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<p id="par1">understanding the physics of rotation-powered millisecond pulsars (msps) presents a number of challenges compared to that of the non-recycled pulsar population. even though their fast rotation rates can produce high spin-down power<index-term id="iterm1"><term>spin-down power</term></index-term> and accelerating electric fields, their relatively low surface magnetic fields make the production of electron-positron pairs required for radio emission difficult. the fermi gamma-ray space telescope has discovered pulsed γ-rays from a large fraction of the msp population which have gamma-ray light curves surprisingly similar to those of young pulsars. however, their very compact magnetospheres enable magnetic fields at the light cylinder that are comparable to those of the most energetic pulsars. this fact and recent global magnetosphere models showing that particle acceleration takes place near and beyond the light cylinder, now makes the γ-rays from msps plausible. the large increase in binary systems harboring msps has revitalized the study of shock acceleration and high-energy emission in such systems, with many showing orbitally-modulated x-rays. this chapter will review the history and our current studies of the mechanisms for multiwavelength emission from msps. | the emission physics of millisecond pulsars |
the millisecond pulsar psr j1713+0747 has undergone a distinct change in the shape of its pulse profile. using data from the fast telescope, in combination with the kunming 40 meter radio telescope and telescopes of the european pulsar timing array (nrt, effelsberg, srt, lovell and leap) we have determined that the event must have occurred between april 15 (mjd 59319) and april 17 (mjd 59321). | a sustained pulse shape change in psr j1713+0747 possibly associated with timing and dm events |
we present a timing and glitch analysis of the young x-ray pulsar psr j0537-6910, located within the large magellanic cloud, using 13 yr of data from the now-decommissioned rossi x-ray timing explorer. rotating with a spin period of 16 ms, psr j0537-6910 is the fastest-spinning and most energetic young pulsar known. it also displays the highest glitch activity of any known pulsar. we have found 42 glitches over the data span, corresponding to a glitch rate of 3.2 yr-1, with an overall glitch activity rate of 8.8× {10}-7 {{yr}}-1. the high glitch frequency has allowed us to study the glitch behavior in ways that are inaccessible in other pulsars. we observe a strong linear correlation between spin frequency glitch magnitude and wait time to the following glitch. we also find that the post-glitch spin-down recovery is well described by a single two-component model fit to all glitches for which we have adequate input data. this consists of an exponential amplitude a=(7.6+/- 1.0)× {10}-14 {{{s}}}-2, decay timescale τ ={27}-6+7 {day}s, and linear slope m=(4.1+/- 0.4)× {10}-16 {{{s}}}-2 {{day}}-1. the latter slope corresponds to a second frequency derivative \ddot{ν }=(4.7+/- 0.5)× {10}-22 {{{s}}}-3, from which we find an implied braking index n=7.4+/- 0.8. we also present a maximum likelihood technique for searching for periods in event-time data, which we used to both confirm previously published values and determine rotation frequencies in later observations. we discuss the implied constraints on glitch models from the observed behavior of this system, which we argue cannot be fully explained in the context of existing theories. | the glitches and rotational history of the highly energetic young pulsar psr j0537-6910 |
in an accreting x-ray pulsar, a neutron star accretes matter from a stellar companion through an accretion disk. the high magnetic field of the rotating neutron star disrupts the inner edge of the disc, funneling the gas to flow onto the magnetic poles on its surface. hercules x-1 is in many ways the prototypical x-ray pulsar; it shows persistent x-ray emission and it resides with its companion hz her, a two-solar-mass star, at about 7~kpc from earth. its emission varies on three distinct timescales: the neutron star rotates every 1.2~seconds, it is eclipsed by its companion each 1.7~days, and the system exhibits a superorbital period of 35~days which has remained remarkably stable since its discovery. several lines of evidence point to the source of this variation as the precession of the accretion disc, the precession of the neutron star or both. despite the many hints over the past fifty years, the precession of the neutron star itself has yet not been confirmed or refuted. we here present x-ray polarization measurements with the imaging x-ray polarimetry explorer (ixpe) which probe the spin geometry of the neutron star. these observations provide direct evidence that the 35-day-period is set by the free precession of the neutron star crust, which has the important implication that its crust is somewhat asymmetric fractionally by a few parts per ten million. furthermore, we find indications that the basic spin geometry of the neutron star is altered by torques on timescale of a few hundred days. | x-ray polarization reveals the precessions of the neutron star in hercules x-1 |
we describe the signatures of a circularly polarized gravitational-wave background on the timing residuals obtained with pulsar-timing arrays. most generally, the circular polarization will depend on the gravitational-wave direction, and we describe this angular dependence in terms of spherical harmonics. while the amplitude of the monopole (the overall chirality of the gravitational-wave background) cannot be detected, measures of the anisotropy are theoretically conceivable. we provide expressions for the minimum-variance estimators for the circular-polarization anisotropy. we evaluate the smallest detectable signal as a function of the signal-to-noise ratio with which the isotropic gravitational wave (gw) signal is detected and the number of pulsars (assumed to be roughly uniformly spread throughout the sky) in the survey. we find that the overall dipole of the circular polarization and a few higher overall multipoles, are detectable in a survey with ≳100 pulsars if their amplitude is close to maximal and once the isotropic signal is established with a signal-to-noise ratio ≳400 . even if the anisotropy can be established, though, there will be limited information on its direction. similar arguments apply to astrometric searches for gravitational waves. | chirality of the gravitational-wave background and pulsar-timing arrays |
we investigate the influence of a specific class of slow baryon number violation (bnv) -- one that induces quasi-equilibrium evolution -- on pulsar spin characteristics. this work reveals how bnv can potentially alter observable parameters, including spin-down rates, the second derivative of spin frequency, and braking indices of pulsars. moreover, we demonstrate that bnv could lead to anomalies in pulsar timing, along with a wide array of braking indices, both positive and negative. in addition, we examine the possibility of pulsar spin-up due to bnv, which may result in a novel mechanism for the revival of ``dead'' pulsars. we conclude by assessing the sensitivity required for future pulsar timing efforts to detect such bnv effects, thus highlighting the potential for pulsars to serve as laboratories for testing fundamental physics. | pulsar timing anomalies: a window into baryon number violation |
in this work, we made an extensive study about the possible presence of anisotropies in strange stars. to accomplish this task, we use three different configurations for the strange matter: the unpaired matter, a two-flavor super-conducting (2sc) strange matter, and a fully three-flavor super-conducting strange matter (cfl). for each configuration, we calculate the relevant quantities for the strange stars, such as the mass-radius relation, the dimensionless tidal parameter, the moment of inertia, and the surface curvature for different degrees of anisotropies. whenever possible, we compare our results with constraints found in the literature, especially focusing on the existence of very massive pulsars (psr j0952-0607), as well as very light compact objects (hess j1731-347). | spherically symmetric anisotropic strange stars |
recent advances in numerical algorithms and computational power have enabled first-principles simulations of pulsar magnetospheres using particle-in-cell techniques. these ab initio simulations seem to indicate that pair creation through photon-photon collision at the light cylinder is required to sustain the pulsar engine. however, for many rotation-powered pulsars, pair creation operates effectively only near the stellar surface where magnetic field is high. how these "weak pulsars" fill their magnetospheres without efficient photon-photon pair conversion in the outer magnetosphere is still an open question. in this paper, we present a range of self-consistent solutions to the pulsar magnetosphere that do not require pair production near the light cylinder. when pair production is very efficient near the star, the pulsar magnetosphere converges to previously reported solutions. however, in the intermediate regime, where pair supply is barely enough to sustain the magnetospheric current, we observe a time-dependent solution with a quasi-period about half of the rotation period. this new quasi-periodic solution may explain the observed pulsar death line without invoking multipolar components near the star, and can potentially explain the core versus conal emission patterns observed in pulsar radio signals. | filling the magnetospheres of weak pulsars |
chain inflation is an alternative to slow-roll inflation in which the inflaton tunnels along a large number of consecutive minima in its potential. in this work we perform the first comprehensive calculation of the gravitational wave spectrum of chain inflation. in contrast to slow-roll inflation the latter does not stem from quantum fluctuations of the gravitational field during inflation, but rather from the bubble collisions during the first-order phase transitions associated with vacuum tunneling. our calculation is performed within an effective theory of chain inflation which builds on an expansion of the tunneling rate capturing most of the available model space. the effective theory can be seen as chain inflation's analogue of the slow-roll expansion in rolling models of inflation. we show that chain inflation produces a very characteristic double-peak spectrum: a faint high-frequency peak associated with the gravitational radiation emitted during inflation, and a strong low-frequency peak associated with the graceful exit from chain inflation (marking the transition to the radiation-dominated epoch). there exist very exciting prospects to test the gravitational wave signal from chain inflation at the aligo-avirgo-kagra network, at lisa and /or at pulsar timing array experiments. a particularly intriguing possibility we point out is that chain inflation could be the source of the stochastic gravitational wave background recently detected by nanograv, ppta, epta and cpta. we also show that the gravitational wave signal of chain inflation is often accompanied by running/ higher running of the scalar spectral index to be tested at future cosmic microwave background experiments. | the gravitational wave spectrum of chain inflation |
we explore the phenomenological consequences of breaking discrete global symmetries in quantum gravity (qg). we extend a previous scenario where discrete global symmetries are responsible for scalar dark matter (dm) and domain walls (dws), to the case of fermionic dm, considered as a feebly interacting massive particle, which achieves the correct dm relic density via the freeze-in mechanism. due to the mixing between dm and the standard model neutrinos, various indirect dm detection methods can be employed to constrain the qg scale, the scale of freeze-in, and the reheating temperature simultaneously. since such qg symmetry breaking leads to dw annihilation, this may generate the characteristic gravitational wave background, and hence explain the recent observations of the gravitational wave spectrum by pulsar timing arrays. this work therefore highlights a tantalizing possibility of probing the effective scale of qg from observations. | quantum gravity effects on fermionic dark matter and gravitational waves |
we consider an inflationary kinetic function with an integrable pole that is traversed during inflation. this scenario leads to enhanced spectra of primordial scalar inhomogeneities with detectable signals: formation of primordial black holes (that could explain dark matter) and scalar-induced gravitational waves (that could reproduce the recent pulsar timing array observation, or predict signals in future detectors such as lisa or et). spectral signatures depend on whether the inflaton mass dimension at the pole is above or below 2. values mildly below 2 allow a big power spectrum enhancement with a mild tuning. finally, we discuss the possibility that a kinetic pole can arise as anomalous dimension of the inflaton due to quantum effects of planckian particles that become light at some specific inflaton field value. | traversing a kinetic pole during inflation: primordial black holes and gravitational waves |
some fast-moving pulsars, such as the guitar and the lighthouse, exhibit asymmetric non-thermal emission features that extend well beyond their ram pressure confined pulsar wind nebulae (pwne). based on our 3d relativistic simulations, we analytically explain these features as kinetically streaming pulsar wind particles that escaped into the interstellar medium (ism) due to reconnection between the pwn and ism magnetic fields. the structure of the reconnecting magnetic fields at the incoming and outgoing regions produces highly asymmetric magnetic bottles therefore and result in asymmetric extended features. for the features to become visible, the ism magnetic field should be sufficiently high, bism > 10 μg. we also discuss archival observations of pwne displaying evidence of kinetic jets: the dragonfly pwn (psr j2021 + 3651), g327.1-1.1, and msh 11-62, the latter two of which exhibit symmetric `snail eyes' morphologies. we suggest that in those cases the pulsar is moving along the ambient magnetic field in a frisbee-type configuration. | kinetic `jets' from fast-moving pulsars |
we report on a search for radio transients at 340 mhz with the jansky very large array low-band ionosphere and transient experiment (vlite). between 2015 july 29 and september 27, operating in commensal mode, vlite imaged approximately 2800 pointings covering 12,000 deg2 on the sky, sampling timescales ranging from tens of seconds to several hours on a daily basis. in addition, between 2015 february 25 and may 9, vlite observed 55 epochs of roughly 2-4 hr each toward the cosmos field. using existing radio source catalogs, we have searched all of the daily vlite images for transients, while for the cosmos field we compared individual images and the summed image to search for new sources in repeated observations of the same field. the wide range of timescales makes vlite sensitive to both coherent and incoherent transient source classes. no new transients are found, allowing us to set stringent upper limits on transients at milli-jansky levels and at low frequencies where comparatively few such surveys have been carried out to date. an all-sky isotropic surface density of bursting radio transients with similar rates, durations, and intensities as the unusual transient gcrt j1745-3009, discovered in wide-field monitoring toward the galactic center, is ruled out with high confidence. the resulting non-detections allows us to argue that this is a coherent source, whose properties most resemble the growing class of nulling pulsars. we end with a discussion of the future prospects for the detection of transients by vlite and other experiments. | exploring the transient radio sky with vlite: early results |
the use of pulsars as astrophysical clocks for gravitational wave (gw) experiments demands the highest possible timing precision. pulse times of arrival (toas) are limited by stochastic processes that occur in the pulsar itself, along the line of sight through the interstellar medium, and in the measurement process. on timescales of seconds to hours, the toa variance exceeds that from template-fitting errors due to additive noise. we assess contributions to the total variance from two additional effects: amplitude and phase jitter intrinsic to single pulses and changes in the interstellar impulse response from scattering. the three effects have different dependencies on time, frequency, and pulse signal-to-noise ratio. we use data on 37 pulsars from the north american nanohertz observatory for gws to assess the individual contributions to the overall intraday noise budget for each pulsar. we detect jitter in 22 pulsars and estimate the average value of rms jitter in our pulsars to be ∼ 1% of pulse phase. we examine how jitter evolves as a function of frequency and find evidence for evolution. finally, we compare our measurements with previous noise parameter estimates and discuss methods to improve gw detection pipelines. | the nanograv nine-year data set: noise budget for pulsar arrival times on intraday timescales |
pairs of active galactic nuclei (agn) are observational flags of merger-driven smbh growth, and represent an observable link between galaxy mergers and gravitational wave (gw) events. thus, studying these systems across their various evolutionary phases can help quantify the role mergers play in the growth of smbhs as well as future gw signals expected to be detected by pulsar timing arrays (ptas). at the earliest stage, the system can be classified as a "dual agn" where the smbhs are gravitationally unbound and have typical separations <30 kpc, and at the latest stage the system can be classified as a "binary agn" where the two massive host galaxies have likely been interacting for hundreds of megayears to gigayears. however, detecting and confirming pairs of agn is non-trivial, and is complicated by the unique characteristics of merger-environments. to date, there are less than 50 x-ray confirmed dual agn and only 1 strong binary agn candidate. axis will revolutionize the field of dual agn: the point-spread-function (psf), field-of-view (fov), and effective area (aeff) are expected to result in the detection of hundreds to thousands of new dual agn across the redshift range 0 < z < 4. the axis agn surveys will result in the first x-ray study that quantifies the frequency of dual agn as a function of redshift up to z = 3.5. | tracking smbh mergers from kpc to sub-pc scales with axis |
the most massive globular cluster in our galaxy, omega centauri, is an interesting target for pulsar searches, because of its multiple stellar populations and the intriguing possibility that it was once the nucleus of a galaxy that was absorbed into the milky way. the recent discoveries of pulsars in this globular cluster and their association with known x-ray sources was a hint that, given the large number of known x-ray sources, there is a much larger undiscovered pulsar population. we used the superior sensitivity of the meerkat radio telescope to search for pulsars in omega centauri. in this paper, we present some of the first results of this survey, including the discovery of 13 new pulsars; the total number of known pulsars in this cluster currently stands at 18. at least half of them are in binary systems and preliminary orbital constraints suggest that most of the binaries have light companions. we also discuss the ratio between isolated and binaries pulsars, and how they were formed in this cluster. | meerkat discovery of 13 new pulsars in omega centauri |
ray tracing plays a vital role in black hole imaging, modeling the emission mechanisms of pulsars, and deriving signatures from physics beyond the standard model. in this work we focus on one specific application of ray tracing, namely, predicting radio signals generated from the resonant conversion of axion dark matter in the strongly magnetized plasma surrounding neutron stars. the production and propagation of low-energy photons in these environments are sensitive to both the anisotropic response of the background plasma and curved spacetime; here, we employ a fully covariant framework capable of treating both effects. we implement this both via forward and backward ray tracing. in forward ray tracing, photons are sampled at the point of emission and propagated to infinity, whilst in the backward-tracing approach, photons are traced backwards from an image plane to the point of production. we explore various approximations adopted in prior work, quantifying the importance of gravity, plasma anisotropy, the neutron star mass and radius, and imposing the proper kinematic matching of the resonance. finally, using a more realistic model for the charge distribution of magnetar magnetospheres, we revisit the sensitivity of current and future radio and sub-mm telescopes to spectral lines emanating from the galactic center magnetar, showing such observations may extend sensitivity to axion masses ma∼o (few )×10-3 ev , potentially even probing parameter space of the qcd axion. | generalized ray tracing for axions in astrophysical plasmas |
we describe ixpe polarization observations of the pulsar wind nebula (pwn) msh 15-52, the "cosmic hand." we find x-ray polarization across the pwn, with b-field vectors generally aligned with filamentary x-ray structures. high-significance polarization is seen in arcs surrounding the pulsar and toward the end of the "jet," with polarization degree pd > 70%, thus approaching the maximum allowed synchrotron value. in contrast, the base of the jet has lower polarization, indicating a complex magnetic field at significant angle to the jet axis. we also detect significant polarization from psr b1509-58 itself. although only the central pulse phase bin of the pulse has high individual significance, flanking bins provide lower-significance detections and, in conjunction with the x-ray image and radio polarization, can be used to constrain rotating vector model solutions for the pulsar geometry. | the polarized cosmic hand: ixpe observations of psr b1509-58/msh 15-52 |
we present bskg3, the latest entry in the brussels-skyrme-on-a-grid series of large-scale models of nuclear structure based on an energy density functional. compared to its predecessors, the new model offers a more realistic description of nucleonic matter at the extreme densities relevant to neutron stars. this achievement is made possible by incorporating a constraint on the infinite nuclear matter properties at high densities in the parameter adjustment, ensuring in this way that the predictions of bskg3 for the nuclear equation of state are compatible with the observational evidence for heavy pulsars with m >2 m⊙ . instead of the usual phenomenological pairing terms, we also employ a more microscopically founded treatment of nucleon pairing, resulting in extrapolations to high densities that are in line with the predictions of advanced many-body methods and are hence more suited to the study of superfluidity in neutron stars. by adopting an extended form of the skyrme functional, we are able to reconcile the description of matter at high densities and at saturation density: the new model further refines the description of atomic nuclei offered by its predecessors. a qualitative improvement is our inclusion of ground state reflection asymmetry, in addition to the spontaneous breaking of rotational, axial, and time-reversal symmetry. quantitatively, the model offers lowered root-mean-square deviations on 2457 masses (0.631 mev), 810 charge radii (0.0237 fm) and an unmatched accuracy with respect to 45 primary fission barriers of actinide nuclei (0.33 mev). reconciling the complexity of neutron stars with those of atomic nuclei establishes bskg3 as a tool of choice for applications to nuclear structure, the nuclear equation of state and nuclear astrophysics in general. | skyrme-hartree-fock-bogoliubov mass models on a 3d mesh: iii. from atomic nuclei to neutron stars |
in this work, we investigate the relativistic structure of compact stars within the framework of f(q) gravity, where q is the nonmetricity scalar. in particular, we focus on the f(q) = αq + β gravity model, with α and β being free parameters of the theory. this study is split up into: 1. models of dark energy stars by using metric potentials of tolman-kuchowicz type which are free of singularity. it considers the stellar fluid to be made up of both ordinary matter along with dark energy, where the constants in the metric are determined from observational measurements of some well-known compact stars. part 2 deals with quark stars where their masses and radii are a consequence of integrating the stellar structure equations given a specific equation of state (eos) for the dense matter involved. we use the pulsar sax j1808.4-3658, which has a known mass and radius of m = 0.9-0.3+0.3 m⊙ , and 7 . 95-1+1 km respectively, to explain the physical characteristics of the dark energy star. for various values of α, the causality criteria and the model's dynamical stability are discussed. in light of the discovery of gravitational waves gw190814, we also investigate the possibility of characterizing the secondary component of such an event as a stable dark energy star in the presence of anisotropy using the m - r relation, which characterizes a dark energy star with mass 2 . 57m⊙ and associated radius 9 . 3 km . furthermore, in the case of quark stars with mit bag model eos, we find that both the radius and the mass increase with increasing α for fixed β = 0 . meanwhile, the effect of the parameter β is a substantial increase in the maximum-mass values as β becomes more negative for a fixed value of α. | dark energy stars and quark stars within the context of f(q) gravity |
recent observations of ver j2227+608 reveal a broken power γ-ray spectrum with the spectral index increasing from ∼1.8 in the gev energy range to ∼2.3 in the tev range. such a spectral break can be attributed to radiative energy loss of energetic electrons in the leptonic scenario for the γ-ray emission, which, in combination with the characteristic age of the nearby pulsar, can be used to constrain the magnetic field in the emission region. we show that the radio and x-ray observations can also be explained in such a scenario. in the hadronic scenario, the spectral break can be attributed to diffusion of energetic ions in a turbulent medium and detailed spectral measurement can be used to constrain the diffusion coefficient. these two models, however, predict drastically different spectra above 100 tev, which will be uncovered with future high-resolution observations, such as large high altitude air shower observatory (lhaaso) and/or cherenkov telescope array (cta). | hadronic versus leptonic models for γ-ray emission from ver j2227+608 |
black widow and redback systems are compact binaries in which a millisecond pulsar heats and may even ablate its low-mass companion by its intense wind of relativistic particles and radiation. in such systems, an intrabinary shock can form as a site of particle acceleration and associated nonthermal emission. we model the x-ray and gamma-ray synchrotron and inverse compton spectral components for select spider binaries, including diffusion, convection, and radiative energy losses in an axially symmetric, steady-state approach. our new multizone code simultaneously yields energy-dependent light curves and orbital-phase-resolved spectra. using parameter studies and matching the observed x-ray spectra and light curves, as well as fermi large area telescope spectra where available, with a synchrotron component, we can constrain certain model parameters. for psr j1723-2837 these are notably the magnetic field and bulk flow speed of plasma moving along the shock tangent, the shock acceleration efficiency, and the multiplicity and spectrum of pairs accelerated by the pulsar. this affords a more robust prediction of the expected high-energy and very high energy gamma-ray flux. we find that nearby pulsars with hot or flaring companions may be promising targets for the future cerenkov telescope array. moreover, many spiders are likely to be of significant interest to future mev-band missions such as amego and e-astrogam. | x-ray through very high energy intrabinary shock emission from black widows and redbacks |
in this work, we use the equation of state (eos) of the (2 +1 )-flavor nambu-jona-lasinio (njl) model to study the structure of the strange quark star. with a new 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 . to determine the range of α , we compare the binding energies in the two-flavor and (2 +1 )-flavor cases. we also consider the constraints of chemical equilibrium and electric charge neutrality in the strange quark star and choose six representative eoss with different α and b (bag constant) to study their influence on the structure of the strange quark star. as a result, we find that a larger α and a smaller b correspond to a heavier star with a stiffer eos. furthermore, the heaviest strange quark star is in agreement with not only the recent mass observation of psr j 0740 +6620 and the x-ray observations on radius measurements, but also the constraint on the tidal deformability of gw170817. | strange quark stars within proper time regularized (2 +1 )-flavor njl model |
recent measurements of cosmic-ray electron and positron spectra at energies from a gev to 5 tev, as well as radio, x-ray and a wide range of gamma-ray observations of pulsar-wind nebulae, indicate that pulsars are significant sources of high-energy cosmic-ray electrons and positrons. here, we calculate the local cosmic-ray e± energy spectra from pulsars taking into account models for (a) the distribution of the pulsars spin-down properties, (b) the cosmic-ray source spectra, and (c) the physics of cosmic-ray propagation. we then use the measured cosmic-ray fluxes from ams-02, calet and dampe to constrain the space of pulsar and cosmic-ray-propagation models and, in particular, local cosmic-ray diffusion and energy losses, the pulsars' energy-loss time dependence, and the injected e± spectra. we find that the lower estimates for the local e± energy losses are inconsistent with the data. we also find that pulsar braking indexes of 2.5 or less for sources with ages more than 10 kyr are strongly disfavored. moreover, the cosmic-ray data are consistent with a wide range of assumptions on the e± injection spectral properties and on the distribution of initial spin-down powers. above a tev in energy, we find that pulsars can easily explain the observed change in the e++e- spectral slope. these conclusions are valid as long as pulsars contribute ≳10 % of the observed cosmic-ray e± at energies ≳100 gev . | studying the milky way pulsar population with cosmic-ray leptons |
in this work we consider strange stars formed by quark matter in the color-flavor-locked (cfl) phase of color superconductivity. the cfl phase is described by a nambu-jona-lasinio model with four-fermion vector and diquark interaction channels. the effect of the color superconducting medium on the gluons are incorporated into the model by including the gluon self-energy in the thermodynamic potential. we construct parametrizations of the model by varying the vector coupling gv and comparing the results to the data on tidal deformability from the gw170817 event, the observational data on maximum masses from massive pulsars such as the msp j 0740 +6620 , and the mass/radius fits to nicer data for psr j 003 +0451 . our results point out to windows for the gv parameter space of the model, with and without gluon effects included, that are compatible with all these astrophysical constraints, namely, 0.21 <gv/gs<0.4 , and 0.02 <gv/gs<0.1 , respectively. we also observe a strong correlation between the tidal deformabilites of the gw170817 event and gv. our results indicate that strange stars cannot be ruled out in collisions of compact binaries from the structural point of view. | tidal deformability of strange stars and the gw170817 event |
variations of the dispersion measures (dm) and rotation measures (rm) of fast radio bursts (frbs) 121102 indicate magnetic fields ∼3-17 mg in the dispersing plasma. the electron density may be ${\sim}10^4\,$ cm-3. the observed time scales ∼1 yr constrain the size of the plasma cloud. increasing dm excludes simple models involving an expanding supernova remnant, and the non-zero rm excludes spherical symmetry. the varying dm and rm may be attributable to the motion of plasma into or out of the line of sight to or changing electron density within slower moving plasma. the extraordinarily large rm of frb 121102 implies an environment, and possibly also a formation process and source, qualitatively different from those of other frb. the comparable and comparably varying rm of sgr/psr j1745-2900 suggests it as a frb candidate. appendix a discusses the age of frb 121102 in the context of a 'copernican principle'. | the environment of frb 121102 and possible relation to sgr/psr j1745-2900 |
neutron stars (nss) in scalar-tensor (st) theories of gravitation can acquire scalar charges and generate distinct spacetimes from those in general relativity (gr) through the celebrated phenomenon of spontaneous scalarization. taking on an st theory with the mass term of the scalar field, we determine the theory parameter space for spontaneous scalarization by investigating the linearized scalar field equation. then the full numerical solutions for slowly rotating nss are obtained and studied in great detail. the resulted spacetime is used to calculate test-particle geodesics. the lightlike geodesics are used to construct the profile of x-ray radiation from a pair of hot spots on the surface of scalarized nss, which potentially can be compared with the data from the neutron star interior composition explorer (nicer) mission for testing the st theory. | strong-field effects in massive scalar-tensor gravity for slowly spinning neutron stars and application to x-ray pulsar pulse profiles |
the detection of a stochastic background of low-frequency gravitational waves by pulsar-timing and astrometric surveys will enable tests of gravitational theories beyond general relativity. these theories generally permit gravitational waves with non-einsteinian polarization modes, which may propagate slower than the speed of light. we use the total-angular-momentum wave formalism to derive the angular correlation patterns of observables relevant for pulsar timing arrays and astrometry that arise from a background of subluminal gravitational waves with scalar, vector, or tensor polarizations. we find that the pulsar timing observables for the scalar longitudinal mode, which diverge with source distance in the luminal limit, are finite in the subluminal case. furthermore, we apply our results to f (r ) gravity, which contains a massive scalar degree of freedom in addition to the standard transverse-traceless modes. the scalar mode in this f (r ) theory is a linear combination of the scalar-longitudinal and scalar-transverse modes, exciting only the monopole and dipole for pulsar timing arrays and only the dipole for astrometric surveys. | subluminal stochastic gravitational waves in pulsar-timing arrays and astrometry |
context. psr j1910−5959a is a binary millisecond pulsar in a 0.837 day circular orbit around a helium white dwarf (hewd) companion. the position of this pulsar is 6.3 arcmin (∼74 core radii) away from the optical centre of the globular cluster (gc) ngc 6752. given the large offset, the association of the pulsar with the gc has been debated.aims: we aim to obtain precise measurements of the masses of the stars in the system along with secular orbital parameters, which will help identify if the system belongs to the gc.methods: we have made use of archival parkes 64 m `murriyang' telescope data and carried out observations with the meerkat telescope with different backends and receivers over the last two decades. pulse times of arrival were obtained from these using standard pulsar data reduction techniques and analysed using state-of-the-art bayesian pulsar timing techniques. we also performed an analysis of the pulsar's total intensity and polarisation profile to understand the interstellar scattering along the line of sight, and we determined the pulsar's geometry by fitting the rotating vector model to the polarisation data.results: we obtain precise measurements of several post-keplerian parameters: the range, r = 0.202(6) t⊙, and shape, s = 0.999823(4), of the shapiro delay, from which we infer: the orbital inclination to be 88.9−0.14+0.15 deg; the masses of the pulsar and the companion to be 1.55(7) m⊙ and 0.202(6) m⊙, respectively; a secular change in the orbital period ṗb = −53−6.0+7.4 × 10−15 s s−1 that proves the gc association; and a secular change in the projected semi-major axis of the pulsar, ẋ = −40.7−8.2+7.3 × 10−16 s s−1, likely caused by the spin-orbit interaction from a misaligned hewd spin, at odds with the likely isolated binary evolution of the system. we also discuss some theoretical models for the structure and evolution of white dwarfs in neutron star-white dwarf binaries, using psr j1910−5959a's companion as a test bed.conclusions: psr j1910−5959a is a rare system for which several parameters of both the pulsar and the hewd companion can be accurately measured. as such, it is a test bed for discriminating between alternative models of hewd structure and cooling. | psr j1910-5959a: a rare gravitational laboratory for testing white dwarf models |
we report the detection of x-ray pulsations from the rotation-powered millisecond-period pulsars psr j0740+6620 and psr j1614-2230, two of the most massive neutron stars known, using observations with the neutron star interior composition explorer (nicer). we also analyze x-ray multi-mirror mission (xmm-newton) data for both pulsars to obtain their time-averaged fluxes and study their respective x-ray fields. psr j0740+6620 exhibits a broad double-peaked profile with a separation of ~0.4 in phase. psr j1614-2230, on the other hand, has a broad single-peak profile. we show the nicer detections of x-ray pulsations for both pulsars and also discuss the phase relationship to their radio pulsations. the xmm-newton x-ray spectra of both pulsars shows they are thermally dominated but in the case of psr j1614-2230 a weak nonthermal high energy tail appears to be present in the spectrum. the thermally dominated spectra along with broad modulations for both pulsars are indicative of thermal radiation from one or more small regions of the stellar surface. for psr j0740+6620, this paper documents the data reduction performed to obtain the pulsation detection and prepare for pulse light curve modeling analysis. | nicer detection of thermal x-ray pulsations from the massive millisecond pulsars psr j0740+6620 and psr j1614-2230 |
doppler anisotropies, induced by our relative motion with respect to the source rest frame, are a guaranteed property of stochastic gravitational wave backgrounds of cosmological origin. if detected by future pulsar timing array measurements, they will provide interesting information on the physics sourcing gravitational waves, which is hard or even impossible to extract from measurements of the isotropic part of the background only. we analytically determine the pulsar response function to kinematic anisotropies, including possible effects due to parity violation, to features in the frequency dependence of the isotropic part of the spectrum, as well as to the presence of extra scalar and vector polarizations. for the first time, we show how the sensitivity to different effects crucially depends on the pulsar configuration with respect to the relative motion among frames. correspondingly, we propose examples of strategies of detection, each aimed at exploiting future measurements of kinematic anisotropies for characterizing distinct features of the cosmological gravitational wave background. | kinematic anisotropies and pulsar timing arrays |
neutral hydrogen (hi) is the fundamental component of the interstellar medium. the galactic plane pulsar snapshot (gpps) survey is designed for hunting pulsars by using the five-hundred-meter aperture spherical radio telescope (fast) from the visible galactic plane within ∣b∣≤ 10°. the survey observations are conducted with the l-band 19-beam receivers in the frequency range of 1.0-1.5 ghz, and each pointing has an integration time of 5 min. the piggyback spectral data simultaneously recorded during the fast gpps survey are great resources for studies on the galactic hi distribution and ionized gas. we process the piggyback hi data of the fast gpps survey in the region of 33° ≤ l ≤ 55° and ∣b∣≤ 2°. the rms of the data cube is found to be approximately 40 mk at a velocity resolution of 0.1 km s−1, placing it the most sensitive observations of the galactic hi by far. the high velocity resolution and high sensitivity of the fast gpps hi data enable us to detect weak exquisite hi structures in the interstellar medium. hi absorption line with great details can be obtained against bright continuum sources. the fast gpps survey piggyback hi data cube will be released and updated on the web: http://zmtt.bao.ac.cn/milkywayfast/. | peering into the milky way by fast: i. exquisite hi structures in the inner galactic disk from the piggyback line observations of the fast gpps survey |
we report on observations of psr b1508 + 55's scintillation at the effelsberg 100-m telescope spanning from early 2020 to early 2022. in the autumn of 2020, close to the time the pulsar was predicted to cross echoes in its pulse profile, a sudden transition in the scintillation arcs from peculiar stripe-like features to parabolic arclets was observed. to infer a geometric model of the scattering, we measure the effects of the annual velocity curve of earth, of the relative movement of the line of sight, and of the projection of points on a second scattering screen and develop novel methods to do so. the latter phenomenon was discovered by this study and strongly indicates a two-screen scattering geometry. we derive an analytical two-screen model and demonstrate in a markov chain monte carlo analysis as well as simulations that it can be successfully applied to explain the observations by interpreting the transition as a change of relative amplitudes of images as well as a shift in the orientation of anisotropy. the collection of methods, we demonstrate here is transferable to other pulsars with the potential to strongly improve constraints on scattering models. | double-lens scintillometry: the variable scintillation of pulsar b1508 + 55 |
in this work, a modified nambu-jona-lasinio (njl) model with proper-time regularization is employed to study the properties of hypothetical nonstrange quark stars. the coupling constant of the four-fermion interaction in the conventional njl model is modified as g =g1+g2⟨ψ ¯ ψ ⟩ to highlight the feedback of the quark propagator to the gluon propagator. to study the dependence of the equation of state (eos) on this modification as well as the vacuum pressure, we choose nine representative eoss for comparison. it is found that a smaller g1 leads to a stiffer eos, and a higher vacuum pressure (i.e., a smaller bag constant) yields a softer eos at low energy density. it is further shown that the heaviest quark star under this modified njl model satisfies not only the recent mass measurement of psr j 0740 +6620 , but also the radius constraints from x-ray timing observations. the corresponding tidal deformability is also in agreement with the observations of gw170817. | study of nonstrange quark stars within a modified njl model |
pulsar timing is a technique that uses the highly stable spin periods of neutron stars to investigate a wide range of topics in physics and astrophysics. pulsar timing arrays (ptas) use sets of extremely well-timed pulsars as a galaxy-scale detector with arms extending between earth and each pulsar in the array. these challenging experiments look for correlated deviations in the pulsars' timing that are caused by low-frequency gravitational waves (gws) traversing our galaxy. ptas are particularly sensitive to gws at nanohertz frequencies, which makes them complementary to other space- and ground-based detectors. in this chapter, we will describe the methodology behind pulsar timing; provide an overview of the potential uses of ptas; and summarise where current pta-based detection efforts stand. most predictions expect ptas to successfully detect a cosmological background of gws emitted by supermassive black-hole binaries and also potentially detect continuous-wave emission from binary supermassive black holes, within the next several years. | pulsar timing array experiments |
we present detailed timing and spectral analyses of the transient x-ray pulsar rx j0209.6-7427 in the small magellanic cloud during its 2019 giant outburst. with a better known distance than most galactic x-ray pulsars, its peak luminosity is determined to be (1.11 ± 0.06) × 1039 erg s-1; it is thus a bona fide pulsating ultraluminous x-ray source (pulx). owing to the broad energy band of insight-hxmt, its pulsed x-ray emission was detected from 1 kev up to the 130-180 kev band, which is the highest energy emission detected from any pulxs outside the milky way. this allows us to conclude that its main pulsed x-ray emission is from the fan beam of the accretion column, and its luminosity is thus intrinsic. we also estimate its magnetic field of (4.8-8.6) × 1012 or (1.7-2.2) × 1013 g, from its spin evolution or transition in the accretion column structure during the outburst; we suggest that the two values of the magnetic field strength correspond to the dipole and multipole magnetic fields of the neutron star, similar to the recent discovery in the galactic pulx swift j0243.6+6124. therefore, the nature of the neutron star and its ulx emission can be understood within the current theoretical frame of accreting neutron stars. this may have implications for understanding the nature of those farther away extragalactic pulxs. | fan-beamed x-ray emission from 1 to above 130 kev from the ultraluminous x-ray pulsar rx j0209.6-7427 in the small magellanic cloud |
spectral lag of the low-energy photons with respect to the high-energy ones is a common astrophysical phenomenon (such as gamma-ray bursts and the crab pulsar) and may serve as a key probe to the underlying radiation mechanism. however, spectral lag in kev range of the magnetar bursts has not been systematically studied yet. in this work, we perform a detailed spectral lag analysis with the li et al.'s cross-correlation function (li-ccf) method for sgr j1935+2154 bursts observed by insight-hard x-ray modulation telescope (hxmt), gravitational wave high-energy electromagnetic counterpart all-sky monitor (gecam), and fermi/gamma-ray burst monitor (gbm) from 2014 july to 2022 january. we discover that the spectral lags of about 61 per cent (non-zero significance >1σ) bursts from sgr j1935+2154 are linearly dependent on the photon energy (e) with tlag(e) = α(e/kev) + c, which may be explained by a linear change of the temperature of the blackbody-emitting plasma with time. the distribution of the slope (α) approximately follows a gaussian function with mean and standard deviation of 0.02 ms kev-1 (i.e. high-energy photons arrive earlier) and 0.02 ms kev-1, respectively. we also find that the distribution can be well fitted with three gaussians with mean values of ~-10.009, 0.013, and 0.039 ms kev-1, which may correspond to different origins of the bursts. these spectral lag features may have important implications on the magnetar bursts. | discovery of the linear energy dependence of the spectral lag of x-ray bursts from sgr j1935+2154 |
annual variations of interstellar scintillation can be modelled to constrain parameters of the ionized interstellar medium. if a pulsar is in a binary system, then investigating the orbital parameters is possible through analysis of the orbital variation of scintillation. in observations carried out from 2011 to 2020 by the european pulsar timing array radio telescopes, psrs j0613-0200 and j0636+5128 show strong annual variations in their scintillation velocity, while the former additionally exhibits an orbital fluctuation. bayesian theory and markov-chain-monte-carlo methods are used to interpret these periodic variations. we assume a thin and anisotropic scattering screen model, and discuss the mildly and extremely anisotropic scattering cases. psr j0613-0200 is best described by mildly anisotropic scattering, while psr j0636+5128 exhibits extremely anisotropic scattering. we measure the distance, velocity, and degree of anisotropy of the scattering screen for our two pulsars, finding that scattering screen distances from earth for psrs j0613-0200 and j0636+5128 are 316−20+28 pc and 262−38+96 pc, respectively. the positions of these scattering screens are coincident with the shell of the local bubble towards both pulsars. these associations add to the growing evidence of the local bubble shell as a dominant region of scattering along many sightlines. | periodic interstellar scintillation variations of psrs j0613-0200 and j0636+5128 associated with the local bubble shell |
x persei is a persistent low-luminosity x-ray pulsar of period of ≈ 835 s in a be binary system. the field strength at the neutron star surface is not known precisely, but indirect signs indicate a magnetic field above 1013 g, which makes the object one of the most magnetized known x-ray pulsars. here we present the results of observations x persei performed with the imaging x-ray polarimetry explorer (ixpe). the x-ray polarization signal was found to be strongly dependent on the spin phase of the pulsar. the energy-averaged polarization degree in 3-8 kev band varied from several to ~20 per cent over the pulse with a phase dependence resembling the pulse profile. the polarization angle shows significant variation and makes two complete revolutions during the pulse period, resulting in nearly nil pulse-phase averaged polarization. applying the rotating vector model to the ixpe data we obtain the estimates for the rotation axis inclination and its position angle on the sky, as well as for the magnetic obliquity. the derived inclination is close to the orbital inclination, reported earlier for x persei. the polarimetric data imply a large angle between the rotation and magnetic dipole axes, which is similar to the result reported recently for the x-ray pulsar gro j1008-57. after eliminating the effect of polarization angle rotation over the pulsar phase using the best-fitting rotating vector model, the strong dependence of the polarization degree with energy was discovered, with its value increasing from 0 at ~2 kev to 30per cent at 8 kev. | x-ray polarimetry of x-ray pulsar x persei: another orthogonal rotator? |
with axions now a primary candidate for dark matter, understanding their indirect astrophysical signatures is of paramount importance. key to this is the production of photons from axions in magnetised astrophysical plasmas. while simple formulae for axion-photon mixing in 1d have been sketched several decades ago, there has recently been renewed interest in robust calculations for this process in arbitrary 3d plasmas. these calculations are vital for understanding, amongst other things, the radio production from axion dark matter conversion in neutron stars, which may lead to indirect axion dark matter detection with current telescopes or future searches, e.g., by the ska. in this paper, we derive the relevant transport equations in magnetised plasmas. these equations describe both the production and propagation of photons in an arbitrary 3d medium due to the resonant conversion of axions into photons. they also fully incorporate the refraction of photons, and we find no evidence for a conjectured phenomenon of dephasing. our result is free of divergences which plagued previous calculations, and our kinetic theory description provides a direct link between ray tracing and the production mechanism. these results mark an important step toward solving one of the major open questions concerning indirect searches of axions in recent years, namely how to compute the photon production rate from axions in arbitrary 3d plasmas. | axion-photon conversion in 3d media and astrophysical plasmas |
the population of radio pulsars is observed to demonstrate certain polarization properties not explained by the conventional picture of pulsar polarization, namely frequency evolution of polarization, deviations of the linear polarization angle from a curve of geometric origins, and the presence of features in the circular polarization. we present the partial-coherence model as a way to explain the co-occurrence of these features and to provide an origin for circular polarization in radio pulsar profiles. we describe the mathematics of the model and demonstrate how it can explain these observed features, both on a population level and for the idiosyncrasies of individual pulsars. the partial coherence model can account for complex polarization behaviour, enabling improved access to information about pulsar geometries. we discuss the scientific implications of this for our understanding of pulsar radio emission and propagation. | pulsar polarization: a partial-coherence model |
the detections of four apparently young radio pulsars in the milky way globular clusters are difficult to reconcile with standard neutron star formation scenarios associated with massive star evolution. here, we discuss formation of these young pulsars through white dwarf mergers in dynamically old clusters that have undergone core collapse. based on observed properties of magnetic white dwarfs, we argue neutron stars formed via white dwarf merger are born with spin periods of roughly $10{\!-\!}100\,$ ms and magnetic fields of roughly $10^{11}{\!-\!}10^{13}\,$ g. as these neutron stars spin down via magnetic dipole radiation, they naturally reproduce the four observed young pulsars in the milky way clusters. rates inferred from n-body cluster simulations as well as the binarity, host cluster properties, and cluster offsets observed for these young pulsars hint further at a white dwarf merger origin. these young pulsars may be descendants of neutron stars capable of powering fast radio bursts analogous to the bursts observed recently in a globular cluster in m81. | connecting the young pulsars in milky way globular clusters with white dwarf mergers and the m81 fast radio burst |
understanding the natal kicks received by neutron stars (nss) during formation is a critical component of modelling the evolution of massive binaries. natal kicks are an integral input parameter for population synthesis codes, and have implications for the formation of double ns systems and their subsequent merger rates. however, many of the standard observational kick distributions that are used are obtained from samples created only from isolated nss. kick distributions derived in this way overestimate the intrinsic ns kick distribution. for nss in binaries, we can only directly estimate the effect of the natal kick on the binary system, instead of the natal kick received by the ns itself. here, for the first time, we present a binary kick distribution for nss with low-mass companions. we compile a catalogue of 145 nss in low-mass binaries with the best available constraints on proper motion, distance, and systemic radial velocity. for each binary, we use a three-dimensional approach to estimate its binary kick. we discuss the implications of these kicks on system formation, and provide a parametric model for the overall binary kick distribution, for use in future theoretical modelling work. we compare our results with other work on isolated nss and nss in binaries, finding that the ns kick distributions fit using only isolated pulsars underestimate the fraction of nss that receive low kicks. we discuss the implications of our results on modelling double ns systems, and provide suggestions on how to use our results in future theoretical works. | an observationally derived kick distribution for neutron stars in binary systems |
magnetic fields in the ionized medium of the disk and halo of the milky way impose faraday rotation on linearly polarized radio emission. we compare two surveys mapping the galactic faraday rotation, one showing the rotation measures of extragalactic sources seen through the galaxy, and one showing faraday depth of the diffuse galactic synchrotron emission from the global magneto-ionic medium survey. comparing the two data sets in 5° × 10° bins shows good agreement at intermediate latitudes, 10° < ∣b∣ < 50°, and little correlation between them at lower and higher latitudes. where they agree, both tracers show clear patterns as a function of galactic longitude, ℓ; in the northern hemisphere a strong $\sin \,(2{\ell })$ sin(2ℓ) pattern; and in the southern hemisphere a $\sin \,({\ell }+\pi )$ sin(ℓ+π) pattern. pulsars with height above or below the plane ∣z∣ > 300 pc show similar ℓ dependence in their rotation measures. nearby nonthermal structures show rotation measure shadows as does the orion-eridanus superbubble. we describe families of dynamo models that could explain the observed patterns in the two hemispheres. we suggest that a field reversal, known to cross the plane a few hundred parsecs inside the solar circle, could shift to positive z with increasing galactic radius to explain the $\sin \,(2{\ell })$ sin(2ℓ) pattern in the northern hemisphere. correlation shows that rotation measures from extragalactic sources are one to two times the corresponding rotation measure of the diffuse emission, implying faraday complexity along some lines of sight, especially in the southern hemisphere. | structure in the magnetic field of the milky way disk and halo traced by faraday rotation |
we present baseband radio observations of the millisecond pulsar j1909 - 3744, the most precisely timed pulsar, using the meerkat telescope as part of the meertime pulsar timing array campaign. during a particularly bright scintillation event the pulsar showed strong evidence of pulse mode changing, among the first millisecond pulsars and the shortest duty cycle millisecond pulsar to do so. two modes appear to be present, with the weak (lower signal-to-noise ratio) mode arriving 9.26 ± 3.94 μs earlier than the strong counterpart. further, we present a new value of the jitter noise for this pulsar of 8.20 ± 0.14 ns in one hour, finding it to be consistent with previous measurements taken with the meerkat (9 ± 3 ns) and parkes (8.6 ± 0.8 ns) telescopes, but inconsistent with the previously most precise measurement taken with the green bank telescope (14 ± 0.5 ns). timing analysis on the individual modes is carried out for this pulsar, and we find an approximate $10\, \mathrm{per\,cent}$ improvement in the timing precision is achievable through timing the strong mode only as opposed to the full sample of pulses. by forming a model of the average pulse from templates of the two modes, we time them simultaneously and demonstrate that this timing improvement can also be achieved in regular timing observations. we discuss the impact an improvement of this degree on this pulsar would have on searches for the stochastic gravitational wave background, as well as the impact of a similar improvement on all meertime pta pulsars. | mode changing in j1909 - 3744: the most precisely timed pulsar |
the search for pulsars in a sample of pulsar candidates found based on a multi-year survey conducted with low (six channels; sampling 0.1s) time-frequency resolution on declinations -9° < δ < +42° was carried out with the large phased array of the lebedev physical institute (lpa lpi). lpa is a transit telescope operating at 111 mhz with a bandwidth of 2.5 mhz. search, analysis and evidence of pulsar detection were carried out using a visualization programme of summed up power spectra obtained from the survey data with high (32 channels; sampling 12.5 ms) time-frequency resolution. 11 new pulsars with periods p0 = 0.41-3.75 s and dispersion measure dm = 15-154 pc cm-3 have been discovered. in total, in the survey with a low-time-frequency resolution for the period 2016-2021 in a blind search 203 pulsars were found, among them 42 new and 161 known pulsars. it is shown that in the search on the data with high-time-frequency resolution accumulated over a time interval of seven years, pulsars with a flux density of 0.1-0.2 mjy at the frequency of 111 mhz can be detected. when searching for pulsars with regular (periodic) emission at declinations +21° < δ < +42o, all pulsars located outside the galactic plane having p0 ≥ 0.5 s, dm ≤ 100 pc cm-3, and the flux density s ≥ 0.5 mjy can be detected. | pushchino multibeam pulsar search - i. targeted search of weak pulsars |
we present a framework for modeling astrophysical pulses from radio pulsars and fast radio bursts (frbs). this framework, called fitburst, generates synthetic representations of dynamic spectra that are functions of several physical and heuristic parameters; the heuristic parameters can nonetheless accommodate a vast range of distributions in spectral energy. fitburst is designed to optimize the modeling of features induced by effects that are intrinsic and extrinsic to the emission mechanism, including the magnitude and frequency dependence of pulse dispersion and scatter-broadening. fitburst removes intra-channel smearing through two-dimensional upsampling, and can account for phase wrapping of "folded" signals that are typically acquired during pulsar-timing observations. we demonstrate the effectiveness of fitburst in modeling data containing pulsars and frbs observed with the canadian hydrogen intensity mapping experiment (chime) telescope. | modeling the morphology of fast radio bursts and radio pulsars with fitburst |
context. accretion onto magnetic neutron stars results in x-ray spectra that often exhibit a cyclotron resonance scattering feature (crsf) and, sometimes, higher harmonics of it. two places are suspect for the formation of a crsf: the surface of the neutron star and the radiative shock in the accretion column.aims: here we explore the first possibility: reflection at the neutron-star surface of the continuum produced at the radiative shock. it has been proposed that for high-luminosity sources, as the luminosity increases, the height of the radiative shock increases, thus a larger polar area is illuminated, and as a consequence the energy of the crsf decreases because the dipole magnetic field decreases by a factor of two from the pole to the equator. this model has been specifically proposed to explain the observed anticorrelation of the cyclotron line energy and luminosity of the high-luminosity source v 0332+53.methods: we used a monte carlo code to compute the reflected spectrum from the atmosphere of a magnetic neutron star, when the incident spectrum is a power-law one. we restricted ourselves to cyclotron energies ≪mec2 and used polarization-dependent scattering cross sections, allowing for polarization mode change.results: as expected, a prominent crsf is produced in the reflected spectra if the incident photons are in a pencil beam, which hits the neutron-star surface at a point with a well-defined magnetic field strength. however, the incident beam from the radiative shock has a finite width and thus various magnetic field strengths are sampled. as a result of overlap, the reflected spectra have a crsf, which is close to that produced at the magnetic pole, independent of the height of the radiative shock.conclusions: reflection at the surface of a magnetic neutron star cannot explain the observed decrease in the crsf energy with luminosity in the high-luminosity x-ray pulsar v 0332+53. in addition, it produces absorption lines much shallower than the observed ones. | cyclotron line formation by reflection on the surface of a magnetic neutron star |
we investigate systematically the quark-hadron mixed phase in dense stellar matter and its influence on compact star structures. the properties of quark matter and hadronic matter are fixed based on various model predictions. beside adopting constant values, the surface tension σ for the quark-hadron interface is estimated with the multiple reflection expansion method and equivparticle model. to fix the structures of quark-hadron pasta phases, a continuous dimensionality of the structure is adopted as proposed by ravenhall et al. the corresponding properties of hybrid stars are then obtained and confronted with pulsar observations. it is found that the correlation between radius and tidal deformability in traditional neutron stars preserves in hybrid stars. for those permitted by pulsar observations, in almost all cases, the quark phase persists inside the most massive compact stars. the quark-hadron interface plays an important role in hybrid star structures once quark matter emerges. the surface tension σ estimated with various methods increases with density, which predicts stiffer equation of states (eoss) for the quark-hadron mixed phase and increases the maximum mass of hybrid stars. with or without the emergence of quark matter, the obtained eoss of hybrid star matter are close to each other at densities n ≲0.8 fm-3, while larger uncertainty is expected at higher densities. | systematic study on the quark-hadron mixed phase in compact stars |
pulsar timing array (pta) experiments are becoming increasingly sensitive to gravitational waves (gws) in the nanohertz frequency range, where the main astrophysical sources are supermassive black hole binaries (smbhbs), which are expected to form following galaxy mergers. some of these individual smbhbs may power active galactic nuclei, and thus their binary parameters could be obtained electromagnetically, which makes it possible to apply electromagnetic (em) information to aid the search for a gw signal in pta data. in this work, we investigate the effects of such an em-informed search on binary detection and parameter estimation by performing mock data analyses on simulated pta data sets. we find that by applying em priors, the bayes factor of some injected signals with originally marginal or sub-threshold detectability (i.e., bayes factor ~1) can increase by a factor of a few to an order of magnitude, and thus an em-informed targeted search is able to find hints of a signal when an uninformed search fails to find any. additionally, by combining em and gw data, one can achieve an overall improvement in parameter estimation, regardless of the source's sky location or gw frequency. we discuss the implications for the multi-messenger studies of smbhbs with ptas. | multi-messenger approaches to supermassive black hole binary detection and parameter estimation: implications for nanohertz gravitational wave searches with pulsar timing arrays |
we develop a new theoretical model describing the formation of the radiation spectrum in accretion-powered x-ray pulsars as a result of bulk and thermal comptonization of photons in the accretion column. the new model extends the previous model developed by the authors in four ways: (1) we utilize a conical rather than cylindrical geometry; (2) the radiation components emitted from the column wall and the column top are computed separately; (3) the model allows for a nonzero impact velocity at the stellar surface; and (4) the velocity profile of the gas merges with newtonian freefall far from the star. we show that these extensions allow the new model to simulate sources over a wide range of accretion rates. the model is based on a rigorous mathematical approach in which we obtain an exact series solution for the green's function describing the reprocessing of monochromatic seed photons. emergent spectra are then computed by convolving the green's function with bremsstrahlung, cyclotron, and blackbody photon sources. the range of the new model is demonstrated via applications to the high-luminosity source her x-1, and the low-luminosity source x per. the new model suggests that the observed increase in spectral hardness associated with increasing luminosity in her x-1 may be due to a decrease in the surface impact velocity, which increases the pdv work done on the radiation field by the gas. | a generalized analytical model for thermal and bulk comptonization in accretion-powered x-ray pulsars |
recently ligo collaboration discovered gravitational waves [1] predicted 100 years ago by a. einstein. moreover, in the key paper reporting about the discovery, the joint ligo & virgo team presented an upper limit on graviton mass such as mg < 1.2 × 10-22 ev [2] (see also more details in another ligo paper [3] dedicated to a data analysis to obtain such a small constraint on a graviton mass). since the graviton mass limit is so small the authors concluded that their observational data do not show violations of classical general relativity. we consider another opportunity to evaluate a graviton mass from phenomenological consequences of massive gravity and show that an analysis of bright star trajectories could bound graviton mass with a comparable accuracy with accuracies reached with gravitational wave interferometers and expected with forthcoming pulsar timing observations for gravitational wave detection. it gives an opportunity to treat observations of bright stars near the galactic center as a wonderful tool not only for an evaluation specific parameters of the black hole but also to obtain constraints on the fundamental gravity law such as a modifications of newton gravity law in a weak field approximation. in particular, we obtain bounds on a graviton mass based on a potential reconstruction at the galactic center. | constraining the range of yukawa gravity interaction from s2 star orbits ii: bounds on graviton mass |
fast radio bursts (frbs) are millisecond-duration, luminous radio transients of extragalactic origin. these events have been used to trace the baryonic structure of the universe using their dispersion measure (dm) assuming that the contribution from host galaxies can be reliably estimated. however, contributions from the immediate environment of an frb may dominate the observed dm, thus making redshift estimates challenging without a robust host galaxy association. furthermore, while at least one galactic burst has been associated with a magnetar, other localized frbs argue against magnetars as the sole progenitor model. precise localization within the host galaxy can discriminate between progenitor models, a major goal of the field. until now, localizations on this spatial scale have only been carried out in follow-up observations of repeating sources. here we demonstrate the localization of frb 20210603a with very long baseline interferometry (vlbi) on two baselines, using data collected only at the time of detection. we localize the burst to sdss j004105.82+211331.9, an edge-on galaxy at $z\approx 0.177$, and detect recent star formation in the kiloparsec-scale vicinity of the burst. the edge-on inclination of the host galaxy allows for a unique comparison between the line of sight towards the frb and lines of sight towards known galactic pulsars. the dm, faraday rotation measure (rm), and scattering suggest a progenitor coincident with the host galactic plane, strengthening the link between the environment of frb 20210603a and the disk of its host galaxy. single-pulse vlbi localizations of frbs to within their host galaxies, following the one presented here, will further constrain the origins and host environments of one-off frbs. | a fast radio burst localized at detection to a galactic disk using very long baseline interferometry |
the extended nebulae formed as pulsar winds expand into their surroundings provide information about the composition of the winds, the injection history from the host pulsar, and the material into which the nebulae are expanding. observations from across the electromagnetic spectrum provide constraints on the evolution of the nebulae, the density and composition of the surrounding ejecta, the geometry of the central engines, and the long-term fate of the energetic particles produced in these systems. such observations reveal the presence of jets and wind termination shocks, time-varying compact emission structures, shocked supernova ejecta, and newly formed dust. here i provide a broad overview of the structure of pulsar wind nebulae, with specific examples from observations extending from the radio band to very high-energy gamma rays that demonstrate our ability to constrain the history and ultimate fate of the energy released in the spin-down of young pulsars. | pulsar wind nebulae |
there have been significant developments in the period estimation tools and methods for analysing high energy pulsars in the past few decades. however, these tools lack well-standardised methods for calculating uncertainties in period estimation and other recovered parameters for poisson--dominated data. error estimation is important for assigning confidence intervals to the models we study, but due to their high computational cost, errors in the pulsar periods were largely ignored in the past. furthermore, existing literature has often employed semi-analytical techniques that lack rigorous mathematical foundations or exhibit a predominant emphasis on the analysis of white noise and time series data. we present results from our numerical and analytical study of the error distribution of the recovered parameters of high energy pulsar data using the $z_n^2$ method. we comprehensively formalise the measure of error for the generic pulsar period with much higher reliability than some common methods. our error estimation method becomes more reliable and robust when observing pulsars for few kilo-seconds, especially for typical pulsars with periods ranging from a few milliseconds to a few seconds. we have verified our results with observations of the \emph{crab} pulsar, as well as a large set of simulated pulsars. our codes are publicly available for use. | quantifying period uncertainty in x-ray pulsars with poisson-limited data |
we construct new effective interactions using the relativistic mean-field models with the isoscalar- and isovector-meson mixing, σ2δ2 and ωμωμρνρν. taking into account the particle flow data in heavy-ion collisions, the observed mass of psr j0740+6620, and the tidal deformability of a neutron star from the binary merger event, gw170817, we study the ground-state properties of finite, closed-shell nuclei, and try to explain the recent results from the prex-2 and crex experiments. it is found that the σ-δ mixing is very powerful to understand the terrestrial experiments and astrophysical observations of neutron stars self-consistently. we can predict the large neutron skin thickness of 208pb, rskin208 = 0.243 fm, using the slope parameter of nuclear symmetry energy, l = 70 mev, which is consistent with the prex-2 result. however, to explain the crex data, it is preferable to adopt the small value of l = 20 mev. it is very difficult to understand the prex-2 and crex results simultaneously within relativistic mean-field models. | can the prex-2 and crex results be understood by relativistic mean-field models with the astrophysical constraints? |
in this paper we obtain a new static and spherically symmetric model of compact star whose spacetime satisfies karmarkar's condition (1948). the einstein's field equations are solved by employing a physically reasonable choice of the metric coefficient g_{rr} so that the obtained solution is free from central singularities. our model satisfies all the energy conditions as well as the causality condition. by assigning some particular values mass and radius of the compact stars psr j0347+0432, cen x-3 and vela x-1 have been obtained which are very close to the observational data proposed by antoniadis et al. (science 340:1233232, 2013), abubekerov et al. (astron. rep. 48:89, 2004) and ash et al. (mon. not. r. astron. soc. 307:357, 1999). for the neutron star candidate psr j0348+0432, we expect a very stiff equation of state to support its massive mass which corresponds to a large value of the adiabatic index of 6.66 at the center. | solutions of the einstein's field equations with anisotropic pressure compatible with cold star model |
mems (micro electro mechanical system) gyroscopes have been widely applied to various fields, but mems gyroscope random drift has nonlinear and non-stationary characteristics. it has attracted much attention to model and compensate the random drift because it can improve the precision of inertial devices. this paper has proposed to use wavelet filtering to reduce noise in the original data of mems gyroscopes, then reconstruct the random drift data with psr (phase space reconstruction), and establish the model for the reconstructed data by lssvm (least squares support vector machine), of which the parameters were optimized using cpso (chaotic particle swarm optimization). comparing the effect of modeling the mems gyroscope random drift with bp-ann (back propagation artificial neural network) and the proposed method, the results showed that the latter had a better prediction accuracy. using the compensation of three groups of mems gyroscope random drift data, the standard deviation of three groups of experimental data dropped from 0.00354 ° / s , 0.00412 ° / s , and 0.00328 ° / s to 0.00065 ° / s , 0.00072 ° / s and 0.00061 ° / s , respectively, which demonstrated that the proposed method can reduce the influence of mems gyroscope random drift and verified the effectiveness of this method for modeling mems gyroscope random drift. | modeling and compensation of random drift of mems gyroscopes based on least squares support vector machine optimized by chaotic particle swarm optimization |
the heps plans to adopt on-axis injection scheme because the dynamic aperture of machine is not large enough for off-axis injection for its baseline 7ba lattice design. a couple sets of strip-line kicker and fast pulser of ±15 kv amplitude, 15 ns pulse bottom width are needed for bunch spacing of 10 ns to minimize perturbation on adjacent bunches. to achieve these requirement, a multifaceted r&d program including the strip-line kicker and hv pulser, was initiated last 2 years. so far, the prototype development of a 750 mm long strip-line kicker and a dsrd pulser was completed and the preliminary test results show they can meet the baseline requirement of the heps. | strip-line kicker and fast pulser r&d for the heps on-axis injection system |
fermi large area telescope data reveal an excess of gev gamma rays from the direction of the galactic center and bulge. several explanations have been proposed for this excess including an unresolved population of millisecond pulsars (msps) and self-annihilating dark matter. it has been claimed that a key discriminant for or against the msp explanation can be extracted from the properties of the luminosity function describing this source population. specifically, is the luminosity function of the putative msps in the galactic center consistent with that characterizing the resolved msps in the galactic disk? to investigate this we have used a bayesian markov chain monte carlo to evaluate the posterior distribution of the parameters of the msp luminosity function describing both resolved msps and the galactic center excess. at variance with some other claims, our analysis reveals that, within current uncertainties, both data sets can be well fit with the same luminosity function. | consistency between the luminosity function of resolved millisecond pulsars and the galactic center excess |
this document describes a code to perform parameter estimation and model selection in targeted searches for continuous gravitational waves from known pulsars using data from ground-based gravitational wave detectors. we describe the general workings of the code and characterise it on simulated data containing both noise and simulated signals. we also show how it performs compared to a previous mcmc and grid-based approach to signal parameter estimation. details how to run the code in a variety of cases are provided in appendix a. | a nested sampling code for targeted searches for continuous gravitational waves from pulsars |
if millisecond pulsars (msps) are responsible for the excess gamma-ray emission observed from the region surrounding the galactic center, the same region should also contain a large population of low-mass x-ray binaries (lmxbs). in this study, we compile and utilize a sizable catalog of lmxbs observed in the the milky way's globular cluster system and in the inner galaxy, as well as the gamma-ray emission observed from globular clusters, to estimate the flux of gamma rays predicted from msps in the inner galaxy. from this comparison, we conclude that only up to ~ 4-23% of the observed gamma-ray excess is likely to originate from msps. this result is consistent with, and more robust than, previous estimates which utilized smaller samples of both globular clusters and lmxbs. if msps had been responsible for the entirety of the observed excess, integral should have detected ~ 103 lmxbs from within a 10o radius around the galactic center, whereas only 42 lmxbs (and 46 additional lmxb candidates) have been observed. | low mass x-ray binaries in the inner galaxy: implications for millisecond pulsars and the gev excess |
few statistically compelling correlations are found in pulsar timing data between the size of a rotational glitch and the time to the preceding glitch (backward waiting time) or the succeeding glitch (forward waiting time), except for a strong correlation between sizes and forward waiting times in psr j0537-6910. this situation is counterintuitive if glitches are threshold-triggered events, as in standard theories (e.g., starquakes, superfluid vortex avalanches). here, it is shown that the lack of correlation emerges naturally, when a threshold trigger is combined with secular stellar braking slower than a critical, calculable rate. the pearson and spearman correlation coefficients are computed and interpreted within the framework of a state-dependent poisson process. specific, falsifiable predictions are made regarding what objects currently targeted by long-term timing campaigns should develop strong size-waiting-time correlations as more data are collected in the future. | size-waiting-time correlations in pulsar glitches |
we monitor established and putative redback millisecond pulsars (msps) in time-series photometry, repeatedly covering their 5-6 hr orbital light curves in r‧ or r. on timescales of months, psr j1048+2339 and xmmu j083850.38-282756.8 exhibit similar variability of ≈0.3 mag on the heated side of the companion star. however, the heating light curve is rarely symmetric, suggesting that the intrabinary shock generated by the pulsar wind is skewed in addition to being variable, or that changing magnetic fields intrinsic to the companion channel the pulsar wind. in addition to this variable heating, there are long-lived flaring states that increase the brightness by an additional 0.5 mag, with variability on ≈10 min timescales. these flares also appear to originate on the heated side of the companion, while the “night”-side brightness remains relatively stable. somewhat less active, psr j1628-3205 has an optical light curve that is dominated by tidal distortion (ellipsoidal modulation), although it too shows evidence of variable and asymmetric heating due to shifting magnetic fields or migrating star spots. these effects frustrate any effort to derive system parameters such as inclination angle and roche-lobe filling factor from optical light curves of redback msps. we also report on two chandra x-ray observations of psr j1048+2339 that show strong orbital modulation, possibly due to beaming along the intrabinary shock, and a third observation that is dominated by flaring. the peak flare luminosity in the 0.3-8 kev band is ≈12% of the pulsar’s spin-down power, which may require magnetic reconnection. none of these three systems has yet shown a transition back to an accreting state. | variable heating and flaring of three redback millisecond pulsar companions |
a number of low-mass millisecond pulsar (msp) binaries in their rotation-powered state exhibit double-peaked x-ray orbital modulation centered at inferior pulsar conjunction. this state, which has been known to persist for years, has recently been interpreted as emission from a shock that enshrouds the pulsar. however, the pressure balance for such a configuration is a crucial unresolved issue. we consider two scenarios for pressure balance: a companion magnetosphere and stellar mass loss with gas dominance. it is found that the magnetospheric scenario requires several kilogauss poloidal fields for isobaric surfaces to enshroud the msp, as well as for the magnetosphere to remain stable if there is significant mass loss. for the gas-dominated scenario, it is necessary that the companion wind loses angular momentum prolifically as an advection- or heating-dominated flow. thermal bremsstrahlung cooling in the flow may be observable as a uv to soft x-ray component independent of orbital phase if the mass rate is high. we formulate the general requirements for shock stability against gravitational influences in the pulsar rotation-powered state for the gas-dominated scenario. we explore stabilizing mechanisms, principally irradiation feedback, which anticipates correlated shock emission and companion variability and predicts fγ /f x ≲ 14 for the ratio of pulsar magnetospheric γ-ray to total shock soft-to-hard x-ray fluxes. this stability criterion implies an unbroken extension of x-ray power-law emission to hundreds of kev for some systems. we explore observational discriminants between the gas-dominated and magnetospheric scenarios, motivating contemporaneous radio through γ-ray monitoring of these systems. | pressure balance and intrabinary shock stability in rotation-powered-state redback and transitional millisecond pulsar binary systems |
the population of young, non-recycled pulsars with spin-down energies $\dot{e} \gt 10^{35}$ erg s-1 is sampled predominantly at γ-ray and radio wavelengths. a total of 137 such pulsars are known, with partial overlap between the sources detectable in radio and γ-rays. we use a very small set of assumptions in an attempt to test whether the observed pulsar sample can be explained by a single underlying population of neutron stars. for radio emission we assume a canonical conal beam with a fixed emission height of 300 km across all spin periods and a luminosity law which depends on $\dot{e}^{0.25}$ . for γ-ray emission we assume the outer-gap model and a luminosity law which depends on $\dot{e}^{0.5}$ . we synthesize a population of fast-spinning pulsars with a birth rate of one per 100 yr. we find that this simple model can reproduce most characteristics of the observed population with two caveats. the first is a deficit of γ-ray pulsars at the highest $\dot{e}$ which we surmise to be an observational selection effect due to the difficulties of finding γ-ray pulsars in the presence of glitches without prior knowledge from radio frequencies. the second is a deficit of radio pulsars with interpulse emission, which may be related to radio emission physics. we discuss the implications of these findings. | the galactic population and properties of young, highly energetic pulsars |
we have used the nanshan 25 m radio telescope at xinjiang astronomical observatory to obtain timing observations of 87 pulsars from 2002 july to 2014 march. using the "cholesky" timing analysis method we have determined positions and proper motions for 48 pulsars, 24 of which are improved positions compared to previously published values. we also present the first published proper motions for nine pulsars and improved proper motions for 21 pulsars using the pulsar timing and position-comparison method. the pulsar rotation parameters are derived and are more accurate than previously published values for 36 pulsars. glitches are detected in three pulsars: psrs j1722-3632, j1852-0635, and j1957+2831. for the first two, the glitches are large, with δνg/ν > 10-6, and they are the first detected glitches in these pulsars. psr j1722-3632 is the second oldest pulsar, with a large glitch. for the middle-age pulsars (τc > 105 yr), the calculated braking indices, $| n| $ , are strongly correlated with τc and the numbers of positive and negative values of n are almost equal. for young pulsars (τc < 105 yr), there is no correlation between $| n| $ and τc and most have n > 0. | results of 12 yr of pulsar timing at nanshan. i. |
we present a general relativistic (gr) model of jet variability in active galactic nuclei due to orbiting blobs in helical motion along a funnel or cone-shaped magnetic surface anchored to the accretion disk near the black hole. considering a radiation pressure driven flow in the inner region, we find that it stabilizes the flow, yielding lorentz factors ranging between 1.1 and 7 at small radii for reasonable initial conditions. assuming these as inputs, simulated light curves (lcs) for the funnel model include doppler and gravitational shifts, aberration, light bending, and time delay. these lcs are studied for quasi-periodic oscillations (qpos) and the power spectral density (psd) shape, and yield an increased amplitude (∼12%), a beamed portion and a systematic phase shift with respect to that from a previous special relativistic model. the results strongly justify implementing a realistic magnetic surface geometry in schwarzschild geometry to describe effects on emission from orbital features in the jet close to the horizon radius. a power-law-shaped psd with a typical slope of -2 and qpos with timescales in the range of (1.37-130.7) days consistent with optical variability in blazars, emerges from the simulations for black hole masses {{m}\bullet }=(0.5-5)× {{10}8} {{m}⊙ } and initial lorentz factors {{γ }jet,i}=2-10. the models presented here can be applied to explain radio, optical, and x-ray variability from a range of jetted sources including active galactic nuclei, x-ray binaries, and neutron stars. | kinematics of and emission from helically orbiting blobs in a relativistic magnetized jet |
recently we have proposed a novel method to probe primordial gravitational waves from upper bounds on the abundance of primordial black holes (pbhs). when the amplitude of primordial tensor perturbations generated in the early universe is fairly large, they induce substantial scalar perturbations due to their second-order effects. if these induced scalar perturbations are too large when they reenter the horizon, then pbhs are overproduced, their abundance exceeding observational upper limits. that is, primordial tensor perturbations on superhorizon scales can be constrained from the absence of pbhs. in our recent paper we have only shown simple estimations of these new constraints, and hence in this paper, we present detailed derivations, solving the einstein equations for scalar perturbations induced at second order in tensor perturbations. we also derive an approximate formula for the probability density function of induced density perturbations, necessary to relate the abundance of pbhs to the primordial tensor power spectrum, assuming primordial tensor perturbations follow gaussian distributions. our new upper bounds from pbhs are compared with other existing bounds obtained from big bang nucleosynthesis, cosmic microwave background, ligo/virgo and pulsar timing arrays. | primordial black holes as a novel probe of primordial gravitational waves. ii. detailed analysis |
in the presence of massive bosonic degrees of freedom, rotational superradiance can trigger an instability that spins down black holes. this leads to peculiar gravitational-wave signatures and distribution in the spin-mass plane, which in turn can impose stringent constraints on ultralight fields. here, we demonstrate that there is an analogous spindown effect for conducting stars. we show that rotating stars amplify low-frequency electromagnetic waves, and that this effect is largest when the time scale for conduction within the star is of the order of a light crossing time. this has interesting consequences for dark photons, as massive dark photons would cause stars to spin down due to superradiant instabilities. the time scale of the spindown depends on the mass of the dark photon, and on the rotation rate, compactness, and conductivity of the star. existing measurements of the spindown rate of pulsars place direct constraints on models of dark sectors. our analysis suggests that dark photons of mass mv∼10-12 ev are excluded by pulsar-timing observations. these constraints also exclude superradiant instabilities triggered by dark photons as an explanation for the spin limit of observed pulsars. | superradiance in rotating stars and pulsar-timing constraints on dark photons |
thermal x-ray emission from rotation-powered pulsars is believed to originate from localized `hotspots' on the stellar surface occurring where large-scale currents from the magnetosphere return to heat the atmosphere. light-curve modelling has primarily been limited to simple models, such as circular antipodal emitting regions with constant temperature. we calculate more realistic temperature distributions within the polar caps, taking advantage of recent advances in magnetospheric theory, and we consider their effect on the predicted light curves. the emitting regions are non-circular even for a pure dipole magnetic field, and the inclusion of an aligned magnetic quadrupole moment introduces a north-south asymmetry. as the quadrupole moment is increased, one hotspot grows in size before becoming a thin ring surrounding the star. for the pure dipole case, moving to the more realistic model changes the light curves by 5-10 per cent for millisecond pulsars, helping to quantify the systematic uncertainty present in current dipolar models. including the quadrupole gives considerable freedom in generating more complex light curves. we explore whether these simple dipole+quadrupole models can account for the qualitative features of the light curve of psr j0437-4715. | x-ray light curves from realistic polar cap models: inclined pulsar magnetospheres and multipole fields |
in the last decade, the relativistic magnetohydrodynamic (mhd) modelling of pulsar wind nebulae, and of the crab nebula in particular, has been highly successful, with many of the observed dynamical and emission properties reproduced down to the finest detail. here, we critically discuss the results of some of the most recent studies: namely the investigation of the origin of the radio emitting particles and the quest for the acceleration sites of particles of different energies along the termination shock, by using wisp motions as a diagnostic tool; the study of the magnetic dissipation process in high magnetization nebulae by means of new long-term three-dimensional simulations of the pulsar wind nebula evolution; the investigation of the relativistic tearing instability in thinning current sheets, leading to fast reconnection events that might be at the origin of the crab nebula gamma-ray flares. | multi-d magnetohydrodynamic modelling of pulsar wind nebulae: recent progress and open questions |
we describe the history, methods, tools, and challenges of using pulsars to detect gravitational waves. pulsars act as celestial clocks detecting gravitational perturbations in space-time at wavelengths of light-years. the field is poised to make its first detection of nanohertz gravitational waves in the next 10 years. controversies remain over how far we can reduce the noise in the pulsars, how many pulsars should be in the array, what kind of source we will detect first, and how we can best accommodate our large bandwidth systems. we conclude by considering the important question of how to plan for a post-detection era, beyond the first detection of gravitational waves. | pulsar timing arrays: the promise of gravitational wave detection |
observations of psr b0943+10 with xmm-newton and the lofar, lwa, and arecibo radio telescopes in 2014 november confirm the synchronous x-ray/radio switching between a radio-bright (b) mode and a radio-quiet (q) mode, in which the x-ray flux is a factor ∼2.4 higher than in the b-mode. we discovered x-ray pulsations during the b-mode (0.5-2 kev pulsed fraction of (38 ± 5)%) and confirm their presence in the q-mode, where the pulsed fraction increases with energy from ∼20% to ∼65% at 2 kev. we found marginal evidence for an increase in the x-ray pulsed fraction during the b-mode on a timescale of hours. the x-ray spectrum during the q-mode requires a fit with either a power law plus blackbody or the sum of two blackbodies, while in the b-mode it is well fit by a single blackbody (a single power law is rejected). in the q-mode, the pulsed emission has a blackbody spectrum with temperature ∼ 3.4× {10}6 k and the unpulsed emission is a power law with photon index ∼2.5, while during the b-mode both the pulsed and unpulsed emission can be fit by either a blackbody or a power law with similar values of temperature and index. a chandra image does not show diffuse x-ray emission. these results support a scenario in which unpulsed non-thermal emission, likely magnetospheric, and pulsed thermal emission from a small polar cap (∼1500 m2) with a non-dipolar field (∼1014 g) are present during both modes and vary in a correlated way. this is broadly consistent with the partially screened gap model and does not necessarily imply global magnetospheric rearrangements to explain the mode switching. | a deep campaign to characterize the synchronous radio/x-ray mode switching of psr b0943+10 |
searches for millisecond-duration, dispersed single pulses have become a standard tool used during radio pulsar surveys in the last decade. they have enabled the discovery of two new classes of sources: rotating radio transients and fast radio bursts. however, we are now in a regime where the sensitivity to single pulses in radio surveys is often limited more by the strong background of radio frequency interference (rfi, which can greatly increase the false-positive rate) than by the sensitivity of the telescope itself. to mitigate this problem, we introduce the single-pulse searcher (sps). this is a new machine-learning classifier designed to identify astrophysical signals in a strong rfi environment, and optimized to process the large data volumes produced by the new generation of aperture array telescopes. it has been specifically developed for the lofar tied-array all-sky survey (lotaas), an ongoing survey for pulsars and fast radio transients in the northern hemisphere. during its development, sps discovered seven new pulsars and blindly identified ∼80 known sources. the modular design of the software offers the possibility to easily adapt it to other studies with different instruments and characteristics. indeed, sps has already been used in other projects, e.g. to identify pulses from the fast radio burst source frb 121102. the software development is complete and sps is now being used to re-process all lotaas data collected to date. | single-pulse classifier for the lofar tied-array all-sky survey |
we present first results for faraday rotation of compact polarized sources (1-2 ghz continuum) in the h i/oh/recombination line (thor) survey of the inner galaxy. in the galactic longitude range 39° < ℓ < 52°, we find rotation measures (rms) in the range -310 rad m-2 ≤ rm ≤ +4219 rad m-2, with the highest values concentrated within a degree of ℓ = 48° at the sagittarius arm tangent. most of the high rms arise in diffuse plasma, along lines of sight that do not intersect h ii regions. for ℓ > 49°, rm drops off rapidly, while at ℓ < 47°, the mean rm is higher with a larger standard deviation than at ℓ > 49°. we attribute the rm structure to the compressed diffuse warm ionized medium in the spiral arm, upstream of the major star formation regions. the sagittarius arm acts as a significant faraday screen inside the galaxy. this has implications for models of the galactic magnetic field and the expected amount of faraday rotation of fast radio bursts from their host galaxies. we emphasize the importance of sensitivity to high faraday depth in future polarization surveys. | strong excess faraday rotation on the inside of the sagittarius spiral arm |
it has been widely argued that type-i superluminous supernovae (slsne-i) are driven by powerful central engines with a long-lasting energy injection after the core-collapse of massive progenitors. one of the popular hypotheses is that the hidden engines are fast-rotating pulsars with a magnetic field of b ∼ 1013-1015 g. murase, kashiyama & mészáros proposed that quasi-steady radio/submm emission from non-thermal electron-positron pairs in nascent pulsar wind nebulae can be used as a relevant counterpart of such pulsar-driven supernovae (sne). in this work, focusing on the nascent slsn-i remnants, we examine constraints that can be placed by radio emission. we show that the atacama large millimeter/submillimetre array can detect the radio nebula from sne at dl ∼ 1 gpc in a few years after the explosion, while the jansky very large array can also detect the counterpart in a few decades. the proposed radio follow-up observation could solve the parameter degeneracy in the pulsar-driven sn model for optical/uv light curves, and could also give us clues to young neutron star scenarios for slsne-i and fast radio bursts. | radio emission from embryonic superluminous supernova remnants |
symmetries play important roles in modern theories of physical laws. in this paper, we review several experimental tests of important symmetries associated with the gravitational interaction, including the universality of free fall for self-gravitating bodies, time-shift symmetry in the gravitational constant, local position invariance and local lorentz invariance of gravity, and spacetime translational symmetries. recent experimental explorations for post-newtonian gravity are discussed, of which, those from pulsar astronomy are highlighted. all of these tests, of very different aspects of gravity theories, at very different length scales, favor to very high precision the predictions of the strong equivalence principle (sep) and, in particular, general relativity which embodies sep completely. as the founding principles of gravity, these symmetries are motivated to be promoted to even stricter tests in future. | tests of gravitational symmetries with radio pulsars |
we have collected and analyzed the complete archive of xmm-newton (116), chandra (151), and rxte (952) observations of the small magellanic cloud (smc), spanning 1997-2014. the resulting observational library provides a comprehensive view of the physical, temporal, and statistical properties of the smc pulsar population across the luminosity range of {l}x={10}31.2{--}{10}38 erg s-1. from a sample of 65 pulsars we report ∼1654 individual pulsar detections, yielding ∼1260 pulse-period measurements. our pipeline generates a suite of products for each pulsar detection: spin period, flux, event list, high time-resolution light curve, pulse profile, periodogram, and spectrum. combining all three satellites, we generated complete histories of the spin periods, pulse amplitudes, pulsed fractions, and x-ray luminosities. some pulsars show variations in pulse period due to the combination of orbital motion and accretion torques. long-term spin-up/spin-down trends are seen in 12/11 pulsars, respectively, pointing to sustained transfer of mass and angular momentum to the neutron star on decadal timescales. of the sample, 30 pulsars have a relatively very small spin period derivative and may be close to equilibrium spin. the distributions of pulse detection and flux as functions of spin period provide interesting findings: mapping boundaries of accretion-driven x-ray luminosity and showing that fast pulsars (p < 10 s) are rarely detected, which as of yet are more prone to giant outbursts. accompanying this paper is an initial public release of the library so that it can be used by other researchers. we intend the library to be useful in driving improved models of neutron star magnetospheres and accretion physics. | a comprehensive library of x-ray pulsars in the small magellanic cloud: time evolution of their luminosities and spin periods |
in this paper we report on ∼ 10 yr of observations of psr j2051-0827, at radio frequencies in the range 110-4032 mhz. we investigate the eclipse phenomena of this black widow pulsar using model fits of increased dispersion and scattering of the pulsed radio emission as it traverses the eclipse medium. these model fits reveal variability in dispersion features on time-scales as short as the orbital period, and previously unknown trends on time-scales of months-years. no clear patterns are found between the low-frequency eclipse widths, orbital period variations, and trends in the intrabinary material density. using polarization calibrated observations we present the first available limits on the strength of magnetic fields within the eclipse region of this system; the average line of sight field is constrained to be 10^{-4} g ≲ b_{||} ≲ 10^2 g, while for the case of a field directed near-perpendicular to the line of sight we find b_{\perp } ≲ 0.3 g. depolarization of the linearly polarized pulses during the eclipse is detected and attributed to rapid rotation measure fluctuations of σ _{rm} ≳ 100 rad m^{-2} along, or across, the line of sights averaged over during a subintegration. the results are considered in the context of eclipse mechanisms, and we find scattering and/or cyclotron absorption provide the most promising explanation, while dispersion smearing is conclusively ruled out. finally, we estimate the mass-loss rate from the companion to be \dot{m}c ∼ 10^{-12} m_⊙ yr^{-1}, suggesting that the companion will not be fully evaporated on any reasonable time-scale | long-term variability of a black widow's eclipses - a decade of psr j2051-0827 |
we present new observations of the c-band continuum emission and masers to assess high-mass (>8 {m}⊙ ) star formation at early evolutionary phases in the inner 200 pc of the central molecular zone (cmz) of the galaxy. the continuum observation is complete to free-free emission from stars above 10-11 {m}⊙in 91% of the covered area. we identify 104 compact sources in the continuum emission, among which five are confirmed ultracompact h ii regions, 12 are candidates of ultracompact h ii regions, and the remaining 87 sources are mostly massive stars in clusters, field stars, evolved stars, pulsars, extragalactic sources, or of unknown nature that is to be investigated. we detect class ii ch3oh masers at 23 positions, among which six are new detections. we confirm six known h2co masers in two high-mass star-forming regions and detect two new h2co masers toward the sgr c cloud, making it the ninth region in the galaxy that contains masers of this type. in spite of these detections, we find that current high-mass star formation in the inner cmz is only taking place in seven isolated clouds. the results suggest that star formation at early evolutionary phases in the cmz is about 10 times less efficient than expected from the dense gas star formation relation, which is in line with previous studies that focus on more evolved phases of star formation. this means that if there will be any impending, next burst of star formation in the cmz, it has not yet begun. | a census of early-phase high-mass star formation in the central molecular zone |
the construction of accurate and consistent initial data for various binary parameters is a critical ingredient for numerical relativity simulations of the compact binary coalescence. in this article, we present an upgrade of the pseudospectral uc(sgrid) code, which enables us to access even larger regions of the binary neutron star parameter space. as a proof of principle, we present a selected set of first simulations based on initial configurations computed with the new code version. in particular, we simulate two millisecond pulsars close to their breakup spin, highly compact neutron stars with masses at about 98% of the maximum supported mass of the employed equation of state, and unequal-mass systems with mass ratios even outside the range predicted by population synthesis models (q =2.03 ). the discussed code extension will help us to simulate previously unexplored binary configurations. this is a necessary step to construct and test new gravitational-wave approximants and to interpret upcoming binary neutron star merger observations. when we construct initial data, we have to specify various parameters, such as a rotation parameter for each star. some of these parameters do not have direct physical meaning, which makes comparisons with other methods or models difficult. to facilitate this, we introduce simple estimates for the initial spin, momentum, mass, and center of mass (c.m.) of each individual star. | constructing binary neutron star initial data with high spins, high compactnesses, and high mass ratios |
the direct detection of gravitational waves now provides a new channel for testing gravity theories. despite that the parametrized post-einsteinian framework is a powerful tool to quantitatively investigate the effects of modifications to gravity theory, the gravitational waveform in this framework is still extendable. one such extension is to take into account the gradual activation of dipole radiation due to massive fields, which are still only very weakly constrained if their mass m is greater than 10^{-16} ev from pulsar observations. ground-based gravitational-wave detectors (ligo, virgo, and kagra) are sensitive to this activation in the mass range 10^{-14} ev ≲ m ≲ 10^{-13} ev. hence, we discuss a dedicated test for dipole radiation due to a massive field using the ligo/virgo collaboration's open data. in addition, assuming einstein dilaton gauss bonnet (edgb) type coupling, we combine the results of the analysis of binary black hole events to obtain 90% confidence level constraints on the coupling parameter α_edgb as √{α_edgb} ≲ 2.47 km for any mass less than 6 × 10^{-14} ev for the first time, including √{α_edgb} ≲ 1.85 km in the massless limit. | testing massive-field modifications of gravity via gravitational waves |
the very long baseline interferometry (vlbi) technique offers angular resolutions superior to any other instruments at other wavelengths, enabling unique science applications of high-resolution imaging of radio sources and high-precision astrometry. the east asia vlbi network (eavn) is a collaborative effort in the east asian region. the eavn currently consists of 21 telescopes with diverse equipment configurations and frequency setups, allowing flexible subarrays for specific science projects. the eavn provides the highest resolution of 0.5 mas at 22 ghz, allowing the fine imaging of jets in active galactic nuclei, high-accuracy astrometry of masers and pulsars, and precise spacecraft positioning. the soon-to-be-operational five-hundred-meter aperture spherical radio telescope (fast) will open a new era for the eavn. this state-of-the-art vlbi array also provides easy access to and crucial training for the burgeoning asian astronomical community. this perspective summarizes the status, capabilities and prospects of the eavn. | capabilities and prospects of the east asia very long baseline interferometry network |
certain physical quantities that characterize neutron stars and quark stars (e.g. their mass, spin angular momentum, and quadrupole moment) have recently been found to be interrelated in a manner that is approximately insensitive to their internal structure. such approximately universal relations are useful to break degeneracies in data analysis and model selection for future radio, x-ray, and gravitational wave observations. although the pressure inside compact stars is most likely nearly isotropic, certain scenarios have been put forth that suggest otherwise, for example due to magnetic fields or phase transitions in their interior. we investigate here whether pressure anisotropy affects the approximate universal relations and, if so, whether it prevents their use in future astrophysical observations. we achieve this by numerically constructing slowly rotating and tidally deformed, anisotropic, compact stars in general relativity to third order in stellar rotation relative to the mass shedding limit. we adopt simple models for pressure anisotropy where the matter stress-energy tensor is diagonal for a spherically symmetric spacetime but the tangential pressure differs from the radial one. we find that the equation-of-state variation increases as one increases the amount of anisotropy, but within the anisotropy range studied in this paper (motivated from anisotropy due to crystallization of the core and pion condensation), anisotropy affects the universal relations only weakly. the relations become less universal by a factor of 1.5-3 relative to the isotropic case when anisotropy is maximal, but even then they remain approximately universal to 10%. we find evidence that this increase in variability is strongly correlated to an increase in the eccentricity variation of isodensity contours, which provides further support for the emergent approximate symmetry explanation of universality. whether one can use universal relations in actual observations ultimately depends on the currently unknown amount of anisotropy inside stars, but within the range studied in this paper, anisotropy does not prevent the use of universal relations in gravitational wave astrophysics or in experimental relativity. we provide an explicit example of the latter by simulating a binary pulsar/gravitational wave test of dynamical chern-simons gravity with anisotropic neutron stars. the increase in variability of the universal relations due to pressure anisotropy could affect their use in future x-ray observations of hot spots on rotating compact stars. given expected observational uncertainties, however, the relations remain sufficiently universal for use in such observations if the anisotropic modifications to the moment of inertia and the quadrupole moment are less than 10% of their isotropic values. | i-love-q anisotropically: universal relations for compact stars with scalar pressure anisotropy |
we have explored exact solutions free from any physical and geometrical singularities, as well as the existence of compact stellar systems throughout linear and starobinsky- f(r , t) - gravity theory. as we generally well-known, the general exact solutions of the altered einstein field equations (efes) in the background of this gravity theory are one of the most complex tasks. to acquire simpler solution of the altered field equations, we consider linear and starobinsky shape of the algebraic function as f(r , t) = r + 2 χt and f(r , t) = r + ξr2 + 2 χt (where r is scalar curvature, t is the trace of the stress-energy tensor and χ & ξ denotes a coupling constants). in this regards, we propose metric potentials eλ, and obtain the other metric potentials (eν) under the embedding class one condition. we then compare the cases when ξ = χ = 0 [gr], ξ = 0 , χ = 0.5 [fl(r , t) ], ξ = 0.5 , χ = 0 [fs(r , t) ] and ξ = χ = 0.5 [fs+l(r , t) ]. the obtained solution is well-behaved in all physical and mathematical points of view. further, we provided a detailed physical acceptability of the solution by exploring main salient characteristics under different physical analysis in the linear f(r , t) - gravity. moreover, the generalizing m - r and m - i curves from our solution are well fitted with observational data of the three compact objects viz., psr j1614-2230, vela x-1 and 4u 1820-30. we also found the beautiful results that the equation of state (eos) is stiffest in χ = 0 than χ ≠ 0 , and the sensitivity in eos is better in i - m graph than in m - r graph. finally, we have successfully represented the effects of all the physical requirements in the arena of f(r , t) - gravity and we compared them with the standard gr results which can be recovered at χ = 0 . | physical properties of class i compact star model for linear and starobinsky - f(r , t) functions |
rare earth elements (ree) include the lanthanide series elements (la, ce, pr, nd, pm, sm, eu, gd, tb, dy, ho, er, tm, yb, and lu) plus sc and y. currently these metals have become very critical to several modern technologies ranging from cell phones and televisions to led light bulbs and wind turbines. this article summarizes the occurrence of these metals in the earth's crust, their mineralogy, different types of deposits both on land and oceans from the standpoint of the new data with more examples from the indian subcontinent. in addition to their utility to understand the formation of the major earth reservoirs, multi-faceted updates on the applications of ree in agriculture and medicine including new emerging ones are presented. environmental hazards including human health issues due to ree mining and large-scale dumping of e-waste containing significant concentrations of ree are summarized. new strategies for the future supply of ree including recent developments in the extraction of ree from coal fired ash and recycling from e-waste are presented. recent developments in individual ree separation technologies in both metallurgical and recycling operations have been highlighted. an outline of the analytical methods for their precise and accurate determinations required in all these studies, such as, x-ray fluorescence spectrometry (xrf), laser induced breakdown spectroscopy (libs), instrumental neutron activation analysis (inaa), inductively coupled plasma optical emission spectrometry (icp-oes), glow discharge mass spectrometry (gd-ms), inductively coupled plasma mass spectrometry (including icp-ms, icp-tof-ms, hr-icp-ms with laser ablation as well as solution nebulization) and other instrumental techniques, in different types of materials are presented. | rare earth elements: a review of applications, occurrence, exploration, analysis, recycling, and environmental impact |
magic is a system of two imaging atmospheric cherenkov telescopes located in the canary island of la palma, spain. during summer 2011 and 2012 it underwent a series of upgrades, involving the exchange of the magic-i camera and its trigger system, as well as the upgrade of the readout system of both telescopes. we use observations of the crab nebula taken at low and medium zenith angles to assess the key performance parameters of the magic stereo system. for low zenith angle observations, the standard trigger threshold of the magic telescopes is ∼ 50 gev. the integral sensitivity for point-like sources with crab nebula-like spectrum above 220 gev is (0.66 ± 0.03)% of crab nebula flux in 50 h of observations. the angular resolution, defined as the σ of a 2-dimensional gaussian distribution, at those energies is ≲ 0.07°, while the energy resolution is 16%. we also re-evaluate the effect of the systematic uncertainty on the data taken with the magic telescopes after the upgrade. we estimate that the systematic uncertainties can be divided in the following components: < 15% in energy scale, 11%-18% in flux normalization and ± 0.15 for the energy spectrum power-law slope. | the major upgrade of the magic telescopes, part ii: a performance study using observations of the crab nebula |
we present the first catalog of tev gamma-ray sources realized with data from the newly completed high altitude water cherenkov observatory (hawc). it is the most sensitive wide field-of-view tev telescope currently in operation, with a one-year survey sensitivity of ∼5%-10% of the flux of the crab nebula. with an instantaneous field of view >1.5 sr and >90% duty cycle, it continuously surveys and monitors the sky for gamma-ray energies between hundreds of gev and tens of tev. hawc is located in mexico, at a latitude of 19° n, and was completed in 2015 march. here, we present the 2hwc catalog, which is the result of the first source search performed with the complete hawc detector. realized with 507 days of data, it represents the most sensitive tev survey to date for such a large fraction of the sky. a total of 39 sources were detected, with an expected number of false detections of 0.5 due to background fluctuation. out of these sources, 19 are new sources that are not associated with previously known tev sources (association criteria: <0.°5 away). the source list, including the position measurement, spectrum measurement, and uncertainties, is reported, then each source is briefly discussed. of the 2hwc associated sources, 10 are reported in tevcat as pwn or snr: 2 as blazars and the remaining eight as unidentified. | the 2hwc hawc observatory gamma-ray catalog |
this paper presents and discusses algorithms, hardware, and software architecture developed by the team costar (collaborative subterranean autonomous robots), competing in the darpa subterranean challenge. specifically, it presents the techniques utilized within the tunnel (2019) and urban (2020) competitions, where costar achieved 2nd and 1st place, respectively. we also discuss costar's demonstrations in martian-analog surface and subsurface (lava tubes) exploration. the paper introduces our autonomy solution, referred to as nebula (networked belief-aware perceptual autonomy). nebula is an uncertainty-aware framework that aims at enabling resilient and modular autonomy solutions by performing reasoning and decision making in the belief space (space of probability distributions over the robot and world states). we discuss various components of the nebula framework, including: (i) geometric and semantic environment mapping; (ii) a multi-modal positioning system; (iii) traversability analysis and local planning; (iv) global motion planning and exploration behavior; (i) risk-aware mission planning; (vi) networking and decentralized reasoning; and (vii) learning-enabled adaptation. we discuss the performance of nebula on several robot types (e.g. wheeled, legged, flying), in various environments. we discuss the specific results and lessons learned from fielding this solution in the challenging courses of the darpa subterranean challenge competition. | nebula: quest for robotic autonomy in challenging environments; team costar at the darpa subterranean challenge |
language models (lms) can be directed to perform target tasks by using labeled examples or natural language prompts. but selecting examples or writing prompts for can be challenging--especially in tasks that involve unusual edge cases, demand precise articulation of nebulous preferences, or require an accurate mental model of lm behavior. we propose to use *lms themselves* to guide the task specification process. in this paper, we introduce **generative active task elicitation (gate)**: a learning framework in which models elicit and infer intended behavior through free-form, language-based interaction with users. we study gate in three domains: email validation, content recommendation, and moral reasoning. in preregistered experiments, we show that lms prompted to perform gate (e.g., by generating open-ended questions or synthesizing informative edge cases) elicit responses that are often more informative than user-written prompts or labels. users report that interactive task elicitation requires less effort than prompting or example labeling and surfaces novel considerations not initially anticipated by users. our findings suggest that lm-driven elicitation can be a powerful tool for aligning models to complex human preferences and values. | eliciting human preferences with language models |
we present our new atacama large millimeter/submillimeter array (alma) observations targeting [o iii]88 μm, [c ii]158 μm, [n ii]122 μm, and dust-continuum emission for three lyman break galaxies at z = 6.0293-6.2037, identified in the subaru/hyper suprime-cam survey. we clearly detect [o iii] and [c ii] lines from all of the galaxies at 4.3-11.8σ levels, and identify multi-band dust-continuum emission in two of the three galaxies, allowing us to estimate infrared luminosities and dust temperatures simultaneously. in conjunction with previous alma observations for six galaxies at z > 6, we confirm that all the nine z = 6-9 galaxies have high [o iii]/[c ii] ratios of ${l}_{[{\rm{o}}{\rm{iii}}]}/{l}_{[{\rm{c}}{\rm{ii}}]}\sim 3\mbox{--}20$, ∼10 times higher than z ∼ 0 galaxies. we also find a positive correlation between the [o iii]/[c ii] ratio and the lyα equivalent width (ew) at the ∼90% significance level. we carefully investigate physical origins of the high [o iii]/[c ii] ratios at z = 6-9 using cloudy, and find that high density of the interstellar medium, low c/o abundance ratio, and the cosmic microwave background attenuation are responsible to only a part of the z = 6-9 galaxies. instead, the observed high [o iii]/[c ii] ratios are explained by 10-100 times higher ionization parameters or low photodissociation region (pdr) covering fractions of 0%-10%, both of which are consistent with our [n ii] observations. the latter scenario can be reproduced with a density-bounded nebula with pdr deficit, which would enhance the lyα, lyman continuum, and ${{\rm{c}}}^{+}$ ionizing photons escape from galaxies, consistent with the [o iii]/[c ii]-lyα ew correlation we find. | large population of alma galaxies at z > 6 with very high [o iii] 88 μm to [c ii] 158 μm flux ratios: evidence of extremely high ionization parameter or pdr deficit? |
the crab nebula is the brightest tev gamma-ray source in the sky and has been used for the past 25 years as a reference source in tev astronomy, for calibration and verification of new tev instruments. the high altitude water cherenkov observatory (hawc), completed in early 2015, has been used to observe the crab nebula at high significance across nearly the full spectrum of energies to which hawc is sensitive. hawc is unique for its wide field of view, nearly 2 sr at any instant, and its high-energy reach, up to 100 tev. hawc’s sensitivity improves with the gamma-ray energy. above ∼1 tev the sensitivity is driven by the best background rejection and angular resolution ever achieved for a wide-field ground array. we present a time-integrated analysis of the crab using 507 live days of hawc data from 2014 november to 2016 june. the spectrum of the crab is fit to a function of the form φ {(e)={φ }0(e/{e}0)}-α -β \cdot {ln(e/{e}0)}. the data is well fitted with values of α = 2.63 ± 0.03, β = 0.15 ± 0.03, and {{log}}10({φ }0 {{cm}}2 {{s}} {tev})=-12.60+/- 0.02 when e 0 is fixed at 7 tev and the fit applies between 1 and 37 tev. study of the systematic errors in this hawc measurement is discussed and estimated to be ±50% in the photon flux between 1 and 37 tev. confirmation of the crab flux serves to establish the hawc instrument’s sensitivity for surveys of the sky. the hawc all-sky survey will be the deepest survey of the northern sky ever conducted in the multi-tev band. | observation of the crab nebula with the hawc gamma-ray observatory |
we use integral field spectroscopy from the phangs-muse survey, which resolves the ionised interstellar medium structure at ∼50 pc resolution in 19 nearby spiral galaxies, to study the origin of the diffuse ionised gas (dig). we examine the physical conditions of the diffuse gas by first removing morphologically defined h ii regions and then binning the low-surface-brightness areas to achieve significant detections of the key nebular lines in the dig. a simple model for the leakage and propagation of ionising radiation from h ii regions is able to reproduce the observed distribution of hα in the dig. this model infers a typical mean free path for the ionising radiation of 1.9 kpc for photons propagating within the disc plane. leaking radiation from h ii regions also explains the observed decrease in line ratios of low-ionisation species ([s ii]/hα, [n ii]/hα, and [o i]/hα) with increasing hα surface brightness (σhα). emission from hot low-mass evolved stars, however, is required to explain: (1) the enhanced low-ionisation line ratios observed in the central regions of some of the galaxies in our sample; (2) the observed trends of a flat or decreasing [o iii]/hβ with σhα; and (3) the offset of some dig regions from the typical locus of h ii regions in the baldwin-phillips-terlevich (bpt) diagram, extending into the area of low-ionisation (nuclear) emission-line regions (li[n]ers). hot low-mass evolved stars make a small contribution to the energy budget of the dig (2% of the galaxy-integrated hα emission), but their harder spectra make them fundamental contributors to [o iii] emission. the dig might result from a superposition of two components, an energetically dominant contribution from young stars and a more diffuse background of harder ionising photons from old stars. this unified framework bridges observations of the milky way dig with li(n)er-like emission observed in nearby galaxy bulges. | a tale of two digs: the relative role of h ii regions and low-mass hot evolved stars in powering the diffuse ionised gas (dig) in phangs-muse galaxies |
for some decades now, nanotechnology has been touted as the 'next big thing' with potential impact comparable to the steam, electricity or internet revolutions -- but has it lived up to these expectations? while advances in top-down nanolithography, now reaching 10-nm resolution, have resulted in devices that are rapidly approaching mass production, attempts to produce nanoscale devices using bottom-up approaches have met with only limited success. we have been inundated with nanoparticles of almost any shape, material and composition, but their societal impact has been far from revolutionary, with growing concerns over their toxicity. despite nebulous hopes that making hierarchical nanomaterials will lead to new, emergent properties, no breakthrough applications seem imminent. in this perspective, we argue that the time is ripe to look beyond individual nano-objects and their static assemblies, and instead focus on systems comprising different types of 'nanoparts' interacting and/or communicating with one another to perform desired functions. such systems are interesting for a variety of reasons: they can act autonomously without external electrical or optical connections, can be dynamic and reconfigurable, and can act as 'nanomachines' by directing the flow of mass, energy or information . in thinking how this systems nanoscience approach could be implemented to design useful -- as opposed to toy-model -- nanosystems, our choice of applications and our nanoengineering should be inspired by living matter. | the nanotechnology of life-inspired systems |
when a star is tidally disrupted by a supermassive black hole (smbh), roughly half of its mass falls back to the smbh at super-eddington rates. as this gas is tenuously gravitationally bound and unable to cool radiatively, only a small fraction fin ≪ 1 may accrete, with the majority instead becoming unbound in an outflow of velocity ∼104 km s-1. the outflow spreads laterally as it expands to large radii, encasing the smbh and blocking the inner disc's euv/x-ray radiation, which becomes trapped in a radiation-dominated nebula. ionizing nebular radiation heats the inner edge of the ejecta, converting the emission to optical/near-uv wavelengths where photons more readily escape due to the lower opacity. this can explain the unexpectedly low and temporally constant effective temperatures of optically discovered tidal disruption event (tde) flares. for high-mass smbhs, m• ≳ 107 m⊙, the ejecta can become fully ionized at an earlier stage, or for a wider range of viewing angles, producing a tde flare accompanied by thermal x-ray emission. the peak optical luminosity is suppressed as the result of adiabatic losses in the inner disc wind when m• ≪ 107 m⊙, possibly contributing to the unexpected dearth of optical tdes in galaxies with low-mass smbhs. in the classical picture, where fin ≈ 1, tdes de-spin supermassive smbhs and cap their maximum spins well below theoretical accretion physics limits. this cap is relaxed in our model, and existing fe kα spin measurements provide preliminary evidence that fin < 1. | a bright year for tidal disruptions |
we present photometric and spectroscopic data for sn 2022joj, a nearby peculiar type ia supernova (sn ia) with a fast decline rate ($\rm{\delta m_{15,b}=1.4}$ mag). sn 2022joj shows exceedingly red colors, with a value of approximately ${b-v \approx 1.1}$ mag during its initial stages, beginning from $11$ days before maximum brightness. as it evolves the flux shifts towards the blue end of the spectrum, approaching ${b-v \approx 0}$ mag around maximum light. furthermore, at maximum light and beyond, the photometry is consistent with that of typical sne ia. this unusual behavior extends to its spectral characteristics, which initially displayed a red spectrum and later evolved to exhibit greater consistency with typical sne ia. we consider two potential explanations for this behavior: double detonation from a helium shell on a sub-chandrasekhar-mass white dwarf and chandrasekhar-mass models with a shallow distribution of $\rm{^{56}ni}$. the shallow nickel models could not reproduce the red colors in the early light curves. spectroscopically, we find strong agreement between sn 2022joj and double-detonation models with white dwarf masses around 1 $\rm{m_{\odot}}$ and thin he-shell between 0.01 and 0.02 $\rm{m_{\odot}}$. moreover, the early red colors are explained by line-blanketing absorption from iron-peak elements created by the double detonation scenario in similar mass ranges. however, the nebular spectra composition in sn 2022joj deviates from expectations for double detonation, as we observe strong [fe iii] emission instead of [ca ii] lines as anticipated from double detonation models. more detailed modeling, e.g., including viewing angle effects, is required to test if double detonation models can explain the nebular spectra. | sn 2022joj: a potential double detonation with a thin helium shell |
we report on the highest energy photons from the crab nebula observed by the tibet air shower array with the underground water-cherenkov-type muon detector array. based on the criterion of a muon number measured in an air shower, we successfully suppress 99.92% of the cosmic-ray background events with energies e >100 tev . as a result, we observed 24 photonlike events with e >100 tev against 5.5 background events, which corresponds to a 5.6 σ statistical significance. this is the first detection of photons with e >100 tev from an astrophysical source. | first detection of photons with energy beyond 100 tev from an astrophysical source |
we present tev gamma-ray observations of the crab nebula, the standard reference source in ground-based gamma-ray astronomy, using data from the high altitude water cherenkov (hawc) gamma-ray observatory. in this analysis we use two independent energy estimation methods that utilize extensive air shower variables such as the core position, shower angle, and shower lateral energy distribution. in contrast, the previously published hawc energy spectrum roughly estimated the shower energy with only the number of photomultipliers triggered. this new methodology yields a much-improved energy resolution over the previous analysis and extends hawc’s ability to accurately measure gamma-ray energies well beyond 100 tev. the energy spectrum of the crab nebula is well fit to a log-parabola shape ≤ft(\tfrac{{dn}}{{de}}={φ }0{≤ft(e/7{tev}\right)}-α -β {ln≤ft(e/7{tev}\right)}\right) with emission up to at least 100 tev. for the first estimator, a ground parameter that utilizes fits to the lateral distribution function to measure the charge density 40 m from the shower axis, the best-fit values are {φ }o=(2.35+/- {0.04}-0.21+0.20)× {10}-13 (tev cm2 s)-1, α =2.79+/- {0.02}-0.03+0.01, and β =0.10+/- {0.01}-0.03+0.01. for the second estimator, a neural network that uses the charge distribution in annuli around the core and other variables, these values are {φ }o=(2.31+/- {0.02}-0.17+0.32)× {10}-13 (tev cm2 s)-1, α =2.73+/- {0.02}-0.02+0.03, and β = 0.06 ± 0.01 ± 0.02. the first set of uncertainties is statistical; the second set is systematic. both methods yield compatible results. these measurements are the highest-energy observation of a gamma-ray source to date. | measurement of the crab nebula spectrum past 100 tev with hawc |
forthcoming observational facilities will make the exploration of the early universe routine, likely probing large populations of galaxies at very low metallicities. it will therefore be important to have diagnostics that can solidly identify and distinguish different classes of objects in such low metallicity regimes. we use new photoionization models to develop diagnostic diagrams involving various nebular lines. we show that combinations of these diagrams allow the identification and discrimination of the following classes of objects in the early universe: popiii and direct collapse black holes (dcbh) in pristine environments, popiii and dcbh embedded in slightly enriched interstellar medium (ism; $\rm z\sim 10^{-5}-10^{-4}$), and (metal poor) popii and active galactic nucleus in enriched ism. diagnostics involving rest-frame optical lines (that will be accessible by james webb space telescope) have a better discriminatory power but also rest-frame ultraviolet diagnostics can provide very useful information. interestingly, we find that metal lines such as [o iii]λ5007 and c ivλ1549 can remain relatively strong (about a factor of 0.1-1 relative h β and he iiλ1640, respectively), even in extremely metal poor environments ($\rm z\sim 10^{-5}-10^{-4}$), which could be embedding popiii galaxies and dcbh. | diagnostics for popiii galaxies and direct collapse black holes in the early universe |
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