abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
a pressure–state–response framework was customized to outline the watershed health (wh) concept. to achieve this, the watershed indicators of pressure, state (s), and response (r) were conceptualized according to 17 climatic, anthropogenic, and hydrologic criteria. four node years of 1986, 1998, 2008, and 2014 were selected to provide a running picture of the shazand watershed condition. the wh index was then calculated using geometric mean of pressure, s, and r indicators and assigned a range of values varied from 0 (unhealthiest) to 1 (healthiest). (a) the main pressures on the shazand watershed come from climatic factors in 1998 and 2008 and human factors in all study years. (b) the climatic factor and then anthropogenic factors had the maximum effectiveness in explaining the s indicator. (c) in calculating r indicator, the anthropogenic factors in 1986 and the hydrologic factors in other study years played significant contributions. (d) the greatest percentage of the study area were assigned to moderate condition of s indicator in 1986, 1998, and 2008 with value of 42, 46, and 73%, respectively, whereas in 2014, 44 and 42% of the watershed were respectively recognized as relatively healthy and moderately healthy in terms of s indicator. (e) for the first to fourth study node years, some 53, 77, 78, and 60% of the shazand watershed had the relatively unhealthy condition, respectively. (f) the shazand wh decreased about 12% during periods of 1986–1998 and 1986–2008. (g) an improving trend was also found in wh for some sub‑watersheds. | watershed health assessment using the pressure–state–response (psr) framework |
recent experimental and ab initio theory investigations of the 208pb neutron skin thickness have the potential to inform the neutron star equation of state. in particular, the strong correlation between the 208pb neutron skin thickness and the pressure of neutron matter at normal nuclear densities leads to modified predictions for the radii, tidal deformabilities, and moments of inertia of typical 1.4m⊙ neutron stars. in the present work, we study the relative impact of these recent analyses of the 208pb neutron skin thickness on bulk properties of neutron stars within a bayesian statistical analysis. two models for the equation of state prior are employed in order to highlight the role of the highly uncertain high-density equation of state. from our combined bayesian analysis of nuclear theory, nuclear experiment, and observational constraints on the dense matter equation of state, we find at the 90% credibility level r1.4=12.36‑0.73+0.38 km for the radius of a 1.4m⊙ neutron star, r2.0=11.96‑0.71+0.94 km for the radius of a 2.0m⊙ neutron star, λ1.4=440‑144+103 for the tidal deformability of a 1.4m⊙ neutron star, and i1.338=1.425‑0.146+0.074×1045gcm2 for the moment of inertia of psr j0737-3039a whose mass is 1.338m⊙. | neutron star radii, deformabilities, and moments of inertia from experimental and ab initio theory constraints of the 208pb neutron skin thickness |
the interstellar medium hosts a population of scattering screens, most of unknown origin. scintillation studies of pulsars provide a sensitive tool for resolving these scattering screens and a means of measuring their properties. in this paper, we report our analysis of 34 yr of arecibo observations of psr b1133 + 16, from which we have obtained high-quality dynamic spectra and their associated scintillation arcs, arising from the scattering screens located along the line of sight to the pulsar. we have identified six individual scattering screens that are responsible for the observed scintillation arcs, which persist for decades. using the assumption that the scattering screens have not changed significantly in this time, we have modeled the variations in arc curvature throughout the earth's orbit and extracted information about the placement, orientation, and velocity of five of the six screens, with the highest-precision distance measurement placing a screen at just ${5.46}_{-0.59}^{+0.54}$ pc from the earth. we associate the more distant of these screens with an underdense region of the local bubble. | probing the local interstellar medium with scintillometry of the bright pulsar b1133 + 16 |
the low-frequency polarisation properties of radio sources are poorly studied, particularly in statistical samples. however, the new generation of low-frequency telescopes, such as the murchison widefield array (the precursor for the low-frequency component of the square kilometre array) offers an opportunity to probe the physics of radio sources at very low radio frequencies. in this paper, we present a catalogue of linearly polarised sources detected at 216 mhz, using data from the galactic and extragalactic all-sky murchison widefield array survey. our catalogue covers the declination range -17° to -37° and 24 h in right ascension, at a resolution of around 3 arcminutes. we detect 81 sources (including both a known pulsar and a new pulsar candidate) with linearly polarised flux densities in excess of 18 mjy across a survey area of approximately 6 400 deg2, corresponding to a surface density of 1 source per 79 deg2. the level of faraday rotation measured for our sources is broadly consistent with those recovered at higher frequencies, with typically more than an order of magnitude improvement in the uncertainty compared to higher-frequency measurements. however, our catalogue is likely incomplete at low faraday rotation measures, due to our practice of excluding sources in the region where instrumental leakage appears. the majority of sources exhibit significant depolarisation compared to higher frequencies; however, a small sub-sample repolarise at 216 mhz. we also discuss the polarisation properties of four nearby, large-angular-scale radio galaxies, with a particular focus on the giant radio galaxy eso 422-g028, in order to explain the striking differences in polarised morphology between 216 mhz and 1.4 ghz. | the polarised gleam survey (pogs) i: first results from a low-frequency radio linear polarisation survey of the southern sky |
the recent discovery of gravitational-wave events has offered us unique test beds of gravity in the strong and dynamical field regime. one possible modification to general relativity is the gravitational parity violation that arises naturally from quantum gravity. such parity violation gives rise to the so-called amplitude birefringence in gravitational waves, in which one of the circularly polarized modes is amplified while the other one is suppressed during their propagation. in this paper, we study how well one can measure gravitational parity violation via the amplitude birefringence effect of gravitational waves sourced by stellar-mass black hole binaries. we choose chern-simons gravity as an example and work within an effective field theory formalism to ensure that the approximate theory is well posed. we consider gravitational waves from both individual sources and stochastic gravitational-wave backgrounds. regarding bounds from individual sources, we estimate such bounds using a fisher analysis and carry out monte carlo simulations by randomly distributing sources over their sky location and binary orientation. we find that the bounds on the scalar field evolution in chern-simons gravity from the recently discovered gravitational-wave events are too weak to satisfy the weak chern-simons approximation, while aligo with its design sensitivity can place meaningful bounds. regarding bounds from stochastic gravitational-wave backgrounds, we set the threshold signal-to-noise ratio for detection of the parity-violation mode as 5 and estimate projected bounds with future detectors assuming that signals are consistent with no parity violation. in an ideal situation in which all the source parameters and binary black hole merger-rate history are known a priori, we find that a network of two third-generation detectors is able to place bounds that are comparable to or slightly stronger than binary pulsar bounds. in a more realistic situation in which one does not have such information beforehand, approximate bounds can be derived if the regular parity-insensitive mode is detected and the peak redshift of the merger-rate history is known theoretically. since gravitational-wave observations probe either the difference in parity violation between the source and the detector (with individual sources) or the line-of-sight cosmological integration of the scalar field (with gravitational-wave backgrounds), such bounds are complementary to local measurements from solar system experiments and binary pulsar observations. | probing gravitational parity violation with gravitational waves from stellar-mass black hole binaries |
the five-hundred-meter aperture spherical radio telescope (fast) will become one of the world-leading telescopes for pulsar timing array (pta) research. the primary goals for ptas are to detect (and subsequently study) ultra-low-frequency gravitational waves, to develop a pulsar-based time standard and to improve solar system planetary ephemerides. fast will have the sensitivity to observe known pulsars with significantly improved signal-to-noise ratios and will discover a large number of currently unknown pulsars. we describe how fast will contribute to pta research and show that jitter- and timing-noise will be the limiting noise processes for fast data sets. jitter noise will limit the timing precision achievable over data spans of a few years while timing noise will limit the precision achievable over many years. | the role of fast in pulsar timing arrays |
deep nustar observation of x-ray pulsar a 0535+262, performed at a very low luminosity of ∼7 × 1034 erg s-1, revealed the presence of two spectral components. we argue that the high-energy component is associated with cyclotron emission from recombination of electrons collisionally excited to the upper landau levels. the cyclotron line energy of ecyc = 47.7 ± 0.8 kev was measured at the luminosity of almost an order of magnitude lower than what was achieved before. the data firmly exclude a positive correlation of the cyclotron energy with the mass accretion rate in this source. | cyclotron emission, absorption, and the two faces of x-ray pulsar a 0535+262 |
in this paper, we construct anisotropic model representing salient features of strange stars in the framework of massive brans–dicke gravity. we formulate the field equations for tolman–kuchowicz ansatz by incorporating the mit bag model. junction conditions are applied on the boundary of the stellar model to evaluate the unknown constants in terms of mass and radius of the star. the radius of the strange star candidate psr j1614-2230 is predicted by assuming maximum anisotropy at the surface of the star for different values of the coupling parameter, mass of the scalar field and bag constant. we examine various properties as well as the viability and stability of the anisotropic sphere. we conclude that the astrophysical model agrees with the essential criteria of a physically realistic model for higher values of the coupling parameter as well as mass of the scalar field. | quark stars in massive brans–dicke gravity with tolman–kuchowicz spacetime |
context. classical supergiant x-ray binaries (sgxbs) and supergiant fast x-ray transients (sfxts) are two types of high-mass x-ray binaries (hmxbs) that present similar donors but, at the same time, show very different behavior in the x-rays. the reason for this dichotomy of wind-fed hmxbs is still a matter of debate. among the several explanations that have been proposed, some of them invoke specific stellar wind properties of the donor stars. only dedicated empiric analysis of the donors' stellar wind can provide the required information to accomplish an adequate test of these theories. however, such analyses are scarce.aims: to close this gap, we perform a comparative analysis of the optical companion in two important systems: igr j17544-2619 (sfxt) and vela x-1 (sgxb). we analyze the spectra of each star in detail and derive their stellar and wind properties. as a next step, we compare the wind parameters, giving us an excellent chance of recognizing key differences between donor winds in sfxts and sgxbs.methods: we use archival infrared, optical and ultraviolet observations, and analyze them with the non-local thermodynamic equilibrium (nlte) potsdam wolf-rayet model atmosphere code. we derive the physical properties of the stars and their stellar winds, accounting for the influence of x-rays on the stellar winds.results: we find that the stellar parameters derived from the analysis generally agree well with the spectral types of the two donors: o9i (igr j17544-2619) and b0.5iae (vela x-1). the distance to the sources have been revised and also agree well with the estimations already available in the literature. in igr j17544-2619 we are able to narrow the uncertainty to d = 3.0 ± 0.2 kpc. from the stellar radius of the donor and its x-ray behavior, the eccentricity of igr j17544-2619 is constrained to e< 0.25. the derived chemical abundances point to certain mixing during the lifetime of the donors. an important difference between the stellar winds of the two stars is their terminal velocities (ν∞ = 1500 km s-1 in igr j17544-2619 and ν∞ = 700 km s-1 in vela x-1), which have important consequences on the x-ray luminosity of these sources.conclusions: the donors of igr j17544-2619 and vela x-1 have similar spectral types as well as similar parameters that physically characterize them and their spectra. in addition, the orbital parameters of the systems are similar too, with a nearly circular orbit and short orbital period. however, they show moderate differences in their stellar wind velocity and the spin period of their neutron star which has a strong impact on the x-ray luminosity of the sources. this specific combination of wind speed and pulsar spin favors an accretion regime with a persistently high luminosity in vela x-1, while it favors an inhibiting accretion mechanism in igr j17544-2619. our study demonstrates that the relative wind velocity is critical in class determination for the hmxbs hosting a supergiant donor, given that it may shift the accretion mechanism from direct accretion to propeller regimes when combined with other parameters. | measuring the stellar wind parameters in igr j17544-2619 and vela x-1 constrains the accretion physics in supergiant fast x-ray transient and classical supergiant x-ray binaries |
we have conducted a systematic survey for the x-ray properties of millisecond pulsars (msps). currently, there are 47 msps with confirmed x-ray detections. we have also placed the upper limits for the x-ray emission from the other 36 msps by using the archival data. we have normalized their x-ray luminosities lxand their effective photon indices γ into a homogeneous data set, which enables us to carry out a detailed statistical analysis. based on our censored sample, we report a relation of {l}x≃ {10}31.05{(\dot{e}/{10}35)}1.31 erg s-1 (2-10 kev) for the msps. the inferred x-ray conversion efficiency is found to be lower than the previously reported estimate that could be affected by selection bias. lxalso correlates/anti-correlates with the magnetic field strength at the light cylinder b lc/characteristic age τ. on the other hand, there is no correlation between lxand their surface magnetic field strength bs . we have further divided the sample into four classes: (i) black-widows, (ii) redbacks, (iii) isolated msps, and (iv) other msp binaries, and compare the properties among them. we noted that while the rotational parameters and the orbital periods of redbacks and black-widows are similar, lxof redbacks are significantly higher than those of black-widows in the 2-10 kev band. also the γ of redbacks are apparently smaller than those of black-widows, which indicates that the x-ray emission of redbacks are harder than that of black-widows. this can be explained by the different contribution of intrabinary shocks in the x-ray emission of these two classes. | x-ray census of millisecond pulsars in the galactic field |
despite more than 30 years of searching, the compact object in supernova (sn) 1987a has not yet been detected. we present new limits on the compact object in sn 1987a using millimeter, near-infrared, optical, ultraviolet, and x-ray observations from alma, vlt, hst, and chandra. the limits are approximately 0.1 mjy (0.1× {10}-26 erg s-1 cm-2 hz-1) at 213 ghz, 1 l ⊙ (6× {10}-29 erg s-1 cm-2 hz-1) in the optical if our line of sight is free of ejecta dust, and 1036 erg s-1 (2× {10}-30 erg s-1 cm-2 hz-1) in 2-10 kev x-rays. our x-ray limits are an order of magnitude less constraining than previous limits because we use a more realistic ejecta absorption model based on three-dimensional neutrino-driven sn explosion models. the allowed bolometric luminosity of the compact object is 22 l ⊙ if our line of sight is free of ejecta dust, or 138 l ⊙ if dust-obscured. depending on assumptions, these values limit the effective temperature of a neutron star (ns) to < 4-8 mk and do not exclude models, which typically are in the range 3-4 mk. for the simplest accretion model, the accretion rate for an efficiency η is limited to < {10}-11 {η }-1 m ⊙ yr-1, which excludes most predictions. for pulsar activity modeled by a rotating magnetic dipole in vacuum, the limit on the magnetic field strength (b) for a given spin period (p) is b≲ {10}14 {p}2 g s-2, which firmly excludes pulsars comparable to the crab. by combining information about radiation reprocessing and geometry, we infer that the compact object is a dust-obscured thermally emitting ns, which may appear as a region of higher-temperature ejecta dust emission. | the 30 year search for the compact object in sn 1987a |
the globular cluster (gc) 47 tuc has recently been proposed to host an intermediate-mass black hole (imbh) or a population of stellar mass black holes (bhs). to shed light on its dark content, we present an application of self-consistent multimass models with a varying mass function and content of stellar remnants, which we fit to various observational constraints. our best-fitting model successfully matches the observables and correctly predicts the radial distribution of millisecond pulsars and their gravitational accelerations inferred from long-term timing observations. the data favours a population of bhs with a total mass of 430^{+386}_{-301} m⊙, but the most likely model has very few bhs. since our models do not include a central imbh and accurately reproduce the observations, we conclude that there is currently no need to invoke the presence of an imbh in 47 tuc. the global present-day mass function inferred is significantly depleted in low-mass stars (power-law slope α =-0.52^{+0.17}_{-0.16}). given the orbit and predicted mass-loss history of this massive gc, the dearth of low-mass stars is difficult to explain with a standard initial mass function (imf) followed by long-term preferential escape of low-mass stars driven by two-body relaxation, and instead suggests that 47 tuc may have formed with a bottom-light imf. we discuss alternative evolutionary origins for the flat mass function and ways to reconcile this with the low bh retention fraction. finally, by capturing the effect of dark remnants, our method offers a new way to probe the imf in a gc above the current main-sequence turn-off mass, for which we find a slope of -2.49 ± 0.08. | on the black hole content and initial mass function of 47 tuc |
we describe a systematic search for x-ray counterparts of radio pulsars. the search was accomplished by cross-correlating the radio timing positions of all radio pulsars from the atnf pulsar database (version 1.54) with archival xmm-newton and chandra observations publicly released by july 1st 2016. in total, 178 of the archival xmm-newton observations and 213 of the archival chandra datasets where found to have a radio pulsar serendipitously in the field of view. from the 288 radio pulsars covered by these datasets we identified 20 previously undetected x-ray counterparts. for 6 of them the statistics was sufficient to model the energy spectrum with one- or two-component models. for the remaining new detections and for those pulsars for which we determined an upper limit to their counting rate we computed the energy flux by assuming a crab-like spectrum. additionally, we derived upper limits on the neutron stars' surface temperature and on the non-thermal x-ray efficiency for those pulsars for which the spin-down energy was known. the temperature upper limits where compared with predictions from various neutron star cooling models and where found to be in agreement with the minimal cooling paradigm | a search for x-ray counterparts of radio pulsars |
the observed relation between the x-ray and radio properties of low-luminosity accreting black holes (bhs) has enabled the identification of multiple candidate black hole x-ray binaries (bhxbs) in globular clusters (gcs). here, we report an identification of the radio source vla j213002.08+120904 (aka m15 s2), recently reported in kirsten et al., as a bhxb candidate. they showed that the parallax of this flat-spectrum variable radio source indicates a {2.2}-0.3+0.5 kpc distance, which identifies it as lying in the foreground of the gc m15. we determine the radio characteristics of this source and place a deep limit on the x-ray luminosity of ∼4 × 1029 erg s-1. furthermore, we astrometrically identify a faint red stellar counterpart in archival hubble images with colors consistent with a foreground star; at 2.2 kpc, its inferred mass is 0.1-0.2 m ⊙. we rule out that this object is a pulsar, neutron star x-ray binary, cataclysmic variable, or planetary nebula, concluding that vla j213002.08+120904 is the first accreting bhxb candidate discovered in quiescence outside of a gc. given the relatively small area over which parallax studies of radio sources have been performed, this discovery suggests a much larger population of quiescent bhxbs in our galaxy, 2.6 × 104-1.7 × 108 bhxbs at 3σ confidence, than has been previously estimated (∼102-104) through population synthesis. | the first low-mass black hole x-ray binary identified in quiescence outside of a globular cluster |
we study the problem of optimizing expensive blackbox functions over combinatorial spaces (e.g., sets, sequences, trees, and graphs). bocs (baptista and poloczek, 2018) is a state-of-the-art bayesian optimization method for tractable statistical models, which performs semi-definite programming based acquisition function optimization (afo) to select the next structure for evaluation. unfortunately, bocs scales poorly for large number of binary and/or categorical variables. based on recent advances in submodular relaxation (ito and fujimaki, 2016) for solving binary quadratic programs, we study an approach referred as parametrized submodular relaxation (psr) towards the goal of improving the scalability and accuracy of solving afo problems for bocs model. psr approach relies on two key ideas. first, reformulation of afo problem as submodular relaxation with some unknown parameters, which can be solved efficiently using minimum graph cut algorithms. second, construction of an optimization problem to estimate the unknown parameters with close approximation to the true objective. experiments on diverse benchmark problems show significant improvements with psr for bocs model. the source code is available at https://github.com/aryandeshwal/submodular_relaxation_bocs . | scalable combinatorial bayesian optimization with tractable statistical models |
in the canonical model of a pulsar, rotational energy is transmitted through the surrounding plasma via two electrical circuits, each connecting to the star over a small region known as a “polar cap.” for a dipole-magnetized star, the polar caps coincide with the magnetic poles (hence the name), but in general, they can occur at any place and take any shape. in light of their crucial importance to most models of pulsar emission (from radio to x-ray to wind), we develop a general technique for determining polar cap properties. we consider a perfectly conducting star surrounded by a force-free magnetosphere and include the effects of general relativity. using a combined numerical-analytical technique that leverages the rotation rate as a small parameter, we derive a general analytic formula for the polar cap shape and charge-current distribution as a function of the stellar mass, radius, rotation rate, moment of inertia, and magnetic field. we present results for dipole and quadrudipole fields (superposed dipole and quadrupole) inclined relative to the axis of rotation. the inclined dipole polar cap results are the first to include general relativity, and they confirm its essential role in the pulsar problem. the quadrudipole pulsar illustrates the phenomenon of thin annular polar caps. more generally, our method lays a foundation for detailed modeling of pulsar emission with realistic magnetic fields. | inclined pulsar magnetospheres in general relativity: polar caps for the dipole, quadrudipole, and beyond |
in the next decades, ultra-high-energy neutrinos in the eev energy range will be potentially detected by next-generation neutrino telescopes. although their primary goals are to observe cosmogenic neutrinos and to gain insight into extreme astrophysical environments, they can also indirectly probe the nature of dark matter. in this paper, we study the projected sensitivity of up-coming neutrino radio telescopes, such as rno-g, grand and icecube-gen2 radio array, to decaying dark matter scenarios. we investigate different dark matter decaying channels and masses, from 107 to 1015 gev. by assuming the observation of cosmogenic or newborn pulsar neutrinos, we forecast conservative constraints on the lifetime of heavy dark matter particles. we find that these limits are competitive with and highly complementary to previous multi-messenger analyses. | heavy decaying dark matter at future neutrino radio telescopes |
in this work we revisit the quantum hadrodynamics (qhd) formalism to investigate hyperonic and hybrid stars with hyperon-meson couplings fixed via broken su(6) group, in favor of a more general flavor group su(3). we also employ an additional channel, the strangeness-hidden ϕ meson, which couples only to the hyperons. in hybrid stars, the quark phase is built with the su(3) njl model also with an additional vector channel in the lagrangian. we found that within the models chosen the hyperon onset cannot be avoided by the quark-hadron phase transition, once the hyperon threshold always happens at lower density. also, the contribution of the quark core in a hybrid star is more relevant to the radius than to the mass, and strongly depends on the quark equation of state. we are able to reproduce 2.21 m⊙ hyperonic star and 2.10 m⊙ hybrid star. both results are in agreement with the recently detected hyper massive pulsar msp j0740+6620. | broken su(6) symmetry and massive hybrid stars |
we present a population of 19 radio-luminous supernovae (sne) with emission reaching lν~ 1026-1029 erg s-1 hz-1 in the first epoch of the very large array sky survey (vlass) at 2-4 ghz. our sample includes one long gamma-ray burst, sn 2017iuk/grb 171205a, and 18 core-collapse sne detected at ≈1-60 yr after explosion. no thermonuclear explosion shows evidence for bright radio emission, and hydrogen-poor progenitors dominate the subsample of core-collapse events with spectroscopic classification at the time of explosion (79%). we interpret these findings in the context of the expected radio emission from the forward shock interaction with the circumstellar medium (csm). we conclude that these observations require a departure from the single wind-like density profile (i.e., ρ csm ∝ r -2) that is expected around massive stars and/or from a spherical newtonian shock. viable alternatives include the shock interaction with a detached, dense shell of csm formed by a large effective progenitor mass-loss rate, $\dot{m}\sim {10}^{-4}\mbox{--}{10}^{-1}\,{m}_{\odot }$ ṁ~10-4-10-1m⊙ yr-1 (for an assumed wind velocity of 1000 km s-1); emission from an off-axis relativistic jet entering our line of sight; or the emergence of emission from a newly born pulsar-wind nebula. the relativistic sn 2012ap that is detected 5.7 and 8.5 yr after explosion with lν~ 1028 erg s-1 hz-1 might constitute the first detections of an off-axis jet+cocoon system in a massive star. however, none of the vlass sne with archival data points are consistent with our model off-axis jet light curves. future multiwavelength observations will distinguish among these scenarios. our vlass source catalogs, which were used to perform the vlass cross-matching, are publicly available at https://doi.org/10.5281/zenodo.4895112. | luminous late-time radio emission from supernovae detected by the karl g. jansky very large array sky survey (vlass) |
high-precision measurements of the pulsar dispersion measure (dm) are possible using telescopes with low-frequency wideband receivers. we present an initial study of the application of the wideband timing technique, which can simultaneously measure the pulsar times of arrivals (toas) and dms, for a set of five pulsars observed with the upgraded giant metrewave radio telescope (ugmrt) as part of the indian pulsar timing array (inpta) campaign. we have used the observations with the 300-500 mhz band of the ugmrt for this purpose. we obtain high precision in dm measurements with precisions of the order 10-6 cm-3 pc. the toas obtained have sub-μs precision and the rms of the post-fit toa residuals are in the sub-μs range. we find that the uncertainties in the dms and toas obtained with this wideband technique, applied to low-frequency data, are consistent with the results obtained with traditional pulsar timing techniques and comparable to high-frequency results from other ptas. this work opens up an interesting possibility of using low-frequency wideband observations for precision pulsar timing and gravitational wave detection with similar precision as high-frequency observations used conventionally. | low-frequency wideband timing of inpta pulsars observed with the ugmrt |
we consider a simple extension of standard model by adding two complex singlet scalars with a u(1) symmetry. a discrete z2×z2' symmetry is imposed in the model and the added scalars acquire a non zero vacuum expectation value (vev) when the imposed symmetry is broken spontaneously. the real (cp even) parts of the complex scalars mix with the sm higgs and give three physical mass eigenstates. one of these physical mass eigenstates is attributed to the sm like higgs boson with mass 125.09 gev. in the present scenario, domain walls are formed in the early universe due to the breaking of discrete z2×z2' symmetry. in order to ensure the unstability of the domain wall this discrete symmetry is also explicitly broken by adding a bias potential to the lagrangian. the unstable annihilating domain walls produce a significant amount of gravitational waves (gws). in addition, we also explore the possibility of the production of gw emission from the strong first-order phase transition. we calculate the intensities and frequencies of each of such gravitational waves originating from two different phenomena of the early universe namely annihilating domain walls and strong first-order phase transition. finally, we investigate the observational signatures from these gws at the future gw detectors such as alia, bbo, decigo, lisa, tianqin, taiji, aligo, aligo+ and pulsar timing arrays such as ska, ipta, epta, ppta, nanograv11 and nanograv12.5. | gravitational wave signatures from domain wall and strong first-order phase transitions in a two complex scalar extension of the standard model |
context. the vela supernova remnant (snr) is one of the most nearby and extended objects in the x-ray sky. it constitutes a unique laboratory for studying the thermal and nonthermal x-ray emission from an evolved snr and its central plerion at an unprecedented level of detail.aims: our goal is to characterize the hot ejecta and shocked interstellar medium (ism) associated with the vela snr, as well as the synchrotron-emitting relativistic electrons injected into the ambient medium by the central pulsar. to achieve this, we analyzed the dataset of vela acquired by srg/erosita during its first four all-sky surveys.methods: we present and analyze the energy-dependent morphology of vela using x-ray images extracted in multiple energy bands. a quantitative view of the physical parameters affecting the observed thermal and nonthermal emission is obtained by performing spatially resolved x-ray spectroscopy of over 500 independent regions using multicomponent spectral models.results: imaging demonstrates that the x-ray emission of the vela snr consists of at least three morphologically and energetically distinct components, with shell-like structures dominating below 0.6 kev, radial outward-directed features becoming apparent at medium energies, and the pulsar wind nebula (pwn) dominating the hard emission above 1.4 kev. our spectroscopy reveals a highly structured distribution of x-ray absorption column densities, which intriguingly appears to lack any correlation with optical extinction measurements, possibly due to dust destruction or a clumpy ism. the shock-heated plasma in vela is found to be comparatively cool, with a median temperature of 0.19 kev, but exhibits several, often ejecta-rich, warmer regions. within the observed ejecta clumps, we find an unexpectedly high concentration of neon and magnesium relative to oxygen, when compared to nucleosynthetic predictions. this includes the bright "shrapnel d", in which we can separate shocked ism in the soft bow-shock from a hot, ejecta-rich clump at its apex, based on the new data. finally, we find an extremely extended, smoothly decreasing distribution of synchrotron emission from the pwn, which extends up to three degrees (14 pc) from the pulsar. the integrated x-ray luminosity of the pwn in the 0.5-8.0 kev energy band corresponds to 1.5 × 10−3 of the pulsar's present-day spin-down power. the extended pwn emission likely traces the diffusion of a high-energy electron population in an ism-level magnetic field, which requires the existence of a tev counterpart powered by inverse compton radiation. | a detailed look at the thermal and nonthermal x-ray emission from the vela supernova remnant with srg/erosita |
gravitational waves (gws) emanating from unstable quasi-normal modes in neutron stars (nss) could be accessible with the improved sensitivity of the current gw detectors or with the next-generation gw detectors and, therefore, can be employed to study the ns interior. assuming f-mode excitation in isolated pulsars with typical energy of pulsar glitches and considering potential f-mode gw candidates for a+ (upgraded ligo detectors operating at fifth observing run design sensitivity) and einstein telescope (et), we demonstrate the inverse problem of ns asteroseismology within a bayesian formalism to constrain the nuclear parameters and ns equation of state (eos). we describe the ns interior within relativistic mean-field formalism. taking the example of glitching pulsars, we find that for a single event in a+ and et, among the nuclear parameters, the nucleon effective mass (m*) within 90% credible interval can be restricted within 10% and 5%, respectively. at the same time, the incompressibility (k) and the slope of the symmetry energy (l) are only loosely constrained. considering multiple (10) events in a+ and et, all the nuclear parameters are well constrained, especially m*, which can be constrained to 3% and 2% in a+ and et, respectively. uncertainty in the observables of a 1.4 m ⊙ ns such as radius ( ${r}_{1.4{m}_{\odot }}$ ), f-mode frequency ( ${f}_{1.4{m}_{\odot }}$ ), damping time ( ${\tau }_{1.4{m}_{\odot }}$ ), and a few eos properties including squared speed of sound (cs2) are also estimated. | constraining nuclear parameters using gravitational waves from f-mode oscillations in neutron stars |
a new population of millisecond pulsars is a long-standing proposed explanation for the excess of gev-scale gamma rays emanating from the region surrounding the center of the milky way (the "galactic center excess"). we examine several simple parameterizations of possible luminosity functions for this population, as well as several benchmark luminosity functions proposed in the literature, and compare the predicted populations of resolved point sources to the fermi 4fgl-dr2 point source catalog and a sub-population recently identified using wavelet-based methods. we provide general results that can be used to translate upper limits on the number of resolved point sources associated with the excess, and the fraction of the flux in the excess that can be attributed to resolved sources, into limits on the luminosity function parameter space. we discuss a number of important systematic uncertainties, including in the detection threshold model and the total flux attributed to the excess. we delineate regions of parameter space (containing existing benchmark models) where there is no apparent tension with current data, and the number of total pulsars needed to explain the excess is in the range of 𝒪(104-5). in the future, lowered point source detection thresholds could be achieved either by new analysis methods or new data. an order-of-magnitude reduction in the sensitivity threshold (which may already be achieved by novel analyses probing sub-threshold source populations) could hope to resolve more than 30% of the flux of the excess even in pessimistic scenarios. | luminosity functions consistent with a pulsar-dominated galactic center excess |
millisecond pulsars are perfect laboratories to test possible matter-geometry coupling and its physical implications in light of recent neutron star interior composition explorer (nicer) observations. we apply rastall field equations of gravity, where matter and geometry are nonminimally coupled, to krori-barua interior spacetime whereas the matter source is assumed to be anisotropic fluid. we show that all physical quantities inside the star can be expressed in terms of rastall, ϵ, and compactness, c = 2gm/rc 2, parameters. using nicer and x-ray multi-mirror newton x-ray-observational constraints on the mass and radius of the pulsar psr j0740+6620, we determine the rastall parameter to be at most ϵ = 0.041 in the positive range. the obtained solution provides a stable compact object; in addition the squared sound speed does not violate the conjectured sound speed ${c}_{s}^{2}\leqslant {c}^{2}/3$ unlike the general relativistic treatment. we note that no equations of state are assumed; the model however fits well with linear patterns with bag constants. in general, for ϵ > 0, the theory predicts a slightly larger-size star in comparison to general relativity for the same mass. this has been explained as an additional force, due to matter-geometry coupling, in the hydrodynamic equilibrium equation, which contributes to partially diminishing the gravitational force effect. consequently, we calculate the maximal compactness as allowed by the strong energy condition to be c = 0.735, which is ~2% higher than general relativity prediction. moreover, for the surface density at saturation nuclear density ρ nuc = 2.7 × 1014 g cm-3, we estimate the maximum mass m = 4m ⊙ at radius r = 16 km. | impact of rastall gravity on mass, radius, and sound speed of the pulsar psr j0740+6620 |
recent observations discovered that some repeating fast radio bursts (frbs) show complicated variations and reversals of faraday rotation measures (rms), indicating that the sources of these frbs are embedded in a dynamically magnetized environment. one possible scenario is that repeating frbs are generated by pulsars in binary systems, especially containing a high-mass companion with strong stellar outflows. here we study the rm variations caused by stellar winds and a possible stellar disk. if the magnetic field is radial in the stellar wind, rms will not reverse except if the magnetic axis inclination angle is close to 90°. for the toroidal magnetic field in the wind, rms will reverse at the superconjunction. for the case of the toroidal field in the disk, the rm variations may have a multimodal and multiple reversal profile because the radio signals travel through different components of the disk during periastron passage. we also apply this model to frb 20180916b. by assuming that its 16.35 day period is from a slowly rotating or freely precessing magnetar, we find that the secular rm variation can be explained by the periastron passage of a magnetar in a massive binary system. in addition, the clumps in the stellar wind and disk can cause short timescale (<1 day) variations or reversals of rm. therefore, long-term monitoring of rm variations can reveal the environments of repeating frbs. | rotation measure variations and reversals of repeating frbs in massive binary systems |
tempo analyzes pulsar timing data. pulse times of arrival (toas), pulsar model parameters, and coded instructions are read from one or more input files. the toas are fitted by a pulse timing model incorporating transformation to the solar-system barycenter, pulsar rotation and spin-down and, where necessary, one of several binary models. program output includes parameter values and uncertainties, residual pulse arrival times, chi-squared statistics, and the covariance matrix of the model. in prediction mode, ephemerides of pulse phase behavior (in the form of polynomial expansions) are calculated from input timing models. tempo is the basis for the tempo2 (ascl:1210.015) code. | tempo: pulsar timing data analysis |
a gravitational-wave background can be detected in pulsar-timing-array data as hellings-downs correlations among the timing residuals measured for different pulsars. the optimal statistic implements this concept as a classical null-hypothesis statistical test: a null model with no correlations can be rejected if the observed value of the statistic is very unlikely under that model. to address the dependence of the statistic on the uncertain pulsar noise parameters, the pulsar-timing-array community has adopted a hybrid classical-bayesian scheme [s. j. vigeland et al., phys. rev. d 98, 044003 (2018)., 10.1103/physrevd.98.044003] in which the posterior distribution of the noise parameters induces a posterior distribution for the statistic. in this article we propose a rigorous interpretation of the hybrid scheme as an instance of posterior predictive checking, and we introduce a new summary statistic (the bayesian signal-to-noise ratio) that should be used to accurately quantify the statistical significance of an observation instead of the mean posterior signal-to-noise ratio, which does not support such a direct interpretation. in addition to falsifying the no-correlation hypothesis, the bayesian signal-to-noise ratio can also provide evidence supporting the presence of hellings-downs correlations. we demonstrate our proposal with simulated datasets based on nanograv's 12.5-yr data release. we also establish a relation between the posterior distribution of the statistic and the bayes factor in favor of correlations, thus calibrating the bayes factor in terms of hypothesis-testing significance. | posterior predictive checking for gravitational-wave detection with pulsar timing arrays. i. the optimal statistic |
external magnetic fields impose diverse effects on low-temperature plasmas. we study these in a low-pressure capacitively coupled radio frequency plasma in argon via self-consistent kinetic simulations. the primary effect of the transversal magnetic field, that manifests itself in the trapping of electrons at lower excitation frequencies and, thus, in an increase of the plasma density as a function of the magnetic field, is overruled at higher excitation frequencies by the attenuation of the self-excitation of plasma series resonance oscillations and the attenuation of non-linear electron resonance heating, which lead to a reduced plasma density. at higher magnetic fields the plasma density increases again due to (i) a longer interaction time between the electrons and the edges of the expanding sheaths and (ii) the electric field reversals that develop at the collapsing sheath edges to overcome the trapping of electrons and accelerate them towards the electrodes. | magnetic attenuation of the self-excitation of the plasma series resonance in low-pressure capacitively coupled discharges |
the development of pressure sensor arrays capable of distinguishing the shape and texture details of objects is of considerable interest in the emerging fields of smart robots, prostheses, human-machine interfaces, and artificial intelligence (ai). here we report an integrated pressure sensor array, by combining solution-processed two-dimensional (2d) mos2 van der waals (vdw) thin film transistor (tft) active matrix and conductive micropyramidal pressure-sensitive rubber (psr) electrodes made of polydimethylsiloxane/carbon nanotube composites, to achieve spatially revolved pressure mapping with excellent contrast and low power consumption. we demonstrate a 10 × 10 active matrix by using the 2d mos2 vdw-tfts with high on-off ratio > 106, minimal hysteresis, and excellent device-to-device uniformity. the combination of the vdw-tft active matrix with the highly uniform micropyramidal psr electrodes creates an integrated pressure sensing array for spatially resolved pressure mapping. this study demonstrates that the solution-processed 2d vdw-tfts offer a solution for active-matrix control of pressure sensor arrays, and could be extended for other active-matrix arrays of electronic or optoelectronic devices. | two-dimensional van der waals thin film transistors as active matrix for spatially resolved pressure sensing |
the international pulsar timing array (ipta) is a galactic-scale gravitational-wave observatory that monitors an array of millisecond pulsars. the timing precision of these pulsars is such that one can measure the correlated changes in pulse arrival times accurately enough to search for the signature of a stochastic gravitational-wave background. as we add more pulsars to the array, and extend the length of our dataset, we are able to observe at ever lower gravitational-wave frequencies. as our dataset matures we are approaching a regime where a detection is expected, and therefore testing current data analysis tools is crucial, as is the development of new tools and techniques. in this spirit, here we introduce the second ipta mock data challenge, and briefly review the first. the purpose of this challenge is to foster the development of detection tools for pulsar timing arrays and to cultivate interaction with the international gravitational-wave community. ipta mock datasets can be found at the ipta github page, https://github.com/ipta/mdc2 . | the second international pulsar timing array mock data challenge |
the gravitational waves of hořava gravity, their polarization states, and their possible observational signatures are discussed. using the gauge-invariant variable formalism, we find the three polarization modes in hořava gravity excited by the three physical degrees of freedom contained in this theory. in particular, the scalar degree of freedom excites a mix of the transverse breathing and the longitudinal polarizations. the constraints from the previous experimental observations are taken into account, especially including the speed bound from the observations of gw170817 and grb 170817a. we find that the hořava theory is highly constrained. within the experimentally allowed parametric space, we study whether the pulsar timing arrays and the gaia mission can be used to distinguish the different polarizations. after calculating the cross-correlation functions between the redshifts of photons and the astrometric positions of stars, we conclude that it is possible to use pulsar timing arrays and the gaia mission to tell whether the scalar polarization exists. | gravitational waves and the polarizations in hořava gravity after gw170817 |
context radio continuum surveys of the galactic plane can find and characterize h ii regions, supernova remnants (snrs), planetary nebulae (pne), and extragalactic sources. a number of surveys at high angular resolution (≤25″) at different wavelengths exist to study the interstellar medium (ism), but no comparable high-resolution and high-sensitivity survey exists at long radio wavelengths around 21 cm.aims: our goal is to investigate the 21 cm radio continuum emission in the northern galactic plane at < 25″ resolution. methods we observed a large percentage of the galactic plane in the first quadrant of the milky way (l = 14.0-67.4° and |b| ≤ 1.25°) with the karl g. jansky very large array (vla) in the c-configuration covering six continuum spectral windows (spw). these data provide a detailed view on the compact as well as extended radio emission of our galaxy and thousands of extragalactic background sources. results we used the blobcat software and extracted 10 916 sources. after removing spurious source detections caused by the side lobes of the synthesized beam, we classified 10 387 sources as reliable detections. we smoothed the images to a common resolution of 25″ and extracted the peak flux density of each source in each spw to determine the spectral indices α (assuming i(ν) ∝ να). by cross-matching with catalogs of h ii regions, snrs, pne, and pulsars, we found radio counterparts for 840 h ii regions, 52 snrs, 164 pne, and 38 pulsars. we found 79 continuum sources that are associated with x-ray sources. we identified 699 ultra-steep spectral sources (α < -1.3) that could be high-redshift galaxies. about 9000 of the sources we extracted are not classified specifically, but based on their spatial and spectral distribution, a large percentage of these are likely to be extragalactic background sources. more than 7750 sources do not have counterparts in the simbad database and more than 3760 sources do not have counterparts in the ned database. conclusions studying the long wavelengths centimeter continuum emission and the associated spectral indices allows us to characaterize a large percentage of galactic and extragalactic radio sources in the area of the northern inner milky way. this database will be extremely useful for future studies of a diverse set of astrophysical objects. the full continuum catalog, the full table 4, and all the fits files of the continuum data are available at the project website http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/619/a124 | radio continuum emission in the northern galactic plane: sources and spectral indices from the thor survey |
we report the timing results for psr j2234+0611, a 3.6 ms pulsar in a 32 day, eccentric (e = 0.13) orbit with a helium white dwarf. the precise timing and eccentric nature of the orbit allow measurements of an unusual number of parameters: (a) a precise proper motion of 27.10(3) mas yr-1 and a parallax of 1.05(4) mas resulting in a pulsar distance of 0.95(4) kpc; enabling an estimate of the transverse velocity, 123(5) km s-1. together with previously published spectroscopic measurements of the systemic radial velocity, this allows a 3d determination of the system’s velocity; (b) precise measurements of the rate of advance of periastron yields a total system mass of {1.6518}-0.0035+0.0033 m ⊙ (c) a shapiro delay measurement, h 3 = 82 ± 14 ns, despite the orbital inclination not being near 90° combined with the measurement of the total mass yields a pulsar mass of {1.353}-0.017+0.014 {m}⊙and a companion mass of {0.298}-0.012+0.015 {m}⊙ ; (d) we measure precisely the secular variation of the projected semimajor axis and detect a significant annual orbital parallax; together these allow a determination of the 3d orbital geometry of the system, including an unambiguous orbital inclination (i={138.7}-2.2+2.5 \deg ) and a position angle for the line of nodes ({{ω }}={44}-4+5 \deg ). we discuss the component masses to investigate the hypotheses previously advanced to explain the origin of eccentric msps. the unprecedented determination of the 3d position, motion, and orbital orientation of the system, plus the precise pulsar and wd masses and the latter’s optical detection make this system a unique test of our understanding of white dwarfs and their atmospheres. | psr j2234+0611: a new laboratory for stellar evolution |
the recent discovery of a mega-jansky radio burst occurring simultaneously with short x-ray bursts from the galactic magnetar (strongly magnetized neutron star (ns)) sgr 1935+2154 is a smoking gun for the hypothesis that some cosmological fast radio bursts (frbs) arise from magnetar bursts. we argue that the x-ray bursts with high temperature t ≳ 30 kev entail an electron-positron (e±) outflow from a trapped-expanding fireball, polluting the ns magnetosphere before the frb emission. the e± outflow is opaque to induced compton scatterings of frb photons, and is strongly compton-dragged by the x-ray bursts. nevertheless, the frb photons can break out of the e± outflow with radiation forces if the frb emission radius is larger than a few tens of ns radii. a frb is choked if the frb is weaker or the x-ray bursts are stronger, possibly explaining why there are no frbs with giant flares and no detectable x-ray bursts with weak frbs. we also speculate that the e± outflow may be inevitable for frbs, solving the problem of why the frbs occur only with high-t x-ray bursts. the breakout physics is important for constraining the emission mechanism and electromagnetic counterparts to future frbs. | fast radio burst breakouts from magnetar burst fireballs |
neutron stars are unique cosmic laboratories in which fundamental physics can be probed in extreme conditions not accessible to terrestrial experiments. in particular, the precise timing of rotating magnetized neutron stars (pulsars) reveals sudden jumps in rotational frequency in these otherwise steadily spinning-down objects. these 'glitches' are thought to be due to the presence of a superfluid component in the star, and offer a unique glimpse into the interior physics of neutron stars. in this paper we propose an innovative method to constrain the mass of glitching pulsars, using observations of the maximum glitch observed in a star, together with state-of-the-art microphysical models of the pinning interaction between superfluid vortices and ions in the crust. we study the properties of a physically consistent angular momentum reservoir of pinned vorticity, and we find a general inverse relation between the size of the maximum glitch and the pulsar mass. we are then able to estimate the mass of all the observed glitchers that have displayed at least two large events. our procedure will allow current and future observations of glitching pulsars to constrain not only the physics of glitch models but also the superfluid properties of dense hadronic matter in neutron star interiors. | constraints on pulsar masses from the maximum observed glitch |
alpha magnetic spectrometer (ams-02) recently published its lepton spectra measurement. the results show that the positron fraction no longer increases above ∼ 200 gev. the aim of this work is to investigate the possibility that the excess of positron fraction is due to pulsars. nearby known pulsars from the atnf catalog are considered to be a possible primary positron source of the high energy positrons. we find that the pulsars with age t∼eq (0.45{-}4.5)× 105 year and distance d<0.5 kpc can explain the behavior of positron fraction of ams-02 in the range of high energy. we show that each of the four pulsars—geminga, j1741-2054, monogem, and j0942-5552—is able to be a single source satisfying all considered physical requirements. we also discuss the possibility that these high energy e{}^{± } are from multiple pulsars. the multiple pulsar contribution predicts a positron fraction with some structures at higher energies. | pulsar interpretation of lepton spectra measured by ams-02 |
in this work we have estimated upper and lower limits to the strength of the magnetic dipole moment of all 14 accreting millisecond x-ray pulsars observed with the rossi x-ray timing explorer (rxte). for each source we searched the archival rxte data for the highest and lowest flux levels with a significant detection of pulsations. we assume these flux levels to correspond to the closest and farthest location of the inner edge of the accretion disc at which channelled accretion takes place. by estimating the accretion rate from the observed luminosity at these two flux levels, we place upper and lower limits on the magnetic dipole moment of the neutron star, using assumptions from standard magnetospheric accretion theory. finally, we discuss how our field strength estimates can be further improved as more information on these pulsars is obtained. | the magnetic-field strengths of accreting millisecond pulsars |
we report on the analysis of two deep xmm-newton observations of the magnetar swift j1834.9-0846 and its surrounding extended emission taken in 2014 march and october, 2.5 and 3.1 yr after the source went into outburst. the magnetar is only weakly detected in the first observation, with an absorption-corrected flux {f}0.5-10{kev}≈ 4× {10}-14 erg s-1 cm-2 and a 3σ upper limit during the second observation of about 3 × 10-14 erg s-1 cm-2. this flux level is more than 3 orders of magnitude lower than the flux measured at the outburst onset in 2011 september. the extended emission, centered at the magnetar position and elongated toward the southwest, is clearly seen in both observations; it is best fit by a highly absorbed power law (pl), with a hydrogen column density of {n}{{h}}=8.0× {10}22 cm-2 and pl photon index {{γ }}=2.2+/- 0.2. its flux is constant between the two observations at {f}0.5-10{kev}=1.3× {10}-12 erg s-1 cm-2. we find no statistically significant changes in the spectral shape or the flux of this extended emission over a period of 9 yr from 2005 to 2014. these new results strongly support the extended emission nature as a wind nebula and firmly establish swift j1834.9-0846 as the first magnetar to show a surrounding wind nebula. further, our results imply that such nebulae are no longer exclusive to rotation-powered pulsars and narrow the gap between these two subpopulations of isolated neutron stars. the size and spectrum of the nebula are compatible with those of pulsar-wind nebulae, but its radiative efficiency {η }{{x}}={l}{{x}}/\dot{e}≈ 0.1 is markedly high, possibly pointing to an additional wind component in swift j1834.9-0846. | the wind nebula around magnetar swift j1834.9-0846 |
we consider the x-ray properties of the redback class of eclipsing millisecond pulsars. these are transitional systems between accreting low-mass x-ray binaries and binary millisecond pulsars orbiting white dwarfs, and hence their companions are non-degenerate and nearly roche-lobe filling. the x-ray luminosity seems to scale with the fraction of the pulsar sky subtended by the companion, suggesting the shock region is not much larger than the companion, which is supported by modeling of the orbital light curves. the typical x-ray photon spectral index is $\sim 1$ and the typical 0.3-8 kev x-ray efficiency, assuming a shock size on the order of the companion's roche lobe cross-section, is on the order of 10%. we present an overview of previous investigations, and present new observations of two redbacks, a chandra observation of psr j1628$-$3205 and a xmm-newton observation of psr j2129$-$0429. the latter shows a clearly double peaked orbital light curve with variation of the non-thermal flux by a factor of $\sim 11$, with peaks around orbital phases 0.6 and 0.9. we suggest the magnetic field of the companion plays a significant role in the x-ray emission from intrabinary shocks in redbacks. | x-ray studies of redbacks |
with an average density higher than the nuclear density, neutron stars (ns) provide a unique test-ground for nuclear physics, quantum chromodynamics (qcd), and nuclear superfluidity. determination of the fundamental interactions that govern matter under such extreme conditions is one of the major unsolved problems of modern physics, and -- since it is impossible to replicate these conditions on earth -- a major scientific motivation for ska. the most stringent observational constraints come from measurements of ns bulk properties: each model for the microscopic behaviour of matter predicts a specific density-pressure relation (its `equation of state', eos). this generates a unique mass-radius relation which predicts a characteristic radius for a large range of masses and a maximum mass above which ns collapse to black holes. it also uniquely predicts other bulk quantities, like maximum spin frequency and moment of inertia. the ska, in phase 1 and particularly in phase 2 will, thanks to the exquisite timing precision enabled by its raw sensitivity, and surveys that dramatically increase the number of sources: 1) provide many more precise ns mass measurements (high mass ns measurements are particularly important for ruling out eos models); 2) allow the measurement of the ns moment of inertia in highly relativistic binaries such as the double pulsar; 3) greatly increase the number of fast-spinning ns, with the potential discovery of spin frequencies above those allowed by some eos models; 4) improve our knowledge of new classes of binary pulsars such as black widows and redbacks (which may be massive as a class) through sensitive broad-band radio observations; and 5) improve our understanding of dense matter superfluidity and the state of matter in the interior through the study of rotational glitches, provided that an ad-hoc campaign is developed. | probing the neutron star interior and the equation of state of cold dense matter with the ska |
we present two methods for determining the significance of a stochastic gravitational-wave (gw) background affecting a pulsar-timing array, where detection is based on evidence for quadrupolar spatial correlations between pulsars. rather than constructing noise simulations, we eliminate the gwb spatial correlations in the true data sets to assess detection significance with all real data features intact. in our first method, we perform random phase shifts in the signal-model basis functions. this phase shifting eliminates signal phase coherence between pulsars, while keeping the statistical properties of the pulsar timing residuals intact. we then explore a method to null correlations between pulsars by using a "scrambled" overlap-reduction function in the signal model for the array. this scrambled function is orthogonal to what we expect of a real gw background signal. we demonstrate the efficacy of these methods using bayesian model selection on a set of simulated data sets that contain a stochastic gw signal, timing noise, undiagnosed glitches, and uncertainties in the solar system ephemeris. finally, we introduce an overarching formalism under which these two techniques are naturally linked. these methods are immediately applicable to all current pulsar-timing array data sets, and should become standard tools for future analyses. | all correlations must die: assessing the significance of a stochastic gravitational-wave background in pulsar timing arrays |
in this work, we consider the consequences of phase transition in dense qcd on the properties of compact stars and implications for the observational program in gravitational wave and x-ray astrophysics. the key underlying assumption of our modeling is a strong first-order phase transition past the point where the hadronic branch of compact stars reaches the two-solar mass limit. our analysis predicts ultracompact stars with very small radii—in the range of 6-9 km—living on compact star sequences that are entirely consistent with the current multimessenger data. we show that sequences featuring two-solar mass hadronic stars consistent with radio-pulsar observations are also consistent with the inferences of large radii for massive neutron stars by nicer x-ray observations of neutron stars and the small radii predicted by gravitational waves analysis of the binary neutron star inspiral event gw170817 for our models that feature a strong first-order qcd phase transition. | ultracompact hybrid stars consistent with multimessenger astrophysics |
the crab pulsar's radio emission is unusual, consisting predominantly of giant pulses, with durations of about a microsecond but structure down to the nanosecond level, and brightness temperatures of up to 1037 k. it is unclear how giant pulses are produced, but they likely originate near the pulsar's light cylinder, where corotating plasma approaches the speed of light. we report observations in the 400-800 mhz frequency band, where the pulses are broadened by scattering in the surrounding crab nebula. we find that some pulse frequency spectra show strong bands, which vary during the scattering tail, in one case showing a smooth upward drift. while the banding may simply reflect interference between nanosecond scale pulse components, the variation is surprising, as in the scattering tail the only difference is that the source is observed via slightly longer paths, bent by about an arcsecond in the nebula. the corresponding small change in viewing angle could nevertheless reproduce the observed drift by a change in doppler shift, if the plasma that emitted the giant pulses moved highly relativistically, with a lorentz factor γ ~ 104 (and without much spread in γ). if so, this would support models that appeal to highly relativistic plasma to transform ambient magnetic structures to coherent gigahertz radio emission, be it for giant pulses or for potentially related sources, such as fast radio bursts. | kinematics of crab giant pulses |
the latest ams-02 data on cosmic-ray electrons show a break in the energy spectrum around 40 gev, with a change in the slope of about 0.1. we perform a combined fit to the newest ams-02 positron and electron flux data above 10 gev using a semianalytical diffusion model where sources include production of pairs from pulsar wind nebulae (pwne), electrons from supernova remnants (snrs), and both species from spallation of hadronic cosmic rays with interstellar medium atoms. we demonstrate that within our setup the change in the slope in the ams-02 electron data is well explained by the interplay between the flux contributions from snrs and pwne. in fact, the relative contribution to the data of these two populations changes by a factor of about 13 from 10 to 1000 gev. the pwn contribution has a significance of at least 4 σ , depending on the model used for the propagation, interstellar radiation field, and energy losses. we check the stability of this result against low-energy effects by numerically solving the transport equation. as well as adding possible breaks in the injection spectrum of snrs. the effect of the energy losses alone, when the inverse compton scattering is properly computed within a fully numerical treatment of the klein-nishina cross section, cannot explain the break in the e- flux data, as recently proposed in the literature. | novel interpretation of the latest ams-02 cosmic-ray electron spectrum |
the crab pulsar and its nebula are among the most studied astrophysical systems, and constitute one of the most promising environments where high-energy processes and particle acceleration can be investigated. they are the only objects for which significant x-ray polarization was detected in the past. here we present the imaging x-ray polarimetry explorer (ixpe) observation of the crab pulsar and nebula. the total pulsar pulsed emission in the [2-8] kev energy range is unpolarized. significant polarization up to 15% is detected in the core of the main peak. the nebula has a total space integrated polarized degree of 20% and polarization angle of 145°. the polarized maps show a large variation in the local polarization, and regions with a polarized degree up to 45-50%. the polarization pattern suggests a predominantly toroidal magnetic field. our findings for the pulsar are inconsistent with most inner magnetospheric models, and suggest emission is more likely to come from the wind region. for the nebula, the polarization map suggests a patchy distribution of turbulence, uncorrelated with the intensity, in contrast with simple expectations from numerical models. | simultaneous space and phase resolved x-ray polarimetry of the crab pulsar and nebula |
we propose pulsar, an efficient sphere-based differentiable renderer that is orders of magnitude faster than competing techniques, modular, and easy-to-use due to its tight integration with pytorch. differentiable rendering is the foundation for modern neural rendering approaches, since it enables end-to-end training of 3d scene representations from image observations. however, gradient-based optimization of neural mesh, voxel, or function representations suffers from multiple challenges, i.e., topological inconsistencies, high memory footprints, or slow rendering speeds. to alleviate these problems, pulsar employs: 1) a sphere-based scene representation, 2) an efficient differentiable rendering engine, and 3) neural shading. pulsar executes orders of magnitude faster than existing techniques and allows real-time rendering and optimization of representations with millions of spheres. using spheres for the scene representation, unprecedented speed is obtained while avoiding topology problems. pulsar is fully differentiable and thus enables a plethora of applications, ranging from 3d reconstruction to general neural rendering. | pulsar: efficient sphere-based neural rendering |
thanks to dedicated long-term missions like voyager and goes over the past 50 years, much insight has been gained on the activity of our sun, the solar wind, its interaction with the interstellar medium, and, thus, about the formation, the evolution, and the structure of the heliosphere. additionally, with the help of multi-wavelength observations by the hubble space telescope, kepler, and tess, we not only were able to detect a variety of extrasolar planets and exomoons but also to study the characteristics of their host stars, and thus became aware that other stars drive bow shocks and astrospheres. although features like, e.g., stellar winds, could not be measured directly, over the past years several techniques have been developed allowing us to indirectly derive properties like stellar mass-loss rates and stellar wind speeds, information that can be used as direct input to existing astrospheric modeling codes. in this review, the astrospheric modeling efforts of various stars will be presented. starting with the heliosphere as a benchmark of astrospheric studies, investigating the paleo-heliospheric changes and the balmer hα projections to 1 pc, we investigate the surroundings of cool and hot stars, but also of more exotic objects like neutron stars. while pulsar wind nebulae (pwns) might be a source of high-energy galactic cosmic rays (gcrs), the astrospheric environments of cool and hot stars form a natural shield against gcrs. their modulation within these astrospheres, and the possible impact of turbulence, are also addressed. this review shows that all of the presented modeling efforts are in excellent agreement with currently available observations. | astrospheres of planet-hosting cool stars and beyond ⋅ when modeling meets observations |
we perform magnetospheric studies in the modified gravity (mog) framework to investigate effects of mog on radio pulsar energetics with the main question being "can mog explain how radio pulsars turn into radio-quiet ones?" in order to realize our aim, first, we have obtained exact vacuum analytical solutions of maxwell equations for magnetic fields in the exterior of neutron stars in mog. then we have derived the analytical expressions for goldreich-julian charge density and unscreened parallel electric field solving the poisson equation in the mog frame. calculations have shown that effects of mog shift the radio pulsar death line up in p p ˙ diagram rend-ring objects that are radio loud in general relativity radio quiet in mog. using observational data, we estimate the upper limit for parameter α for the millisecond pulsars j2145-0750, j0024-7204d, and j0024-7204h, as α =1.6011 , 3.06528, and 0.9747, respectively. | can modified gravity silence radio-loud pulsars? |
we present the first systematic study of the gravitational collapse of rotating and magnetized neutron stars to charged and rotating (kerr-newman) black holes. in particular, we consider the collapse of magnetized and rotating neutron stars assuming that no pair-creation takes place and that the charge density in the magnetosphere is so low that the stellar exterior can be described as an electrovacuum. under these assumptions, which are rather reasonable for a pulsar that has crossed the 'death line', we show that when the star is rotating, it acquires a net initial electrical charge, which is then trapped inside the apparent horizon of the newly formed back hole. we analyse a number of different quantities to validate that the black hole produced is indeed a kerr-newman one and show that, in the absence of rotation or magnetic field, the end result of the collapse is a schwarzschild or kerr black hole, respectively. | gravitational collapse to a kerr-newman black hole |
a charged compact star model has been determined for anisotropic fluid distribution. we have solved the einstein-maxwell field equations to construct the charged compact star model by using the radial pressure, the metric function e^{λ} and the electric charge function. the generic charged anisotropic solution is verified by exploring different physical conditions like causality condition, mass-radius relation and stability of the solution (via the adiabatic index, tov equations and the herrera cracking concept). it is observed that the present charged anisotropic compact star model is compatible with the star psr 1937+21. moreover, we also presented the eos ρ = f(p) for the present charged compact star model. | modeling of charged anisotropic compact stars in general relativity |
giant pulsar frequency glitches as detected in the emblematic vela pulsar have long been thought to be the manifestation of a neutron superfluid permeating the inner crust of a neutron star. however, this superfluid has been recently found to be entrained by the crust, and as a consequence it does not carry enough angular momentum to explain giant glitches. the extent to which pulsar-timing observations can be reconciled with the standard vortex-mediated glitch theory is studied considering the current uncertainties on dense-matter properties. to this end, the crustal moment of inertia of glitching pulsars is calculated employing a series of different unified dense-matter equations of state. | giant pulsar glitches and the inertia of neutron star crusts |
we report on the discovery of three new millisecond pulsars (msps; namely j1748-2446aj, j1748-2446ak, and j1748-2446al) in the inner regions of the dense stellar system terzan 5. these pulsars have been discovered thanks to a method, alternative to the classical search routines, that exploited the large set of archival observations of terzan 5 acquired with the green bank telescope over five years (from 2010 to 2015). this technique allowed the analysis of stacked power spectra obtained by combining ∼206 hr of observation. j1748-2446aj has a spin period of ∼2.96 ms, j1748-2446ak of ∼1.89 ms (thus it is the fourth fastest pulsar in the cluster) and j1748-2446al of ∼5.95 ms. all three msps are isolated, and currently we have timing solutions only for j1748-2446aj and j1748-2446ak. for these two systems, we evaluated the contribution to the measured spin-down rate of the acceleration due to the cluster potential field, thus estimating the intrinsic spin-down rates, which are in agreement with those typically measured for msps in globular clusters (gcs). our results increase the number of pulsars known in terzan 5 to 37, which now hosts 25% of the entire pulsar population identified, so far, in gcs. | discovery of three new millisecond pulsars in terzan 5 |
the milky way centre exhibits an intense flux in the gamma and x-ray bands, whose origin is partly ascribed to the possible presence of a large population of millisecond pulsars (msps) and cataclysmic variables (cvs), respectively. however, the number of sources required to generate such an excess is much larger than what is expected from in situ star formation and evolution, opening a series of questions about the formation history of the galactic nucleus. in this paper, we make use of direct n-body simulations to investigate whether these sources could have been brought to the galactic centre by a population of star clusters that underwent orbital decay and formed the galactic nuclear star cluster (nsc). our results suggest that the gamma-ray emission is compatible with a population of msps that were mass segregated in their parent clusters, while the x-ray emission is consistent with a population of cvs born via dynamical interactions in dense star clusters. combining observations with our modelling, we explore how the observed γ-ray flux can be related to different nsc formation scenarios. finally, we show that the high-energy emission coming from the galactic central regions can be used to detect black holes heavier than 105 m⊙ in nearby dwarf galaxies. | gamma-ray and x-ray emission from the galactic centre: hints on the nuclear star cluster formation history |
the presence of neutron stars in at least three ultraluminous x-ray sources is now firmly established and offers an unambiguous view of super-critical accretion. all three systems show long-time-scale periods (60-80 d) in the x-rays and/or optical, two of which are known to be super-orbital in nature. should the flow be classically super critical, i.e. the eddington limit is reached locally in the disc (implying surface dipole fields that are sub-magnetar in strength), then the large scale-height flow can precess through the lense-thirring effect which could provide an explanation for the observed super-orbital periods. by connecting the details of the lense-thirring effect with the observed pulsar spin period, we are able to infer the moment of inertia and therefore equation of state of the neutron star without relying on the inclination of or distance to the system. we apply our technique to the case of ngc 7793 p13 and demonstrate that stronger magnetic fields imply stiffer equations of state. we discuss the caveats and uncertainties, many of which can be addressed through forthcoming radiative magnetohydrodynamic (rmhd) simulations and their connection to observation. | lense-thirring precession in ulxs as a possible means to constrain the neutron star equation of state |
we have observed and analysed the eclipses of the black widow pulsar j1810+1744 at low radio frequencies. using low-frequency array (lofar) and westerbork synthesis radio telescope observations between 2011 and 2015, we have measured variations in flux density, dispersion measure, and scattering around eclipses. high-time resolution, simultaneous beamformed, and interferometric imaging lofar observations show concurrent disappearance of pulsations and total flux from the source during the eclipses, with a 3σ upper limit of 36 mjy ( < 10 per cent of the pulsar's averaged out-of-eclipse flux density). the dispersion measure variations are highly asymmetric, suggesting a tail of material swept back due to orbital motion. the egress deviations are variable on time-scales shorter than the 3.6 h orbital period and are indicative of a clumpy medium. additional pulse broadening detected during egress is typically < 20 per cent of the pulsar's spin period, showing no evidence of scattering the pulses beyond detectability in the beamformed data. the eclipses, lasting ∼ 13 per cent of the orbit at 149 mhz, are shown to be frequency-dependent with total duration scaling as ∝ ν-0.41 ± 0.03. the results are discussed in the context of the physical parameters of the system, and an examination of eclipse mechanisms reveals cyclotron-synchrotron absorption as the most likely primary cause, although non-linear scattering mechanisms cannot be quantitatively ruled out. the inferred mass-loss rate is a similar order of magnitude to the mean rate required to fully evaporate the companion in a hubble time. | the low-frequency radio eclipses of the black widow pulsar j1810+1744 |
the pulsar/massive star binary system psr b1259-63/ls 2883 is one of the best-studied gamma-ray binaries, a class of systems whose bright gamma-ray flaring can provide important insights into high-energy physics. using the australian long baseline array, we have conducted very long baseline interferometric observations of psr b1259-63 over 4.4 years, fully sampling the 3.4-year orbital period. from our measured parallax of 0.38 ± 0.05 mas- we use a bayesian approach to infer a distance of 2.6^{+0.4}_{-0.3} kpc. we find that the binary orbit is viewed at an angle of 154 ± 3° to the line of sight, implying that the pulsar moves clockwise around its orbit as viewed on the sky. taking our findings together with previous results from pulsar timing observations, all seven orbital elements for the system are now fully determined. we use our measurement of the inclination angle to constrain the mass of the stellar companion to lie in the range 15-31 m⊙. our measured distance and proper motion are consistent with the system having originated in the cen ob1 association and receiving a modest natal kick, causing it to have moved ∼8 pc from its birthplace over the past ∼3 × 105 years. the orientation of the orbit on the plane of the sky matches the direction of motion of the x-ray synchrotron-emitting knot observed by the chandra x-ray observatory to be moving away from the system. | the geometric distance and binary orbit of psr b1259-63 |
we show that the fine structure of the electron spectrum in cosmic rays, especially the excess claimed by ams-02 at energies ≳42 gev , is fully accounted for in terms of inverse compton losses in the photon background dominated by ultraviolet, infrared, and cosmic microwave background photons, plus the standard synchrotron losses in the galactic magnetic field. the transition to the klein-nishina regime on the ultraviolet background causes the feature. hence, contrary to previous statements, observations do not require the overlap of different components. we stress that the feature observed by ams-02 at energies ≳42 gev is not related to the positron excess, which instead requires the existence of positron sources, such as pulsars. because energy losses are the physical explanation of this feature, we indirectly confirm that the transport of leptons in the galaxy is loss dominated down to energies of the order of tens of gev. this finding imposes strong constraints on the feasibility of alternative theories of cosmic transport in which the grammage is accumulated in cocoons concentrated around sources, requiring that electrons and positrons become loss dominated only at very high energies. | signature of energy losses on the cosmic ray electron spectrum |
the recent discovery by bachetti et al. of a pulsar in m82 that can reach luminosities of up to 1040 erg s-1, a factor of ∼100 times the eddington luminosity for a 1.4 m⊙ compact object, poses a challenge for accretion physics. in order to better understand the nature of this source and its duty cycle, and in light of several physical models that have been subsequently published, we conduct a spectral and temporal analysis of the 0.5-8 kev x-ray emission from this source from 15 years of chandra observations. we analyze 19 acis observations where the point-spread function (psf) of the pulsar is not contaminated by nearby sources. we fit the chandra spectra of the pulsar with a power-law model and a disk blackbody model, subjected to interstellar absorption in m82. we carefully assess for the effect of pile-up in our observations, where four observations have a pile-up fraction of >10%, which we account for during spectral modeling with a convolution model. when fitted with a power-law model, the average photon index when the source is at high luminosity (lx > 1039 erg s-1) is γ = 1.33 ± 0.15. for the disk blackbody model, the average temperature is tin = 3.24 ± 0.65 kev, the spectral shape being consistent with other luminous x-ray pulsars. we also investigated the inclusion of a soft excess component and spectral break, finding that the spectra are also consistent with these features common to luminous x-ray pulsars. in addition, we present spectral analysis from nustar over the 3-50 kev range where we have isolated the pulsed component. we find that the pulsed emission in this band is best fit by a power-law with a high-energy cutoff, where γ = 0.6 ± 0.3 and {e}{{c}}={14}-3+5 kev. while the pulsar has previously been identified as a transient, we find from our longer-baseline study that it has been remarkably active over the 15-year period, where for 9/19 (47%) observations that we analyzed, the pulsar appears to be emitting at a luminosity in excess of 1039 erg s-1, greater than 10 times its eddington limit. | spectral and temporal properties of the ultraluminous x-ray pulsar in m82 from 15 years of chandra observations and analysis of the pulsed emission using nustar |
the sensitivity of pulsar timing arrays to gravitational waves (gws) depends on the noise present in the individual pulsar timing data. noise may be either intrinsic or extrinsic to the pulsar. intrinsic sources of noise will include rotational instabilities, for example. extrinsic sources of noise include contributions from physical processes which are not sufficiently well modelled, for example, dispersion and scattering effects, analysis errors and instrumental instabilities. we present the results from a noise analysis for 42 millisecond pulsars (msps) observed with the european pulsar timing array. for characterizing the low-frequency, stochastic and achromatic noise component, or `timing noise', we employ two methods, based on bayesian and frequentist statistics. for 25 msps, we achieve statistically significant measurements of their timing noise parameters and find that the two methods give consistent results. for the remaining 17 msps, we place upper limits on the timing noise amplitude at the 95 per cent confidence level. we additionally place an upper limit on the contribution to the pulsar noise budget from errors in the reference terrestrial time standards (below 1 per cent), and we find evidence for a noise component which is present only in the data of one of the four used telescopes. finally, we estimate that the timing noise of individual pulsars reduces the sensitivity of this data set to an isotropic, stochastic gw background by a factor of >9.1 and by a factor of >2.3 for continuous gws from resolvable, inspiralling supermassive black hole binaries with circular orbits. | the noise properties of 42 millisecond pulsars from the european pulsar timing array and their impact on gravitational-wave searches |
we observed the nearby millisecond pulsar j2124-3358 with the hubble space telescope in broad far-uv (fuv) and optical filters. the pulsar is detected in both bands with fluxes f(1250-2000 å) = (2.5 ± 0.3) × 10-16 erg s-1 cm-2 and f(3800-6000 å) = (6.4 ± 0.4) × 10-17 erg s-1 cm-2, which corresponds to luminosities of ≈5.8 × 1027 and 1.4 × 1027 erg s-1, for d = 410 pc and e(b - v) = 0.03. the optical-fuv spectrum can be described by a power-law model, {f}ν \propto {ν }α , with slope α = 0.18-0.48 for a conservative range of color excess, e(b - v) = 0.01-0.08. since a spectral flux rising with frequency is unusual for pulsar magnetospheric emission in this frequency range, it is possible that the spectrum is predominantly magnetospheric (power law with α < 0) in the optical, while it is dominated by thermal emission from the neutron star surface in the fuv. for a neutron star radius of 12 km, the surface temperature would be between 0.5 × 105 and 2.1 × 105 k for α ranging from -1 to 0, e(b - v) = 0.01-0.08, and d = 340-500 pc. in addition to the pulsar, the fuv images reveal extended emission that is spatially coincident with the known hα bow shock, making psr j2124-3358 the second pulsar (after psr j0437-4715) with a bow shock detected in the fuv. | hubble space telescope detection of the millisecond pulsar j2124-3358 and its far-ultraviolet bow shock nebula |
milagro observations have found bright, diffuse tev emission concentrated along the galactic plane of the milky way. the intensity and spectrum of this emission is difficult to explain with current models of hadronic γ -ray production, and has been named the "tev excess." we show that tev emission from pulsars naturally explains this excess. recent observations have detected "tev halos" surrounding pulsars that are either nearby or particularly luminous. extrapolating this emission to the full population of milky way pulsars indicates that the ensemble of "subthreshold" sources necessarily produces bright tev emission diffusively along the milky way plane. models indicate that the tev halo γ -ray flux exceeds that from hadronic γ rays above an energy of ∼500 gev . moreover, the spectrum and intensity of tev halo emission naturally matches the tev excess. finally, we show that upcoming hawc observations will resolve a significant fraction of the tev excess into individual tev halos, conclusively confirming, or ruling out, this model. | pulsar tev halos explain the diffuse tev excess observed by milagro |
we propose to use pulsar-black hole binaries as a probe of gravitational collider physics. induced by the gravitation of the pulsar, the atomic transitions of the boson cloud around the black hole backreact on the orbital motion. this leads to the deviation of the binary period decrease from that predicted by general relativity, which can be directly probed by the rømer delay of pulsar times of arrival. the sensitivity and accuracy of this approach are estimated for two typical atomic transitions. it is shown that once the transitions happen within the observable window, the pulsar-timing accuracy is almost always sufficient to capture the resonance phenomenon. | gravitational collider physics via pulsar-black hole binaries |
it has been proposed that a large population of unresolved millisecond pulsars (msps) could potentially account for the excess of gev-scale gamma-rays observed from the region surrounding the galactic center. the viability of this scenario depends critically on the gamma-ray luminosity function of this source population, which determines how many msps fermi should have already detected as resolved point sources. in this paper, we revisit the gamma-ray luminosity function of msps, without relying on uncertain distance measurements. our determination, based on a comparison of models with the observed characteristics of the msp population, suggests that fermi should have already detected a significant number of sources associated with such a hypothesized inner galaxy population. we cannot rule out a scenario in which the msps residing near the galactic center are systematically less luminous than those present in the galactic plane or within globular clusters. | the gamma-ray luminosity function of millisecond pulsars and implications for the gev excess |
we have constructed timing solutions for 81 γ-ray pulsars covering more than five years of fermi data. the sample includes 37 radio-quiet or radio-faint pulsars which cannot be timed with other telescopes. these timing solutions and the corresponding pulse times of arrival are prerequisites for further study, e.g., phase-resolved spectroscopy or searches for mode switches. many γ-ray pulsars are strongly affected by timing noise (tn), and we present a new method for characterizing the noise process and mitigating its effects on other facets of the timing model. we present an analysis of tn over the population using a new metric for characterizing its strength and spectral shape, namely, its time-domain correlation. the dependence of the strength on ν and \dot{ν } is in good agreement with previous studies. we find that noise process power spectra s(f) for unrecycled pulsars are steep, with strong correlations over our entire data set and spectral indices s(f)\propto {f}-αof α ∼ 5-9. one possible explanation for these results is the occurrence of unmodeled, episodic “microglitches.” finally, we show that our treatment of tn results in robust parameter estimation, and in particular we measure a precise timing position for each pulsar. we extensively validate our results with multi-wavelength astrometry, and using our updated position, we firmly identify the x-ray counterpart of psr j1418-6058. | timing gamma-ray pulsars with the fermi large area telescope: timing noise and astrometry |
we investigate whether current data on the distribution of observed flux densities of fast radio bursts (frbs) are consistent with a constant source density in euclidean space. we use the number of frbs detected in two surveys with different characteristics along with the observed signal-to-noise ratios of the detected frbs in a formalism similar to a v/vmax-test to constrain the distribution of flux densities. we find consistency between the data and a euclidean distribution. any extension of this model is therefore not data-driven and needs to be motivated separately. as a byproduct we also obtain new improved limits for the frb rate at 1.4 ghz, which had not been constrained in this way before. | the euclidean distribution of fast radio bursts |
x-ray polarimetry is a unique way to probe the geometrical configuration of highly magnetized accreting neutron stars (x-ray pulsars). gro j1008−57 is the first transient x-ray pulsar observed at two different flux levels by the imaging x-ray polarimetry explorer (ixpe) during its outburst in november 2022. we find the polarization properties of gro j1008−57 to be independent of its luminosity, with the polarization degree varying between nondetection and about 15% over the pulse phase. fitting the phase-resolved spectro-polarimetric data with the rotating vector model allowed us to estimate the pulsar inclination (130°, which is in good agreement with the orbital inclination), the position angle (75°) of the pulsar spin axis, and the magnetic obliquity (∼74°). this makes gro j1008−57 the first confidently identified nearly orthogonal rotator among x-ray pulsars. we discuss our results in the context of the neutron star atmosphere models and theories of the axis alignment of accreting pulsars. | x-ray pulsar gro j1008−57 as an orthogonal rotator |
in this paper, we explore from a conceptual standpoint the possibility of using natural astrophysical sources to accelerate spacecraft to relativistic speeds. we focus on light sails and electric sails, which are reliant on momentum transfer from photons and protons, respectively, because these two classes of spacecraft are not required to carry fuel on board. the payload is assumed to be stationed near the astrophysical source, and the sail is subsequently unfolded and activated when the source is functional. by considering a number of astrophysical objects such as massive stars, microquasars, supernovae, pulsar wind nebulae, and active galactic nuclei, we show that terminal speeds approaching the speed of light might be realizable under idealized circumstances provided that sufficiently advanced sail materials and control techniques exist. we also investigate the constraints arising from the sail's material properties, the voyage through the ambient source environment, and the passage through the interstellar medium. while all of these considerations pose significant challenges to spacecraft, our analysis indicates that they are not insurmountable in optimal conditions. finally, we sketch the implications for carrying out future technosignature searches. | propulsion of spacecraft to relativistic speeds using natural astrophysical sources |
the companions of evaporating binary pulsars (black widows and related systems) show optical emission suggesting strong heating. in a number of cases, large observed temperatures and asymmetries are inconsistent with direct radiative heating for the observed pulsar spindown power and expected distance. here we describe a heating model in which the pulsar wind sets up an intrabinary shock (ibs) against the companion wind and magnetic field, and a portion of the shock particles duct along this field to the companion magnetic poles. we show that a variety of heating patterns, and improved fits to the observed light curves, can be obtained at expected pulsar distances and luminosities, at the expense of a handful of model parameters. we test this “ibs-b” model against three well-observed binaries and comment on the implications for system masses. | b-ducted heating of black widow companions |
nasa's neutron star interior composition explorer (nicer) observed x-ray emission from the pulsar psr j0030+0451 in 2018. riley et al. reported bayesian parameter measurements of the mass and the star's radius using pulse-profile modeling of the x-ray data. this paper reproduces their result using the open-source software x-psi and publicly available data within expected statistical errors. we note the challenges we faced in reproducing the results and demonstrate that the analysis can be reproduced and reused in future works by changing the prior distribution for the radius and the sampler configuration. we find no significant change in the measurement of the mass and radius, demonstrating that the original result is robust to these changes. finally, we provide a containerized working environment that facilitates third-party reproduction of the measurements of mass and radius of psr j0030+0451 using the nicer observations. | reproducing the results for nicer observation of psr j0030+0451 |
we introduce pinta, a pipeline for reducing the upgraded giant metre-wave radio telescope (ugmrt) raw pulsar timing data, developed for the indian pulsar timing array experiment. we provide a detailed description of the workflow and usage of pinta, as well as its computational performance and rfi mitigation characteristics. we also discuss a novel and independent determination of the relative time offsets between the different back-end modes of ugmrt and the interpretation of the ugmrt observation frequency settings and their agreement with results obtained from engineering tests. further, we demonstrate the capability of pinta to generate data products which can produce high-precision toas using psr j1909 $-$ 3744 as an example. these results are crucial for performing precision pulsar timing with the ugmrt. | pinta: the ugmrt data processing pipeline for the indian pulsar timing array |
gravitational wave (gw) detections have considerably enriched our understanding of the universe. to date, all gw events from individual sources have been found by interferometer-type detectors. in this paper, we study a gw detection technique based on astrometric solutions from photometric surveys and demonstrate that it offers a highly flexible frequency range that can uniquely complement existing detection methods. from repeated point-source astrometric measurements, periodic gw-induced deflections can be extracted and wave parameters inferred. we emphasize that this method can be applied widely to any photometric surveys relying on relative astrometric measurements, in addition to surveys designed to measure absolute astrometry, such as gaia. we illustrate how high-cadence observations of the galactic bulge, such as offered by the roman space telescope's exoplanet microlensing (eml) survey, have the potential to be a potent gw probe with a complementary frequency range to gaia, pulsar timing arrays, and the laser interferometer space antenna. we calculate that the roman eml survey is sensitive to gws with frequencies ranging from 7.7 ×10-8 hz to 5.6 ×10-4 hz , which opens up a unique gw observing window for supermassive black hole binaries and their waveform evolution. while the detection threshold assuming the currently expected performance proves too high for detecting individual gws in light of the expected supermassive black hole binary population distribution, we show that binaries with chirp mass mc>108.3 m⊙ out to 100 mpc can be detected if the telescope is able to achieve an astrometric accuracy of 0.11 mas. to confidently detect binaries with mc>107 m⊙ out to 50 mpc, a factor of 100 sensitivity improvement is required. we propose several improvement strategies, including recovering the mean astrometric deflection and increasing astrometric accuracy, number of observed stars, field-of-view size, and observational cadence. we also discuss how other existing and planned photometric surveys could contribute to detecting gws via astrometry. | gravitational wave detection with photometric surveys |
aims: most pulsar nulling observations have been conducted at frequencies lower than 1400 mhz. we aim to understand the nulling behaviors of pulsars at relatively high frequencies, and to decipher whether or not nulling is caused by a global change in the pulsar magnetosphere.methods: we used the jiamusi 66 m telescope to observe 20 bright pulsars at 2250 mhz with unprecedented lengths of time. we estimated the nulling fractions of these pulsars, and identified the null and emission states of the pulses. we also calculated the nulling degrees and scales of the emission-null pairs to describe the distributions of emission and null lengths.results: three pulsars, psrs j0248+6021, j0543+2329, and j1844+00, are found to null for the first time. the details of null-to-emission and emission-to-null transitions within the pulse window are observed for the first time for psr j1509+5531, which is a low-probability event. a complete cycle of long nulls with timescales of hours is observed for psr j1709-1640. for most of these pulsars, the k-s tests of nulling degrees and nulling scales reject the hypothesis that null and emission are caused by random processes at high significance levels. emission-null sequences of some pulsars exhibit quasi-periodic, low-frequency or featureless modulations, which might be related to different origins. during transitions between emission and null states, pulse intensities have diverse tendencies for variation. significant correlations are found between respectively nulling fraction, nulling cadence, and nulling scale and the energy loss rate of the pulsars. combined with the nulling fractions reported in the literature for 146 nulling pulsars, we find that statistically large nulling fractions are more tightly related to pulsar period than to characteristic age or energy-loss rate. the pulse sequences of all pulsars are available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/644/a73 and at http://zmtt.bao.ac.cn/psr-jms/ | jiamusi pulsar observations. iii. nulling of 20 pulsars |
the stability and equation of state of quark matter are studied within both two-flavor and (2 +1 )-flavor nambu-jona-lasinio (njl) models including the vector interactions. with a free parameter α , the lagrangian is constructed by two parts, the original njl lagrangian and the fierz transformation of it, as l =(1 -α )lnjl+α lfierz. we find that there is a possibility for both u d nonstrange and u d s strange matter being absolute stable, depending on the interplay of the confinement with quark vector interaction and the exchange interaction channels. the calculated quark star properties can reconcile with the recently measured masses and radii of psr j 0030 +0451 and psr j 0740 +6620 , as well as the tidal deformability of gw170817. furthermore, the more strongly interacting quark matter in the nonstrange stars allows a stiffer equation of state and consequently a higher maximum mass (∼2.7 m⊙) than the strange ones (∼2.1 m⊙). the sound velocities in strange and nonstrange quark star matter are briefly discussed compared to those of neutron star matter. | interacting u d and u d s quark matter at finite densities and quark stars |
in general relativity (gr), gravitational waves (gws) propagate the well-known plus and cross tensorial polarization modes, which are the signature of a massless spin-2 field. however, diffraction of gws caused by intervening objects along the line of sight can cause the apparent rise of additional polarizations due to gw-curvature interactions. in this paper, we continue the analysis by two of the authors of the present article, on lensing of gravitational waves beyond geometric optics. in particular, we calculate the lensing effect caused by a pointlike lens in the regime where its schwarzschild radius rs is much smaller than the wavelength λ of the signal, itself smaller than the impact parameter b . in this case, the curvature of spacetime induces distortions in the polarization of the wave such that diffraction effects may be misinterpreted as effective scalar and vector polarizations. we find that the amplitude of these apparent nontensor polarizations is suppressed by a factor rsλ /b2 with respect to the amplitude of the tensor modes. we estimate the probability to develop these extra polarization modes for a nearly monochromatic gw in the pulsar timing arrays band traveling through a distribution of galaxies. | polarization distortions of lensed gravitational waves |
the detection of the stochastic gravitational wave background (sgwb) is essential for understanding black hole populations, especially for supermassive black hole binaries. the recent promising results from various pulsar timing array (pta) collaborations allude to an imminent detection. in this paper, we investigate the relative astrometric gravitational wave detection method, which can contribute to sgwb studies in the microhertz range. we consider the roman space telescope and gaia as candidates and quantitatively discuss the survey sensitivity in both the frequency and spatial domains. we emphasize the importance of survey specific constraints on performance estimates by considering mean field of view (fov) signal subtraction and angular power spectrum binning. we conclude that if the sgwb is at a similar level as in pta estimates, both roman and gaia have the potential to detect this frequency-domain power excess. however, both roman and gaia are subject to fov limitations, and are unlikely to be sensitive to the spatial pattern of the sgwb. | constraining the stochastic gravitational wave background with photometric surveys |
the decay of rydberg-atom-ion molecules (raims) due to nonadiabatic couplings between electronic potential-energy surfaces is investigated. we employ the born-huang representation and perform numerical simulations using a crank-nicolson algorithm. the nonadiabatic lifetimes of rubidium raims for the lowest ten vibrational states, ν , are computed for selected rydberg principal quantum numbers, n . the nonadiabatic lifetimes are found to generally exceed the radiative rydberg-atom lifetimes. we observe and explain a trend of the lifetimes as a function of ν and n , and attribute irregularities to quantum interference arising from a shallow potential well in an inner potential surface. our results will be useful for future spectroscopic studies of raims. | pulsar microstructure: periodicities, polarization and probes of pulsar magnetospheres |
incredible progress on the theoretical uncertainty of the spatial correlations of the stochastic gravitational wave (gw) background were recently made. however, it remains to realize the impact of this theoretical uncertainty on pta cross correlations analysis. this paper pushes forward in this direction, as a proof-of-principle: showing the potential role that theoretical uncertainty has on unburying the stochastic gw background signal in noisy pta cross correlation measurements. we consider both a mock data set and the noise-marginalized 12.5 years nanograv spatial correlation measurements, and find optimistic conclusions regardless of the physical content of the gw background and the nature of the noise in the data. very briefly, we show through various cases a modest result that looking out for a stochastic signal is better when two of its moments are utilized. or, in terms of gws, we show that the theoretical uncertainty can play a substantial role in the hunt for the stochastic gw background. | hunting the stochastic gravitational wave background in pulsar timing array cross correlations through theoretical uncertainty |
geminga is an enigmatic radio-quiet γ-ray pulsar located at a mere 250 pc distance from earth. extended very-high-energy γ-ray emission around the pulsar was discovered by milagro and later confirmed by hawc, which are both water cherenkov detector-based experiments. however, evidence for the geminga pulsar wind nebula in gamma rays has long evaded detection by imaging atmospheric cherenkov telescopes (iacts) despite targeted observations. the detection of γ-ray emission on angular scales ≳2º poses a considerable challenge for the background estimation in iact data analysis. with recent developments in understanding the complementary background estimation techniques of water cherenkov and atmospheric cherenkov instruments, the h.e.s.s. iact array can now confirm the detection of highly extended γ-ray emission around the geminga pulsar with a radius of at least 3º in the energy range 0.5-40 tev. we find no indications for statistically significant asymmetries or energy-dependent morphology. a flux normalisation of (2.8 ± 0.7) × 10−12 cm−2 s−1 tev−1 at 1 tev is obtained within a 1º radius region around the pulsar. to investigate the particle transport within the halo of energetic leptons around the pulsar, we fitted an electron diffusion model to the data. the normalisation of the diffusion coefficient obtained of d0 = 7.6−1.2+1.5 × 1027 cm2 s−1, at an electron energy of 100 tev, is compatible with values previously reported for the pulsar halo around geminga, which is considerably below the galactic average. | detection of extended γ-ray emission around the geminga pulsar with h.e.s.s. |
the class of scalar-tensor theories with the scalar field coupling to the gauss-bonnet invariant has drawn great interest since solutions of spontaneous scalarization were found for black holes in these theories. we contribute to the existing literature a detailed study of the spontaneously scalarized neutron stars (nss) in a typical theory where the coupling function of the scalar field takes the quadratic form and the scalar field is massive. the investigation here includes the spherical solutions of the nss as well as their perturbative properties, namely the tidal deformability and the moment of inertia, treated in a unified and extendable way under the framework of spherical decomposition. we find that while the mass, the radius, and the moment of inertia of the spontaneously scalarized nss show very moderate deviations from those of the nss in general relativity (gr), the tidal deformability exhibits significant differences between the solutions in gr and the solutions of spontaneous scalarization for certain values of the parameters in the scalar-gauss-bonnet theory. as a result, the celebrated universal relation between the moment of inertia and the tidal deformability of neutron stars breaks down. with the mass and the tidal deformability of nss attainable in the gravitational waves from binary ns mergers, the radius measurable using the x-ray satellites, and the moment of inertia accessible via the high-precision pulsar timing techniques, future multimessenger observations can be contrasted with the theoretical results and provide us necessary information for building up theories beyond gr. | neutron stars in massive scalar-gauss-bonnet gravity: spherical structure and time-independent perturbations |
the parabolic structure of the secondary or conjugate spectra of pulsars is often the result of isolated one-dimensional (or at least highly anisotropic) lenses in the interstellar medium (ism). the curvature of these features contains information about the velocities of the earth, ism, and pulsar along the primary axis of the lens. as a result, measuring variations in the curvature over the course of a year, or the orbital period for pulsars in binaries, can constrain properties of the screen and pulsar. in particular, the pulsar distance and orbital inclination for binary systems can be found for multiple screens or systems with prior information on sin(i). by mapping the conjugate spectra into a space where the main arc and inverted arclets are straight lines, we are able to make use of the full information content from the inverted arclet curvatures, amplitudes, and phases using eigenvectors to uniquely and optimally retrieve phase information. this allows for a higher precision measurement than the standard hough transform for systems where these features are available. our technique also directly yields the best-fitting one-dimensional impulse response function for the interstellar lens given in terms of the doppler shift, time delay, and magnification of images on the sky as seen from a single observatory. this can be extended for use in holographic imaging of the lens by combining multiple telescopes. we present examples of this new method for both simulated data and actual observations of psr b0834+06. | interstellar interferometry: precise curvature measurement from pulsar secondary spectra |
binaries harbouring millisecond pulsars (msps) enable a unique path to determine neutron star (ns) masses: radio pulsations reveal the motion of the ns, while that of the companion can be characterized through studies in the optical range. psr j1012+5307 is an msp in a 14.5-h orbit with a helium-core white dwarf (wd) companion. in this work we present the analysis of an optical spectroscopic campaign, where the companion star absorption features reveal one of the lightest known wds. we determine a wd radial velocity semi-amplitude of $k_2 = 218.9 \pm 2.2\, \rm km\, s^{-1}$ , which combined with that of the pulsar derived from the precise radio timing, yields a mass ratio of q = 10.44 ± 0.11. we also attempt to infer the wd mass from observational constraints using new binary evolution models for extremely low-mass (elm) wds, but find that they cannot reproduce all observed parameters simultaneously. in particular, we cannot reconcile the radius predicted from binary evolution with the measurement from the photometric analysis ( $r_{\rm wd}=0.047_{-0.002}^{+0.003}\, \mathrm{ r}_{\odot }$ ). our limited understanding of elm wd evolution, which results from binary interaction, therefore comes as the main factor limiting the precision with which we can measure the mass of the wd in this system. our conservative wd mass estimate of $m_{\rm wd} = 0.165 \pm 0.015\, \mathrm{ m}_{\rm \odot }$ , along with the mass ratio enables us to infer a pulsar mass of $m_{\rm ns} = 1.72 \pm 0.16\, \mathrm{ m}_{\rm \odot }$ . this value is clearly above the canonical $\sim 1.4\, \mathrm{ m}_{\rm \odot }$ , therefore adding psr j1012+5307 to the growing list of massive msps. | psr j1012+5307: a millisecond pulsar with an extremely low-mass white dwarf companion |
we present herein a new class of singularity-free interior solutions to describe realistic anisotropic compact stellar objects with spherically symmetric matter distribution. a specific form of anisotropy is assumed to obtain the exact solution for the field equation. smooth matching of interior solutions thus obtained with the schwarzschild exterior metric over the bounding surface of a compact star, together with the condition that the radial pressure vanishes at the boundary, is used to obtain the mathematical form for the model parameters. the pulsar 4u1608-52 with its current estimated data (mass =1.57 m ⊙ and radius =9.8 ±0.8 km; özel et al. in apj 820:28, 2016) is used to study the model graphically. | anisotropic compact stellar solution in general relativity |
the maxi/gsc nova alert system triggered a bright x-ray transient source on 2022 december 29 (mjd 59942). assuming that the source flux was constant over the transits, we obtain the source position at (r.a., dec) = (70.253 deg, 44.378 deg) = (04 41 00, +44 22 40) (j2000) with a 90% c.l. statistical error of 0.13 deg and an additional systematic uncertainty of 0.1 deg (90% containment radius). | maxi/gsc detection of an x-ray brightening from the be/x-ray binary pulsar ls v +44 17 |
we aim at contributing to the resolution of three of the fundamental puzzles related to the still unsolved problem of the structure of the dense core of compact stars (cs): (i) the hyperon puzzle: how to reconcile pulsar masses of 2 m⊙ with the hyperon softening of the equation of state (eos); (ii) the masquerade problem: modern eos for cold, high density hadronic and quark matter are almost identical; and (iii) the reconfinement puzzle: what to do when after a deconfinement transition the hadronic eos becomes favorable again? we show that taking into account the compositeness of baryons (by excluded volume and/or quark pauli blocking) on the hadronic side and confining and stiffening effects on the quark matter side results in an early phase transition to quark matter with sufficient stiffening at high densities which removes all three present-day puzzles of cs interiors. moreover, in this new class of eos for hybrid cs falls the interesting case of a strong first order phase transition which results in the observable high mass twin star phenomenon, an astrophysical observation of a critical endpoint in the qcd phase diagram. | high-mass twins & resolution of the reconfinement, masquerade and hyperon puzzles of compact star interiors |
rotating neutron star or pulsar can be a possible source of pseudo nambu goldstone bosons or axions which can mediate long range axionic hair outside of the pulsar. when the electromagnetic radiation is emitted from a pulsar and passes through the long range axion hair, the axion rotates the polarization of the electromagnetic radiation and produces birefringence. we obtain the angle of birefringence due to this long range axionic hair as 0.42°. this value is within the accuracy of measuring the linear polarization angle of pulsar light which is ≤1.0 ° . our result continues to hold as long as the range of the axion hair (inverse of axion mass) is greater than the radius of the pulsar, i.e., ma<10-11 ev and the axion decay constant fa≲o (1017 gev ) . | probing the angle of birefringence due to long range axion hair from pulsars |
the crab nebula is one of the most-studied cosmic particle accelerators, shining brightly across the entire electromagnetic spectrum up to very-high-energy gamma rays1,2. it is known from observations in the radio to gamma-ray part of the spectrum that the nebula is powered by a pulsar, which converts most of its rotational energy losses into a highly relativistic outflow. this outflow powers a pulsar wind nebula, a region of up to ten light-years across, filled with relativistic electrons and positrons. these particles emit synchrotron photons in the ambient magnetic field and produce very-high-energy gamma rays by compton up-scattering of ambient low-energy photons. although the synchrotron morphology of the nebula is well established, it has not been known from which region the very-high-energy gamma rays are emitted3-8. here we report that the crab nebula has an angular extension at gamma-ray energies of 52 arcseconds (assuming a gaussian source width), much larger than at x-ray energies. this result closes a gap in the multi-wavelength coverage of the nebula, revealing the emission region of the highest-energy gamma rays. these gamma rays enable us to probe a previously inaccessible electron and positron energy range. we find that simulations of the electromagnetic emission reproduce our measurement, providing a non-trivial test of our understanding of particle acceleration in the crab nebula. | resolving the crab pulsar wind nebula at teraelectronvolt energies |
we explore the impact of pulsar electromagnetic dipole and fallback accretion emission on the luminosity of a suite of kilonova models. the pulsar models are varied over pulsar magnetic field strength, pulsar lifetime, ejecta mass, and elemental abundances; the fallback models are varied over fallback accretion rate and ejecta mass. for the abundances, we use fe and nd as representatives of the wind and dynamical ejecta, respectively. we simulate radiative transfer in the ejecta in either 1d spherical or 2d cylindrical spatial geometry. for the grid of 1d simulations, the mass fraction of nd is 0, 10-4, or 10-3, and the rest is fe. our models that fit the bolometric luminosity of at 2017gfo (the kilonova associated with the first neutron star merger discovered in gravitational waves, gw170817) do not simultaneously fit the b, v, and i time evolution. however, we find that the trends of the evolution in b and v magnitudes are better matched by the fallback model relative to the pulsar model, implying the time-dependence of the remnant source influences the color evolution. further exploration of the parameter space and model deficiencies is needed before we can describe at 2017gfo with a remnant source. | impact of pulsar and fallback sources on multifrequency kilonova models |
context. the observation of the first pulse-to-pulse glitch in the vela pulsar opens a new window among theoretical speculations on the internal dynamics of neutron stars as it allows us for testing models to factor in the circumstances of the first moments of a glitch. several works in the literature have already considered the observational and physical parameters of the star by employing a minimal model with three rigidly rotating components.aims: we improve the analytical study of the minimal three-component model for pulsar glitches by solving it with generic initial conditions for the two initial lags of their superfluid components. the purpose is to use this solution to fit the data of the 2016 vela glitch by employing a bayesian approach and to obtain a probability distribution for the physical parameters of the model and for observational parameters, such as the glitch rise time and the relaxation timescale.methods: the fit is achieved through bayesian inference. due to the presence of an increase in the timing residuals near the glitch time, an extra magnetospheric component was added to the three-component model to deal with this phenomenon. a physically reasonable, non-informative prior was set on the different parameters of the model, so that the posterior distribution could be compared with state-of-the-art information obtained from microphysical calculations. by considering a model with a tightened prior on the moment of inertia fractions and by comparing it with the original model by means of bayesian model selection, we studied the possibility of a crust-limited superfluid reservoir.results: we obtained the posterior distribution for the moment of inertia fractions of the superfluid components, the coupling parameters, and the initial velocity lags between the components. an analysis of the inferred posterior also confirmed the presence of an overshoot in that glitch and set an upper limit of ∼6 s on the glitch rise timescale. the comparison between the two models with different priors on the moment of inertia fractions appears to indicate a need for a core participation in the glitch phenomenon, regardless of the uncertain strength of the entrainment coupling. | bayesian estimate of the superfluid moments of inertia from the 2016 glitch in the vela pulsar |
fast radio bursts (frbs) have excessive dispersion measures (dms) and an all-sky distribution, which point toward an extragalactic or even a cosmological origin. we develop a method to extract the mean host galaxy dm (< {{dm}}{hg,{loc}}> ) and the characterized luminosity (l) of frbs using the observed dm-flux data, based on the assumption of a narrow luminosity distribution. applying bayesian inference to the data of 21 frbs, we derive a relatively large mean host dm, i.e., < {{dm}}{hg,{loc}}> ∼ 270 {pc} {{cm}}-3 with a large dispersion. a relatively large dmhg of frbs is also supported by the millisecond scattering times of some frbs and the relatively small redshift z = 0.19273 of frb 121102 (which gives {{dm}}{hg,{loc}}∼ 210 {pc} {{cm}}-3). the large host galaxy dm may be contributed by the interstellar medium (ism) or a near-source plasma in the host galaxy. if it is contributed by the ism, the type of the frb host galaxies would not be milky way-like, consistent with the detected host of frb 121102. we also discuss the possibility of having a near-source supernova remnant, pulsar wind nebula, or h ii region that gives a significant contribution to the observed dmhg. | large host-galaxy dispersion measure of fast radio bursts |
we present evidence for three spin-down glitches (or “anti-glitches”) in the ultraluminous accreting x-ray pulsar ngc 300 ulx-1, in timing observations made with the neutron star interior composition explorer. our timing analysis reveals three sudden spin-down events of magnitudes δν = -23, -30, and -43 μhz (fractional amplitudes δν/ν = -4.4, -5.5, and -7.7 × 10-4). we determined fully phase-coherent timing solutions through the first two glitches, giving us high confidence in their detection, while the third candidate glitch is somewhat less secure. these are larger in magnitude (and opposite in sign) than any known radio pulsar glitch. this may be caused by the prolonged rapid spin up of the pulsar, causing a sudden transfer of angular momentum between the superfluid and non-superfluid components of the star. we find no evidence for profile or spectral changes at the epochs of the glitches, supporting the conclusion that these are due to the same process as in normal pulsar glitches, but in reverse. | anti-glitches in the ultraluminous accreting pulsar ngc 300 ulx-1 observed with nicer |
we report observations of gamma-ray emissions with energies in the 100-tev energy region from the cygnus region in our galaxy. two sources are significantly detected in the directions of the cygnus ob1 and ob2 associations. based on their positional coincidences, we associate one with a pulsar psr j 2032 +4127 and the other mainly with a pulsar wind nebula pwn g 75.2 +0.1 , with the pulsar moving away from its original birthplace situated around the centroid of the observed gamma-ray emission. this work would stimulate further studies of particle acceleration mechanisms at these gamma-ray sources. | gamma-ray observation of the cygnus region in the 100-tev energy region |
psr j1024-0719 is a millisecond pulsar that was long thought to be isolated. however, puzzling results concerning its velocity, distance, and low rotational period derivative have led to a reexamination of its properties. we present updated radio timing observations along with new and archival optical data which show that psr j1024-0719 is most likely in a long-period (2-20 kyr) binary system with a low-mass (≈ 0.4 {m}⊙ ), low-metallicity (z≈ -0.9 dex) main-sequence star. such a system can explain most of the anomalous properties of this pulsar. we suggest that this system formed through a dynamical exchange in a globular cluster that ejected it into a halo orbit, which is consistent with the low observed metallicity for the stellar companion. further astrometric and radio timing observations such as measurement of the third period derivative could strongly constrain the range of orbital parameters. | psr j1024-0719: a millisecond pulsar in an unusual long-period orbit |
black holes in binaries with other compact objects can provide natural venues for indirect detection of axions or other ultralight fields. the superradiant instability associated with a rapidly spinning black hole leads to the creation of an axion cloud which carries energy and angular momentum from the black hole. this cloud will then decay via gravitational wave emission. we show that the energy lost as a result of this process tends toward an outspiraling of the binary orbit. a given binary system is sensitive to a narrow range of axion masses, determined by the mass of the black hole. this proposal provides a complementary alternative to other approaches for detecting or constraining light particles created by superradiance, such as directly measuring the black hole spin or detecting the resulting gravitational wave signal. pulsar-black hole binaries, once detected in the electromagnetic band, will allow high-precision measurements of black hole mass loss via timing measurements of the companion pulsar. this avenue of investigation is particularly promising in light of the recent preliminary announcements of two candidate black hole-neutron star mergers by ligo/virgo (#s190814bv and #s190426c). we demonstrate that for such a binary system with a typical millisecond pulsar and a 3msolar black hole, axions with masses between 2.7 × 10-12 ev and 3.2 × 10-12 ev are detectable. recent gravitational wave observations by ligo/virgo of binary black hole mergers imply that, for these binaries, gravitational radiation from the rotating quadrupole moment is a dominant effect, causing an inspiraling orbit. with some reasonable assumptions about the period of the binary when it formed and the spins of the black holes, these observations rule out possible axion masses between 3 × 10-13 ev and 6 × 10-13 ev . future binary black hole observations, for example by lisa, are expected to provide more robust bounds. in some circumstances, neutron stars may also undergo superradiant instabilities, and binary pulsars could be used to exclude axions with certain masses and matter couplings. | accessing the axion via compact object binaries |
we introduce a technique for gravitational-wave analysis, where gaussian process regression is used to emulate the strain spectrum of a stochastic background by training on population-synthesis simulations. this leads to direct bayesian inference on astrophysical parameters. for pulsar timing arrays specifically, we interpolate over the parameter space of supermassive black-hole binary environments, including three-body stellar scattering, and evolving orbital eccentricity. we illustrate our approach on mock data, and assess the prospects for inference with data similar to the nanograv 9-yr data release. | constraints on the dynamical environments of supermassive black-hole binaries using pulsar-timing arrays |
we report on multifrequency radio observations of the new magnetar swift j1818.0-1607, following it for more than one month with high cadence. the observations commenced less than 35 h after its registered first outburst. we obtained timing, polarization, and spectral information. swift j1818.0-1607 has an unusually steep spectrum for a radio emitting magnetar and also has a relatively narrow and simple pulse profile. the position angle swing of the polarization is flat over the pulse profile, possibly suggesting that our line of sight grazes the edge of the emission beam. this may also explain the steep spectrum. the spin evolution shows large variation in the spin-down rate, associated with four distinct timing events over the course of our observations. those events may be related to the appearance and disappearance of a second pulse component. the first timing event coincides with our actual observations, while we did not detect significant changes in the emission properties that could reveal further magnetospheric changes. characteristic ages inferred from the timing measurements over the course of months vary by nearly an order of magnitude. a longer-term spin-down measurement over approximately 100 d suggests a characteristic age of about 500 yr, larger than previously reported. though swift j1818.0-1607 could still be one of the youngest neutron stars (and magnetars) detected so far, we caution using the characteristic age as a true-age indicator given the caveats behind its calculation. | high-cadence observations and variable spin behaviour of magnetar swift j1818.0-1607 after its outburst |
the diffuse backgrounds of relic gravitons with frequencies ranging between the ahz band and the ghz region encode the ultimate information on the primeval evolution of the plasma and on the underlying theory of gravity well before the electroweak epoch. while the temperature and polarization anisotropies of the microwave background radiation probe the low-frequency tail of the graviton spectra, during the next score year the pulsar timing arrays and the wide-band interferometers (both terrestrial and hopefully space-borne) will explore a much larger frequency window encompassing the nhz domain and the audio band. the salient theoretical aspects of the relic gravitons are reviewed in a cross-disciplinary perspective touching upon various unsettled questions of particle physics, cosmology and astrophysics. | primordial backgrounds of relic gravitons |
the radio emission in many pulsars shows sudden changes, usually within a period, that cannot be related to the steady state processes within the inner acceleration region (iar) above the polar cap. these changes are often quasi-periodic in nature, where regular transitions between two or more stable emission states are seen. the durations of these states show a wide variety ranging from several seconds to hours at a time. there are strong, small-scale magnetic field structures and huge temperature gradients present at the polar cap surface. we have considered several processes that can cause temporal modifications of the local magnetic field structure and strength at the surface of the polar cap. using different magnetic field strengths and scales, and also assuming realistic scales of the temperature gradients, the evolutionary time-scales of different phenomena affecting the surface magnetic field were estimated. we find that the hall drift results in faster changes in comparison to both ohmic decay and thermoelectric effects. a mechanism based on the partially screened gap (psg) model of the iar has been proposed, where the hall and thermoelectric oscillations perturb the polar cap magnetic field to alter the sparking process in the psg. this is likely to affect the observed radio emission resulting in the observed state changes. | rapid modification of neutron star surface magnetic field: a proposed mechanism for explaining radio emission state changes in pulsars |
supernova remnants (snrs) have long been considered to be the dominant source of galactic cosmic rays, which implied that they provided most of the energy to power cosmic rays as well as being pevatrons. the lack of evidence for pev cosmic rays in snrs, as well as theoretical considerations, has made this scenario untenable. at the same time the latest lhaaso and other gamma-ray results suggest that pevatrons lurk inside starforming regions. here i will discuss why snrs should still be considered the main sources of galactic cosmic rays at least up to 10 tev, but that the cosmic-ray data allow for a second component of cosmic rays with energies up to several pev. this second component could be a subset of supernovae/snrs, reacceleration inside starforming regions, or pulsars. as a special case i show that the recent observations of westerlund 1 by h.e.s.s. suggest a low value of the diffusion coefficient inside this region, which is, together with an alfvén speed > 100 km/s, a prerequisite for making a starforming region collectively a pevatron due to second order fermi acceleration. | what sources are the dominant galactic cosmic-ray accelerators? |
the recent observation of 4he favors a large lepton asymmetry at the big bang nucleosynthesis. if q-balls with a lepton charge decay after the electroweak phase transition, such a large lepton asymmetry can be generated without producing too large baryon asymmetry. in this scenario, q-balls dominate the universe before the decay and induces the sharp transition from the early matter-dominated era to the radiation-dominated era. in this transition, the gravitational waves (gws) are enhanced through a second-order effect of the scalar perturbations. we evaluate the density of the produced gws and show that pulsar timing array observations can probe this scenario depending on the amplitude of the scalar perturbations. | enhancement of second-order gravitational waves at q-ball decay |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.