (2015) with a more accurate treatment of the effects of ultrastrong b≳ 3× {10}12 g magnetic fields and emission processes of primary and secondary particles. we include pairs produced by curvature and synchrotron radiation photons as well as resonant compton-scattered photons. we develop a semianalytical model of electron-positron cascades that can efficiently simulate pair cascades with an arbitrary number of microphysical processes and use it to explore cascade properties for a wide range of pulsar parameters. we argue that the maximum cascade multiplicity cannot exceed ∼ {{a}} {{few}}× {10}5 and that the multiplicity has a rather weak dependence on pulsar period. the highest multiplicity is achieved in pulsars with magnetic field 4× {10}12≲ b≲ {10}13{{g}} and hot surfaces, with t ≳ 106 k. we also derive analytical expressions for several physical quantities relevant for electromagnetic cascade in pulsars, which may be useful in future works on pulsar cascades, including the upper limit on cascade multiplicity and various approximations for the parameter χ, the exponential factor in the expression for photon attenuation in strong magnetic fields. | on the maximum pair multiplicity of pulsar cascades |
the mergers of supermassive black hole binaries (smbhbs) promise to be incredible sources of gravitational waves (gws). while the oscillatory part of the merger gravitational waveform will be outside the frequency sensitivity range of pulsar timing arrays, the nonoscillatory gw memory effect is detectable. further, any burst of gws will produce gw memory, making memory a useful probe of unmodeled exotic sources and new physics. we searched the north american nanohertz observatory for gravitational waves (nanograv) 11 yr data set for gw memory. this data set is sensitive to very low-frequency gws of ∼3 to 400 nhz (periods of ∼11 yr-1 month). finding no evidence for gws, we placed limits on the strain amplitude of gw memory events during the observation period. we then used the strain upper limits to place limits on the rate of gw memory causing events. at a strain of 2.5 × 10-14, corresponding to the median upper limit as a function of source sky position, we set a limit on the rate of gw memory events at <0.4 yr-1. that strain corresponds to an smbhb merger with reduced mass of ηm ∼ 2 × 1010 ${m}_{\odot }$ and inclination of ι = π/3 at a distance of 1 gpc. as a test of our analysis, we analyzed the nanograv 9 yr data set as well. this analysis found an anomolous signal, which does not appear in the 11 yr data set. this signal is not a gw, and its origin remains unknown. | the nanograv 11 yr data set: limits on gravitational wave memory |
the widths, dispersion measures (dms), dispersion indices, and fluences of fast radio bursts (frbs) impose coupled constraints that all models must satisfy. the non-monotonic dependence of burst widths (after deconvolution of instrumental effects) on dms excludes the intergalactic medium as the location of scattering that broadens the frbs in time. temporal broadening far greater than that of pulsars at similar high galactic latitudes implies that scattering occurs close to the sources where high densities and strong turbulence or heterogeneity are plausible. frb energetics are consistent with supergiant pulses from young, fast, high-field pulsars at cosmological distances. the distribution of frb dms is: (1) inconsistent with that of expanding clouds (such as snrs); (2) inconsistent with space-limited source populations (such as the local supercluster); and (3) consistent with intergalactic dispersion of a homogeneous source population at cosmological distances. finally, the frb {log}\n-{log} s relation also indicates a cosmological distribution aside from the anomalously bright lorimer burst. | inferences from the distributions of fast radio burst pulse widths, dispersion measures, and fluences |
spontaneous scalarization is a gravitational phenomenon in which deviations from general relativity arise once a certain threshold in curvature is exceeded, while being entirely absent below that threshold. for black holes, scalarization is known to be triggered by a coupling between a scalar and the gauss-bonnet invariant. a coupling with the ricci scalar, which can trigger scalarization in neutron stars, is instead known to not contribute to the onset of black hole scalarization, and has so far been largely ignored in the literature when studying scalarized black holes. in this paper, we study the combined effect of both these couplings on black hole scalarization. we show that the ricci coupling plays a significant role in the properties of scalarized solutions and their domain of existence. this work is an important step in the construction of scalarization models that evade binary pulsar constraints and have general relativity as a cosmological late-time attractor, while still predicting deviations from general relativity in black hole observations. | black hole scalarization with gauss-bonnet and ricci scalar couplings |
written by a leading expert, this monograph presents recent developments on supernova remnants, with the inclusion of results from various satellites and ground-based instruments. the book details the physics and evolution of supernova remnants, as well as provides an up-to-date account of recent multiwavelength results. supernova remnants provide vital clues about the actual supernova explosions from x-ray spectroscopy of the supernova material, or from the imprints the progenitors had on the ambient medium supernova remnants are interacting with - all of which the author discusses in great detail. the way in which supernova remnants are classified, is reviewed and explained early on. a chapter is devoted to the related topic of pulsar wind nebulae, and neutron stars associated with supernova remnants. the book also includes an extended part on radiative processes, collisionless shock physics and cosmic-ray acceleration, making this book applicable to a wide variety of astronomical sub-disciplines. with its coverage of fundamental physics and careful review of the state of the field, the book serves as both textbook for advanced students and as reference for researchers in the field. | physics and evolution of supernova remnants |
we present photometry and spectroscopy of ps1-14bj, a hydrogen-poor superluminous supernova (slsn) at redshift z = 0.5215 discovered in the last months of the pan-starrs1 medium deep survey. ps1-14bj stands out because of its extremely slow evolution, with an observed rise of ≳ 125 rest-frame days, and exponential decline out to ∼250 days past peak at a measured rate of 0.01 {mag} {{day}}-1, consistent with fully trapped 56co decay. this is the longest rise time measured in an slsn to date, and the first slsn to show a rise time consistent with pair-instability supernova (pisn) models. compared to other slowly evolving slsne, it is spectroscopically similar to the prototype sn 2007bi at maximum light, although lower in luminosity ({l}{peak}≃ 4.6× {10}43 {erg} {{{s}}}-1) and with a flatter peak than previous events. ps1-14bj shows a number of peculiar properties, including a near-constant color temperature for \gt 200 days past peak, and strong emission lines from [o iii] λ5007 and [o iii] λ4363 with a velocity width of ∼3400 km s-1 in its late-time spectra. these both suggest there is a sustained source of heating over very long timescales, and are incompatible with a simple 56ni-powered/pisn interpretation. a modified magnetar model including emission leakage at late times can reproduce the light curve, in which case the blue continuum and [o iii] features are interpreted as material heated and ionized by the inner pulsar wind nebula becoming visible at late times. alternatively, the late-time heating could be due to interaction with a shell of h-poor circumstellar material. | ps1-14bj: a hydrogen-poor superluminous supernova with a long rise and slow decay |
we demonstrate that future radius measurements of the nicer mission have the potential to reveal the existence of a strong phase transition in dense neutron star matter by confirming the existence of so-called twin stars, compact star configurations with the same mass but different radii. the latest radius constraints from nicer for the pulsars j0740+6620 as well as j0030+0451 are discussed using relativistic mean field equations of state with varying stiffness, connected with a first-order phase transition to quark matter. we show that twin star solutions are compatible with the new radius constraint but are located at radii below the present constraints from nicer, serving as a smoking gun for a strong phase transition in neutron star matter. this scenario is realized if a strong phase transition takes place in neutron stars of the first branch with masses above 2 m ⊙. | confirming the existence of twin stars in a nicer way |
a long-lived scalar field (φ) which couples weakly to the right-handed (rh) neutrinos (nri), generates small rh neutrino masses (mi) in low-scale-leptogenesis (lsl) mechanisms, despite having a large vacuum expectation value vφ. in this case, the correlation shared by the mis and the duration of the non-standard cosmic history driven by the φ provides an excellent opportunity to study lsl signatures on primordial gravitational waves (gws). we find it engaging, specifically for the gravitational waves that originate due to the inflationary blue-tilted tensor power spectrum and propagate through the non-standard cosmic epoch. depending on mi, broadly, the scenario has two significant consequences. first, if lsl is at play, gws with a sizeable blue tilt do not contradict the big-bang-nucleosynthesis (bbn) bound even for the post-inflationary models with very high-scale reheating. second, it opens up a possibility to probe lsls via a low-frequency and a complementary high-frequency measurement of gw-spectral shapes which are typically double-peaked. for a case study, we consider the recent results on gws from the pulsar-timing-arrays (ptas) as a `measurement' at the low frequencies and forecast the signatures of lsl mechanisms at the higher frequencies. | gravitational waves-tomography of low-scale-leptogenesis |
using data from the hawc gamma-ray telescope, we have studied a sample of 37 millisecond pulsars (msps), selected for their spindown power and proximity. from among these msp, we have identified four which favor the presence of very high-energy gamma-ray emission at a level of (2 δ ln l )1/2≥2.5 . adopting a correlation between the spindown power and gamma-ray luminosity of each pulsar, we performed a stacked likelihood analysis of these 37 msps, finding that the data supports the conclusion that these sources emit very high-energy gamma-rays at a level of (2 δ ln l )1/2=4.24 . among sets of randomly selected sky locations within hawc's field-of-view, less than 1% of such realizations yielded such high statistical significance. our analysis suggests that msps produce very high-energy gamma-ray emission with a similar efficiency to that observed from the geminga tev-halo, ηmsp=(0.39 -1.08 )×ηgeminga. this conclusion poses a significant challenge for pulsar interpretations of the galactic center gamma-ray excess, as it suggests that any population of msps potentially capable of producing the gev excess would also produce tev-scale emission in excess of that observed by hess from this region. future observations by cta will be able to substantially clarify this situation. | evidence of tev halos around millisecond pulsars |
the 6.67 hr periodicity and the variable x-ray flux of the central compact object (cco) at the center of the supernova remnant rcw 103, named 1e 161348-5055, have been always difficult to interpret within the standard scenarios of an isolated neutron star (ns) or a binary system. on 2016 june 22, the burst alert telescope (bat) on board swift detected a magnetar-like short x-ray burst from the direction of 1e 161348-5055, also coincident with a large long-term x-ray outburst. here, we report on chandra, nuclear spectroscopic telescope array, and swift (bat and xrt) observations of this peculiar source during its 2016 outburst peak. in particular, we study the properties of this magnetar-like burst, we discover a hard x-ray tail in the cco spectrum during outburst, and we study its long-term outburst history (from 1999 to 2016 july). we find the emission properties of 1e 161348-5055 consistent with it being a magnetar. however, in this scenario, the 6.67 hr periodicity can only be interpreted as the rotation period of this strongly magnetized ns, which therefore represents the slowest pulsar ever detected, by orders of magnitude. we briefly discuss the viable slow-down scenarios, favoring a picture involving a period of fall-back accretion after the supernova explosion, similarly to what is invoked (although in a different regime) to explain the “anti-magnetar” scenario for other ccos. | magnetar-like activity from the central compact object in the snr rcw103 |
context. the sardinia radio telescope (srt) is the new 64 m dish operated by the italian national institute for astrophysics (inaf). its active surface, comprised of 1008 separate aluminium panels supported by electromechanical actuators, will allow us to observe at frequencies of up to 116 ghz. at the moment, three receivers, one per focal position, have been installed and tested: a 7-beam k-band receiver, a mono-feed c-band receiver, and a coaxial dual-feed l/p band receiver. the srt was officially opened in september 2013, upon completion of its technical commissioning phase. in this paper, we provide an overview of the main science drivers for the srt, describe the main outcomes from the scientific commissioning of the telescope, and discuss a set of observations demonstrating the scientific capabilities of the srt.aims: the scientific commissioning phase, carried out in the 2012-2015 period, proceeded in stages following the implementation and/or fine-tuning of advanced subsystems such as the active surface, the derotator, new releases of the acquisition software, etc. one of the main objectives of scientific commissioning was the identification of deficiencies in the instrumentation and/or in the telescope subsystems for further optimization. as a result, the overall telescope performance has been significantly improved.methods: as part of the scientific commissioning activities, different observing modes were tested and validated, and the first astronomical observations were carried out to demonstrate the science capabilities of the srt. in addition, we developed astronomer-oriented software tools to support future observers on site. in the following, we refer to the overall scientific commissioning and software development activities as astronomical validation.results: the astronomical validation activities were prioritized based on technical readiness and scientific impact. the highest priority was to make the srt available for joint observations as part of european networks. as a result, the srt started to participate (in shared-risk mode) in european vlbi network (evn) and large european array for pulsars (leap) observing sessions in early 2014. the validation of single-dish operations for the suite of srt first light receivers and backends continued in the following year, and was concluded with the first call for shared-risk early-science observations issued at the end of 2015. as discussed in the paper, the srt capabilities were tested (and optimized when possible) for several different observing modes: imaging, spectroscopy, pulsar timing, and transients. | the sardinia radio telescope . from a technological project to a radio observatory |
enterprise (enhanced numerical toolbox enabling a robust pulsar inference suite) is a pulsar-timing analysis code which performs noise analysis, gravitational-wave searches, and timing model analysis. it uses tempo2 (ascl:1210.015) to find the maximum-likelihood fit for the timing parameters and the basis of the fit for the red noise parameters if they are significant. | enterprise: enhanced numerical toolbox enabling a robust pulsar inference suite |
the discovery of the first binary pulsar in 1974 has opened up a completely new field of experimental gravity. in numerous important ways, pulsars have taken precision gravity tests quantitatively and qualitatively beyond the weak-field slow-motion regime of the solar system. apart from the first verification of the existence of gravitational waves, binary pulsars for the first time gave us the possibility to study the dynamics of strongly self-gravitating bodies with high precision. to date there are several radio pulsars known which can be utilized for precision tests of gravity. depending on their orbital properties and the nature of their companion, these pulsars probe various different predictions of general relativity and its alternatives in the mildly relativistic strong-field regime. in many aspects, pulsar tests are complementary to other present and upcoming gravity experiments, like gravitational-wave observatories or the event horizon telescope. this review gives an introduction to gravity tests with radio pulsars and its theoretical foundations, highlights some of the most important results, and gives a brief outlook into the future of this important field of experimental gravity. | gravity tests with radio pulsars |
we provide a systematic study of hybrid neutron star equations of state (eos) consisting of a relativistic density functional for the hadronic phase and a covariant nonlocal nambu-jona-lasinio (nlnjl) model to describe the color superconducting quark matter phase. changing the values of the two free parameters, the dimensionless vector and diquark coupling strengths ηv and ηd results in a set of eos with varying stiffness and deconfinement onset. the favorable parameters are obtained from a systematic bayesian analysis for which the multimessenger constraint on the neutron star radius at 14 m⊙ and the combined mass-radius constraint for psr j 0740 +6620 from nicer experiment are used as the constraints. additionally, the transition from hadronic matter to deconfined quark matter is constrained to occur above nuclear saturation density. hybrid stars modeled with these favorable parameters are compatible with the nicer results for the radius of the highest known mass neutron star, psr j 0740 +6620 . three new observations interesting for neutron star phenomenology are reported: (i) we show that the constant sound speed (css) eos provides an excellent fit to that of the nlnjl model which implies the squared speed of sound at high densities to be about 0.5 for the optimized parameters; (ii) we give a simple functional form for the mapping between the parameter spaces of these two models valid for the whole range of relevant chemical potentials and (iii) we observe that the special point property of hybrid eos based on css quark matter generalizes to a set of lines consisting of special points when two eos parameters are varied instead of one. a lower limit for the maximum mass of hybrid stars as a function of the vector coupling strength is obtained. | constraining free parameters of a color superconducting nonlocal nambu-jona-lasinio model using bayesian analysis of neutron stars mass and radius measurements |
context. the formation of a large-scale current sheet is a generic feature of pulsar magnetospheres. if the magnetic axis is misaligned with the star rotation axis, the current sheet is an oscillatory structure filling an equatorial wedge determined by the inclination angle, known as the striped wind. relativistic reconnection could lead to significant dissipation of magnetic energy and particle acceleration, although the efficiency of this process is debated in this context.aims: in this study, we aim at reconciling global models of pulsar wind dynamics and reconnection in the stripes within the same numerical framework in order to shed new light on dissipation and particle acceleration in pulsar winds.methods: to this end, we perform large three-dimensional particle-in-cell simulations of a split-monopole magnetosphere, from the stellar surface up to 50 light-cylinder radii away from the pulsar.results: plasmoid-dominated reconnection efficiently fragments the current sheet into a dynamical network of interacting flux ropes separated by secondary current sheets that consume the field efficiently at all radii, even past the fast magnetosonic point. our results suggest there is a universal dissipation radius solely determined by the reconnection rate in the sheet, lying well upstream from the termination shock radius in isolated pair-producing pulsars. the wind bulk lorentz factor is much less relativistic than previously thought. in the co-moving frame, the wind is composed of hot pairs trapped within flux ropes with a hard broad power-law spectrum, whose maximum energy is limited by the magnetization of the wind at launch.conclusions: we conclude that the striped wind is most likely fully dissipated when it enters the pulsar wind nebula. the predicted wind particle spectrum after dissipation is reminiscent of the crab nebula radio-emitting electrons. | dissipation of the striped pulsar wind and non-thermal particle acceleration: 3d pic simulations |
we investigate the effects of the modified f(r, t) gravity on the charged strange quark stars with the standard choice of f(r, t)=r+2χ t. those types of stars are supposed to be made of strange quark matter (sqm) whose distribution is governed by the phenomenological mit bag eos as p=1/3(ρ-4b), where b is the bag constant, while the form of charge distribution is chosen to be q(r)=q(r/script r)3=α r3 with α as a constant. we derive the values of the unknown parameters by matching the interior spacetime to the exterior reissner-nordstr{öm metric followed by the appropriate choice of the values of the parameters χ and α. our study reveals that besides sqm, a new kind of matter distribution originates due to the interaction between the matter and the extra geometric term, while the modification of the tolman-oppenheimer-volkoff (tov) equation invokes the presence of a new force fc. the accumulation of the electric charge distribution reaches its maximum at the surface, and the predicted values of the corresponding electric charge and electric field are of the order of 1019-20c and 1021-22 v/cm, respectively. to examine the physical validity of our solutions, we perform tests of the energy conditions, stability against the equilibrium of the forces, the adiabatic index, etc., and find that the proposed f(r, t) model survives all these critical tests. therefore, our model can describe the non-singular charged strange stars and justify the supermassive compact stellar objects having their masses beyond the maximum mass limit for the compact stars in the standard scenario. our model also supports the existence of several exotic astrophysical objects like super-chandrasekhar white dwarfs, massive pulsars, and even magnetars, which remain unexplained in the framework of general relativity (gr). | study on charged strange stars in f(r, t) gravity |
this study simulates strange stars in f(q) gravity with an additional source under an electric field using gravitational decoupling by means of the complete geometric deformation (cgd) technique. by employing the tolman ansatz and the mit bag model equation of state (eos), we explore bounded star configurations derived from the $\theta _0^0 = \rho$ and $\theta _1^1 = p_r$ sectors within the cgd formalism. our models are subjected to physical viability tests, and we analyse the impact of anisotropy and the electric charge parameter e0 as well as the coupling parameters α and β1. comparisons are made with observational constraints, including gw190814, neutron stars psr j1614-2230, psr j1903 + 6620, cen x-3, and lmc x-4. notably, we achieve the presence of a lower 'mass gap' component by adjusting parameters α and β1. our models exhibit well-behaved mass profiles, internal regularity, and stability, along with the absence of gravitational collapse verified through the buchdahl-andréasson's limit. in addition, we present a detailed physical analysis based on three parameters, α (decoupling strength), β1 (f(q)-coupling), and q (surface charge). this study provides insights into the behaviour of compact objects in f(q) gravity and expands our understanding of strange star configurations within this framework. | influence of three parameters on maximum mass and stability of strange star under linear f(q) - action |
we suggest that fast-rising blue optical transients (fbots) and the brightest event of the class, at2018cow, result from an electron-capture collapse to a neutron star following the merger of a massive onemg white dwarf (wd) with another wd. two distinct evolutionary channels lead to the disruption of the less-massive wd during the merger and the formation of a shell-burning non-degenerate star incorporating the onemg core. during the shell-burning stage, a large fraction of the envelope is lost to the wind, while mass and angular momentum are added to the core. as a result, the electron-capture collapse occurs with a small envelope mass, after ∼102-104 yr. during the formation of a neutron star, as little as {∼ } 10^{-2} m_\odot of the material is ejected at the bounce-off with mildly relativistic velocities and total energy of about a few 1050 erg. this ejecta becomes optically thin on a time-scale of days - this is the fbot. during the collapse, the neutron star is spun up and the magnetic field is amplified. the ensuing fast magnetically dominated relativistic wind from the newly formed neutron star shocks against the ejecta, and later against the wind. the radiation-dominated forward shock produces the long-lasting optical afterglow, while the termination shock of the relativistic wind produces the high-energy emission in a manner similar to pulsar wind nebulae. if the secondary wd was of the da type, the wind will likely have {∼ } 10^{-4} m_\odot of hydrogen; this explains the appearance of hydrogen late in the afterglow spectrum. the model explains many of the puzzling properties of fbots/at2018cow: host galaxies, a fast and light anisotropic ejecta producing a bright optical peak, afterglow high-energy emission of similar luminosity to the optical, and late infrared features. | fast-rising blue optical transients and at2018cow following electron-capture collapse of merged white dwarfs |
the deep synoptic array 10-dish prototype (dsa-10) is an instrument designed to detect and localize fast radio bursts with arcsecond accuracy in real time. deployed at owens valley radio observatory, it consists of ten 4.5-m diameter dishes, equipped with a 250-mhz bandwidth dual polarization receiver, centred at 1.4 ghz. the 20 input signals are digitized and field programmable gate arrays are used to transform the data to the frequency domain and transmit it over ethernet. a series of computer servers buffer both raw data samples and perform a real time search for fast radio bursts on the incoherent sum of all inputs. if a pulse is detected, the raw data surrounding the pulse are written to disc for coherent processing and imaging. the prototype system was operational from 2017 june to 2018 february conducting a drift scan search. giant pulses from the crab pulsar were used to test the detection and imaging pipelines. the 10-dish prototype system was brought online again in 2019 march, and will gradually be replaced with the new dsa-110, a 110-dish system, over the next 2 yr to improve sensitivity and localization accuracy. | dsa-10: a prototype array for localizing fast radio bursts |
the ams-02 collaboration has just released its first result of the cosmic positron fraction e+ / (e- +e+) with high precision up to ∼350 gev. the ams-02 result shows the same trend with the previous pamela result, which requires extra electron/positron sources on top of the conventional cosmic ray background, either from astrophysical sources or from dark matter annihilation/decay. in this paper we try to figure out the nature of the extra sources by fitting to the ams-02 e+ / (e- +e+) data, as well as the electron and proton spectra by pamela and the (e- +e+) spectrum by fermi and hess. we adopt the galprop package to calculate the propagation of the galactic cosmic rays and the markov chain monte carlo sampler to do the fit. we find that under the conventional assumptions about the background and the extra source of the e- +e+ , we cannot fit the ams-02 and fermi/hess data well simultaneously. the ams-02 data require less electrons/positrons from the extra sources than that required by fermi/hess. it may indicate that the model needs to be refined or the data between these experiments have systematic uncertainties. the pulsar scenario generally fits the data better than the dm scenario. furthermore, the constraints from γ-rays also disfavor the dm scenario to explain the cosmic ray lepton data. | implications of the ams-02 positron fraction in cosmic rays |
integrating femtosecond (fs) lasers to electron microscopies has enabled direct imaging of transient structures and morphologies of materials in real time and space, namely, ultrafast electron microscopy (uem). here we report the development of a laser-free uem offering the same capability of real-time imaging with high spatiotemporal resolutions but without requiring expensive fs lasers and intricate instrumental modifications. we create picosecond electron pulses for probing dynamic events by chopping a continuous beam with a radiofrequency (rf)-driven pulser, where the repetition rate of the electron pulses is tunable from 100 mhz to 12 ghz. a same broadband of electromagnetic wave is enabled for sample excitation. as a first application, we studied the ghz electromagnetic wave propagation dynamics in an interdigitated comb structure which is one of the basic building blocks for rf micro-electromechanical systems. a series of pump-probe images reveals, on nanometer space and picosecond time scales, the transient oscillating electromagnetic field around the tines of the combs, and time-resolved polarization, amplitude, and nonlinear local field enhancement. the success of this study demonstrates the feasibility of the low-cost laser-free uem in real-space visualizing of dynamics for many research fields, especially the electrodynamics in devices associated with information processing technology. | direct visualization of electromagnetic wave dynamics by laser-free ultrafast electron microscopy |
prospects of establishing the radii of massive neutron stars in psr j1614 - 2230 and psr j0740 + 6620 from neutron star interior composition explorer and chandra observatories hold the potential to constrain the equation of state (eos) of matter to densities well beyond those encountered in canonical stars of mass $\sim 1.4\,{m}_{\odot }$. in this work, we investigate the relation between the radii of very massive neutron stars up to the maximum mass, ${m}_{\max }$, supported by dense matter eoss. results from models with hadronic matter are contrasted with those that include a first-order hadron-to-quark phase transition. we find that a lower bound on ${m}_{\max }$ with an upper bound on the radius of massive pulsars serves to rule out quark matter that is too soft, and an upper bound on ${m}_{\max }$ with a lower bound on the radius of massive pulsars strongly disfavors a transition into quark matter that is too stiff appearing at low densities. the complementary role played by radius inferences from future gravitational-wave events of inspiraling binary neutron stars is also briefly discussed. | on the minimum radius of very massive neutron stars |
the north american nanohertz observatory for gravitational waves (nanograv) has recently reported strong statistical evidence for a common-spectrum red-noise process for all pulsars, as seen in their 12.5-yr analysis for an isotropic stochastic gravitational-wave signal. however, there is currently very little evidence for quadrupolar spatial correlations across the pulsars in the array, which is needed to make a confident claim of detection of a stochastic gravitational-wave background. in this paper, we provide a "back-of-the-envelope" illustration of the nanograv 12.5-yr results for the nonexpert reader, using a very simple signal +noise model and frequentist statistics. we show that the current lack of evidence for spatial correlations is consistent with the magnitude of the correlation coefficients for pairs of earth-pulsar baselines in the array and the fact that pulsar timing arrays are most likely operating in the intermediate-signal regime. we derive analytic expressions that allow one to compare the expected values of the signal-to-noise ratios for both common-spectrum and cross-correlation estimators. | common-spectrum process versus cross-correlation for gravitational-wave searches using pulsar timing arrays |
qcd axions or axionlike particles are among the most popular candidates for cold dark matter (dm) in the universe. we proposed to detect axionlike dm, using linearly polarized pulsar light as a probe. because of birefringence effect potentially caused by an oscillating galactic axion dm background, when pulsar light travels across the galaxy, its linear polarization angle may vary with time. with a soliton +nfw galactic dm halo profile, we show that this strategy can potentially probe an axion-photon coupling as small as ∼10-13 gev-1 for axion mass ma∼10-22- 10-20 ev , given the current measurement accuracy. an exclusion limit stronger than cast (∼10-10 gev-1 ) and sn1987a (∼10-11 gev-1 ) could be extended up to ma∼10-18 ev and ∼10-19 ev , respectively. | detecting axionlike dark matter with linearly polarized pulsar light |
recently, the radius of neutron star (ns) psr j 0740 +6620 was measured by neutron star interior composition explorer (nicer), and an updated measurement of neutron skin thickness of 208pb (rskin208 ) was reported by the prex-ii experiment. these new measurements can help us better understand the unknown equation of state (eos) of dense matter. in this work, we adopt a hybrid parameterization method, which incorporates the nuclear empirical parameterization and some widely used phenomenological parameterizations, to analyze the results of nuclear experiments and astrophysical observations. with the joint bayesian analysis of gw170817, psr j 0030 +0451 , and psr j 0740 +6620 , the parameters that characterize the ultradense matter eos are constrained. we find that the slope parameter l is approximately constrained to 70-18+21 mev , which predicts rskin208=0.20 4-0.026+0.030 fm by using the universal relation between rskin208 and l . the bulk properties of canonical 1.4 m⊙ ns (e.g., r1.4 and λ1.4) as well as the pressure (p2 ρsat) at two times the nuclear saturation density are well constrained by the data; i.e., r1.4, λ1.4, and p2 ρsat are approximately constrained to 12.3 ±0.7 km , 330-100+140, and 4.1-1.2+1.5×1034 dyn cm-2 , respectively. besides, we find that the bayes evidences of the hybrid star and normal ns assumptions are comparable, which indicates that current observation data are compatible with quarkyonic matter existing in the core of massive star. finally, in the case of normal ns assumption, we obtain a constraint for the maximum mass of nonrotating ns mtov=2.3 0-0.18+0.30 m⊙. based on this result and the current observational and theoretical knowledge about the ns population and its eos, we find that a binary black hole merger scenario for gw190814 is more plausible. all of the uncertainties reported above are for 68.3% credible levels. | constraints on the phase transition and nuclear symmetry parameters from psr j 0740 +6620 and multimessenger data of other neutron stars |
inspired by the conundrum of the gravitational event gw190814, which brings to light the coalescence of a 23 m ⊙ black hole with a yet-to-be-determined secondary component, we look to modeling compact objects within the framework of $f({ \mathcal q })$ gravity by employing the method of gravitational decoupling. we impose a quadratic equation of state (eos) for the interior matter distribution, which in the appropriate limit reduces to the mit bag model. the governing field equations arising from gravitational decoupling bifurcate into the $\rho ={\theta }_{0}^{0}$ and ${p}_{r}={\theta }_{1}^{1}$ sectors, leading to two distinct classes of solutions. both families of solutions are subjected to rigorous tests, qualifying them to describe a plethora of compact objects, including neutron stars, strange stars, and the possible progenitor of the secondary component of gw190814. using observational data of mass-radius relations for compact objects lmc x-4, cen x-3, psr j1614-2230, and psr j0740+6620, we show that it is possible to generate stellar masses and radii beyond 2.0 m ⊙ for neutron stars. our findings reveal that the most suitable and versatile model in this framework is the quadratic eos, which accounts for a range of low-mass stars and typical stellar candidates describing the secondary component of gw190814. | the effect of gravitational decoupling on constraining the mass and radius for the secondary component of gw190814 and other self-bound strange stars in f(q) gravity theory |
axion dark matter can be converted into photons in the magnetospheres of neutron stars leading to a spectral line centered on the compton wavelength of the axion. due to the rotation of the star and the plasma effects in the magnetosphere the signal is predicted to be periodic with significant time variation that persists across phase but is narrow in frequency—a unique smoking gun for axion dark matter. as a proof of principle and to develop the methodology, we carry out the first time domain search of the signal using data from psr j2144-3933 taken as part of the meertime project on meerkat telescope. we search for specific signal templates using a matched filter technique and discuss when a time-domain analysis (as is typically the case in pulsar observations) gives greater sensitivity to the axion coupling to photons in comparison to a simple time-averaged total flux study. we do not find any candidate signals and, hence, impose an upper limit on the axion-to-photon coupling of ga γ γ<5.5 ×10-11(d /0.165 pc ) gev-1 where d is the pulsar distance, over the mass range ma=3.9 - 4.7 μ ev using this data. this limit relies on psr j2144-3933 not being an extremely aligned rotator, as strongly supported by simple arguments based on the observed pulse profile width. we discuss the possibilities of improving this limit using future observations with meerkat and also ska1-mid and the possibility of using other objects. finally, to evade modeling uncertainties in axion radio signals, we also carry out a generic "any periodic-signal search" in the data, finding no evidence for an axion signal. | searching for time-dependent axion dark matter signals in pulsars |
in this work, we interpreted the high braking index of psr j1640-4631 with a combination of the magneto-dipole radiation and dipole magnetic field decay models. by introducing a mean rotation energy conversion coefficient \overline{\zeta }, the ratio of the total high-energy photon energy to the total rotation energy loss in the whole life of the pulsar, and combining the pulsar’s high-energy and timing observations with a reliable nuclear equation of state, we estimate the pulsar’s initial spin period, {p}0∼ (17{--}44) ms, corresponding to the moment of inertia i∼ (0.8{--}2.1)× {10}45 g cm2. assuming that psr j1640-4631 has experienced a long-term exponential decay of the dipole magnetic field, we calculate the true age {t}{age}, the effective magnetic field decay timescale {τ }{{d}}, and the initial surface dipole magnetic field at the pole {b}p(0) of the pulsar to be 2900-3100 yr, 1.07(2)× {10}5 yr, and (1.84{--}4.20)× {10}13 g, respectively. the measured braking index of n=3.15(3) for psr j1640-4631 is attributed to its long-term dipole magnetic field decay and a low magnetic field decay rate, {{db}}{{p}}/{dt}∼ -(1.66{--}3.85)× {10}8 g yr-1. our model can be applied to both the high braking index (n> 3) and low braking index (n< 3) pulsars, tested by the future polarization, timing, and high-energy observations of psr j1640-4631. | the dipole magnetic field and spin-down evolutions of the high braking index pulsar psr j1640-4631 |
the mpifr-meerkat galactic plane survey at l-band (mmgps-l) is the most sensitive pulsar survey in the southern hemisphere, providing 78 discoveries in an area of 900 sq. deg. here, we present a follow-up study of one of these new discoveries, psr j1208−5936, a 28.71-ms recycled pulsar in a double neutron star system with an orbital period of pb = 0.632 days and an eccentricity of e = 0.348, merging within the hubble time. through timing of almost one year of observations, we detected the relativistic advance of periastron (ω̇ = 0.918(1) deg yr−1), resulting in a total system mass of mt = 2.586(5) m⊙. we also achieved low-significance constraints on the amplitude of the einstein delay and shapiro delay, in turn yielding constraints on the pulsar mass (mp = 1.26−0.25+0.13 m⊙), the companion mass (mc = 1.32−0.13+0.25 m⊙), and the inclination angle (i = 57 ± 12°). this system is highly eccentric compared to other galactic field double neutron stars with similar periods, possibly hinting at a larger-than-usual supernova kick during the formation of the second-born neutron star. the binary will merge within 7.2(2) gyr due to the emission of gravitational waves, making it a progenitor of the neutron star merger events seen by ground-based gravitational wave observatories. with the improved sensitivity of the mmgps-l, we updated the milky way neutron star merger rate to be rmwnew = 25−9+19 myr−1 within 90% credible intervals, which is lower than previous studies based on known galactic binaries owing to the lack of further detections despite the highly sensitive nature of the survey. this implies a local cosmic neutron star merger rate of rlocalnew = 293−103+222 gpc−3 yr−1, which is consistent with ligo and virgo o3 observations. with this, we also predict the observation of 10−4+8 neutron star merger events during the ligo-virgo-kagra o4 run. we predict the uncertainties on the component masses and the inclination angle will be reduced to 5 × 10−3 m⊙ and 0.4° after two decades of timing, and that in at least a decade from now the detection of ṗb and the sky proper motion will serve to make an independent constraint of the distance to the system. | the mpifr-meerkat galactic plane survey. ii. the eccentric double neutron star system psr j1208−5936 and a neutron star merger rate update |
the origin of fast radio bursts (frbs) remains mysterious. recently, the only repeating frb source, frb 121102, was reported to possess an extremely large and variable rotation measure (rm). the inferred magnetic field strength in the burst environment is comparable to that in the vicinity of the supermassive black hole sagittarius a* of our galaxy. here, we show that all of the observational properties of frb 121102 (including the high rm and its evolution, the high linear polarization degree, an invariant polarization angle across each burst and other properties previously known) can be interpreted within the “cosmic comb” model, which invokes a neutron star with typical spin and magnetic field parameters whose magnetosphere is repeatedly and marginally combed by a variable outflow from a nearby low-luminosity accreting supermassive black hole in the host galaxy. we propose three falsifiable predictions (periodic “on/off” states, and periodic/correlated variation of rm and polarization angle) of the model and discuss other frbs within the context of the cosmic comb model as well as the challenges encountered by other repeating frb models in light of the new observations. | frb 121102: a repeatedly combed neutron star by a nearby low-luminosity accreting supermassive black hole |
direct detection of gravitational waves is opening a new window onto our universe. here, we study the sensitivity to continuous-wave strain fields of a kg-scale optomechanical system formed by the acoustic motion of superfluid helium-4 parametrically coupled to a superconducting microwave cavity. this narrowband detection scheme can operate at very high q-factors, while the resonant frequency is tunable through pressurization of the helium in the 0.1-1.5 khz range. the detector can therefore be tuned to a variety of astrophysical sources and can remain sensitive to a particular source over a long period of time. for thermal noise limited sensitivity, we find that strain fields on the order of h∼ {10}-23/\sqrt{{hz}} are detectable. measuring such strains is possible by implementing state of the art microwave transducer technology. we show that the proposed system can compete with interferometric detectors and potentially surpass the gravitational strain limits set by them for certain pulsar sources within a few months of integration time. | detecting continuous gravitational waves with superfluid 4he |
background: an accurate determination of the core-crust transition is necessary in the modeling of neutron stars for astrophysical purposes. the transition is intimately related to the isospin dependence of the nuclear force at low baryon densities. purpose: to study the symmetry energy and the core-crust transition in neutron stars using the finite-range gogny nuclear interaction and to examine the deduced crustal thickness and crustal moment of inertia. methods: the second-, fourth-, and sixth-order coefficients of the taylor expansion of the energy per particle in powers of the isospin asymmetry are analyzed for gogny forces. these coefficients provide information about the departure of the symmetry energy from the widely used parabolic law. the neutron star core-crust transition is evaluated by looking at the onset of thermodynamical instability of the liquid core. the calculation is performed with the exact gogny equation of state (eos) (i.e., the gogny eos with the full isospin dependence) for the β -equilibrated matter of the core, and also with the taylor expansion of the gogny eos in order to assess the influence of isospin expansions on locating the inner edge of neutron star crusts. results: the properties of the core-crust transition derived from the exact eos differ from the predictions of the taylor expansion even when the expansion is carried through sixth order in the isospin asymmetry. gogny forces, using the exact eos, predict the ranges 0.094 fm-3≲ρt≲0.118 fm-3 for the transition density and 0.339 mevfm-3≲pt≲0.665 mevfm-3 for the transition pressure. the transition densities show an anticorrelation with the slope parameter l of the symmetry energy. the transition pressures are not found to correlate with l . neutron stars obtained with gogny forces have maximum masses below 1.74 m⊙ and relatively small moments of inertia. the crustal mass and moment of inertia are evaluated and comparisons are made with the constraints from observed glitches in pulsars. conclusions: the finite-range exchange contribution of the nuclear force, and its associated nontrivial isospin dependence, is key in determining the core-crust transition properties. finite-order isospin expansions do not reproduce the core-crust transition results of the exact eos. the predictions of the gogny d1m force for the stellar crust are overall in broad agreement with those obtained using the skyrme-lyon eos. | higher-order symmetry energy and neutron star core-crust transition with gogny forces |
the neutron star interior composition explorer (nicer) is looking for neutron stars and pulsars from its perch on the international space station. keith gendreau and zaven arzoumanian provide an overview of its capabilities. | searching for a pulse |
radio interferometers have the ability to precisely localize and better characterize the properties of sources. this ability is having a powerful impact on the study of fast radio transients, where a few milliseconds of data is enough to pinpoint a source at cosmological distances. however, recording interferometric data at millisecond cadence produces a terabyte-per-hour data stream that strains networks, computing systems, and archives. this challenge mirrors that of other domains of science, where the science scope is limited by the computational architecture as much as the physical processes at play. here, we present a solution to this problem in the context of radio transients: realfast, a commensal, fast transient search system at the jansky very large array. realfast uses a novel architecture to distribute fast-sampled interferometric data to a 32-node, 64-gpu cluster for real-time imaging and transient detection. by detecting transients in situ, we can trigger the recording of data for those rare, brief instants when the event occurs and reduce the recorded data volume by a factor of 1000. this makes it possible to commensally search a data stream that would otherwise be impossible to record. this system will search for millisecond transients in more than 1000 hr of data per year, potentially localizing several fast radio bursts, pulsars, and other sources of impulsive radio emission. we describe the science scope for realfast, the system design, expected outcomes, and ways in which real-time analysis can help in other fields of astrophysics. | realfast: real-time, commensal fast transient surveys with the very large array |
we present a model for a super-eddington accretion disc around a magnetized neutron star taking into account advection of heat and the mass loss by the wind. the model is semi-analytical and predicts radial profiles of all the basic physical characteristics of the accretion disc. the magnetospheric radius is found as an eigenvalue of the problem. when the inner disc is in radiation-pressure-dominated regime but does not reach its local eddington limit, advection is mild, and the radius of the magnetosphere depends weakly on the accretion rate. once it approaches the local eddington limit the disc becomes advection-dominated, and the scaling for the magnetospheric radius with the mass accretion rate is similar to the classical alfvén relation. allowing for the mass loss in a wind leads to an increase in the magnetospheric radius. our model can be applied to a wide variety of magnetized neutron stars accreting close to or above their eddington limits: ultra-luminous x-ray pulsars, be/x-ray binaries in outbursts, and other systems. in the context of our model we discuss the observational properties of ngc 5907 x-1, the brightest ultra-luminous pulsar currently known, and ngc 300 ulx1, which is apparently a be/x-ray binary experiencing a very bright super-eddington outburst. | super-eddington accretion discs with advection and outflows around magnetized neutron stars |
one very promising technique for measuring the dense matter equation of state exploits hotspots that form on the neutron star surface due to the pulsar mechanism, accretion streams, or during thermonuclear explosions in the neutron star ocean. this article explains how pulse profile modeling of hotspots is being used by the neutron star interior composition explorer (nicer), an x-ray telescope installed on the international space station in 2017 - and why the technique is a mission driver for the next, larger-area generation of telescopes including the enhanced x-ray timing and polarimetry (extp) mission and the spectroscopic time-resolving observatory for broadband energy x-rays (strobe-x). | constraining the neutron star equation of state using pulse profile modeling |
according to the general-relativistic no-hair theorem, astrophysical black holes depend only on their masses and spins and are uniquely described by the kerr metric. mass and spin are the first two multipole moments of the kerr spacetime and completely determine all other moments. the no-hair theorem can be tested by measuring potential deviations from the kerr metric which alter such higher-order moments. in this review, i discuss tests of the no-hair theorem with current and future observations of such black holes across the electromagnetic spectrum, focusing on near-infrared observations of the supermassive black hole at the galactic center, pulsar-timing and very-long baseline interferometric observations, as well as x-ray observations of fluorescent iron lines, thermal continuum spectra, variability, and polarization. | testing the no-hair theorem with observations of black holes in the electromagnetic spectrum |
lorentz symmetry is one of the pillars of both general relativity and the standard model of particle physics. motivated by ideas about quantum gravity, unification theories and violations of cpt symmetry, a significant effort has been put the last decades into testing lorentz symmetry. this review focuses on lorentz symmetry tests performed in the gravitational sector. we briefly review the basics of the pure gravitational sector of the standard-model extension (sme) framework, a formalism developed in order to systematically parametrize hypothetical violations of the lorentz invariance. furthermore, we discuss the latest constraints obtained within this formalism including analyses of the following measurements: atomic gravimetry, lunar laser ranging, very long baseline interferometry, planetary ephemerides, gravity probe b, binary pulsars, high energy cosmic rays, … in addition, we propose a combined analysis of all these results. we also discuss possible improvements on current analyses and present some sensitivity analyses for future observations. | tests of lorentz symmetry in the gravitational sector |
in 2019 november, maxi detected an x-ray outburst from the known be x-ray binary system rx j0209.6-7427 located in the outer wing of the small magellanic cloud. we followed the outburst of the system with nicer, which led to the discovery of x-ray pulsations with a period of 9.3 s. we analysed simultaneous x-ray data obtained with nustar and nicer, allowing us to characterize the spectrum and provide an accurate estimate of its bolometric luminosity. during the outburst, the maximum broad-band x-ray luminosity of the system reached (1-2) × 1039 erg s-1, thus exceeding by about one order of magnitude the eddington limit for a typical 1.4 m⊙ mass neutron star (ns). monitoring observations with fermi/gbm and nicer allowed us to study the spin evolution of the ns and compare it with standard accretion torque models. we found that the ns magnetic field should be of the order of 3 × 1012 g. we conclude that rx j0209.6-7427 exhibited one of the brightest outbursts observed from a be x-ray binary pulsar in the magellanic clouds, reaching similar luminosity level to the 2016 outburst of smc x-3. despite the super-eddington luminosity of rx j0209.6-7427, the ns appears to have only a moderate magnetic field strength. | the 2019 super-eddington outburst of rx j0209.6-7427: detection of pulsations and constraints on the magnetic field strength |
despite significant efforts over the past decade, the origin of the cosmic ray positron excess has still not been unambiguously established. a popular class of candidate sources are pulsars or pulsar wind nebulae but these cannot also account for the observed hard spectrum of cosmic ray antiprotons. we revisit the alternative possibility that the observed high-energy positrons are secondaries created by spallation in supernova remnants during the diffusive shock acceleration of the primary cosmic rays, which are further accelerated by the same shocks. the resulting source spectrum of positrons at high energies is then naturally harder than that of the primaries, as is the spectrum of other secondaries such as antiprotons. we present the first comprehensive investigation of the full parameter space of this model—both the source parameters as well as those governing galactic transport. various parametrizations of the cross sections for the production of positrons and antiprotons are considered, and the uncertainty in the model parameters discussed. we obtain an excellent fit to recent precision measurements by ams-02 of cosmic ray protons, helium, positrons, and antiprotons, as well as of various primary and secondary nuclei. this model thus provides an economical explanation of the spectra of all secondary species—from a single well-motivated population of sources. | explaining cosmic ray antimatter with secondaries from old supernova remnants |
magnetic reconnection in the relativistic regime has been proposed as an important process for the efficient production of nonthermal particles and high-energy emission. using fully kinetic particle-in-cell simulations, we investigate how the guide-field strength and domain size affect the characteristic spectral features and acceleration processes. we study two stages of acceleration: energization up until the injection energy γ inj and further acceleration that generates a power-law spectrum. stronger guide fields increase the power-law index and γ inj, which suppresses acceleration efficiency. these quantities seemingly converge with increasing domain size, suggesting that our findings can be extended to large-scale systems. we find that three distinct mechanisms contribute to acceleration during injection: particle streaming along the parallel electric field, fermi reflection, and the pickup process. the fermi and pickup processes, related to the electric field perpendicular to the magnetic field, govern the injection for weak guide fields and larger domains. meanwhile, parallel electric fields are important for injection in the strong guide-field regime. in the post-injection stage, we find that perpendicular electric fields dominate particle acceleration in the weak guide-field regime, whereas parallel electric fields control acceleration for strong guide fields. these findings will help explain the nonthermal acceleration and emission in high-energy astrophysics, including black hole jets and pulsar wind nebulae. *released january 10, 2023. | particle injection and nonthermal particle acceleration in relativistic magnetic reconnection |
it has recently been discovered that a fraction of ultraluminous x-ray sources (ulxs) exhibit x-ray pulsations, and are therefore powered by super-eddington accretion on to magnetized neutron stars (nss). for typical ulx mass accretion rates ({≳ } 10^{19} {g s^{-1}}), the inner parts of the accretion disc are expected to be in the supercritical regime, meaning that some material is lost in a wind launched from the disc surface, while the rest forms an optically thick envelope around the ns as it follows magnetic field lines from the inner disc radius to the magnetic poles of the star. the envelope hides the central object from a distant observer and defines key observational properties of ulx pulsars: their energy spectrum, polarization, and timing features. the optical thickness of the envelope is affected by the mass losses from the disc. we calculate the mass-loss rate due to the wind in ulx pulsars, accounting for the ns magnetic field strength and advection processes in the disc. we argue that detection of strong outflows from ulx pulsars can be considered evidence of a relatively weak dipole component of the ns magnetic field. we estimate the influence of mass losses on the optical thickness of the envelope and analyse how the envelope affects broad-band aperiodic variability in ulxs. we show that brightness fluctuations at high fourier frequencies can be strongly suppressed by multiple scatterings in the envelope and that the strength of suppression is determined by the mass accretion rate and geometrical size of the magnetosphere. | timing properties of ulx pulsars: optically thick envelopes and outflows |
to date, the most precise tests of general relativity have been achieved through pulsar timing, albeit in the weak-field regime. since pulsars are some of the most precise and stable "clocks" in the universe, present observational efforts are focused on detecting pulsars in the vicinity of supermassive black holes (most notably in the galactic centre), enabling pulsar timing to be used as an extremely precise probe of strong-field gravity. in this paper, a mathematical framework to describe test-particle dynamics in general black-hole spacetimes is presented and subsequently used to study a binary system comprising a pulsar orbiting a black hole. in particular, taking into account the parameterization of a general spherically symmetric black-hole metric, general analytic expressions for both the advance of the periastron and for the orbital period of a massive test particle are derived. furthermore, these expressions are applied to four representative cases of solutions arising in both general relativity and in alternative theories of gravity. finally, this framework is applied to the galactic center s -stars and four distinct pulsar toy models. it is shown that by adopting a fully general-relativistic description of test-particle motion which is independent of any particular theory of gravity, observations of pulsars can help impose better constraints on alternative theories of gravity than is presently possible. | test-particle dynamics in general spherically symmetric black hole spacetimes |
in the present work, we try to find a solution without singularity of einstein's field equations for the spherically symmetric perfect fluid objects, accurately strange quark spheres, taking into consideration schwarzschild metric as the outside space-time. an ensemble of inside solutions found on the basis of the simplest linear state equation in the specific form p_r =α ρ -β . the energy density ρ (r), the radial pressure p_r (r) and the tangential pressure p_t (r) are devoid of any singularity and exhibit a well-behaved nature within the generalized anisotropic solution for compact spherical object. the generalized tov equation is very much preserved inside the system and all energy conditions are excellent. the stability of the matter distribution of our system is checked by the concept of herrera's cracking and the condition of causality is all around fulfilled for our models. the adiabatic index of our specific configuration is greater than 4 / 3 in all interior points of the system and the mass-to-radius ratio in our situation is determined also lies within the buchdahl limit i.e. m/r≤ 4/3 ( {≈ 0.444} ) . we explore the physical characteristics based on the analytical model developed for relativistic compact stellar spheres inside the framework of the general theory of relativity. the evaluated mass and radius are in close concurrence with the observational information. we show that various physical characteristics of the known strange spherical object, viz. psr j1614-2230, vela x-1, 4u 1608-52, psr j1903+327, 4u 1820-30, cen x-3, her x-1, and sax j1808.4-3658, can be described by the current model. | a spherically symmetric model of anisotropic fluid for strange quark spheres |
we present the first detection of x-ray coherent pulsations from the transitional millisecond pulsar xss j12270-4859, while it was in a sub-luminous accretion disc state characterized by a 0.5-10 kev luminosity of 5 × 1033 erg s-1 (assuming a distance of 1.4 kpc). pulsations were observed by xmm-newton at an rms amplitude of (7.7 ± 0.5) per cent with a second harmonic stronger than the fundamental frequency, and were detected when the source is neither flaring nor dipping. the most likely interpretation of this detection is that matter from the accretion disc was channelled by the neutron star magnetosphere and accreted on to its polar caps. according to standard disc accretion theory, for pulsations to be observed the mass inflow rate in the disc was likely larger than the amount of plasma actually reaching the neutron star surface; an outflow launched by the fast rotating magnetosphere then probably took place, in agreement with the observed broad-band spectral energy distribution. we also report about the non-detection of x-ray pulsations during a recent observation performed while the source behaved as a rotationally-powered radio pulsar. | x-ray coherent pulsations during a sub-luminous accretion disc state of the transitional millisecond pulsar xss j12270-4859. |
we initiate a study on various cosmological imprints of string axions whose scalar potentials have plateau regions. in such cases, we show that a delayed onset of oscillation rather generically leads to a parametric resonance instability. in particular, for ultralight axions, the parametric resonance can enhance the power spectrum slightly below the jeans scale, alleviating the tension with the lyman α forest observations. we also argue that a sustainable resonance can lead to an emission of gravitational waves at the frequency bands which are detectable by gravitational wave interferometers and pulsar timing arrays and also to a succeeding oscillon formation. | cosmological imprints of string axions in plateau |
we identify new astrophysical signatures of dark matter that implodes neutron stars (nss), which could decisively test whether ns-imploding dark matter is responsible for missing pulsars in the milky way galactic center, the source of some r -process elements, and the origin of fast-radio bursts. first, ns-imploding dark matter forms ∼10-10 solar mass or smaller black holes inside neutron stars, which proceed to convert neutron stars into ∼1.5 solar mass black holes (bhs). this decreases the number of neutron star mergers seen by ligo/virgo (lv) and associated merger kilonovae seen by telescopes like des, blackgem, and ztf, instead producing a population of "black mergers" containing ∼1.5 solar mass black holes. second, dark matter-induced neutron star implosions may create a new kind of kilonovae that lacks a detectable, accompanying gravitational signal, which we call "quiet kilonovae." using des data and the milky way's r-process abundance, we constrain quiet kilonovae. third, the spatial distribution of neutron star merger kilonovae and quiet kilonovae in galaxies can be used to detect dark matter. ns-imploding dark matter destroys most neutron stars at the centers of disc galaxies, so that neutron star merger kilonovae would appear mostly in a donut at large radii. we find that as few as ten neutron star merger kilonova events, located to ∼1 kpc precision could validate or exclude dark matter-induced neutron star implosions at 2 σ confidence, exploring dark matter-nucleon cross-sections 4-10 orders of magnitude below current direct detection experimental limits. similarly, ns-imploding dark matter as the source of fast radio bursts can be tested at 2 σ confidence once 20 bursts are located in host galaxies by radio arrays like chime and hirax. | searching for dark matter with neutron star mergers and quiet kilonovae |
this work presents an algorithm for modeling a static spherically symmetric compact object satisfying the eiesland condition (eiesland in am math soc 27:213, 1925), a necessary and sufficient condition that a general centro-symmetric space shall be of the class 1. the model parameters are obtained accordingly by employing the boundary conditions to the interior solutions. the equation of state has been extracted from the solution and one found that it is almost linear. these models are free of physical and geometric singularities and satisfy the necessary physical conditions to have astrophysical significance. the central and surface densities, and pressures of some compact stars like psr j1614-2230, vela x-1 have been calculated from these models. detailed analyses of these models have also been made with the help of numerical and graphical studies. | some families of relativistic anisotropic compact stellar models embedded in pseudo-euclidean space e^5: an algorithm |
superconductors are excellent testbeds for studying vortices, topological excitations that also appear in superfluids, liquid crystals and bose-einstein condensates. vortex motion can be disruptive; it can cause phase transitions, glitches in pulsars, and losses in superconducting microwave circuits, and it limits the current-carrying capacity of superconductors. understanding vortex dynamics is fundamentally and technologically important, and the competition between thermal energy and energy barriers defined by material disorder is not completely understood. specifically, early measurements of thermally activated vortex motion (creep) in iron-based superconductors unveiled fast rates (s) comparable to measurements of yba 2cu3o7-δ (refs ,,,,,). this was puzzling because s is thought to somehow correlate with the ginzburg number (gi), and gi is significantly lower in most iron-based superconductors than in yba 2cu3o7-δ. here, we report very slow creep in bafe 2(as0.67p0.33)2 films, and propose the existence of a universal minimum realizable s ~ gi1/2(t/tc) (tc is the superconducting transition temperature) that has been achieved in our films and few other materials, and is violated by none. this limitation provides new clues about designing materials with slow creep and the interplay between material parameters and vortex dynamics. | universal lower limit on vortex creep in superconductors |
binary neutron star mergers can be sources of gravitational waves coincident with electromagnetic counterpart emission across the spectrum. to solidify their role as multimessenger sources, we present fully 3d, general relativistic, magnetohydrodynamic simulations of highly spinning binary neutrons stars initially on quasicircular orbits that merge and undergo delayed collapse to a black hole. the binaries consist of two identical stars modeled as γ =2 polytropes with spin χns=0.36 aligned along the direction of the total orbital angular momentum l . each star is initially threaded by a dynamical unimportant interior dipole magnetic field. the field is extended into the exterior where a nearly force-free magnetosphere resembles that of a pulsar. the magnetic dipole moment μ is either aligned or perpendicular to l and has the same initial magnitude for each orientation. for comparison, we also impose symmetry across the orbital plane in one case where μ in both stars is aligned along l . we find that the lifetime of the transient hypermassive neutron star remnant, the jet launching time, and the ejecta (which can give rise to a detectable kilonova) are very sensitive to the magnetic field orientation. by contrast, the physical properties of the black hole +disk remnant , such as the mass and spin of the black hole, the accretion rate, and the electromagnetic (poynting) luminosity, are roughly independent of the initial magnetic field orientation. in addition, we find imposing symmetry across the orbital plane does not play a significant role in the final outcome of the mergers. our results suggest that, as in the black hole-neutron star merger scenario, an incipient jet emerges only when the seed magnetic field has a sufficiently large-scale poloidal component aligned to the initial orbital angular momentum. the lifetime [δ t ≳140 (mns/1.625 m⊙) ms ] and poynting luminosities [lem≃1052 erg /s ] of the jet, when it forms, are consistent with typical short gamma-ray bursts, as well as with the blandford-znajek mechanism for launching jets. | magnetohydrodynamic simulations of binary neutron star mergers in general relativity: effects of magnetic field orientation on jet launching |
pulsar dispersion measures (dms) have been used to model the electron density of the interstellar medium (ism) in the galactic disk as a plane-parallel medium, despite significant scatter in the dm-distance distribution and strong evidence for inhomogeneities in the ism. we use a sample of pulsars with independent distance measurements to evaluate a model of the local ism in the thick disk of the galaxy that incorporates turbulent fluctuations, clumps, and voids in the electron density. the latter two components are required because about one-third of the lines of sight are discrepant from a strictly plane-parallel model. a likelihood analysis for smooth components of the model yields a scale height ${z}_{0}={1.57}_{-0.14}^{+0.15}$ kpc and a mid-plane density n0 = 0.015 ± 0.001 cm-3. the scatter in the dm-distance distribution is dominated by clumps and voids but receives significant contributions from a broad spectrum of density fluctuations, such as a kolmogorov spectrum. the model is used to identify lines of sight with outlier values of dm. three of these pulsars, j1614-2230, j1623-0908, and j1643-1224, lie behind known h ii regions, and the electron density model is combined with hα intensity data to constrain the filling factors and other substructure properties of the h ii regions (sh 2-7 and sh 2-27). several pulsars also exhibit enhanced dm fluctuations that are likely caused by an intersection of their lines of sight with the superbubble gsh 238+00+09. | electron density structure of the local galactic disk |
we build a model of radius-to-frequency mapping in magnetospheres of neutron stars and apply it to frequency drifts observed in fast radio bursts (frbs). we assume that an emission patch propagates along the dipolar magnetic field lines, producing coherent emission with frequency, direction, and polarization defined by the local magnetic field. the observed temporal evolution of the frequency depends on the relativistic effects of time contraction and the curvature of the magnetic field lines. the model generically produces linear scaling of the drift rate, $\dot{\omega }\propto -\omega $ , matching both numerically and parametrically the rates observed in fbrs; a more complicated behavior of $\dot{\omega }$ is also possible. fast rotating magnetospheres produce higher drifts rates for similar viewing parameters than the slowly rotating ones. in the case of repeaters, the same source may show variable drift patterns depending on the observing phase. we expect rotational of polarization position angle through a burst, though by smaller amount than in radio pulsars. all of these findings compare favorably with properties of fbrs, strengthening their possible loci in the magnetospheres of neutron stars. | radius-to-frequency mapping and frb frequency drifts |
the anomalous x-ray pulsar xte j1810-197 was the first magnetar found to emit pulsed radio emission. after spending almost a decade in a quiescent, radio-silent state, the magnetar was reported to have undergone a radio outburst in 2018 december. we observed radio pulsations from xte j1810-197 during this early phase of its radio revival using the ultra-wideband low receiver system of the parkes radio telescope, obtaining wideband (704-4032 mhz) polarization pulse profiles, single pulses, and flux density measurements. dramatic changes in polarization and rapid variations of the position angle of linear polarization across the main pulse and in time have been observed. the pulse profile exhibits similar structures throughout our three observations (over a week timescale), displaying a small amount of profile evolution in terms of polarization and pulse width across the wideband. we measured a flat radio spectrum across the band with a positive spectral index, in addition to small levels of flux and spectral index variability across our observing span. the observed wideband polarization properties are significantly different compared to those taken after the 2003 outburst, and therefore provide new information about the origin of radio emission. | wideband polarized radio emission from the newly revived magnetar xte j1810-197 |
ngc 300 ulx1 is an ultraluminous x-ray pulsar, showing an unprecedented spin evolution, from about 126 s to less than 20 s in only 4 yr, consistent with steady mass accretion rate. following its discovery we have been monitoring the system with swift and nicer to further study its properties. we found that even though the observed flux of the system dropped by a factor of ≳20, the spin-up rate remained almost constant. a possible explanation is that the decrease in the observed flux is a result of increased absorption of obscuring material due to outflows or a precessing accretion disc. | ngc 300 ulx1: spin evolution, super-eddington accretion, and outflows |
the repeating fast radio burst (frb) 121102 was recently localized in a dwarf galaxy at a cosmological distance. the dispersion measure (dm) derived for each burst from frb 121102 so far has not shown significant evolution, even though an apparent increase was recently seen with newly detected vla bursts. it is expected that more repeating frb sources may be detected in the future. in this work, we investigate a list of possible astrophysical processes that might cause dm variation of a particular frb source. the processes include (1) cosmological scale effects such as hubble expansion and large-scale structure fluctuations; (2) frb local effects such as gas density fluctuation, expansion of a supernova remnant (snr), a pulsar wind nebula, and an h ii region; and (3) the propagation effect due to plasma lensing. we find that the dm variations contributed by the large-scale structure are extremely small, and any observable dm variation is likely caused by the plasma local to the frb source. in addition to mechanisms that decrease dm over time, we suggest that an frb source in an expanding snr around a nearly neutral ambient medium during the deceleration (sedov-taylor and snowplow) phases or in a growing h ii region can increase dm. some effects (e.g., an frb source moving in an h ii region or plasma lensing) can produce either positive or negative dm variations. future observations of dm variations of frb 121102 and other repeating frb sources can provide important clues regarding the physical origin of these sources. | dispersion measure variation of repeating fast radio burst sources |
we describe the x-ray pulse profile models we use and how we use them to analyze neutron star interior composition explorer (nicer) observations of rotation-powered millisecond pulsars to obtain information about the mass-radius relation of neutron stars and the equation of state of the dense matter in their cores. here we detail our modeling of the observed profile of psr j0030+0451 that we analyzed in miller et al. and riley et al. and describe a cross-verification of computations of the pulse profiles of a star with r/m 3, in case stars this compact need to be considered in future analyses. we also present our early cross-verification efforts of the parameter estimation procedures used by miller et al. and riley et al. by analyzing two distinct synthetic data sets. both codes yielded credible regions in the mass-radius plane that are statistically consistent with one another, and both gave posterior distributions for model parameter values consistent with the values that were used to generate the data. we also summarize the additional tests of the parameter estimation procedure of miller et al. that used synthetic pulse profiles and the nicer pulse profile of psr j0030+0451. we then illustrate how the precision of mass and radius estimates depends on the pulsar's spin rate and the size of its hot spot by analyzing four different synthetic pulse profiles. finally, we assess possible sources of systematic error in the estimates made using this technique, some of which may warrant further investigation. | constraining the neutron star mass-radius relation and dense matter equation of state with nicer. iii. model description and verification of parameter estimation codes |
hyperons are essential constituents in the neutron star interior. the poorly known hyperonic interaction is a source of uncertainty for studying laboratory hypernuclei and neutron star observations. in this work, we perform bayesian inference of phenomenological hyperon-nucleon interactions using the tidal deformability measurement of the gw170817 binary neutron star merger as detected by ligo/virgo and the mass-radius measurements of psr j0030+0541 and psr j0740+6620 as detected by nicer. the analysis is based on a set of stiff relativistic neutron star matter equation of states with hyperons from the relativistic mean-field theory, naturally fulfilling the causality requirement and empirical nuclear matter properties. we specifically utilize the strong correlation recently deduced between the scalar and vector meson-hyperon couplings, imposed by the measured λ separation energy in single-λ hypernuclei, and perform four different tests with or without the strong correlation. we find that the laboratory hypernuclear constraint ensures a large enough λ-scalar-meson coupling to match the large vector coupling in hyperon star matter. when adopting the current most probable intervals of hyperon couplings from the joint analysis of laboratory and astrophysical data, we find the maximum mass of hyperon stars is at most ${2.176}_{-0.202}^{+0.085}{m}_{\odot }$ (68% credible interval) from the chosen set of stiff equation of states. the reduction of the stellar radius due to hyperons is quantified based on our analysis and various hyperon star properties are provided. | astrophysical implications on hyperon couplings and hyperon star properties with relativistic equations of states |
supermassive black hole binary systems (smbhbs) emitting gravitational waves may be traced by periodic light curves. we assembled a catalog of 149 such periodic light curves, and using their masses, distances, and periods, predicted the gravitational-wave strain and detectability of each binary candidate using all-sky detection maps. we found that the international pulsar timing array (ipta) provides almost uniform sky coverage-a unique ability of the ipta-and by 2025 will improve nanograv's current minimum detectable strain by a factor of 6 and its volume by a factor of 216. moreover, ipta will reach detection sensitivities for three candidates by 2025, and 13 by the end of the decade, enabling us to constrain the underlying empirical relations used to estimate supermassive black hole masses. we find that we can in fact already constrain the mass of a binary in mrk 504 to m < 3.3 × 109 m⊙. we also identify 24 high-mass, high-redshift galaxies that, according to our models, should not be able to host smbhbs. importantly, the gw detection of even one of these candidates would be an essentially eternal multimessenger system, and identifying common false-positive signals from nondetections will be useful to filter the data from future large-scale surveys such as lsst. | multimessenger pulsar timing array constraints on supermassive black hole binaries traced by periodic light curves |
with the first multi messenger observation of a binary neutron star merger (gw170817), new constraints became available for masses and radii of neutron stars. we introduce a class of hybrid eos that fulfills all these constraints and predicts a region in the mass radius diagram that could be populated only by hybrid neutron stars with quark matter cores. a confirmation of this conjecture would be provided when the nicer radius measurement for the high mass pulsar psr j0740 + 6620 yields a radius significantly less than 11 km. would this radius measurement yield a result in excess of 12 km, this would allow for both, a purely hadronic and a hybrid nature of this star. in the latter case, the maximum mass could reach 2.6 m⊙ so that the lighter object in the asymmetric binary merger gw190814 could have been a hybrid star. we demonstrate that this high mass can be compatible with an early onset of deconfinement for stars with masses below 1 m⊙ and the occurrence of low mass twin stars. in such a case, the remnant of gw170817 could be a long lived hypermassive pulsar. | studying the onset of deconfinement with multi messenger astronomy of neutron stars |
a successful measurement of the stochastic gravitational wave background (sgwb) in pulsar timing arrays (ptas) would open up a new window through which to test the predictions of general relativity (gr). we consider how these measurements might reveal deviations from gr by studying the overlap reduction function - the quantity that in gr is approximated by the hellings-downs curve - in some sample modifications of gravity, focusing on the generic prediction of a modified dispersion relation for gravitational waves. we find a distinct signature of such modifications to gr - a shift in the minimum angle of the angular distribution - and demonstrate that this shift is quantitatively sensitive to any change in the phase velocity. in a given modification of gravity, this result can be used, in some regions of parameter space, to distinguish the effect of a modified dispersion relation from that due to the presence of extra polarization modes. | a test of gravity with pulsar timing arrays |
we show that gravitational wave emission from neutron star binaries can be used to discover any generic long-ranged muonic force due to the large inevitable abundance of muons inside neutron stars. as a minimal consistent example, we focus on a gauged u(1 ) lμ-lτ symmetry. in pulsar binaries, such u(1 ) lμ-lτ vectors induce an anomalously fast decay of the orbital period through the emission of dipole radiation. we study a range of different pulsar binaries, finding the most powerful constraints for vector masses below o (10-18 ev ) . for merging binaries, the presence of muons in neutron stars can result in dipole radiation as well as a modification of the chirp mass during the inspiral phase. we make projections for a prospective search using both the gw170817 and s190814bv events and find that current data can discover light vectors with masses below o (10-10 ev ) . in both cases, the limits attainable with neutron stars reach gauge coupling g'≲10-20, which are many orders of magnitude stronger than previous constraints. we also show projections for next generation experiments, such as einstein telescope and cosmic explorer. | probing muonic forces with neutron star binaries |
the galactic center excess (gce) of gev gamma rays can be explained as a signal of annihilating dark matter or of emission from unresolved astrophysical sources, such as millisecond pulsars. evidence for the latter is provided by a statistical procedure—referred to as non-poissonian template fitting (nptf)—that distinguishes the smooth distribution of photons expected for dark matter annihilation from a "clumpy" photon distribution expected for point sources. in this paper, we perform an extensive study of the nptf on simulated data, exploring its ability to recover the flux and luminosity function of unresolved sources at the galactic center. when astrophysical background emission is perfectly modeled, we find that the nptf successfully distinguishes between the dark matter and point source hypotheses when either component makes up the entirety of the gce. when the gce is a mixture of dark matter and point sources, the nptf may fail to reconstruct the correct contribution of each component. these results are related to the fact that in the ultrafaint limit, a population of unresolved point sources is exactly degenerate with poissonian emission. we further study the impact of mismodeling the galactic diffuse backgrounds, finding that while a dark matter signal could be attributed to point sources in some outlying cases for the scenarios we consider, the significance of a true point source signal remains robust. our work enables us to comment on a recent study by leane and slatyer (2019) that questions prior nptf conclusions because the method does not recover an artificial dark matter signal injected on actual fermi data. we demonstrate that the failure of the nptf to extract an artificial dark matter signal can be natural when point sources are present in the data—with the effect further exacerbated by the presence of diffuse mismodeling—and does not on its own invalidate the conclusions of the nptf analysis in the inner galaxy. | characterizing the nature of the unresolved point sources in the galactic center: an assessment of systematic uncertainties |
we explore the effects of strangeness and δ resonance in baryonic matter and compact stars within the relativistic-mean-field models. the parameter set pkdd is adopted for n -n interaction, parameters fixed based on finite hypernuclei and neutron stars are taken for the hyperon-meson couplings, and the universal baryon-meson coupling scheme is adopted for the δ -meson couplings. in light of the recent observations of gw170817 with the dimensionless combined tidal deformability 197 ≤λ ¯≤720 , we find it is essential to include the δ resonances in compact stars, and small δ -ρ coupling gρ δ is favored if the mass 2.27-0.15+0.17 m⊙ of psr j 2215 +5135 is confirmed. | strangeness and δ resonance in compact stars with relativistic-mean-field models |
fast radio bursts (frbs) are millisecond radio signals that exhibit dispersion larger than what the galactic electron density can account for. we have conducted a 1446 h survey for frbs at 145 mhz, covering a total of 4193 deg2 on the sky. we used the uk station of the low frequency array (lofar) radio telescope - the rawlings array - accompanied for a majority of the time by the lofar station at nançay, observing the same fields at the same frequency. our real-time search backend, advanced radio transient event monitor and identification system - artemis, utilizes graphics processing units to search for pulses with dispersion measures up to 320 cm-3 pc. previous derived frb rates from surveys around 1.4 ghz, and favoured frb interpretations, motivated this survey, despite all previous detections occurring at higher dispersion measures. we detected no new frbs above a signal-to-noise threshold of 10, leading to the most stringent upper limit yet on the frb event rate at these frequencies: 29 sky-1 d-1 for five ms-duration pulses above 62 jy. the non-detection could be due to scatter-broadening, limitations on the volume and time searched, or the shape of frb flux density spectra. assuming the latter and that frbs are standard candles, the non-detection is compatible with the published frb sky rate, if their spectra follow a power law with frequency (∝ να), with α ≳ +0.1, demonstrating a marked difference from pulsar spectra. our results suggest that surveys at higher frequencies, including the low frequency component of the square kilometre array, will have better chances to detect, estimate rates and understand the origin and properties of frbs. | limits on fast radio bursts at 145 mhz with artemis, a real-time software backend |
it is currently not known if repeating fast radio bursts (frbs) are fundamentally different from those that have not been seen to repeat. one striking difference between repeaters and apparent non-repeaters in the canadian hydrogen intensity mapping experiment sample is that the once-off events are typically shorter in duration than sources that have been detected two or more times. we offer a simple explanation for this discrepancy based on a selection effect due to beamed emission, in which highly beamed frbs are less easily observed to repeat, but are abundant enough to detect often as once-off events. the explanation predicts that there is a continuous distribution of burst duration - not a static bimodal one - with a correlation between repetition rate and width. pulse width and opening angle may be related by relativistic effects in shocks, where short-duration bursts have small solid angles due to a large common lorentz factor. alternatively, the relationship could be a geometric effect where narrow beams sweep past the observer more quickly, as with pulsars. our model has implications for the frb emission mechanism and energy scale, volumetric event rates, and the application of frbs to cosmology. | beaming as an explanation of the repetition/width relation in frbs |
we report on a search for dark matter axion conversion photons from the magnetosphere of the galactic center magnetar psr j1745-2900 using spectra obtained from the karl g. jansky very large array (the national radio astronomy observatory is a facility of the national science foundation operated under cooperative agreement by associated universities, inc.). no significant spectral features are detected. using a hybrid model for psr j1745-2900 and canonical assumptions about the dark matter density profile, we exclude axion models with axion-photon coupling ga γ γ>6 - 34 ×10-12 gev-1 with 95% confidence over the mass ranges 4.2-8.4, 18.6-26.9, 33.0-41.4, 53.7-62.1, and 126.0 - 159.3 μ ev . if there is a dark matter cusp, the limits reduce to ga γ γ>6 - 34 ×10-14 gev-1 , which overlap some axion models for the observed mass ranges >33 μ ev . these limits may be improved by modeling the stimulated emission that can boost the axion-photon conversion process. | search for axionic dark matter using the magnetar psr j1745-2900 |
radio pulsar observations probe the lives of galactic double neutron star (dns) systems while gravitational waves enable us to study extragalactic dns in their final moments. by combining measurements from radio and gravitational-wave astronomy, we seek to gain a more complete understanding of dns from formation to merger. we analyze the recent gravitational-wave binary neutron star mergers gw170817 and gw190425 in the context of other dns known from radio astronomy. by employing a model for the birth and evolution of dns, we measure the mass distribution of dns at birth, at midlife (in the radio), and at death (in gravitational waves). we consider the hypothesis that the high-mass gravitational-wave event gw190425 is part of a subpopulation formed through unstable case bb mass transfer, which quickly merge in ∼10-100 myr. we find only mild evidence to support this hypothesis and that gw190425 is not a clear outlier from the radio population as previously claimed. if there are fast-merging binaries, we estimate that they constitute 8%-79% of dns at birth (90% credibility). we estimate the typical delay time between the birth and death of fast-merging binaries to be ≈5-401 myr (90% credibility). we discuss the implications for radio and gravitational-wave astronomy. | heavy double neutron stars: birth, midlife, and death |
binary pulsars provide some of the tightest current constraints on modified theories of gravity and these constraints will only get tighter as radio astronomers continue timing these systems. these binary pulsars are particularly good at constraining scalar-tensor theories in which gravity is mediated by a scalar field in addition to the metric tensor. scalar-tensor theories can predict large deviations from general relativity due to the fact that they allow for violation of the strong-equivalence principle through a phenomenon known as scalarization. this effect appears directly in the timing model for binary pulsars, and as such, it can be tightly constrained through precise timing. in this paper, we investigate these constraints for two scalar-tensor theories and a large set of realistic equations of state. we calculate the constraints that can be placed by saturating the current bounds on single post-keplerian parameters, as well as employing bayesian methods through markov-chain-monte-carlo simulations to explore the constraints that can be achieved when one considers all measured parameters simultaneously. our results demonstrate that both methods are able to place similar constraints and that they are both indeed dominated by the measurements of the orbital period decay. the bayesian approach, however, allows one to simultaneously explore the posterior distributions of not only the theory parameters but of the masses as well. | binary pulsar constraints on massless scalar-tensor theories using bayesian statistics |
we report on a detailed spectral analysis of the transient x-ray pulsar 1a 0535+262, which underwent the brightest giant outburst ever recorded for this source from 2020 november to december with a peak luminosity of 1.2 × 1038 erg s-1. thanks to the unprecedented energy coverage and high-cadence observations provided by insight-hxmt, we were able to find for the first time evidence for a transition of the accretion regime. at high luminosity, above the critical luminosity 6.7 × 1037 erg s-1, the cyclotron absorption line energy anticorrelates with luminosity. below the critical luminosity, a positive correlation is observed. therefore, 1a 0535+262 becomes the second source after v0332+53, which clearly shows an anticorrelation above and transition between correlation and anticorrelation around the critical luminosity. the evolution of both the observed crsf line energy and broadband x-ray continuum spectrum throughout the outburst exhibits significant differences during the rising and fading phases; that is, for a similar luminosity, the spectral parameters take different values, which results in hysteresis patterns for several spectral parameters including the cyclotron line energy. we argue that, similar to v0332+53, these changes might be related to the different geometry of the emission region in rising and declining parts of the outburst, probably due to changes in the accretion disk structure and its interaction with the magnetosphere of the neutron star. | luminosity dependence of the cyclotron line energy in 1a 0535+262 observed by insight-hxmt during the 2020 giant outburst |
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