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by using observations of the hulse-taylor pulsar, we constrain the gravitational wave (gw) speed to the level of 1 0-2 . we apply this result to scalar-tensor theories that generalize galileon 4 and 5 models, which display anomalous propagation speed and coupling to matter for gws. we argue that this effect survives conventional screening due to the persistence of a scalar field gradient inside virialized overdensities, which effectively "pierces" the vainshtein screening. in specific branches of solutions, our result allows us to directly constrain the cosmological couplings in the effective field theory of dark energy formalism. | evading the vainshtein mechanism with anomalous gravitational wave speed: constraints on modified gravity from binary pulsars |
context. the environment of sagittarius a* (sgr a*), the central black hole of the milky way, is the only place in the universe where we can currently study the interaction between a nuclear star cluster and a massive black hole and infer the properties of a nuclear cluster from observations of individual stars.aims: this work aims to explore the star formation history of the nuclear cluster and the structure of the innermost stellar cusp around sgr a*.methods: we combined and analysed multi epoch high quality ao observations. for the region close to sgr a* we apply the speckle holography technique to the ao data and obtain images that are ≥50% complete down to ks ≈ 19 within a projected radius of 5″ around sgr a*. we used h-band images to derive extinction maps.results: we provide ks photometry for roughly 39 000 stars and h-band photometry for ∼11 000 stars within a field of about 40″ × 40″, centred on sgr a*. in addition, we provide ks photometry of ∼3000 stars in a very deep central field of 10″ × 10″, centred on sgr a*. we find that the ks luminosity function (klf) is rather homogeneous within the studied field and does not show any significant changes as a function of distance from the central black hole on scales of a few 0.1 pc. by fitting theoretical luminosity functions to the klf, we derive the star formation history of the nuclear star cluster. we find that about 80% of the original star formation took place 10 gyr ago or longer, followed by a largely quiescent phase that lasted for more than 5 gyr. we clearly detect the presence of intermediate-age stars of about 3 gyr in age. this event makes up about 15% of the originally formed stellar mass of the cluster. a few percent of the stellar mass formed in the past few 100 myr. our results appear to be inconsistent with a quasi-continuous star formation history. the mean metallicity of the stars is consistent with being slightly super solar. the stellar density increases exponentially towards sgr a* at all magnitudes between ks = 15-19. we also show that the precise properties of the stellar cusp around sgr a* are hard to determine because the star formation history suggests that the star counts can be significantly contaminated, at all magnitudes, by stars that are too young to be dynamically relaxed. we find that the probability of observing any young (non-millisecond) pulsar in a tight orbit around sgr a* and beamed towards earth is very low. we argue that typical globular clusters, such as they are observed in and around the milky way today, have probably not contributed to the nuclear cluster's mass in any significant way. the nuclear cluster may have formed following major merger events in the early history of the milky way. full tables c.1 and c.2 and reduced images are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/641/a102 | the milky way's nuclear star cluster: old, metal-rich, and cuspy. structure and star formation history from deep imaging |
this paper presents the new photometer ce318-t, able to perform daytime and night-time photometric measurements using the sun and the moon as light source. therefore, this new device permits a complete cycle of diurnal aerosol and water vapour measurements valuable to enhance atmospheric monitoring to be extracted. in this study we have found significantly higher precision of triplets when comparing the ce318-t master instrument and the cimel aerosol robotic network (aeronet) master (ce318-aeronet) triplets as a result of the new ce318-t tracking system. regarding the instrument calibration, two new methodologies to transfer the calibration from a reference instrument using only daytime measurements (sun ratio and sun-moon gain factor techniques) are presented and discussed. these methods allow the reduction of the previous complexities inherent to nocturnal calibration. a quantitative estimation of ce318-t aod uncertainty by means of error propagation theory during daytime revealed aod uncertainties (udaod) for langley-calibrated instruments similar to the expected values for other reference instruments (0.002-0.009). we have also found udaod values similar to the values reported in sun photometry for field instruments ( ∼ 0.015). in the case of the night-time period, the ce318-t-estimated standard combined uncertainty (unaod) is dependent not only on the calibration technique but also on illumination conditions and the instrumental noise. these values range from 0.011-0.018 for lunar langley-calibrated instruments to 0.012-0.021 for instruments calibrated using the sun ratio technique. in the case of moon-calibrated instruments using the sun-moon gain factor method and sun-calibrated using the langley technique, we found unaod ranging from 0.016 to 0.017 (up to 0.019 in 440 nm channel), not dependent on any lunar irradiance model.a subsequent performance evaluation including ce318-t and collocated measurements from independent reference instruments has served to assess the ce318-t performance as well as to confirm its estimated uncertainty. daytime aod evaluation, performed at izaña station from march to june 2014, encompassed measurements from a reference ce318-t, a ce318-aeronet master instrument, a precision filter radiometer (pfr) and a precision spectroradiometer (psr) prototype, reporting low aod discrepancies between the four instruments (up to 0.006). the nocturnal aod evaluation was performed using ce318-t- and star-photometer-collocated measurements and also by means of a day/night coherence transition test using the ce318-t master instrument and the ce318 daytime data from the ce318-aeronet master instrument. results showed low discrepancies with the star photometer at 870 and 500 nm channels ( ≤ 0.013) and differences with aeronet daytime data (1 h after and before sunset and sunrise) in agreement with the estimated unaod values at all illumination conditions in the case of channels within the visible spectral range, and only for high moon's illumination conditions in the case of near-infrared channels.precipitable water vapour (pwv) validation showed a good agreement between ce318-t and global navigation satellite system (gnss) pwv values for all illumination conditions, within the expected precision for sun photometry.finally, two case studies have been included to highlight the ability of the new ce318-t to capture the diurnal cycle of aerosols and water vapour as well as short-term atmospheric variations, critical for climate studies. | the new sun-sky-lunar cimel ce318-t multiband photometer - a comprehensive performance evaluation |
there is growing evidence that the galactic center excess identified in the fermi-lat gamma-ray data arises from a population of faint astrophysical sources. we provide compelling supporting evidence by showing that the morphology of the excess traces the stellar over-density of the galactic bulge. by adopting a template of the bulge stars obtained from a triaxial 3d fit to the diffuse near-infrared emission, we show that it is detected at high significance. the significance deteriorates when either the position or the orientation of the template is artificially shifted, supporting the correlation of the gamma-ray data with the galactic bulge. in deriving these results, we have used more sophisticated templates at low-latitudes for the fermi bubbles compared to previous work and the three-dimensional inverse compton (ic) maps recently released by the galprop team. our results provide strong constraints on millisecond pulsar (msp) formation scenarios proposed to explain the excess. we find that an admixture formation scenario, in which some of the relevant binaries are primordial and the rest are formed dynamically, is preferred over a primordial-only formation scenario at 7.6σ confidence level. our detailed morphological analysis also disfavors models of the disrupted globular clusters scenario that predict a spherically symmetric distribution of msps in the galactic bulge. for the first time, we report evidence of a high energy tail in the nuclear bulge spectrum that could be the result of ic emission from electrons and positrons injected by a population of msps and star formation activity from the same site. | strong evidence that the galactic bulge is shining in gamma rays |
magnetic reconnection is a leading mechanism for dissipating magnetic energy and accelerating nonthermal particles in poynting-flux-dominated flows. in this letter, we investigate nonthermal particle acceleration during magnetic reconnection in a magnetically dominated ion-electron plasma using fully kinetic simulations. for an ion-electron plasma with a total magnetization of {σ }0={b}2/(4π n({m}i+{m}e){c}2), the magnetization for each species is {σ }i∼ {σ }0 and {σ }e∼ ({m}i/{m}e){σ }0, respectively. we have studied the magnetically dominated regime by varying σe = 103-105 with initial ion and electron temperatures {t}i={t}e=5-20{m}e{c}2 and mass ratio {m}i/{m}e=1-1836. the results demonstrate that reconnection quickly establishes power-law energy distributions for both electrons and ions within several (2-3) light-crossing times. for the cases with periodic boundary conditions, the power-law index is 1\lt s\lt 2 for both electrons and ions. the hard spectra limit the power-law energies for electrons and ions to be {γ }{be}∼ {σ }e and {γ }{bi}∼ {σ }i, respectively. the main acceleration mechanism is a fermi-like acceleration through the drift motions of charged particles. when comparing the spectra for electrons and ions in momentum space, the spectral indices sp are identical as predicted in fermi acceleration. we also find that the bulk flow can carry a significant amount of energy during the simulations. we discuss the implication of this study in the context of poynting-flux dominated jets and pulsar winds, especially the applications for explaining nonthermal high-energy emissions. | efficient production of high-energy nonthermal particles during magnetic reconnection in a magnetically dominated ion-electron plasma |
accreting millisecond x-ray pulsars (amxps) are an important subset of low-mass x-ray binaries (lmxbs) in which coherent x-ray pulsations can be observed during occasional, bright outbursts (x-ray luminosity {l}{{x}}∼ {10}36 {erg} {{{s}}}-1). these pulsations show that matter is being channeled onto the neutron star’s magnetic poles. however, such sources spend most of their time in a low-luminosity, quiescent state ({l}{{x}}≲ {10}34 {erg} {{{s}}}-1), where the nature of the accretion flow onto the neutron star (if any) is not well understood. here we report that the millisecond pulsar/lmxb transition object psr j1023+0038 intermittently shows coherent x-ray pulsations at luminosities nearly 100 times fainter than observed in any other amxp. we conclude that in spite of its low luminosity, psr j1023+0038 experiences episodes of channeled accretion, a discovery that challenges existing models for accretion onto magnetized neutron stars. | accretion-powered pulsations in an apparently quiescent neutron star binary |
this study explores the implications of dark matter in neutron stars (dmans) by focusing on two specific astronomical objects: hess j1731-347 and psr j0952-0607. varying the fermi momentum k$f^{\rm dm}$ of dm, the study analyzes the eos for the inrs model with and without dm. results show the robustness of the model, with most eos curves within chiral effective field theory bounds. our model predicts a maximum mass of $2.343 \ m_\odot$ for psr j0952-0607, satisfying nicer bounds. the analysis suggests hess j1731-347 could be a dmans. constraints on dm within nss are established, and tidal deformability lies within gw event limits. nonradial $f$-mode oscillations increase with dm, concluding low mass stars pulsate at higher frequencies. | dark matter admixed neutron star in the light of hess j1731-347 and psr j0952-0607 |
the possible detection of a compact object in the remnant of sn 1987a presents an unprecedented opportunity to follow its early evolution. the suspected detection stems from an excess of infrared emission from a dust blob near the compact object's predicted position. the infrared excess could be due to the decay of isotopes like 44ti, accretion luminosity from a neutron star or black hole, magnetospheric emission or a wind originating from the spin down of a pulsar, or to thermal emission from an embedded, cooling neutron star (ns 1987a). it is shown that the last possibility is the most plausible as the other explanations are disfavored by other observations and/or require fine-tuning of parameters. not only are there indications that the dust blob overlaps the predicted location of a kicked compact remnant, but its excess luminosity also matches the expected thermal power of a 30 yr old neutron star. furthermore, models of cooling neutron stars within the minimal cooling paradigm readily fit both ns 1987a and cas a, the next-youngest known neutron star. if correct, a long heat transport timescale in the crust and a large effective stellar temperature are favored, implying relatively limited crustal n-1s0 superfluidity and an envelope with a thick layer of light elements, respectively. if the locations do not overlap, then pulsar spin down or accretion might be more likely, but the pulsar's period and magnetic field or the accretion rate must be rather finely tuned. in this case, ns 1987a may have enhanced cooling and/or a heavy-element envelope. | ns 1987a in sn 1987a |
we present a search for continuous gravitational-wave emission due to r-modes in the pulsar psr j0537-6910 using data from the ligo-virgo collaboration observing run o3. psr j0537-6910 is a young energetic x-ray pulsar and is the most frequent glitcher known. the inter-glitch braking index of the pulsar suggests that gravitational-wave emission due to r-mode oscillations may play an important role in the spin evolution of this pulsar. theoretical models confirm this possibility and predict emission at a level that can be probed by ground-based detectors. in order to explore this scenario, we search for r-mode emission in the epochs between glitches by using a contemporaneous timing ephemeris obtained from nicer data. we do not detect any signals in the theoretically expected band of 86-97 hz, and report upper limits on the amplitude of the gravitational waves. our results improve on previous amplitude upper limits from r-modes in j0537-6910 by a factor of up to 3 and place stringent constraints on theoretical models for r-mode-driven spin-down in psr j0537-6910, especially for higher frequencies at which our results reach below the spin-down limit defined by energy conservation. | constraints from ligo o3 data on gravitational-wave emission due to r-modes in the glitching pulsar psr j0537-6910 |
gravitational wave detectors are formidable tools to explore strong-field gravity, especially black holes and neutron stars. these compact objects are extraordinarily efficient at producing electromagnetic and gravitational radiation. as such, they are ideal laboratories for fundamental physics and have an immense discovery potential. the detection of black hole binaries by third-generation earth-based detectors, space-based detectors and pulsar timing arrays will provide exquisite tests of general relativity. loud "golden" events and extreme mass-ratio inspirals can strengthen the observational evidence for horizons by mapping the exterior spacetime geometry, inform us on possible near-horizon modifications, and perhaps reveal a breakdown of einstein's gravity. measurements of the black-hole spin distribution and continuous gravitational-wave searches can turn black holes into efficient detectors of ultralight bosons across ten or more orders of magnitude in mass. a precise monitoring of the phase of inspiralling binaries can constrain the existence of additional propagating fields and characterize the environment in which the binaries live, bounding the local dark matter density and properties. gravitational waves from compact binaries will probe general relativity and fundamental physics in previously inaccessible regimes, and allow us to address fundamental issues in our current understanding of the cosmos. | snowmass2021 cosmic frontier white paper: fundamental physics and beyond the standard model |
several pulsar timing array (pta) collaborations recently announced the first detection of a stochastic gravitational wave (gw) background, leaving open the question of its source. we explore the possibility that it originates from cosmic inflation, a guaranteed source of primordial gw. the inflationary gw background amplitude is enhanced at pta scales by a non-standard early cosmological evolution, driven by dirac-born-infeld (dbi) scalar dynamics motivated by string theory. the resulting gw energy density has a broken power-law frequency profile, entering the pta band with a peak amplitude consistent with the recent gw detection. after this initial dbi kination epoch, the dynamics starts a new phase mainly controlled by the scalar potential. it provides a realization of an early dark energy scenario aimed at relaxing the h 0 tension, and a late dark energy model which explains the current cosmological acceleration with no need of a cosmological constant. hence our mechanism - besides providing a possible explanation for the recent pta results - connects them with testable properties of the physics of the dark universe. | dark energy, d-branes and pulsar timing arrays |
in the axion monodromy inflation, the inflation is driven by the axion with super-planckian field values in a monomial potential with superimposed sinusoidal modulations. the coupling of the axion to massless gauge fields can induce copious particle production during inflation, resulting in large non-gaussian curvature perturbation that leads to the formation of primordial black holes. in this paper, we explore the parameter space in the axion monodromy inflation model that favors the formation of primordial black holes with masses ranging from 108 grams to 20 solar masses. we also study the associated gravitational waves and their detection in pulsar timing arrays and interferometry experiments. | primordial black holes and associated gravitational waves in axion monodromy inflation |
the discovery of two neutron star-black hole coalescences by ligo and virgo brings the total number of likely neutron stars observed in gravitational waves to six. we perform the first inference of the mass distribution of this extragalactic population of neutron stars. in contrast to the bimodal galactic population detected primarily as radio pulsars, the masses of neutron stars in gravitational-wave binaries are thus far consistent with a uniform distribution, with a greater prevalence of high-mass neutron stars. the maximum mass in the gravitational-wave population agrees with that inferred from the neutron stars in our galaxy and with expectations from dense matter. | the mass distribution of neutron stars in gravitational-wave binaries |
we describe the survey for pulsars and extragalactic radio bursts (superb), an ongoing pulsar and fast transient survey using the parkes radio telescope. superb involves real-time acceleration searches for pulsars and single-pulse searches for pulsars and fast radio bursts. we report on the observational set-up, data analysis, multiwavelength/messenger connections, survey sensitivities to pulsars and fast radio bursts and the impact of radio frequency interference. we further report on the first 10 pulsars discovered in the project. among these is psr j1306-40, a millisecond pulsar in a binary system where it appears to be eclipsed for a large fraction of the orbit. psr j1421-4407 is another binary millisecond pulsar; its orbital period is 30.7 d. this orbital period is in a range where only highly eccentric binaries are known, and expected by theory; despite this its orbit has an eccentricity of 10-5. | the survey for pulsars and extragalactic radio bursts - i. survey description and overview |
if cosmic strings are formed in the early universe, their associated loops emit gravitational waves during the whole cosmic history and contribute to the stochastic gravitational wave background at all frequencies. we provide a new estimate of the stochastic gravitational wave spectrum by considering a realistic cosmological loop distribution, in scaling, as it can be inferred from nambu-goto numerical simulations. our result takes into account various effects neglected so far. we include both gravitational wave emission and backreaction effects on the loop distribution and show that they produce two distinct features in the spectrum. concerning the string microstructure, in addition to the presence of cusps and kinks, we show that gravitational wave bursts created by the collision of kinks could dominate the signal for wiggly strings, a situation which may be favoured in the light of recent numerical simulations. in view of these new results, we propose four prototypical scenarios, within the margin of the remaining theoretical uncertainties, for which we derive the corresponding signal and estimate the constraints on the string tension put by both the ligo and european pulsar timing array (epta) observations. the less constrained of these scenarios is shown to have a string tension gu <= 7.2 × 10-11, at 95% of confidence. smooth loops carrying two cusps per oscillation verify the two-sigma bound gu <= 1.0 × 10-11 while the most constrained of all scenarios describes very kinky loops and satisfies gu <= 6.7× 10-14 at 95% of confidence. | stochastic gravitational waves from cosmic string loops in scaling |
we describe the aperture tile in focus (apertif) system, a phased array feed (paf) upgrade of the westerbork synthesis radio telescope that transforms this telescope into a high-sensitivity, wide-field-of-view l-band imaging and transient survey instrument. using novel paf technology, up to 40 partially overlapping beams are formed on the sky simultaneously, significantly increasing the survey speed of the telescope. with this upgraded instrument, an imaging survey covering an area of 2300 deg2 is being performed that will deliver both continuum and spectral line datasets, of which the first data have been publicly released. in addition, a time domain transient and pulsar survey covering 15 000 deg2 is in progress. an overview of the apertif science drivers, hardware, and software of the upgraded telescope is presented, along with its key performance characteristics. | apertif: phased array feeds for the westerbork synthesis radio telescope. system overview and performance characteristics |
we study a family of equations of state (eos) for hybrid neutron star matter. the hybrid eos are obtained by a maxwell construction of the first-order phase transition between a hadronic phase described by the relativistic density-functional eos of the "dd2" class with excluded volume effects and a deconfined quark matter phase modeled by an instantaneous nonlocal version of the nambu-jona-lasinio model in su(2) f with vector interactions and color superconductivity. the form factor in the nonlocal quark matter model is fitted to lattice qcd results in the coulomb gauge. owing to strong coupling in the vector meson and diquark channels, a coexistence phase of color superconductivity and chiral symmetry breaking occurs. our results show an approximately constant behavior for the squared speed of sound with values of 0.4-0.6 in the density region relevant for neutron star interiors. to simultaneously fulfill the constraints from the neutron star interior composition explorer radius measurement for psr j 0740 +6620 and tidal deformability from gw170817 it is necessary to consider a μ -dependent bag pressure that mimics confinement. | quark-nuclear hybrid equation of state for neutron stars under modern observational constraints |
the variables and slow transients survey (vast) on the australian square kilometre array pathfinder (askap) is designed to detect highly variable and transient radio sources on timescales from 5 s to $∼ 5$ yr. in this paper, we present the survey description, observation strategy and initial results from the vast phase i pilot survey. this pilot survey consists of $∼ 162$ h of observations conducted at a central frequency of 888 mhz between 2019 august and 2020 august, with a typical rms sensitivity of $0.24 mjy beam^{-1}$ and angular resolution of $12-20$ arcseconds. there are 113 fields, each of which was observed for 12 min integration time, with between 5 and 13 repeats, with cadences between 1 day and 8 months. the total area of the pilot survey footprint is 5 131 square degrees, covering six distinct regions of the sky. an initial search of two of these regions, totalling 1 646 square degrees, revealed 28 highly variable and/or transient sources. seven of these are known pulsars, including the millisecond pulsar j2039-5617. another seven are stars, four of which have no previously reported radio detection (scr j0533-4257, lehpm 2-783, ucac3 89-412162 and 2mass j22414436-6119311). of the remaining 14 sources, two are active galactic nuclei, six are associated with galaxies and the other six have no multi-wavelength counterparts and are yet to be identified. | the askap variables and slow transients (vast) pilot survey |
we report the discovery of psr j1757-1854, a 21.5-ms pulsar in a highly-eccentric, 4.4-h orbit with a neutron star (ns) companion. psr j1757-1854 exhibits some of the most extreme relativistic parameters of any known pulsar, including the strongest relativistic effects due to gravitational-wave damping, with a merger time of 76 myr. following a 1.6-yr timing campaign, we have measured five post-keplerian parameters, yielding the two component masses (mp = 1.3384(9) m⊙ and mc = 1.3946(9) m⊙) plus three tests of general relativity, which the theory passes. the larger mass of the ns companion provides important clues regarding the binary formation of psr j1757-1854. with simulations suggesting 3-σ measurements of both the contribution of lense-thirring precession to the rate of change of the semimajor axis and the relativistic deformation of the orbit within ∼7-9 yr, psr j1757-1854 stands out as a unique laboratory for new tests of gravitational theories. | the high time resolution universe pulsar survey - xiii. psr j1757-1854, the most accelerated binary pulsar |
dark matter substructure on small scales is currently weakly constrained, and its study may shed light on the nature of the dark matter. in this work we study the gravitational effects of dark matter substructure on measured pulsar phases in pulsar timing arrays (ptas). due to the stability of pulse phases observed over several years, dark matter substructure around the earth-pulsar system can imprint discernible signatures in gravitational doppler and shapiro delays. we compute pulsar phase correlations induced by general dark matter substructure, and project constraints for a few models such as monochromatic primordial black holes (pbhs), and cold dark matter (cdm)-like nfw subhalos. this work extends our previous analysis, which focused on static or single transiting events, to a stochastic analysis of multiple transiting events. we find that stochastic correlations, in a pta similar to the square kilometer array (ska), are uniquely powerful to constrain subhalos as light as ~ 10-13 msolar, with concentrations as low as that predicted by standard cdm. | observability of dark matter substructure with pulsar timing correlations |
gravitational wave memory is theorized to arise from the integrated history of gravitational wave emission, and manifests as a spacetime deformation in the wake of a propagating gravitational wave. we explore the detectability of the memory signals from a population of coalescencing supermassive black hole binaries with pulsar timing arrays and the laser interferometer space antenna (lisa). we find that current pulsar timing arrays have poor prospects, but it is likely that between 1 and 10 memory events with signal-to-noise ratio in excess of 5 will occur within lisa's planned 4-year mission. | prospects for memory detection with low-frequency gravitational wave detectors |
we study the dynamics of (i) neutral test particles, (ii) magnetically charged test particles, and (iii) test magnetic dipole around a regular bardeen black hole surrounded by perfect fluid dark matter (pfdm). it has been shown how the magnetic charge of the black hole and the parameter of the surrounding pfdm can influence the innermost stable circular orbit (isco) radius of a test particle. we have found that the isco radius is strongly affected as a consequence of the combined effect of the magnetic charge parameter and the perfect fluid dark matter. the black hole magnetic charge parameter g and the combined effect of perfect fluid dark matter can mimic the black hole rotation parameter up to a /m ≈0.9 . it has been observed that the isco for magnetic dipole disappears at the values exceeding the calculated upper value for the magnetic interaction parameter β . the upper limit decreases with the increase of both the dark matter and magnetic charge parameters. finally, as an astrophysical application, we have analyzed degeneracy effects of spin of kerr black holes and magnetic charge of regular bardeen black holes for the different values of the dark matter parameter providing exactly the same value for isco radius of a magnetic dipole with the same value of the parameter β =10.2 of the magnetar called psr j1745-2900 orbiting around supermassive black hole sagittarius a*. it has been observed that the magnetic charge of the pure regular bardeen black hole can mimic the spin of a kerr black hole up to a /m ≃0.8085 , while upper limit for the magnetic charge which may provide isco for the magnetic dipole is gupper≃0.65 m . in the presence of pfdm with the parameter α =0.01 (0.05 ), the upper limit for the magnetic charge decreases and equals to gupper≃0.62 m (0.548 m ) and consequently mimicker value for the spin parameter of black hole lies in the range of a /m ∈(0.0106 ÷0.8231 ) (a /m ∈(0.0816 ÷0.8595 )). we also show that the same values of the spin of kerr black hole and the magnetic charge of regular bardeen black hole surrounded by pfdm provide the same values for the isco radius of the chosen magnetar. | dynamics of test particles around a bardeen black hole surrounded by perfect fluid dark matter |
we explore the correlation of γ-ray emitting blazars with icecube neutrinos by using three very recently completed, and independently built, catalogues and the latest neutrino lists. we introduce a new observable, namely the number of neutrino events with at least one γ-ray counterpart, nν. in all three catalogues we consistently observe a positive fluctuation of nν with respect to the mean random expectation at a significance level of 0.4-1.3 per cent. this applies only to extreme blazars, namely strong, very high energy γ-ray sources of the high energy peaked type, and implies a model-independent fraction of the current icecube signal ∼10-20 per cent. an investigation of the hybrid photon - neutrino spectral energy distributions of the most likely candidates reveals a set of ≈5 such sources, which could be linked to the corresponding icecube neutrinos. other types of blazars, when testable, give null correlation results. although we could not perform a similar correlation study for galactic sources, we have also identified two (further) strong galactic γ-ray sources as most probable counterparts of icecube neutrinos through their hybrid spectral energy distributions. we have reasons to believe that our blazar results are not constrained by the γ-ray samples but by the neutrino statistics, which means that the detection of more astrophysical neutrinos could turn this first hint into a discovery. | extreme blazars as counterparts of icecube astrophysical neutrinos |
partial observability -- where agents can only observe partial information about the true underlying state of the system -- is ubiquitous in real-world applications of reinforcement learning (rl). theoretically, learning a near-optimal policy under partial observability is known to be hard in the worst case due to an exponential sample complexity lower bound. recent work has identified several tractable subclasses that are learnable with polynomial samples, such as partially observable markov decision processes (pomdps) with certain revealing or decodability conditions. however, this line of research is still in its infancy, where (1) unified structural conditions enabling sample-efficient learning are lacking; (2) existing sample complexities for known tractable subclasses are far from sharp; and (3) fewer sample-efficient algorithms are available than in fully observable rl. this paper advances all three aspects above for partially observable rl in the general setting of predictive state representations (psrs). first, we propose a natural and unified structural condition for psrs called \emph{b-stability}. b-stable psrs encompasses the vast majority of known tractable subclasses such as weakly revealing pomdps, low-rank future-sufficient pomdps, decodable pomdps, and regular psrs. next, we show that any b-stable psr can be learned with polynomial samples in relevant problem parameters. when instantiated in the aforementioned subclasses, our sample complexities improve substantially over the current best ones. finally, our results are achieved by three algorithms simultaneously: optimistic maximum likelihood estimation, estimation-to-decisions, and model-based optimistic posterior sampling. the latter two algorithms are new for sample-efficient learning of pomdps/psrs. | partially observable rl with b-stability: unified structural condition and sharp sample-efficient algorithms |
we report on imaging x-ray polarimetry explorer (ixpe) observations of the be-transient x-ray pulsar ls v +44 17/rx j0440.9+4431 made at two luminosity levels during the giant outburst in january-february 2023. considering the observed spectral variability and changes in the pulse profiles, the source was likely caught in supercritical and subcritical states with significantly different emission-region geometry, associated with the presence of accretion columns and hot spots, respectively. we focus here on the pulse-phase-resolved polarimetric analysis and find that the observed dependencies of the polarization degree and polarization angle (pa) on the pulse phase are indeed drastically different for the two observations. the observed differences, if interpreted within the framework of the rotating vector model (rvm), imply dramatic variations in the spin axis inclination, the position angle, and the magnetic colatitude by tens of degrees within the space of just a few days. we suggest that the apparent changes in the observed pa phase dependence are predominantly related to the presence of an unpulsed polarized component in addition to the polarized radiation associated with the pulsar itself. we then show that the observed pa phase dependence in both observations can be explained with a single set of rvm parameters defining the pulsar's geometry. we also suggest that the additional polarized component is likely produced by scattering of the pulsar radiation in the equatorial disk wind. | complex variations in x-ray polarization in the x-ray pulsar ls v +44 17/rx j0440.9+4431 |
the optically good quality single crystals of triphenylphosphine oxide 4-nitrophenol (tp4n) with maximum dimension of 15 × 10 × 5 mm3 were grown by slow evaporation solution technique (sest) at room temperature. the cell dimensions of the grown tp4n crystal were confirmed by single crystal x-ray diffraction (sxrd) and the crystalline purity was confirmed and planes were indexed by powder x-ray diffraction (pxrd) analysis. functional groups of tp4n crystal were confirmed by fourier transform infrared (ftir) spectral analysis. the optical transmittance of the grown crystal was determined by the uv-vis nir spectral analysis and it has good optical transparency in the entire visible region. the band tail (urbach) energy of the grown crystal was analyzed and it appears to be minimum, which indicates that the tp4n has good crystallinity. the position of valence band (ev) and conduction band (ec) of the tp4n have been determined from the electron affinity energy (ea) and the ionization energy (ei) of its elements and using the optical band gap. the thermal behaviour of the grown crystal was investigated by thermogravimetric and differential thermal analysis (tg-dta). vickers microhardness analysis was carried out to identify the mechanical stability of the grown crystal and their indentation size effect (ise) was explained by the meyer's law (ml), hays-kendall's (hk) approach, proportional specimen resistance (psr) model, modified psr model (mpsr), elastic/plastic deformation (epd) model and indentation induced cracking (iic) model. chemical etching study was carried out to find the etch pit density (epd) of the grown crystal. laser damage threshold (ldt) value was measured by using nd:yag laser (1064 nm). the dielectric permittivity (ɛ՛) and dielectric loss (tan δ) as a function of frequency was measured. the electronic polarizability (α) of the tp4n crystal was calculated. it is well matched to the value which was calculated from clausius-mossotti relation, lorentz-lorentz equation, optical band gap and coupled dipole method (cdm). the z-scan technique was carried out using solid state laser (640 nm) to analyze the nonlinear optical properties of the tp4n crystal. it exhibits the self-defocusing and saturable absorbance effect during analysis of closed and open aperture respectively. the nonlinear optical parameters such as refractive index (n2), absorption coefficient (β) and the third order nonlinear optical susceptibility (χ(3)) were analyzed. | crystal growth, structural, optical, thermal, mechanical, laser damage threshold and electrical properties of triphenylphosphine oxide 4-nitrophenol (tp4n) single crystals for nonlinear optical applications |
using simulations of non-rotating supernova progenitors, we explore the kicks imparted to and the spins induced in the compact objects birthed in core collapse. we find that the recoil due to neutrino emissions can be a factor affecting core recoil, comparable to and at times larger than the corresponding kick due to matter recoil. this result would necessitate a revision of the general model of the origin of pulsar proper motions. in addition, we find that the sign of the net neutrino momentum can be opposite to the sign of the corresponding matter recoil. as a result, at times the pulsar recoil and ejecta can be in the same direction. moreover, our results suggest that the duration of the dipole in the neutrino emissions can be shorter than the duration of the radiation of the neutron-star binding energy. this allows a larger dipole asymmetry to arise, but for a shorter time, resulting in kicks in the observed pulsar range. furthermore, we find that the spin induced by the aspherical accretion of matter can leave the residues of collapse with spin periods comparable to those inferred for radio pulsars and that there seems to be a slight anticorrelation between the direction of the induced spin and the net kick direction. this could explain such a correlation among observed radio pulsars. finally, we find that the kicks imparted to black holes are due to the neutrino recoil alone, resulting in birth kicks ≤100 km s-1 most of the time. | kicks and induced spins of neutron stars at birth |
in this work, we are guided by the gravitational wave events gw 170817 and gw 190814 together with observations of neutron stars psr j1614-2230, psr j1903+6620, and lmc x-4 to model compact objects within the framework of einstein-gauss-bonnet (egb) gravity. in addition, we employ the extended gravitational decoupling (egd) method to explore the impact of anisotropy by varying the decoupling parameter. we model strange quark stars in which the interior stellar fluid obeys the mit bag equation of state which represents a degenerated fermi gas comprising of up, down, and strange quarks. in order to close the system of field equations describing the seed solution, we employ the buchdahl ansatz for one of the metric functions. the θ sector is solved under the bifurcation: $\epsilon =\theta ^0_0$ and $p_r=\theta ^1_1$ leading to two new families of solutions. in order to test the physical viability of the models, we vary the egb parameter (α) or the decoupling constant (β) to achieve the observed masses and radii of compact objects. our models are able to account for low-mass stars for a range of β values while α is fixed. the present models mimic the secondary component of the gw 190814 with a mass range of 2.5-2.67 m⊙ and radii typically of the order of 11.76$^{+0.14}_{-0.19}$ km for large values of the egb parameter and the decoupling constant. the energy exchange between fluids inside the stellar object is sensitive to model parameters which lead to stable configurations. | observational constraints on maximum mass limit and physical properties of anisotropic strange star models by gravitational decoupling in einstein-gauss-bonnet gravity |
we present a statistical study of the glitch population and the behaviour of the glitch activity across the known population of neutron stars. an unbiased glitch database was put together based on systematic searches of radio timing data of 898 rotation-powered pulsars obtained with the jodrell bank and parkes observatories. glitches identified in similar searches of 5 magnetars were also included. the database contains 384 glitches found in the rotation of 141 of these neutron stars. we confirm that the glitch size distribution is at least bimodal, with one sharp peak at approximately 20 μhz, which we call large glitches, and a broader distribution of smaller glitches. we also explored how the glitch activity ν˙g, defined as the mean frequency increment per unit of time due to glitches, correlates with the spin frequency ν, spin-down rate |ν˙|, and various combinations of these, such as energy loss rate, magnetic field, and spin-down age. it is found that the activity is insensitive to the magnetic field and that it correlates strongly with the energy loss rate, though magnetars deviate from the trend defined by the rotation-powered pulsars. however, we find that a constant ratio ν˙g/|ν˙| = 0.010 ± 0.001 is consistent with the behaviour of all rotation-powered pulsars and magnetars. this relation is dominated by large glitches, which occur at a rate directly proportional to |ν˙|. for low |ν˙|, only small glitches have been detected, making the inferred glitch activity formally lower than that predicted by the constant ratio, in many cases zero. however, we can attribute this to the low predicted rate for large glitches, together with the insufficient observing time, which makes it unlikely to detect any large glitches in this range. taking this into consideration, we show that the behaviour of each rotation-powered pulsar and magnetar is statistically consistent with the above relationship, including those objects where no glitches have been detected so far. the only exception are the rotation-powered pulsars with the highest values of |ν˙|, such as the crab pulsar and psr b0540-69, which exhibit a much smaller glitch activity, intrinsically different from each other and from the rest of the population. the activity due to small glitches also shows an increasing trend with |ν˙|, but this relation is biased by selection effects. | the glitch activity of neutron stars |
we point out that the observed time delay between the detection of the signal at the hanford and livingston ligo sites from the gravitational wave event gw150914 places an upper bound on the speed of propagation of gravitational waves, c gw ≲ 1.7 in the units of speed of light. combined with the lower bound from the absence of gravitational cherenkov losses by cosmic rays that rules out most of subluminal velocities, this gives a model-independent double-sided constraint 1 ≲ c gw ≲ 1.7. we compare this result to model-specific constraints from pulsar timing and cosmology. | on constraining the speed of gravitational waves following gw150914 |
we study the screening mechanism in the most general scalar-tensor theories that leave gravitational waves unaffected and are thus compatible with recent ligo/virgo observations. using the effective field theory of the dark energy approach, we consider the general action for perturbations beyond linear order, focusing on the quasistatic limit. when restricting to the subclass of theories that satisfy the gravitational wave constraints, the fully nonlinear effective lagrangian contains only three independent parameters. one of these, β1, is uniquely present in degenerate higher-order theories. we compute the two gravitational potentials for a spherically symmetric matter source, and we find that for β1≥0 they decrease as the inverse of the distance, as in standard gravity, while the case β1<0 is ruled out. for β1>0 , the two potentials differ and their gravitational constants are not the same on the inside and outside of the body. generically, the bound on anomalous light bending in the solar system implies β1≲10-5. standard gravity can be recovered outside the body by tuning the parameters of the model, in which case β1≲10-2 from the hulse-taylor pulsar. theories conformally related to general relativity admit 0 ≤β1≲10-6, at least for a specific choice of conformal couplings. | vainshtein regime in scalar-tensor gravity: constraints on degenerate higher-order scalar-tensor theories |
pulsar timing and laser-interferometer gravitational-wave (gw) detectors are superb laboratories to study gravity theories in the strong-field regime. here, we combine these tools to test the mono-scalar-tensor theory of damour and esposito-farèse (def), which predicts nonperturbative scalarization phenomena for neutron stars (nss). first, applying markov-chain monte carlo techniques, we use the absence of dipolar radiation in the pulsar-timing observations of five binary systems composed of a ns and a white dwarf, and eleven equations of state (eoss) for nss, to derive the most stringent constraints on the two free parameters of the def scalar-tensor theory. since the binary-pulsar bounds depend on the ns mass and the eos, we find that current pulsar-timing observations leave scalarization windows, i.e., regions of parameter space where scalarization can still be prominent. then, we investigate if these scalarization windows could be closed and if pulsar-timing constraints could be improved by laser-interferometer gw detectors, when spontaneous (or dynamical) scalarization sets in during the early (or late) stages of a binary ns (bns) evolution. for the early inspiral of a bns carrying constant scalar charge, we employ a fisher-matrix analysis to show that advanced ligo can improve pulsar-timing constraints for some eoss, and next-generation detectors, such as the cosmic explorer and einstein telescope, will be able to improve those bounds for all eleven eoss. using the late inspiral of a bns, we estimate that for some of the eoss under consideration, the onset of dynamical scalarization can happen early enough to improve the constraints on the def parameters obtained by combining the five binary pulsars. thus, in the near future, the complementarity of pulsar timing and direct observations of gws on the ground will be extremely valuable in probing gravity theories in the strong-field regime. | constraining nonperturbative strong-field effects in scalar-tensor gravity by combining pulsar timing and laser-interferometer gravitational-wave detectors |
the observation of gravitational waves from a binary neutron star merger by ligo/virgo and the associated electromagnetic counterpart provides a high precision test of orbital dynamics, and therefore a new and sensitive probe of extra forces and new radiative degrees of freedom (d.o.f.). axions are one particularly well-motivated class of extensions to the standard model leading to new forces and sources of radiation, which we focus on in this paper. using an effective field theory (eft) approach, we calculate the first post-newtonian corrections to the orbital dynamics, radiated power, and gravitational waveform for binary neutron star mergers in the presence of an axion. this result is applicable to many theories which add an extra massive scalar d.o.f. to general relativity. we then perform a detailed forecast of the potential for advanced ligo to constrain the free parameters of the eft, and map these to the mass ma and decay constant fa of the axion. at design sensitivity, we find that advanced ligo can potentially exclude axions with ma≲10-11 ev and fa∼(1014-1017) gev . there are a variety of complementary observational probes over this region of parameter space, including the orbital decay of binary pulsars, black hole superradiance, and laboratory searches. we comment on the synergies between these various observables. | prospects for axion searches with advanced ligo through binary mergers |
we present the discovery of 24 pulsars in 15 globular clusters (gcs) using the five-hundred-meter aperture spherical radio telescope (fast). these include the first pulsar discoveries in m2, m10, and m14. most of the new systems are either confirmed or likely members of binary systems. m53c and ngc 6517h and i are the only three pulsars confirmed to be isolated. m14a is a black widow pulsar with an orbital period of 5.5 hr and a minimum companion mass of 0.016 m⊙. m14e is an eclipsing binary pulsar with an orbital period of 20.3 hr. with the other 8 discoveries that have been reported elsewhere, in total 32 gc pulsars have been discovered by fast so far. in addition, we detected m3a twice. this was enough to determine that it is a black widow pulsar with an orbital period of 3.3 hr and a minimum companion mass of 0.0125 m⊙. | fast globular cluster pulsar survey: twenty-four pulsars discovered in 15 globular clusters |
if dark matter has a sizable scattering cross section with nucleons, it can efficiently be captured by a neutron star. its energy is then transferred to the neutron star as heat through the scattering and annihilation inside the star. this heating effect may be detectable via dedicated temperature observations of nearby old pulsars, providing an alternative method for dark matter searches. in this paper, we show that for electroweak multiplet dark matter, this search strategy can probe the parameter region which is out of reach of future dark matter direct detection experiments. to see this systematically, we classify such dark matter candidates in terms of their electroweak charges and investigate the effect of ultraviolet physics by means of higher-dimensional effective operators. we then show that if the effect of ultraviolet physics is sizable, the dark matter-nucleon elastic scattering cross section becomes sufficiently large, whilst if it is suppressed, then the mass splittings among the components of the dark matter multiplet get small enough so that the inelastic scattering processes are operative. in any case, the electroweak multiplet dark matter particles are efficiently captured in neutron stars, making the search strategy with the temperature observation of old neutron stars promising. | capture of electroweak multiplet dark matter in neutron stars |
we present an overview of the lofar tied-array all-sky survey (lotaas) for radio pulsars and fast transients. the survey uses the high-band antennas of the lofar superterp, the dense inner part of the lofar core, to survey the northern sky (δ > 0°) at a central observing frequency of 135 mhz. a total of 219 tied-array beams (coherent summation of station signals, covering 12 square degrees), as well as three incoherent beams (covering 67 square degrees) are formed in each survey pointing. for each of the 222 beams, total intensity is recorded at 491.52 μs time resolution. each observation integrates for 1 hr and covers 2592 channels from 119 to 151 mhz. this instrumental setup allows lotaas to reach a detection threshold of 1-5 mjy for periodic emission. thus far, the lotaas survey has resulted in the discovery of 73 radio pulsars. among these are two mildly recycled binary millisecond pulsars (p = 13 and 33 ms), as well as the slowest-spinning radio pulsar currently known (p = 23.5 s). the survey has thus far detected 311 known pulsars, with spin periods ranging from 4 ms to 5.0 s and dispersion measures from 3.0 to 217 pc cm-3. known pulsars are detected at flux densities consistent with literature values. we find that the lotaas pulsar discoveries have, on average, longer spin periods than the known pulsar population. this may reflect different selection biases between lotaas and previous surveys, though it is also possible that slower-spinning pulsars preferentially have steeper radio spectra. lotaas is the deepest all-sky pulsar survey using a digital aperture array; we discuss some of the lessons learned that can inform the approach for similar surveys using future radio telescopes such as the square kilometre array. | the lofar tied-array all-sky survey (lotaas): survey overview and initial pulsar discoveries |
this paper is the second in a series where we report the results of the long-term timing of the millisecond pulsars (msps) in 47 tucanae with the parkes 64-m radio telescope. we obtain improved timing parameters that provide additional information for studies of the cluster dynamics: (a) the pulsar proper motions yield an estimate of the proper motion of the cluster as a whole (μα = 5.00 ± 0.14 mas yr - 1, μδ = - 2.84 ± 0.12 mas yr - 1) and the motion of the pulsars relative to each other. (b) we measure the second spin-period derivatives caused by the change of the pulsar line-of-sight accelerations; 47 tuc h, u and possibly j are being affected by nearby objects. (c) for 10 binary systems, we now measure changes in the orbital period caused by their acceleration in the gravitational field of the cluster. from all these measurements, we derive a cluster distance no smaller than ∼4.69 kpc and show that the characteristics of these msps are very similar to their counterparts in the galactic disc. we find no evidence in favour of an intermediate mass black hole at the centre of the cluster. finally, we describe the orbital behaviour of four 'black widow' systems. two of them, 47 tuc j and o, exhibit orbital variability similar to that observed in other such systems, while for 47 tuc i and r the orbits seem to be remarkably stable. it appears therefore that not all 'black widows' have unpredictable orbital behaviour. | long-term observations of the pulsars in 47 tucanae - ii. proper motions, accelerations and jerks |
the fermi large area telescope has observed an excess of ∼gev energy gamma rays from the center of the milky way, which may arise from near-thermal dark matter annihilation. firmly establishing the dark matter origin for this excess is however complicated by challenges in modeling diffuse cosmic-ray foregrounds as well as unresolved astrophysical sources, such as millisecond pulsars. non-poissonian template fitting (nptf) is one statistical technique that has previously been used to show that at least some fraction of the gev excess is likely due to a population of dim point sources. these results were recently called into question by leane and slatyer (2019), who showed that a synthetic dark matter annihilation signal injected on top of the real fermi data is not recovered by the nptf procedure. in this work, we perform a dedicated study of the fermi data and explicitly show that the central result of leane and slatyer (2019) is likely driven by the fact that their choice of model for the galactic foreground emission does not provide a sufficiently good description of the data. we repeat the nptf analyses using a state-of-the-art model for diffuse gamma-ray emission in the milky way and introduce a novel statistical procedure, based on spherical-harmonic marginalization, to provide an improved description of the galactic diffuse emission in a data-driven fashion. with these improvements, we find that the nptf results continue to robustly favor the interpretation that the galactic center excess is due, in part, to unresolved astrophysical point sources across the analysis variations that we have explored. | foreground mismodeling and the point source explanation of the fermi galactic center excess |
the two-body problem under the influence of both dark energy and post-newtonian modifications is studied. in this unified framework, we demonstrate that dark energy plays the role of a critical period with $t_{\lambda} = 2\pi/c \sqrt{\lambda} \approx 60~\text{gyr}$. we also show that the ratio between orbital and critical period naturally emerges from the kretschmann scalar, which is a quadratic curvature invariant characterizing all binary systems effectively represented by a de sitter-schwarzschild spacetime. the suitability of a binary system to constrain dark energy is determined by the ratio between its keplerian orbital period $t_\text{k}$ and the critical period $t_\lambda$. systems with $t_\text{k} \approx t_\lambda$ are optimal for constraining the cosmological constant $\lambda$, such as the local group and the virgo cluster. systems with $t_{\text{k}} \ll t_\lambda$ are dominated by attractive gravity (which are best suited for studying modified gravity corrections). systems with $t_{\text{k}} \gg t_\lambda$ are dominated by repulsive dark energy and can thus be used to constrain $\lambda$ from below. we use our unified framework of post-newtonian and dark-energy modifications to calculate the precession of bounded and unbounded astrophysical systems and infer constraints on $\lambda$ from them. pulsars, the solar system, s stars around sgr a*, the local group, and the virgo cluster, having orbital periods of days to gigayears, are analyzed. the results reveal that the upper bound on the cosmological constant decreases when the orbital period of the system increases, emphasizing that $\lambda$ is a critical period in binary motion. | dark energy as a critical period in binary motion: bounds from multi-scale binaries |
big bang nucleosynthesis (bbn) is very sensitive to the cosmological expansion rate. if the gravitational constant g took a different value during the nucleosynthesis epoch than today, the primordial abundances of light elements would be affected. in this work, we improve the bounds on this variation using recent determinations of the primordial element abundances, updated nuclear and weak reaction rates and observations of the cosmic microwave background (cmb). when combining the measured abundances and the baryon density from cmb observations by planck, we find gbbn/g0=0 .99-0.05+0.06 at 2 σ confidence level. if the variation of g is linear in time, we find g ˙/g0=0 .7-4.3+3.8×10-12year-1 , again at 2 σ . these bounds are significantly stronger than those from previous primordial nucleosynthesis studies, and are comparable and complementary to cmb, stellar, solar system, lunar laser ranging, pulsar timing and gravitational wave constraints. | improved bbn constraints on the variation of the gravitational constant |
xss j12270-4859 is an x-ray binary associated with the fermi large area telescope gamma-ray source 1fgl j1227.9-4852. in 2012 december, this source underwent a transition where the x-ray and optical luminosity dropped and the spectral signatures of an accretion disk disappeared. we report the discovery of a 1.69 millisecond pulsar (msp), psr j1227-4853, at a dispersion measure of 43.4 pc cm-3 associated with this source, using the giant metrewave radio telescope (gmrt) at 607 mhz. this demonstrates that, post-transition, the system hosts an active radio msp. this is the third system after psr j1023+0038 and psr j1824-2452i showing evidence of state switching between radio msp and low-mass x-ray binary states. we report timing observations of psr j1227-4853 with the gmrt and parkes, which give a precise determination of the rotational and orbital parameters of the system. the companion mass measurement of 0.17-0.46 m⊙ suggests that this is a redback system. psr j1227-4853 is eclipsed for about 40% of its orbit at 607 mhz with additional short-duration eclipses at all orbital phases. we also find that the pulsar is very energetic, with a spin-down luminosity of ∼1035 erg s-1. we report simultaneous imaging and timing observations with the gmrt, which suggests that eclipses are caused by absorption rather than dispersion smearing or scattering. | discovery of psr j1227-4853: a transition from a low-mass x-ray binary to a redback millisecond pulsar |
double neutron stars (dns) have to survive two supernovae (sne) and still remain bound. this sets strong limits on the nature of the second collapse in these systems. we consider the masses and orbital parameters of the dns population and constrain the two distributions of mass ejection and kick velocities directly from observations with no a priori assumptions regarding evolutionary models and/or the types of the sne involved. we show that there is strong evidence for two distinct types of sne in these systems, where the second collapse in the majority of the observed systems involved small mass ejection (δm ≲ 0.5 m⊙) and a corresponding low-kick velocity (vk ≲ 30 km s-1). this formation scenario is compatible, for example, with an electron-capture sn. only a minority of the systems have formed via the standard sn scenario involving larger mass ejection of ∼2.2 m⊙ and kick velocities of up to 400 km s-1. due to the typically small kicks in most dns (which are reflected by rather low proper motion), we predict that most of these systems reside close to the galactic disc. in particular, this implies that more ns-ns mergers occur close to the galactic plane. this may have non-trivial implications to the estimated merger rates of dns and to the rate of ligo/virgo detections. | formation of double neutron star systems as implied by observations |
we consider the three currently known pulsing ultraluminous x-ray sources (pulxs). we show that in one of them the observed spin-up rate requires super-eddington accretion rates at the magnetospheric radius, even if magnetar-strength fields are assumed. in the two other systems, a normal-strength neutron star field implies super-eddington accretion at the magnetosphere. adopting super-eddington mass transfer as the defining characteristic of ulx systems, we find the parameters required for self-consistent simultaneous fits of the luminosities and spin-up rates of the three pulsed systems. these imply near equality between their magnetospheric radii rm and the spherization radii rsph where radiation pressure becomes important and drives mass-loss from the accretion disc. we interpret this near equality as a necessary condition for the systems to appear as pulsed, since if it is violated the pulse fraction is small. we show that as a consequence all pulxs must have spin-up rates \dot{ν }≳ 10^{-10} s^{-2}, an order of magnitude higher than in any other pulsing neutron-star binaries. the fairly tight conditions required for ulxs to show pulsing support our earlier suggestion that many unpulsed ulx systems must actually contain neutron stars rather than black holes. | pulsing ulxs: tip of the iceberg? |
the microscopic quantum nature of elementary particles, chirality, leads to macroscopic phenomena like the chiral anomaly, chiral magnetic effect, and chiral plasma instability. we review recent progress of the studies of these chiral effects in high-energy astrophysics, such as pulsar kicks, magnetars, and core-collapse supernovae, and early universe cosmology, such as the primordial magnetic field, baryogenesis, and chiral gravitational waves. we also provide a pedagogical introduction to the chiral effects and low-energy effective theories to describe them in and out of equilibrium-the chiral (magneto)hydrodynamics, chiral kinetic theory, and chiral radiation transport theory for neutrinos. | chiral effects in astrophysics and cosmology |
the canadian hydrogen intensity mapping experiment (chime) has become a leading facility for detecting fast radio bursts (frbs) through the chime/frb backend. chime/frb searches for fast transients in polarization-summed intensity data streams that have 24 khz spectral and 1 ms temporal resolution. the intensity beams are pointed to predetermined locations in the sky. a triggered baseband system records the coherent electric field measured by each antenna in the chime array at the time of frb detections. here we describe the analysis techniques and automated pipeline developed to process these full-array baseband data recordings. whereas the real-time frb detection pipeline has a localization limit of several arcminutes, offline analysis of baseband data yields source localizations with subarcminute precision, as characterized by using a sample of pulsars and one repeating frb with known positions. the baseband pipeline also enables resolving temporal substructure on a microsecond scale and the study of polarization including detections of faraday rotation. | an analysis pipeline for chime/frb full-array baseband data |
this work analyses the hydrostatic equilibrium configurations of strange stars in a non-minimal geometry-matter coupling (gmc) theory of gravity. those stars are made of strange quark matter, whose distribution is governed by the mit equation of state. the non-minimal gmc theory is described by the following gravitational action: f (r ,l )=r /2 +l +σ r l , where r represents the curvature scalar, l is the matter lagrangian density, and σ is the coupling parameter. when considering this theory, the strange stars become larger and more massive. in particular, when σ =50 km2, the theory can achieve the 2.6 m⊙, which is suitable for describing the pulsars psr j2215+5135 and psr j1614-2230, and the mass of the secondary object in the gw190814 event. the 2.6 m⊙ is a value hardly achievable in general relativity, even considering fast rotation effects, and is also compatible with the mass of psr j0952-0607 (m =2.35 ±0.17 m⊙ ), the heaviest and fastest pulsar in the disk of the milky way, recently measured, supporting the possible existence of strange quark matter in its composition. the non-minimal gmc theory can also give feasible results to describe the macroscopical features of strange star candidates. | quark stars with 2.6 m⊙ in a non-minimal geometry-matter coupling theory of gravity |
gamma-ray observations have established energetic isolated pulsars as outstanding particle accelerators and antimatter factories. however, many questions are still open regarding the acceleration and radiation processes involved, as well as the locations where they occur. the radiation spectra of all gamma-ray pulsars observed to date show strong cutoffs or a break above energies of a few gigaelectronvolts. using the high energy stereoscopic system's cherenkov telescopes, we discovered a radiation component from the vela pulsar which emerges beyond this generic cutoff and extends up to energies of at least 20 teraelectronvolts. this is an order of magnitude larger than in the case of the crab pulsar, the only other pulsar detected in the teraelectronvolt energy range. our results challenge the state-of-the-art models for the high-energy emission of pulsars. furthermore, they pave the way for investigating other pulsars through their multiteraelectronvolt emission, thereby imposing additional constraints on the acceleration and emission processes in their extreme energy limit. | discovery of a radiation component from the vela pulsar reaching 20 teraelectronvolts |
this paper presents the first systematic study of proto-neutron star (pns) convection in three dimensions (3d) based on our latest numerical fornax models of core-collapse supernova (ccsn). we confirm that pns convection commonly occurs, and then quantify the basic physical characteristics of the convection. by virtue of the large number of long-term models, the diversity of pns convective behaviour emerges. we find that the vigour of pns convection is not correlated with ccsn dynamics at large radii, but rather with the mass of pns - heavier masses are associated with stronger pns convection. we find that pns convection boosts the luminosities of νμ, ντ, $\bar{\nu }_{\mu }$ , and $\bar{\nu }_{\tau }$ neutrinos, while the impact on other species is complex due to a competition of factors. finally, we assess the consequent impact on ccsn dynamics and the potential for pns convection to generate pulsar magnetic fields. | a systematic study of proto-neutron star convection in three-dimensional core-collapse supernova simulations |
in this letter we propose that coherent radio emission of the crab pulsar, other young energetic pulsars, and millisecond pulsars is produced in the magnetospheric current sheet beyond the light cylinder. we carry out global and local 2d kinetic plasma simulations of reconnection to illustrate the coherent emission mechanism. reconnection in the current sheet beyond the light cylinder proceeds in the very efficient plasmoid-dominated regime, where the current layer gets fragmented into a dynamic chain of plasmoids that undergo successive coalescence. mergers of sufficiently large plasmoids produce secondary perpendicular current sheets, which are also plasmoid unstable. collisions of plasmoids with each other and with the upstream magnetic field eject fast magnetosonic waves, which propagate upstream across the background field and successfully escape from the plasma as electromagnetic waves that fall in the radio band. this model successfully explains many important features of the observed radio emission from the crab and other pulsars with high magnetic field at the light cylinder: phase coincidence with the high-energy emission, nanosecond duration (nanoshots), and extreme instantaneous brightness of individual pulses. | pulsar radio emission mechanism: radio nanoshots as a low-frequency afterglow of relativistic magnetic reconnection |
the newly discovered second repeating fast radio burst (frb) source, frb 180814.j0422+73, was reported to exhibit a time-frequency downward drifting pattern, which is also seen in the first repeater frb 121102. we propose a generic geometrical model to account for the observed downward drifting of sub-pulse frequency, within the framework of coherent curvature radiation by bunches of electron-positron pairs in the magnetosphere of a neutron star (ns). a sudden trigger event excites these coherent bunches of charged particles, which stream outward along open field lines. as the field lines sweep across the line of sight, the bunches seen later travel farther into the less-curved part of the magnetic field lines, thus emitting at lower frequencies. we use this model to explain the time-frequency downward drifting in two frb generation scenarios, the transient pulsar-like sparking from the inner gap region of a slowly rotating ns, and the externally triggered magnetosphere reconfiguration known as the “cosmic comb.” | on the time-frequency downward drifting of repeating fast radio bursts |
millisecond pulsars have been discussed as a possible source of the gamma-ray excess observed from the region surrounding the galactic center. with this in mind, we use the observed population of bright low-mass x-ray binaries to estimate the number of millisecond pulsars in the inner galaxy. this calculation suggests that only ~ 1-5% of the excess is produced by millisecond pulsars. we also use the luminosity function derived from local measurements of millisecond pulsars, along with the number of point sources resolved by fermi, to calculate an upper limit for the diffuse emission from such a population. while this limit is compatible with the millisecond pulsar population implied by the number of low-mass x-ray binaries, it strongly excludes the possibility that most of the excess originates from such objects. | challenges in explaining the galactic center gamma-ray excess with millisecond pulsars |
we search for the isotropic stochastic gravitational-wave background, including the nontensorial polarizations that are allowed in general metric theories of gravity, in the parkes pulsar timing array (ppta) second data release (dr2). we find no statistically significant evidence that the common-spectrum process reported by the ppta collaboration has tensor transverse, scalar transverse, vector longitudinal, or scalar longitudinal correlations in ppta dr2. therefore, we place a 95% upper limit on the amplitude of each polarization mode, as ${{ \mathcal a }}_{\mathrm{tt}}\lesssim 3.2\times {10}^{-15}$ , ${{ \mathcal a }}_{\mathrm{st}}\lesssim 1.8\times {10}^{-15}$ , ${{ \mathcal a }}_{\mathrm{vl}}\lesssim 3.5\times {10}^{-16}$ , and ${{ \mathcal a }}_{\mathrm{sl}}\lesssim 4.2\times {10}^{-17};$ or, equivalently, a 95% upper limit on the energy density parameter per logarithm frequency, as ${{\rm{\omega }}}_{\mathrm{gw}}^{\mathrm{tt}}\lesssim 1.4\times {10}^{-8}$ , ${{\rm{\omega }}}_{\mathrm{gw}}^{\mathrm{st}}\lesssim 4.5\times {10}^{-9}$ , ${{\rm{\omega }}}_{\mathrm{gw}}^{\mathrm{vl}}\lesssim 1.7\times {10}^{-10}$ , and ${{\rm{\omega }}}_{\mathrm{gw}}^{\mathrm{sl}}\lesssim 2.4\times {10}^{-12}$ , at a frequency of 1/yr. | constraining the polarization of gravitational waves with the parkes pulsar timing array second data release |
the 2015 centenary of the publication of einstein's general theory of relativity, and the first detection of gravitational waves have focused renewed attention on the question of whether einstein was right. this review of experimental gravity provides a detailed survey of the intensive testing of einstein's theory of gravity, including tests in the emerging strong-field dynamical regime. it discusses the theoretical frameworks needed to analyze gravitational theories and interpret experiments. completely revised and updated, this new edition features coverage of new alternative theories of gravity, a unified treatment of gravitational radiation, and the implications of the latest binary pulsar observations. it spans the earliest tests involving the solar system to the latest tests using gravitational waves detected from merging black holes and neutron stars. it is a comprehensive reference for researchers and graduate students working in general relativity, cosmology, particle physics and astrophysics. | theory and experiment in gravitational physics |
we present first results from a lofar census of non-recycled pulsars. the census includes almost all such pulsars known (194 sources) at declinations dec > 8° and galactic latitudes |gb| > 3°, regardless of their expected flux densities and scattering times. each pulsar was observed for ≥20 min in the contiguous frequency range of 110-188 mhz. full-stokes data were recorded. we present the dispersion measures, flux densities, and calibrated total intensity profiles for the 158 pulsars detected in the sample. the median uncertainty in census dispersion measures (1.5 × 10-3 pc cm-3) is ten times smaller, on average, than in the atnf pulsar catalogue. we combined census flux densities with those in the literature and fitted the resulting broadband spectra with single or broken power-law functions. for 48 census pulsars such fits are being published for the first time. typically, thechoice between single and broken power-laws, as well as the location of the spectral break, were highly influenced by the spectral coverage of the available flux density measurements. in particular, the inclusion of measurements below 100 mhz appears essential for investigating the low-frequency turnover in the spectra for most of the census pulsars. for several pulsars, we compared the spectral indices from different works and found the typical spread of values to be within 0.5-1.5, suggesting a prevailing underestimation of spectral index errors in the literature. the census observations yielded some unexpected individual source results, as we describe in the paper. lastly, we will provide this unique sample of wide-band, low-frequency pulse profiles via the european pulsar network database. tables b.1-b.4 are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/591/a134 | a lofar census of non-recycled pulsars: average profiles, dispersion measures, flux densities, and spectra |
we derive constraints on millicharged dark matter and axionlike particles using pulsar timing and fast radio burst observations. for dark matter particles of charge ɛ e , the constraint from time of arrival (toa) of waves is ɛ /mmilli≲10-8 ev-1 , for masses mmilli≳10-6 ev . for axionlike particles, the polarization of the signals from pulsars yields a bound in the axial coupling g /ma≲10-13 gev-1/(10-22 ev ) , for ma≲10-19 ev . both bounds scale as (ρ /ρdm)1 /2 for fractions of the total dark matter energy density ρdm. we make a precise study of these bounds using toa from several pulsars, frb 121102, and polarization measurements of psr j 0437 -4715 . our results rule out a new region of the parameter space for these dark matter models. | constraints on millicharged dark matter and axionlike particles from timing of radio waves |
the aim of this work is to study the imprints that different models for black hole (bh) and neutron star (ns) formation have on the galactic distribution of x-ray binaries (xrbs) that contain these objects. we find that the root mean square of the height above the galactic plane of bh- and ns-xrbs is a powerful proxy to discriminate among different formation scenarios, and that binary evolution following the bh/ns formation does not significantly affect the galactic distributions of the binaries. we find that a population model in which at least some bhs receive a (relatively) high natal kick fits the observed bh-xrbs best. for the ns case, we find that a high natal kick distribution, consistent with the one derived from the measurement of pulsar proper motion, is the most preferable. we also analyse the simple method we previously used to estimate the minimal peculiar velocity of an individual bh-xrb at birth. we find that this method may be less reliable in the bulge of the galaxy for certain models of the galactic potential, but that our estimate is excellent for most of the bh-xrbs. | the galactic distribution of x-ray binaries and its implications for compact object formation and natal kicks |
the 2016 vela glitch observed by the mount pleasant radio telescope provides the first opportunity to study pulse-to-pulse dynamics of a pulsar glitch, opening up new possibilities to study the neutron star's interior. we fit models of the star's rotation frequency to the pulsar data, and present the following three results. first, we constrain the glitch rise time to less than 12.6 s with 90% confidence, almost three-times shorter than the previous best constraint. second, we find definitive evidence for a rotational-frequency overshoot and fast relaxation following the glitch. third, we find evidence for a slowdown of the star's rotation immediately before the glitch. the overshoot is predicted theoretically by some models; we discuss implications of the glitch rise and overshoot decay times on internal neutron-star physics. the slowdown preceding the glitch is unexpected; we propose the slowdown may trigger the glitch by causing a critical lag between crustal superfluid and the crust. | rotational evolution of the vela pulsar during the 2016 glitch |
we determined faraday rotation measures (rms) towards 137 pulsars in the northern sky, using low-frequency array (lofar) observations at 110-190 mhz. this low-frequency rm catalogue, the largest to date, improves the precision of existing rm measurements on average by a factor of 20 - due to the low frequency and wide bandwidth of the data, aided by the rm-synthesis method. we report rms towards 25 pulsars for the first time. the rms were corrected for ionospheric faraday rotation to increase the accuracy of our catalogue to ≈0.1 rad m-2. the ionospheric rm correction is currently the largest contributor to the measurement uncertainty. in addition, we find that the faraday dispersion functions towards pulsars are extremely faraday thin - mostly less than 0.001 rad m-2. we use these new precise rm measurements (in combination with existing rms, dispersion measures, and distance estimates) to estimate the scale height of the galactic halo magnetic field: 2.0 ± 0.3 kpc for galactic quadrants i and ii above and below the galactic plane (we also evaluate the scale height for these regions individually). overall, our initial low-frequency catalogue provides valuable information about the 3d structure of the galactic magnetic field. | low-frequency faraday rotation measures towards pulsars using lofar: probing the 3d galactic halo magnetic field |
the standard model of particle physics is known to be intriguingly successful. however, their rich phenomena represented by the phase transitions (pts) have not been completely understood yet, including the possibility of the existence of unknown dark sectors. in this paper, we investigate the measurement of the equation of state parameter w and the sound speed of the pt plasma with the use of the gravitational waves (gws) of the universe. though the propagation of gw is insensitive to in itself, the sound speed value affects the dynamics of primordial density (or scalar curvature) perturbations, and the induced gw by their horizon reentry can then be an indirect probe both w and . we numerically reveal the concrete spectrum of the predicted induced gw with two simple examples of the scalar perturbation spectrum: the monochromatic and scale-invariant spectra. in the monochromatic case, we see that the resonant amplification and cancellation scales of the induced gw depend on the values at different times respectively. the scale-invariant case gives a more realistic spectrum and its specific shape will be compared with observations. in particular, the qcd phase transition corresponds with the frequency range of the pulsar timing array (pta) observations. if the amplitude of primordial scalar power is in the range of 10-4 ≲ aζ ≲ 10-2, the induced gw is consistent with current observational constraints and detectable in the future observation in square kilometer array. furthermore, the recent possible detection of stochastic gws by nanograv 12.5 yr analysis [1] can be explained by the induced gw if aζ ~ √(7) × 10-3. | induced gravitational waves as a cosmological probe of the sound speed during the qcd phase transition |
the explosion of core-collapse supernova depends on a sequence of events taking place in less than a second in a region of a few hundred kilometers at the centre of a supergiant star, after the stellar core approaches the chandrasekhar mass and collapses into a proto-neutron star, and before a shock wave is launched across the stellar envelope. theoretical efforts to understand stellar death focus on the mechanism which transforms the collapse into an explosion. progress in understanding this mechanism is reviewed with particular attention to its asymmetric character. we highlight a series of successful studies connecting observations of supernova remnants and pulsars properties to the theory of core-collapse using numerical simulations. the encouraging results from first principles models in axisymmetric simulations is tempered by new puzzles in 3d. the diversity of explosion paths and the dependence on the pre-collapse stellar structure is stressed, as well as the need to gain a better understanding of hydrodynamical and mhd instabilities such as standing accretion shock instability and neutrino-driven convection. the shallow water analogy of shock dynamics is presented as a comparative system where buoyancy effects are absent. this dynamical system can be studied numerically and also experimentally with a water fountain. the potential of this complementary research tool for supernova theory is analysed. we also review its potential for public outreach in science museums. | the explosion mechanism of core-collapse supernovae: progress in supernova theory and experiments |
aims: the last comprehensive catalogue of high-mass x-ray binaries in the small magellanic cloud (smc) was published about ten years ago. since then new such systems were discovered, mainly by x-ray observations with chandra and xmm-newton. for the majority of the proposed hmxbs in the smc no x-ray pulsations were discovered as yet, and unless other properties of the x-ray source and/or the optical counterpart confirm their hmxb nature, they remain only candidate hmxbs.methods: from a literature search we collected a catalogue of 148 confirmed and candidate hmxbs in the smc and investigated their properties to shed light on their real nature. based on the sample of well-established hmxbs (the pulsars), we investigated which observed properties are most appropriate for a reliable classification. we defined different levels of confidence for a genuine hmxb based on spectral and temporal characteristics of the x-ray sources and colour-magnitude diagrams from the optical to the infrared of their likely counterparts. we also took the uncertainty in the x-ray position into account.results: we identify 27 objects that probably are misidentified because they lack an infrared excess of the proposed counterpart. they were mainly x-ray sources with a large positional uncertainty. this is supported by additional information obtained from more recent observations. our catalogue comprises 121 relatively high-confidence hmxbs (the vast majority with be companion stars). about half of the objects show x-ray pulsations, while for the rest no pulsations are known as yet. a comparison of the two subsamples suggests that long pulse periods in excess of a few 100 s are expected for the "non-pulsars", which are most likely undetected because of aperiodic variability on similar timescales and insufficiently long x-ray observations. the highest x-ray variability together with the lowest observed minimum fluxes for short-period pulsars indicate that in addition to the eccentricity of the orbit, its inclination against the plane of the be star circum-stellar disc plays a major role in determining the outburst behaviour.conclusions: the large population of hmxbs in the smc, in particular be x-ray binaries, provides the largest homogeneous sample of such systems for statistical population studies. the catalogue is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/586/a81 | high-mass x-ray binaries in the small magellanic cloud |
over 100 millisecond radio pulsars (msps) have been observed in globular clusters (gcs), motivating theoretical studies of the formation and evolution of these sources through stellar evolution coupled to stellar dynamics. here we study msps in gcs using realistic n-body simulations with our cluster monte carlo code. we show that neutron stars (nss) formed in electron-capture supernovae (including both accretion-induced and merger-induced collapse of white dwarfs) can be spun up through mass transfer to form msps. both ns formation and spin-up through accretion are greatly enhanced through dynamical interaction processes. we find that our models for average gcs at the present day with masses ≈2 × 105 m ⊙ can produce up to 10-20 msps, while a very massive gc model with mass ≈106 m ⊙ can produce close to 100. we show that the number of msps is anti-correlated with the total number of stellar-mass black holes (bhs) retained in the host cluster. the radial distributions are also affected: msps are more concentrated toward the center in a host cluster with a smaller number of retained bhs. as a result, the number of msps in a gc could be used to place constraints on its bh population. some intrinsic properties of msp systems in our models (such as the magnetic fields and spin periods) are in good overall agreement with observations, while others (such as the distribution of binary companion types) are less so, and we discuss the possible reasons for such discrepancies. interestingly, our models also demonstrate the possibility of dynamically forming ns-ns and ns-bh binaries in gcs, although the predicted numbers are very small. | millisecond pulsars and black holes in globular clusters |
the millisecond pulsar j1713+0747 underwent a sudden and significant pulse shape change between april 16 and 17, 2021 (mjds 59320 and 59321). subsequently, the pulse shape gradually recovered over the course of several months. we report the results of continued multi-frequency radio observations of the pulsar made using the canadian hydrogen intensity mapping experiment (chime) and the 100-meter green bank telescope (gbt) in a three-year period encompassing the shape change event, between february 2020 and february 2023. as of february 2023, the pulse shape had returned to a state similar to that seen before the event, but with measurable changes remaining. the amplitude of the shape change and the accompanying toa residuals display a strong non-monotonic dependence on radio frequency, demonstrating that the event is neither a glitch (the effects of which should be independent of radio frequency, $\nu$) nor a change in dispersion measure (dm) alone (which would produce a delay proportional to $\nu^{-2}$). however, it does bear some resemblance to the two previous "chromatic timing events" observed in j1713+0747 (demorest et al. 2013; lam et al. 2016), as well as to a similar event observed in psr j1643-1224 in 2015 (shannon et al. 2016). | an unusual pulse shape change event in psr j1713+0747 observed with the green bank telescope and chime |
we review more than 10 yr of continuous monitoring of accreting x-ray pulsars with the all-sky gamma-ray burst monitor (gbm) aboard the fermi gamma-ray space telescope. our work includes data from the start of gbm operations in 2008 august, through to 2019 november. pulsations from 39 accreting pulsars are observed over an energy range of 10-50 kev by gbm. the gbm accreting pulsars program performs data reduction and analysis for each accreting pulsar and makes histories of the pulse frequency and pulsed flux publicly available. we examine in detail the spin histories, outbursts, and torque behaviors of the persistent and transient x-ray pulsars observed by gbm. the spin period evolution of each source is analyzed in the context of disk-accretion and quasi-spherical settling accretion-driven torque models. long-term pulse frequency histories are also analyzed over the gbm mission lifetime and compared to those available from the previous burst and transient source experiment all-sky monitoring mission, revealing previously unnoticed episodes in some of the analyzed sources (such as a torque reversal in 2s 1845-024). we obtain new, or update known, orbital solutions for three sources. our results demonstrate the capabilities of gbm as an excellent instrument for monitoring accreting x-ray pulsars and its important scientific contribution to this field. | the ups and downs of accreting x-ray pulsars: decade-long observations with the fermi gamma-ray burst monitor |
ultralight dark matter (uldm) is proposed as a theoretical candidate of dark matter particles with masses of approximately 10-22 ev . the interactions between uldm particles and standard model particles would cause variations in pulse arrival times of millisecond pulsars, which means that the pulsar timing array (pta) can be used to indirectly detect uldm. in this letter, we use the gamma-ray pta composed of 29 millisecond pulsars observed by the fermi large area telescope (fermi-lat) to test four uldm effects, including gravitational effects for generalized uldm with different spin-0 /1 , the fifth-force coupling effect of dark photons, and the modified gravitational effect of the spin-2 uldm. the gamma-ray pulsar timing is not affected by the ionized interstellar medium and suffers relatively simple noises, unlike that of the radio band. our work is the first time that the gamma-ray pta has been used to search for the uldm. no significant signals of uldm are found based on the fermi-lat pta for all four kinds of uldm models. constraints on uldm parameters are set with the 95% confidence level, which provides a complementary check of the nondetection of uldm for radio ptas and direct detection experiments. | constraining ultralight dark matter using the fermi-lat pulsar timing array |
we investigate the effect of electric charge in anisotropic compact stars with conformal symmetry. we assume that the pressure and the density of the matter inside the stellar structure are large with strong gravitational fields. the strong electric field produces significant effects on the phenomenology of the stellar objects, in order of 10^{20} {v m}^{-1} in mksa units. the conformal symmetry condition produces an integral relationship between the metric functions. we use this condition to find a new anisotropic solution to the einstein-maxwell field equations. this solution is relevant in modelling a relativistic compact star. radii and masses are consistent with stellar objects such psr j1614-2230, vela x1, psr j1903+327 and cen x-3. the mass-radius ratio and the surface red shift are in agreement with realistic constraints. also our model displays constraint on the maximum stellar mass, central density and radius for the upper bound redshift requirements. | effect of electric charge on conformal compact stars |
in this work we discuss the polarization contents of einstein-æther theory and the generalized tensor-vector-scalar (teves) theory, as both theories have a normalized timelike vector field. we derive the linearized equations of motion around the flat spacetime background using the gauge-invariant variables to easily separate physical degrees of freedom. we find the plane wave solutions and identify the polarizations by examining the geodesic deviation equations. we find that there are five polarizations in einstein-æther theory and six polarizations in the generalized teves theory. in particular, the transverse breathing mode is mixed with the pure longitudinal mode. we also discuss the experimental tests of the extra polarizations in einstein-æther theory using pulsar timing arrays combined with the gravitational-wave speed bound derived from the observations on gw 170817 and grb 170817a. it turns out that it might be difficult to use pulsar timing arrays to distinguish different polarizations in einstein-æther theory. the same speed bound also forces one of the propagating modes in the generalized teves theory to travel much faster than the speed of light. since the strong coupling problem does not exist in some parameter subspaces, the generalized teves theory is excluded in these parameter subspaces. | gravitational waves in einstein-æther and generalized teves theory after gw170817 |
the quantity and quality of cosmic structure observations have greatly accelerated in recent years, and further leaps forward will be facilitated by imminent projects. these will enable us to map the evolution of dark and baryonic matter density fluctuations over cosmic history. the way that these fluctuations vary over space and time is sensitive to several pieces of fundamental physics: the primordial perturbations generated by gut-scale physics; neutrino masses and interactions; the nature of dark matter and dark energy. we focus on the last of these here: the ways that combining probes of growth with those of the cosmic expansion such as distance-redshift relations will pin down the mechanism driving the acceleration of the universe. one way to explain the acceleration of the universe is invoke dark energy parameterized by an equation of state w. distance measurements provide one set of constraints on w, but dark energy also affects how rapidly structure grows; the greater the acceleration, the more suppressed the growth of structure. upcoming surveys are therefore designed to probe w with direct observations of the distance scale and the growth of structure, each complementing the other on systematic errors and constraints on dark energy. a consistent set of results will greatly increase the reliability of the final answer. another possibility is that there is no dark energy, but that general relativity does not describe the laws of physics accurately on large scales. while the properties of gravity have been measured with exquisite precision at stellar system scales and densities, within our solar system and by binary pulsar systems, its properties in different environments are poorly constrained. to fully understand if general relativity is the complete theory of gravity we must test gravity across a spectrum of scales and densities. rapid developments in gravitational wave astronomy and numerical relativity are directed at testing gravity in the high curvature, high density regime. cosmological evolution provides a polar opposite test bed, probing how gravity behaves in the lowest curvature, low density environments. there are a number of different implementations of astrophysically relevant modifications of gravity. generically, the models are able to reproduce the distance measurements while at the same time altering the growth of structure. in particular, as detailed below, the poisson equation relating over-densities to gravitational potentials is altered, and the potential that determines the geodesics of relativistic particles (such as photons) differs from the potential that determines the motion of non-relativistic particles. upcoming surveys will exploit these differences to determine whether the acceleration of the universe is due to dark energy or to modified gravity. to realize this potential, both wide field imaging and spectroscopic redshift surveys play crucial roles. projects including des, eboss, desi, pfs, lsst, euclid, and wfirst are in line to map more than a 1000 cubic-billion-light-year volume of the universe. these will map the cosmic structure growth rate to 1% in the redshift range 0 < z < 2 , over the last 3/4 of the age of the universe. | growth of cosmic structure: probing dark energy beyond expansion |
motivated by the large body of literature around the phenomenological properties of accreting black hole (bh) and neutron star (ns) x-ray binaries in the radio:x-ray luminosity plane, we carry out a comparative regression analysis on 36 bhs and 41 nss in hard x-ray states, with data over 7 dex in x-ray luminosity for both. the bhs follow a radio to x-ray (logarithmic) luminosity relation with slope β = 0.59 ± 0.02, consistent with the nss' slope (β =0.44^{+0.05}_{-0.04}) within 2.5σ. the best-fitting intercept for the bhs significantly exceeds that for the nss, cementing bhs as more radio loud, by a factor ∼22. this discrepancy cannot be fully accounted for by the mass or bolometric correction gap, or by the ns boundary layer contribution to the x-rays, and is likely to reflect physical differences in the accretion flow efficiency, or the jet powering mechanism. once importance sampling is implemented to account for the different luminosity distributions, the slopes of the non-pulsating and pulsating ns subsamples are formally inconsistent (>3σ), unless the transitional millisecond pulsars (whose incoherent radio emission mechanism is not firmly established) are excluded from the analysis. we confirm the lack of a robust partitioning of the bh data set into separate luminosity tracks. | hard state neutron star and black hole x-ray binaries in the radio:x-ray luminosity plane |
recently a repeating fast radio burst (frb) 121102 has been confirmed to be an extragalactic event and a persistent radio counterpart has been identified. while other possibilities are not ruled out, the emission properties are broadly consistent with murase et al. that theoretically proposed quasi-steady radio emission as a counterpart of both frbs and pulsar-driven supernovae. here, we constrain the model parameters of such a young neutron star scenario for frb 121102. if the associated supernova has a conventional ejecta mass of m ej ≳ a few m ⊙, a neutron star with an age of t age ∼ 10-100 years, an initial spin period of pi≲ a few ms, and a dipole magnetic field of b dip ≲ a few × 1013 g can be compatible with the observations. however, in this case, the magnetically powered scenario may be favored as an frb energy source because of the efficiency problem in the rotation-powered scenario. on the other hand, if the associated supernova is an ultra-stripped one or the neutron star is born by the accretion-induced collapse with m ej ∼ 0.1 m ⊙, a younger neutron star with t age ∼ 1-10 years can be the persistent radio source and might produce frbs with the spin-down power. these possibilities can be distinguished by the decline rate of the quasi-steady radio counterpart. | testing the young neutron star scenario with persistent radio emission associated with frb 121102 |
isolated spinning neutron stars, asymmetric with respect to their rotation axis, are expected to be sources of continuous gravitational waves. the most sensitive searches for these sources are based on accurate matched filtering techniques that assume the continuous wave to be phase locked with the pulsar beamed emission. while matched filtering maximizes the search sensitivity, a significant signal-to-noise ratio loss will happen in the case of a mismatch between the assumed and the true signal phase evolution. narrow-band algorithms allow for a small mismatch in the frequency and spin-down values of the pulsar while coherently integrating the entire dataset. in this paper, we describe a narrow-band search using ligo o2 data for the continuous wave emission of 33 pulsars. no evidence of a continuous wave signal is found, and upper limits on the gravitational wave amplitude over the analyzed frequency and spin-down ranges are computed for each of the targets. in this search, we surpass the spin-down limit, namely, the maximum rotational energy loss due to gravitational waves emission for some of the pulsars already present in the ligo o1 narrow-band search, such as j 1400 -6325 , j 1813 -1246 , j 1833 -1034 , j 1952 +3252 , and for new targets such as j 0940 -5428 and j 1747 -2809 . for j 1400 -6325 , j 1833 -1034 , and j 1747 -2809 , this is the first time the spin-down limit is surpassed. | narrow-band search for gravitational waves from known pulsars using the second ligo observing run |
recently, an indicative evidence of a stochastic process, reported by the nanograv collaboration based on the analysis of 12.5-year pulsar timing array data which might be interpreted as a potential stochastic gravitational wave signal, has aroused the keen interest of theorists. the first-order color charge confinement phase transition at the qcd scale could be one of the cosmological sources for the nanograv signal. if the phase transition is flavor dependent and happens sequentially, it is important to find that what kind of qcd matter in which the first-order confinement-deconfinement phase transition happens is more likely to be the potential source of the nanograv signal during the evolution of the universe. in this paper, we would like to illustrate that the nanograv signal could be generated from confinement-deconfinement transition in either heavy static quarks with a zero baryon chemical potential, or quarks with a finite baryon chemical potential. in contrast, the gluon confinement could not possibly be the source for the nanograv signal according to the current observation. future observation will help to distinguish between different scenarios. | nanograv signal from first-order confinement-deconfinement phase transition in different qcd-matter scenarios |
a sample of 14 frbs with measured redshifts and scattering times is used to assess contributions to dispersion and scattering from the intergalactic medium (igm), galaxy halos, and the disks of host galaxies. the igm and galaxy halos contribute significantly to dispersion measures (dms) but evidently not to scattering, which is then dominated by host galaxies. this enables the usage of scattering times for estimating dm contributions from host galaxies and also for a combined scattering-dispersion redshift estimator. redshift estimation is calibrated using the scattering of galactic pulsars after taking into account different scattering geometries for galactic and intergalactic lines of sight. the dm-only estimator has a bias of ~0.1 and rms error of ~0.15 in the redshift estimate for an assumed ad hoc value of 50 pc cm-3 for the host galaxy's dm contribution. the combined redshift estimator shows less bias by a factor of 4 to 10 and a 20%-40% smaller rms error. we find that values for the baryonic fraction of the ionized igm f igm ≃ 0.85 ± 0.05 optimize redshift estimation using dispersion and scattering. our study suggests that 2 of the 14 candidate galaxy associations (frb 20190523a and frb 20190611b) should be reconsidered. | redshift estimation and constraints on intergalactic and interstellar media from dispersion and scattering of fast radio bursts |
the nanograv, parkes, european, and international pulsar timing array (pta) collaborations have reported evidence for a common-spectrum process that can potentially correspond to a stochastic gravitational wave background (sgwb) in the 1-100 nhz frequency range. we consider the scenario in which this signal is produced by magnetohydrodynamic (mhd) turbulence in the early universe, induced by a nonhelical primordial magnetic field at the energy scale corresponding to the quark confinement phase transition. we perform mhd simulations to study the dynamical evolution of the magnetic field and compute the resulting sgwb. we show that the sgwb output from the simulations can be very well approximated by assuming that the magnetic anisotropic stress is constant in time, over a time interval related to the eddy turnover time. the analytical spectrum that we derive under this assumption features a change of slope at a frequency corresponding to the gw source duration that we confirm with the numerical simulations. we compare the sgwb signal with the pta data to constrain the temperature scale at which the sgwb is sourced, as well as the amplitude and characteristic scale of the initial magnetic field. we find that the generation temperature is constrained to be in the 1-200 mev range, the magnetic field amplitude must be >1 % of the radiation energy density at that time, and the magnetic field characteristic scale is constrained to be >10 % of the horizon scale. we show that the turbulent decay of this magnetic field will lead to a field at recombination that can help to alleviate the hubble tension and can be tested by measurements in the voids of the large scale structure with gamma-ray telescopes like the cherenkov telescope array. | gravitational wave signal from primordial magnetic fields in the pulsar timing array frequency band |
observations have shown that spatially extended "tev halos" are a common (and potentially generic) feature surrounding young and middle-aged pulsars. however, their morphology is not understood. they are larger than the "compact" region where the stellar remnant dominates the properties of the interstellar medium, but smaller than expected in models of cosmic-ray diffusion through the standard interstellar medium. several explanations have been proposed, but all have shortcomings. here, we revisit a class of models where the cosmic-ray gradient produced by the central source induces a streaming stability that "self-confines" the cosmic-ray population. we find that previous studies significantly underpredicted the degree of cosmic-ray confinement and show that corrected models can significantly inhibit cosmic-ray diffusion throughout the tev halo, especially when similar contributions from the coincident supernova remnant are included. | self-generated cosmic-ray turbulence can explain the morphology of tev halos |
we present the timing and spectral studies of rx j0209.6-7427 during its rare 2019 outburst using observations with the soft x-ray telescope (sxt) and large area x-ray proportional counter (laxpc) instruments on the astrosat satellite. pulsations having a periodicity of 9.29 s were detected for the first time by the nicer mission in the 0.2-10 kev energy band and, as reported here, by astrosat over a broad energy band covering 0.3-80 kev. the pulsar exhibits a rapid spin-up during the outburst. energy resolved folded pulse profiles are generated in several energy bands in 3-80 kev. to the best of our knowledge this is the first report of the timing and spectral characteristics of this be binary pulsar in hard x-rays. there is suggestion of evolution of the pulse profile with energy. the energy spectrum of the pulsar is determined and from the best-fitting spectral values, the x-ray luminosity of rx j0209.6-7427 is inferred to be 1.6 × 1039 erg s-1. our timing and spectral studies suggest that this source has features of an ultraluminous x-ray pulsar in the magellanic bridge. details of the results are presented and discussed in terms of the current ideas. | study of recent outburst in the be/x-ray binary rx j0209.6-7427 with astrosat: a new ultraluminous x-ray pulsar in the magellanic bridge? |
context. the gravitational strong equivalence principle (sep) is a cornerstone of the general theory of relativity (gr). hence, testing the validity of sep is of great importance when confronting gr, or its alternatives, with experimental data. pulsars that are orbited by white dwarf companions provide an excellent laboratory, where the extreme difference in binding energy between neutron stars and white dwarfs allows for precision tests of the sep via the technique of radio pulsar timing.aims: to date, the best limit on the validity of sep under strong-field conditions was obtained with a unique pulsar in a triple stellar system, psr j0337+1715. we report here on an improvement of this test using an independent data set acquired over a period of 6 years with the nançay radio telescope. the improvements arise from a uniformly sampled data set, a theoretical analysis, and a treatment that fixes some short-comings in the previously published results, leading to better precision and reliability of the test.methods: in contrast to the previously published test, we use a different long-term timing data set, developed a new timing model and an independent numerical integration of the motion of the system, and determined the masses and orbital parameters with a different methodology that treats the parameter δ, describing a possible strong-field sep violation, identically to all other parameters.results: we obtain a violation parameter δ = ( + 0.5 ± 1.8) × 10-6 at 95% confidence level, which is compatible with and improves upon the previous study by 30%. this result is statistics-limited and avoids limitation by systematics as previously encountered. we find evidence for red noise in the pulsar spin frequency, which is responsible for up to 10% of the reported uncertainty. we use the improved limit on sep violation to place constraints on a class of well-studied scalar-tensor theories, in particular we find ωbd > 140 000 for the brans-dicke parameter. the conservative limits presented here fully take into account current uncertainties in the equation for state of neutron-star matter. supplementary figures are available at https://www.aanda.org | an improved test of the strong equivalence principle with the pulsar in a triple star system |
the phase state of dense matter in the intermediate density range ($\sim$ 1-10 times the nuclear saturation density) is both intriguing and unclear and can have important observable effects in the present gravitational wave era of neutron stars. as matter density increases in compact stars, the sound velocity is expected to approach the conformal limit ($c_s/c=1/\sqrt{3}$) at high densities and should also fulfill the causality limit ($c_s/c<1$). however, its detailed behavior remains a prominent topic of debate. it was suggested that the sound velocity of dense matter could be an important indicator of a deconfinement phase transition, where a particular shape might be expected for its density dependence. in this work, we explore the general properties of the sound velocity and the adiabatic index of dense matter in hybrid stars as well as in neutron stars and quark stars. various conditions are employed for the hadron-quark phase transition with varying interface tension. we find that the expected behavior of the sound velocity can also be achieved by the nonperturbative properties of the quark phase, in addition to a deconfinement phase transition. moreover, it leads to a more compact star with a similar mass. we then propose a new class of quark star equation of states, which can be tested by future high-precision radius measurements of pulsar-like objects. | sound velocity in dense stellar matter with strangeness and compact stars |
the f (r) gravity can be cast into the form of a scalar-tensor theory, and scalar degree of freedom can be suppressed in high-density regions by the chameleon mechanism. in this article, for the general f (r) gravity, using a scalar-tensor representation with the chameleon mechanism, we calculate the parametrized post-newtonian parameters γ and β, the effective gravitational constant geff, and the effective cosmological constant λeff. in addition, for the general f (r) gravity, we also calculate the rate of orbital period decay of the binary system due to gravitational radiation. then we apply these results to specific f (r) models (hu-sawicki model, tsujikawa model and starobinsky model) and derive the constraints on the model parameters by combining the observations in solar system, cosmological scales and the binary systems. | constraining f(r) gravity in solar system, cosmology and binary pulsar systems |
plasmoids—magnetized quasi-circular structures formed self-consistently in reconnecting current sheets—were previously considered to be the graveyards of energetic particles. in this paper, we demonstrate the important role of plasmoids in shaping the particle energy spectrum in relativistic reconnection (i.e., with upstream magnetization σup ≫ 1). using 2d particle-in-cell simulations in pair plasmas with σup = 10 and 100, we study a secondary particle energization process that takes place inside compressing plasmoids. we demonstrate that plasmoids grow in time, while their interiors compress, amplifying the internal magnetic field. the magnetic field felt by particles injected in an isolated plasmoid increases linearly with time, which leads to particle energization as a result of magnetic moment conservation. for particles injected with a power-law distribution function, this energization process acts in such a way that the shape of the injected power law is conserved, while producing an additional nonthermal tail f(e) ∝ e-3 at higher energies, followed by an exponential cutoff. the cutoff energy, which increases with time as ${e}_{\mathrm{cut}}\propto \sqrt{t}$ , can greatly exceed σupmec2. we analytically predict the secondary acceleration timescale and the shape of the emerging particle energy spectrum, which can be of major importance in certain astrophysical systems, such as blazar jets. | secondary energization in compressing plasmoids during magnetic reconnection |
fast radio bursts (frbs) are millisecond bursts of radio radiation at frequencies of about 1 ghz, recently discovered in pulsar surveys. they have not yet been definitively identified with any other astronomical object or phenomenon. the bursts are strongly dispersed, indicating passage through a high column density of low density plasma. the most economical interpretation is that this is the intergalactic medium, indicating that frb are at “cosmological” distances with redshifts in the range 0.3-1.3. their inferred brightness temperatures are as high as 1037 k, implying coherent emission by “bunched” charges, as in radio pulsars. i review the astronomical sites, objects and emission processes that have been proposed as the origin of frb, with particular attention to soft gamma repeaters (sgrs) and giant pulsar pulses. | fast radio bursts — a brief review: some questions, fewer answers |
fast radio bursts (frbs) display a confounding variety of burst properties and host-galaxy associations. repeating frbs offer insight into the frb population by enabling spectral, temporal, and polarimetric properties to be tracked over time. here, we report on the polarized observations of 12 repeating sources using multiyear monitoring with the canadian hydrogen intensity mapping experiment (chime) over 400-800 mhz. we observe significant rotation measure (rm) variations from many sources in our sample, including rm changes of several hundred radians per square meter over month timescales from frbs 20181119a, 20190303a, and 20190417a, and more modest rm variability (δrm ≲ few tens of radians per square meter) from frbs 20181030a, 20190208a, 20190213b, and 20190117a over equivalent timescales. several repeaters display a frequency-dependent degree of linear polarization that is consistent with depolarization via scattering. combining our measurements of rm variations with equivalent constraints on dm variability, we estimate the average line-of-sight magnetic field strength in the local environment of each repeater. in general, repeating frbs display rm variations that are more prevalent and/or extreme than those seen from radio pulsars in the milky way and the magellanic clouds, suggesting repeating frbs and pulsars occupy distinct magnetoionic environments. | revealing the dynamic magnetoionic environments of repeating fast radio burst sources through multiyear polarimetric monitoring with chime/frb |
the hot big bang is often considered as the origin of all matter and radiation in the universe. primordial nucleosynthesis provides strong evidence that the early universe contained a hot plasma of photons and baryons with a temperature t >mev . however, the earliest probes of dark matter originate from much later times around the epoch of structure formation. in this work we describe a scenario in which dark matter (and possibly dark radiation) can be formed around or even after primordial nucleosynthesis in a second big bang, which we dub the "dark big bang." the latter occurs through a phase transition in the dark sector that transforms dark vacuum energy into a hot dark plasma of particles; in this paper we focus on a first-order phase transition for the dark big bang. the correct dark matter abundance can be set by dark matter cannibalism or by pair annihilation within the dark sector followed by a thermal freeze-out. alternatively ultraheavy "dark-zilla" dark matter can originate directly from bubble collisions during the dark big bang. we will show that the dark big bang is consistent with constraints from structure formation and the cosmic microwave background if it occurred when the universe was less than one month old, corresponding to a temperature in the visible sector above o (kev ). while the dark matter evades direct and indirect detection, the dark big bang gives rise to striking gravity wave signatures to be tested at pulsar timing array experiments. furthermore, the dark big bang allows for realizations of self-interacting and/or warm dark matter, which suggest exciting discovery potential in future small-scale structure observations. | dark matter and gravitational waves from a dark big bang |
we report the discovery of 1.97 ms period gamma-ray pulsations from the 75 minute orbital-period binary pulsar now named psr j1653-0158. the associated fermi large area telescope gamma-ray source 4fgl j1653.6-0158 has long been expected to harbor a binary millisecond pulsar. despite the pulsar-like gamma-ray spectrum and candidate optical/x-ray associations—whose periodic brightness modulations suggested an orbit—no radio pulsations had been found in many searches. the pulsar was discovered by directly searching the gamma-ray data using the gpu-accelerated einstein@home distributed volunteer computing system. the multidimensional parameter space was bounded by positional and orbital constraints obtained from the optical counterpart. more sensitive analyses of archival and new radio data using knowledge of the pulsar timing solution yield very stringent upper limits on radio emission. any radio emission is thus either exceptionally weak, or eclipsed for a large fraction of the time. the pulsar has one of the three lowest inferred surface magnetic-field strengths of any known pulsar with bsurf ≈ 4 × 107 g. the resulting mass function, combined with models of the companion star's optical light curve and spectra, suggests a pulsar mass ≳2 m⊙. the companion is lightweight with mass ∼0.01 m⊙, and the orbital period is the shortest known for any rotation-powered binary pulsar. this discovery demonstrates the fermi large area telescope's potential to discover extreme pulsars that would otherwise remain undetected. | discovery of a gamma-ray black widow pulsar by gpu-accelerated einstein@home |
while pulsars possess exceptional rotational stability, large-scale timing studies have revealed at least two distinct types of irregularities in their rotation: red timing noise and glitches. using modern bayesian techniques, we investigated the timing noise properties of 300 bright southern-sky radio pulsars that have been observed over 1.0-4.8 yr by the upgraded molonglo observatory synthesis telescope (most). we reanalysed the spin and spin-down changes associated with nine previously reported pulsar glitches, report the discovery of three new glitches and four unusual glitch-like events in the rotational evolution of psr j1825-0935. we develop a refined bayesian framework for determining how red noise strength scales with pulsar spin frequency (ν) and spin-down frequency ( $\dot{\nu }$ ), which we apply to a sample of 280 non-recycled pulsars. with this new method and a simple power-law scaling relation, we show that red noise strength scales across the non-recycled pulsar population as $\nu ^{a} |\dot{\nu }|^{b}$ , where $a = -0.84^{+0.47}_{-0.49}$ and $b = 0.97^{+0.16}_{-0.19}$ . this method can be easily adapted to utilize more complex, astrophysically motivated red noise models. lastly, we highlight our timing of the double neutron star psr j0737-3039, and the rediscovery of a bright radio pulsar originally found during the first molonglo pulsar surveys with an incorrectly catalogued position. | the utmost pulsar timing programme - ii. timing noise across the pulsar population |
an equation of state of cold nuclear matter with an arbitrary isotopic composition is studied within a relativistic mean-field approach with hadron masses and coupling constants depending self-consistently on the scalar mean-field. all hadron masses decrease universally with the scalar field growth, whereas meson-nucleon coupling constants can vary differently. more specifically we focus on two modifications of the kvor model studied previously. one extension of the model (kvorcut) demonstrates that the equation of state stiffens if the increase of the scalar-field magnitude with the density is bounded from above at some value for baryon densities above the saturation nuclear density. this can be realized if the nucleon vector-meson coupling constant changes rapidly as a function of the scalar field slightly above the desired value. the other version of the model (mkvor) utilizes a smaller value of the nucleon effective mass at the nuclear saturation density and a saturation of the scalar field in the isospin asymmetric matter induced by a strong variation of the nucleon isovector-meson coupling constant as function of the scalar field. a possibility of hyperonization of the matter in neutron star interiors is incorporated. our equations of state fulfill majority of known empirical constraints including the pressure-density constraint from heavy-ion collisions, direct urca constraint, gravitational-baryon mass constraint for the pulsar j0737-3039b, and the constraint on the maximum mass of the neutron stars. | relativistic mean-field models with scaled hadron masses and couplings: hyperons and maximum neutron star mass |
the nearby radio pulsar b0950$+$08 with full duty cycle is targeted by the five-hundred-meter aperture spherical radio telescope (fast, 110 minutes allocated), via adopting polarization calibration on two ways of baseline determination, in order to understand its magnetospheric radiation geometry as well as the polar cap sparking. % the radiation of the main pulse could not be informative of magnetic field line planes due to its low linear polarization ($<10 \%$) and the position angle jumps, and the polarization position angle in the pulse longitudes whose linear fractions are larger than $ \sim 30 \%$ is thus fitted in the classical rotating vector model (rvm). % the best rvm fit indicates that the inclination angle, $\alpha$, and the impact angle, $\beta$, of this pulsar are $100.5^{\circ}$ and $-33.2^{\circ}$, respectively, suggesting that the radio emission comes from two poles. % polar cap sparking in the vacuum gap model, either the annular gap or the core gap, is therefore investigated in this rvm geometry, resulting in a high-altitude magnetospheric emission at heights from $\sim 0.25r_{\rm lc}$ to $\sim 0.56r_{\rm lc}$, with $r_{\rm lc}$ the light cylinder radius. % it is evident that both sparking points of the main and inter pulses are located mainly away from the magnetic pole, that is meaningful in the physics of pulsar surface and is even relevant to pulsar's inner structure. | radio pulsar b0950$+$08: radiation in magnetosphere and sparks above surface |
axion dark matter can resonantly convert to photons in the magnetosphere of neutron stars, possibly giving rise to radio signals observable on earth. this method for the indirect detection of axion dark matter has recently received significant attention in the literature. the calculation of the radio signal is complicated by a number of effects; most importantly, the gravitational infall of the axions onto the neutron star accelerates them to semi-relativistic speed, and the neutron star magnetosphere is highly anisotropic. both of these factors complicate the calculation of the conversion of axions to photons. in this work, we present the first fully three-dimensional calculation of the axion-photon conversion in highly magnetised anisotropic media. depending on the axion trajectory, this calculation leads to orders-of-magnitude differences in the conversion compared to the simplified one-dimensional calculation used so far in the literature, altering the directionality of the produced photons. our results will have important implications for the radio signal one would observe in a telescope. | axion-photon conversion in strongly magnetised plasmas |
we present a novel calculation of the spectrum of electrons and positrons from random sources, supernova remnants and pulsars, distributed within the spiral arms of the galaxy. the pulsar emissivity in terms of electron-positron pairs is considered as time dependent, following the magnetic dipole spin-down luminosity, and the temporal evolution of the potential drop is accounted for. moreover each pulsar, with the magnetic field and initial spin period selected at random from the observed distribution, is considered as a source of pairs only after it leaves the parent supernova due to its birth kick velocity (also selected at random from the observed distribution). we show that (i) the spectrum of electrons is characterized by a feature at ≳50 gev that proves that their transport is dominated by radiative losses. the flux reduction at e ≳1 tev is explained as a result of lepton transport from sources in the spiral arms. (ii) the spectrum of positrons is very well described by the contribution of pulsars and the rising positron fraction originates naturally. the implications of pulsars as positron sources in terms of positron fraction at very high energies are also discussed. (iii) the role of fluctuations in the high-energy regime is thoroughly discussed and used to draw conclusions on the possibility to single out the contribution of local sources to the lepton spectrum with current and upcoming experiments. | galactic factories of cosmic-ray electrons and positrons |
we provide timing solutions for 45 radio pulsars discovered by the robert c. byrd green bank telescope. these pulsars were found in the green bank north celestial cap pulsar survey, an all-gbt-sky survey being carried out at a frequency of 350 {mhz}. we include pulsar timing data from the green bank telescope and low frequency array. our sample includes five fully recycled millisecond pulsars (msps, three of which are in a binary system), a new relativistic double neutron star system, an intermediate-mass binary pulsar, a mode-changing pulsar, a 138 ms pulsar with a very low magnetic field, and several nulling pulsars. we have measured two post-keplerian parameters and thus the masses of both objects in the double neutron star system. we also report a tentative companion mass measurement via shapiro delay in a binary msp. two of the msps can be timed with high precision and have been included in pulsar timing arrays being used to search for low-frequency gravitational waves, while a third msp is a member of the black widow class of binaries. proper motion is measurable in five pulsars, and we provide an estimate of their space velocity. we report on an optical counterpart to a new black widow system and provide constraints on the optical counterparts to other binary msps. we also present a preliminary analysis of nulling pulsars in our sample. these results demonstrate the scientific return of long timing campaigns on pulsars of all types. | the green bank north celestial cap pulsar survey. iii. 45 new pulsar timing solutions |
we present high signal-to-noise ratio, multifrequency polarization pulse profiles for 24 millisecond pulsars that are being observed as part of the parkes pulsar timing array project. the pulsars are observed in three bands, centred close to 730, 1400 and 3100 mhz, using a dual-band 10 cm/50 cm receiver and the central beam of the 20-cm multibeam receiver. observations spanning approximately six years have been carefully calibrated and summed to produce high s/n profiles. this allows us to study the individual profile components and in particular how they evolve with frequency. we also identify previously undetected profile features. for many pulsars we show that pulsed emission extends across almost the entire pulse profile. the pulse component widths and component separations follow a complex evolution with frequency; in some cases these parameters increase and in other cases they decrease with increasing frequency. the evolution with frequency of the polarization properties of the profile is also non-trivial. we provide evidence that the pre- and post-cursors generally have higher fractional linear polarization than the main pulse. we have obtained the spectral index and rotation measure for each pulsar by fitting across all three observing bands. for the majority of pulsars, the spectra follow a single power-law and the position angles follow a λ2 relation, as expected. however, clear deviations are seen for some pulsars. we also present phase-resolved measurements of the spectral index, fractional linear polarization and rotation measure. all these properties are shown to vary systematically over the pulse profile. | a study of multifrequency polarization pulse profiles of millisecond pulsars |
we report the first star formation history study of the milky ways nuclear star cluster (nsc), which includes observational constraints from a large sample of stellar metallicity measurements. these metallicity measurements were obtained from recent surveys from gemini and the very large telescope of 770 late-type stars within the central 1.5 pc. these metallicity measurements, along with photometry and spectroscopically derived temperatures, are forward modeled with a bayesian inference approach. including metallicity measurements improves the overall fit quality, as the low-temperature red giants that were previously difficult to constrain are now accounted for, and the best fit favors a two-component model. the dominant component contains 93% ± 3% of the mass, is metal-rich ( $\overline{[{\rm{m}}/{\rm{h}}]}\sim 0.45$ ), and has an age of ${5}_{-2}^{+3}$ gyr, which is ~3 gyr younger than earlier studies with fixed (solar) metallicity; this younger age challenges coevolutionary models in which the nsc and supermassive black holes formed simultaneously at early times. the minor population component has low metallicity ( $\overline{[{\rm{m}}/{\rm{h}}]}\sim -1.1$ ) and contains ~7% of the stellar mass. the age of the minor component is uncertain (0.1-5 gyr old). using the estimated parameters, we infer the following nsc stellar remnant population (with ~18% uncertainty): 1.5 × 105 neutron stars, 2.5 × 105 stellar-mass black holes (bhs), and 2.2 × 104 bh-bh binaries. these predictions result in 2-4 times fewer neutron stars compared to earlier predictions that assume solar metallicity, introducing a possible new path to understand the so-called "missing-pulsar problem". finally, we present updated predictions for the bh-bh merger rates (0.01-3 gpc-3yr-1). | the star formation history of the milky way's nuclear star cluster |
radio observations using five-hundred-metre aperture spherical radio telescope (fast) detected a highly polarised radio burst from sgr 1935+2154 at mjd 58969.9048669008. | a highly polarised radio burst detected from sgr 1935+2154 by fast |
with unparalleled rotational stability, millisecond pulsars (msps) serve as ideal laboratories for numerous astrophysical studies, many of which require precise knowledge of the distance and/or velocity of the msp. here, we present the astrometric results for 18 msps of the 'mspsr$\pi$' project focusing exclusively on astrometry of msps, which includes the re-analysis of three previously published sources. on top of a standardized data reduction protocol, more complex strategies (i.e. normal and inverse-referenced 1d interpolation) were employed where possible to further improve astrometric precision. we derived astrometric parameters using sterne, a new bayesian astrometry inference package that allows the incorporation of prior information based on pulsar timing where applicable. we measured significant (${>}3\, \sigma$) parallax-based distances for 15 msps, including 0.81 ± 0.02 kpc for psr j1518+4904 - the most significant model-independent distance ever measured for a double neutron star system. for each msp with a well-constrained distance, we estimated its transverse space velocity and radial acceleration. among the estimated radial accelerations, the updated ones of psr j1012+5307 and psr j1738+0333 impose new constraints on dipole gravitational radiation and the time derivative of newton's gravitational constant. additionally, significant angular broadening was detected for psr j1643-1224, which offers an independent check of the postulated association between the hii region sh 2-27 and the main scattering screen of psr j1643-1224. finally, the upper limit of the death line of γ-ray-emitting pulsars is refined with the new radial acceleration of the hitherto least energetic γ-ray pulsar psr j1730-2304. | the mspsrπ catalogue: vlba astrometry of 18 millisecond pulsars |
neutron stars (nss) obtain kicks, typically of several 100 km s-1, at birth. the gravitational tugboat mechanism can explain these kicks as consequences of asymmetric mass ejection during the supernova (sn) explosion. support for this hydrodynamic explanation is provided by observations of sn remnants with associated nss, which confirm the prediction that the bulk of the explosion ejecta, particularly the chemical elements between silicon and the iron group, are dominantly expelled in the hemisphere opposite to the direction of the ns kick. here, we present a large set of two- and three-dimensional explosion simulations of electron-capture sne, considering explosion energies between ∼3 × 1049 erg and ∼1.6 × 1050 erg. we find that the fast acceleration of the sn shock in the steep density gradient delimiting the o-ne-mg core of the progenitor enables such a rapid expansion of neutrino-heated matter that the growth of neutrino-driven convection freezes out quickly in a high-mode spherical harmonics pattern. because the corresponding momentum asymmetry of the ejecta is very small and the gravitational acceleration by the fast-expanding ejecta abates rapidly, the ns kick velocities are a few km s-1, at most. the extremely low core compactness of o-ne-mg-core progenitors therefore favors hydrodynamic ns kicks much below the ∼160 km s-1 measured for the crab pulsar. this suggests either that the crab nebula is not the remnant of an electron-capture sn, but rather of a low-mass iron-core progenitor; or that the crab pulsar was not accelerated by the gravitational tugboat mechanism, but instead received its kick by a non-hydrodynamic mechanism such as, e.g., anisotropic neutrino emission. | hydrodynamical neutron-star kicks in electron-capture supernovae and implications for the crab supernova |
the regularity of pulsar emissions becomes apparent once we reference the pulses' times of arrivals to the inertial rest frame of the solar system. it follows that errors in the determination of earth's position with respect to the solar system barycenter can appear as a time-correlated bias in pulsar-timing residual time series, affecting the searches for low-frequency gravitational waves performed with pulsar-timing arrays. indeed, recent array data sets yield different gravitational-wave background upper limits and detection statistics when analyzed with different solar system ephemerides. crucially, the ephemerides do not generally provide usable error representations. in this article, we describe the motivation, construction, and application of a physical model of solar system ephemeris uncertainties, which focuses on the degrees of freedom (jupiter's orbital elements) most relevant to gravitational-wave searches with pulsar-timing arrays. this model, bayesephem, was used to derive ephemeris-robust results in nanograv's 11 yr stochastic-background search, and it provides a foundation for future searches by nanograv and other consortia. the analysis and simulations reported here suggest that ephemeris modeling reduces the gravitational-wave sensitivity of the 11 yr data set and that this degeneracy will vanish with improved ephemerides and with pulsar-timing data sets that extend well beyond a single jovian orbital period. | modeling the uncertainties of solar system ephemerides for robust gravitational-wave searches with pulsar-timing arrays |
binary neutron stars (bnss) mergers are prime sites for r-process nucleosynthesis. their rate determines the chemical evolution of heavy elements in the milky way. the merger rate of bns is a convolution of their birth rate and the gravitational radiation spiral-in delay time. using the observed population of galactic bns we show here that the lifetimes of pulsars in observed bnss are sufficiently short that the ages of bnss have little to no effect on the observed merger time distribution. we find that at late times (t ≳ 1 gyr) the gravitational wave delay time distribution (dtd) follows the expected t-1. however, a significant excess of rapidly merging systems (between 40 and 60{{ per cent}} of the entire population) is apparent at shorter times. although the exact shape of the dtd cannot be determined with the existing data, in all models that adequately describe the data we find at least 40{{ per cent}} of bnss with merger times less than 1 gyr. this population of garapid mergers implies a declining deposition rate of r-process materials that is consistent with several independent observations of heavy element abundances in the milky way. at the same time this population that requires initial binary separations of roughly one solar radius clearly indicates that these binaries had common envelope progenitors. our results suggest that a significant fraction of future ligo/virgo bns mergers would reside in star-forming galaxies. | the gravitational waves merger time distribution of binary neutron star systems |
the radio spectral index is a powerful probe for classifying cosmic radio sources and understanding the origin of the radio emission. combining data at 147 mhz and 1.4 ghz from the tifr gmrt sky survey (tgss) and the nrao vla sky survey (nvss), we produced a large-area radio spectral index map of ∼80 per cent of the sky (dec. > - 40 deg), as well as a radio spectral index catalogue containing 1396 515 sources, of which 503 647 are not upper or lower limits. almost every tgss source has a detected counterpart, while this is true only for 36 per cent of nvss sources. we released both the map and the catalogue to the astronomical community. the catalogue is analysed to discover systematic behaviours in the cosmic radio population. we find a differential spectral behaviour between faint and bright sources as well as between compact and extended sources. these trends are explained in terms of radio galaxy evolution. we also confirm earlier reports of an excess of steep-spectrum sources along the galactic plane. this corresponds to 86 compact and steep-spectrum source in excess compared to expectations. the properties of this excess are consistent with normal non-recycled pulsars, which may have been missed by pulsation searches due to larger than average scattering along the line of sight. | a radio spectral index map and catalogue at 147-1400 mhz covering 80 per cent of the sky |
we present a search for quasi-monochromatic gravitational-wave signals from the young, energetic x-ray pulsar psr j0537-6910 using data from the second and third observing runs of ligo and virgo. the search is enabled by a contemporaneous timing ephemeris obtained using neutron star interior composition explorer (nicer) data. the nicer ephemeris has also been extended through 2020 october and includes three new glitches. psr j0537-6910 has the largest spin-down luminosity of any pulsar and exhibits frequent and strong glitches. analyses of its long-term and interglitch braking indices provide intriguing evidence that its spin-down energy budget may include gravitational-wave emission from a time-varying mass quadrupole moment. its 62 hz rotation frequency also puts its possible gravitational-wave emission in the most sensitive band of the ligo/virgo detectors. motivated by these considerations, we search for gravitational-wave emission at both once and twice the rotation frequency from psr j0537-6910. we find no signal, however, and report upper limits. assuming a rigidly rotating triaxial star, our constraints reach below the gravitational-wave spin-down limit for this star for the first time by more than a factor of 2 and limit gravitational waves from the l = m = 2 mode to account for less than 14% of the spin-down energy budget. the fiducial equatorial ellipticity is constrained to less than about 3 ×10-5, which is the third best constraint for any young pulsar. | diving below the spin-down limit: constraints on gravitational waves from the energetic young pulsar psr j0537-6910 |
neutron stars are among the most exotic objects in the universe. a neutron star, with a mass of 1.4-2 solar masses within a radius of about 10-15 km, is the most compact stable configuration of matter in which degeneracy pressure can still balance gravity, since further compression would lead to gravitational collapse and formation of a black hole. as gravity is extreme, rotation is extreme: neutron stars are the fastest rotating stars known, with periods as short as a millisecond. the presence of a magnetic field not aligned with the rotation axis of the star is the origin of pulsating emission from these sources, which for this reason are dubbed pulsars. the discovery in 1998 of the first accreting millisecond x-ray pulsar, started an exciting season of continuing discoveries. in the last 20 years, thanks to the extraordinary performance of astronomical detectors in the radio, optical, x-ray, and gamma-ray bands, astrophysicists had the opportunity to thoroughly investigate the so-called recycling scenario: the evolutionary path leading to the formation of a millisecond-spinning pulsar. in this chapter we review the general properties of accreting millisecond x-ray pulsars, which provide the first evidence that neutron stars are spun up to millisecond periods by accretion of matter and angular momentum from a (low-mass) companion star. we describe the general characteristics of this class of systems with particular attention to their spin and orbital parameters, their short-term and long-term evolution, as well as the information that can be drawn from their x-ray spectra. | accretion powered x-ray millisecond pulsars |
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