bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Thousand-Pulsar-Array programme on MeerKAT – VI. Pulse widths of a large and diverse sample of radio pulsars
Authors: Posselt B , Karastergiou A , Johnston S , Parthasarathy A , Keith M J , Oswald L S , Song X , Weltevrede P , Barr E D , Buchner S , Geyer M , Kramer M , Reardon D J , Serylak M , Shannon R M , Spiewak R , Venkatraman Krishnan V 
Published: September 2021

ABSTRACT
We present pulse width measurements for a sample of radio pulsars observed with the MeerKAT telescope as part of the Thousand-Pulsar-Array (TPA) programme in the MeerTime project. For a centre frequency of 1284 MHz, we obtain 762 W10 measurements across the total bandwidth of 775 MHz, where W10 is the width at the 10 per cent level of the pulse peak. We also measure about 400 W10 values in each of the four or eight frequency sub-bands. Assuming, the width is a function of the rotation period P, this relationship can be described with a power law with power law index μ = −0.29 ± 0.03. However, using orthogonal distance regression, we determine a steeper power law with μ = −0.63 ± 0.06. A density plot of the period-width data reveals such a fit to align well with the contours of highest density. Building on a previous population synthesis model, we obtain population-based estimates of the obliquity of the magnetic axis with respect to the rotation axis for our pulsars. Investigating the width changes over frequency, we unambiguously identify a group of pulsars that have width broadening at higher frequencies. The measured width changes show a monotonic behaviour with frequency for the whole TPA pulsar population, whether the pulses are becoming narrower or broader with increasing frequency. We exclude a sensitivity bias, scattering and noticeable differences in the pulse component numbers as explanations for these width changes, and attempt an explanation using a qualitative model of five contributing Gaussian pulse components with flux density spectra that depend on their rotational phase.
Impact of magnetic braking on high-mass close binary formation
Authors: Harada Naoto , Hirano Shingo , Machida Masahiro N , Hosokawa Takashi 
Published: September 2021

ABSTRACT
Combining numerical simulations and analytical modelling, we investigate whether close binary systems form by the effect of magnetic braking. Using magnetohydrodynamics simulations, we calculate the cloud evolution with a sink, for which we do not resolve the binary system or binary orbital motion to realize long-term time integration. Then, we analytically estimate the binary separation using the accreted mass and angular momentum obtained from the simulation. In unmagnetized clouds, wide binary systems with separations of &gt;100 au form, in which the binary separation continues to increase during the main accretion phase. In contrast, close binary systems with separations of &lt;100 au can form in magnetized clouds. Since the efficiency of magnetic braking strongly depends on both the strength and configuration of the magnetic field, they also affect the formation conditions of a close binary. In addition, the protostellar outflow has a negative impact on close binary formation, especially when the rotation axis of the prestellar cloud is aligned with the global magnetic field. The outflow interrupts the accretion of gas with small angular momentum, which is expelled from the cloud, while gas with large angular momentum preferentially falls from the side of the outflow on to the binary system and widens the binary separation. This study shows that a cloud with a magnetic field that is not parallel to the rotation axis is a favourable environment for the formation of close binary systems.
Strobed imaging as a method for the determination and diagnosis of local seeing
Authors: Stubbs Christopher W 
Published: September 2021

ABSTRACTThe image quality budget of many telescopes can have substantial contributions from local seeing, both ‘mirror’ and ‘dome’, which arise from turbulence and temperature variations that are difficult to quantify, measure directly, and ameliorate. We describe a method to determine the ‘local’ seeing degradation due to wavefront perturbations within the final few metres of the optical path from celestial sources to the focal plane of a ground-based telescope, using the primary instrument and along the same path taken by light from celestial sources. The concept involves placing strobed emitters along the light path to produce images on the main focal plane that ‘freeze’ different realizations of index perturbations. This method has the advantage of measuring directly the image motion and scintillation imparted by the dynamic spatial and temporal structure of local perturbations in the index of refraction along the light path, with a clean separation from seeing induced in the atmosphere above the dome. The strobed-source approach allows for rapid image motion and scintillation to be measured directly on the focal plane, even for large-aperture telescopes with wide-field instruments and slow shutters, such as that being constructed for the Rubin Observatory. A conceptual design is presented that uses the ‘guider’ CCDs in the Rubin telescope focal plane to make local-seeing measurements on demand, perhaps even during science exposures.
Unraveling circular polarimetric images of magnetically arrested accretion flows near event horizon of a black hole
Authors: Mościbrodzka M , Janiuk A , De Laurentis M 
Published: September 2021

ABSTRACT
Magnetically arrested accretion flows are thought to fuel some of the supermassive black holes and to power their relativistic jets. We calculate and study a time sequence of linear and circular polarimetric images of numerical, high resolution, and long-duration simulations of magnetically dominated flows to investigate observational signatures of strong magnetic fields near the event horizon of a non-rotating black hole. We find that the magnitude of resolved linear and circular polarizations is rather sensitive to the assumption of the coupling of electron and ions in the accretion flow. Models with cooler electrons have higher Faraday rotation and conversion depths, which result in scrambled linear polarization and enhanced circular polarization. In those high Faraday thickness cases, the circular polarization is particularly sensitive to dynamics of toroidasl-radial magnetic fields in the accretion flows. The models with high Faraday thickness are characterized by nearly constant handedness of circular polarization, consistent with observations of some accreting black holes. We also find that the emission region produced by light, which is lensed around the black hole, shows inversion of circular polarization handedness with respect to the handedness of the circular polarization of the entire emission region. Such polarity inversions are unique to near horizon emission.
Projecting the likely importance of weak-interaction-driven bulk viscosity in neutron star mergers
Authors: Most Elias R , Harris Steven P , Plumberg Christopher , Alford Mark G , Noronha Jorge , Noronha-Hostler Jacquelyn , Pretorius Frans , Witek Helvi , Yunes Nicolás 
Published: September 2021

ABSTRACT
In this work, we estimate how much bulk viscosity driven by Urca processes is likely to affect the gravitational wave signal of a neutron star coalescence. In the late inspiral, we show that bulk viscosity affects the binding energy at fourth post-Newtonian order. Even though this effect is enhanced by the square of the gravitational compactness, the coefficient of bulk viscosity is likely too small to lead to observable effects in the waveform during the late inspiral, when only considering the orbital motion itself. In the post-merger, however, the characteristic time-scales and spatial scales are different, potentially leading to the opposite conclusion. We post-process data from a state-of-the-art equal-mass binary neutron star merger simulation to estimate the effects of bulk viscosity (which was not included in the simulation itself). In that scenario, we find that bulk viscosity can reach high values in regions of the merger. We compute several estimates of how much it might directly affect the global dynamics of the considered merger scenario, and find that it could become significant. Even larger effects could arise in different merger scenarios or in simulations that include non-linear effects. This assessment is reinforced by a quantitative comparison with relativistic heavy-ion collisions where such effects have been explored extensively.
Dust traffic jams in inclined circumbinary protoplanetary discs – I. Morphology and formation theory
Authors: Aly Hossam , Gonzalez Jean-François , Nealon Rebecca , Longarini Cristiano , Lodato Giuseppe , Price Daniel J 
Published: September 2021

ABSTRACT
Gas and dust in inclined orbits around binaries experience precession induced by the binary gravitational torque. The difference in precession between gas and dust alters the radial drift of weakly coupled dust and leads to density enhancements where the radial drift is minimized. We explore this phenomenon using 3D hydrodynamical simulations to investigate the prominence of these ‘dust traffic jams’ and the evolution of the resulting dust sub-structures at different disc inclinations and binary eccentricities. We then derive evolution equations for the angular momentum of warped dust discs and implement them in a 1D code and present calculations to further explain these traffic jams. We find that dust traffic jams in inclined circumbinary discs provide significant dust density enhancements that are long lived and can have important consequences for planetesimal formation.
CHANG-ES XXIII: influence of a galactic wind in NGC 5775
Authors: Heald G H , Heesen V , Sridhar S S , Beck R , Bomans D J , Brüggen M , Chyży K T , Damas-Segovia A , Dettmar R-J , English J , Henriksen R , Ideguchi S , Irwin J , Krause M , Li J-T , Murphy E J , Nikiel-Wroczyński B , Piotrowska J , Rand R J , Shimwell T , Stein Y , Vargas C J , Wang Q D , van Weeren R J , Wiegert T 
Published: September 2021

ABSTRACT
We present new radio continuum images of the edge-on starburst galaxy NGC 5775, from LOFAR (140 MHz) and the Karl G. Jansky Very Large Array CHANG-ES survey (1500 MHz). We trace the non-thermal radio halo up to 13 kpc from the disc, measuring the non-thermal spectral index and estimating the total equipartition magnetic field strength (≈13 $\mu$G in the disc and ≈7 $\mu$G above the plane). The radio halo has a similar extent at both frequencies, displays evidence for localized cosmic ray streaming coinciding with prominent H α filaments and vertical extensions of the regular magnetic field, and exhibits a boxy morphology especially at 140 MHz. In order to understand the nature of the disc–halo flow, we extend our previous model of cosmic ray propagation by implementing an iso-thermal wind with a tunable ‘flux tube’ (approximately hyperboloidal) geometry. This updated model is successful in matching the vertical distribution of non-thermal radio emission, and the vertical steepening of the associated spectral index, in a consistent conceptual framework with few free parameters. Our new model provides the opportunity to estimate the mass outflow driven by the star formation process, and we find an implied rate of $\dot{M}\approx 3$–$6\, \mathrm{M_{\odot }\, yr^{-1}}$ (≈40–80 per cent of the star formation rate) if the escape velocity is reached, with substantial uncertainty arising from the poorly understood distribution of interstellar medium material entrained in the vertical flow. The wind may play a role in influencing the vertical gradient in rotational velocity.
Searching for orbital decay in a heartbeat star system KIC 3766353
Authors: Ou Jian-Wen , Yu Cong , Jiang Chen , Yang Ming , Niu Hubiao 
Published: September 2021

ABSTRACT
Theory suggests that the orbits of a large fraction of binary systems, including planet–star binary systems, shrink by a few orders of magnitude after formation. But so far, only one hot Jupiter with tidally driven orbital decay has been found by transit timing variations. We propose to search for orbital decay companions in heartbeat star systems because the orbital angular momentum is effectively transferred to the host star, causing tidal dissipation. KIC 3766353 is one of the heartbeat stars with tidally excited oscillations. We acquired the primary and the secondary eclipse time variations from the Kepler photometric light curves. Timing analysis shows that KIC 3766353 is a hierarchical triple system with a hidden third body and a red dwarf (mass 0.35 M⊙, radius 0.34 R⊙) in its inner orbit. The minimum mass of the third body is ∼0.26 M⊙, and the distance from the inner orbital is ∼111.4 R⊙. The period decay rate of the red dwarf is approximately 358 ms yr−1. The combined effects of the light-traveltime and the orbital decay lead to the observed timing variations. Future monitoring with long-time baseline observations is required to delve into the contributions of these two effects.
Decomposition of the CO stretching vibration band of laboratory H2O–CO ices irradiated by heavy ions
Authors: Seperuelo Duarte E , de Barros A L F , da Silveira E F , Domaracka A , Boduch P , Rothard H 
Published: September 2021

ABSTRACT
H2O and CO molecules are the main constituents of the interstellar dust grain ice mantles. Infrared spectra of the ices in line of sights of young stellar objects and background stars have shown that the CO stretching vibration band can be decomposed into three main components: 2143, 2139, and 2136 cm−1, assigned to CO in different environment sites. The relative strengths between the components have been associated with an evolutionary track of the interstellar molecular clouds. H2O:CO (3:2) and (10:1) ice samples were irradiated by 0.79 MeV/u 58Ni13+ ions to simulate the effects produced by heavy ion cosmic rays in typical interstellar ice mixtures. The CO stretching vibration band is decomposed into six Gaussian functions (2150, 2144, 2141, 2138, 2136, and 2133 cm−1) and their integrated absorbances were measured as a function of fluence. The results show that, at the final fluence, the component 2138 cm−1 is the main component of the CO stretching vibration band. The component 2150 cm−1 disappears at the beginning of irradiation. Based on the present and previous results, a time-scale for the components in the interstellar ices is proposed. For H2O:CO ices in the interstellar medium, it is predicted that, after 1 Ma, the main components of the CO stretching vibration band are the 2138 and 2141 cm−1, due to the CO monomers and dimers, respectively.
Modons on tidally synchronized extrasolar planets
Authors: Skinner J W , Cho J Y-K 
Published: September 2021

ABSTRACT
We investigate modons on tidally synchronized extrasolar planet atmospheres. Modons are dynamic, coherent flow structures composed of a pair of storms with opposite signs of vorticity. Modons are important because they can divert flows and lead to recognizable weather patterns. On synchronized planets, powered by the intense irradiation from the host star, large modons reach planetary-scale in size and exhibit quasi-periodic life-cycles – chaotically moving around the planet, breaking and reforming many times over long durations (e.g. thousands of planet days). Additionally, the modons transport and mix planetary-scale patches of hot and cold air around the planet, leading to high-amplitude and quasi-periodic signatures in the disc-averaged temperature flux. Hence, they induce variations of the ‘hotspot’ longitude to either side of the planet’s substellar point – consistent with observations at different epochs. The variability behaviour in our simulations broadly underscores the importance of accurately capturing vortex dynamics in extrasolar planet atmosphere modelling, particularly in understanding current observations.
Measuring cosmic density of neutral hydrogen via stacking the DINGO-VLA data
Authors: Chen Qingxiang , Meyer Martin , Popping Attila , Staveley-Smith Lister , Bryant Julia , Delhaize Jacinta , Holwerda B W , Cluver M E , Loveday J , Lopez-Sanchez Angel R , Zwaan Martin , Taylor E N , Hopkins A M , Wright Angus , Driver Simon , Brough S 
Published: September 2021

ABSTRACT
We use the 21-cm emission-line data from the Deep Investigation of Neutral Gas Origin-Very Large Array (DINGO-VLA) project to study the atomic hydrogen gas H i of the Universe at redshifts z &lt; 0.1. Results are obtained using a stacking analysis, combining the H i signals from 3622 galaxies extracted from 267 VLA pointings in the G09 field of the Galaxy and Mass Assembly Survey (GAMA). Rather than using a traditional one-dimensional spectral stacking method, a three-dimensional cubelet stacking method is used to enable deconvolution and the accurate recovery of average galaxy fluxes from this high-resolution interferometric data set. By probing down to galactic scales, this experiment also overcomes confusion corrections that have been necessary to include in previous single-dish studies. After stacking and deconvolution, we obtain a 30σ H i mass measurement from the stacked spectrum, indicating an average H i mass of ${\rm{M_{\rm{{H}\,\small{I}}}}}=(1.67\pm 0.18)\times 10^{9}~{\rm{{\rm M}_{\odot }}}$. The corresponding cosmic density of neutral atomic hydrogen is ${\rm{\Omega _{\rm{{H}\,\small{I}}}}}=(0.38\pm 0.04)\times 10^{-3}$ at redshift of z = 0.051. These values are in good agreement with earlier results, implying there is no significant evolution of $\Omega _{\rm{{H}\,\small{I}}}$ at lower redshifts.
Spin-based removal of instrumental systematics in 21 cm intensity mapping surveys
Authors: McCallum Nialh , Thomas Daniel B , Bull Philip , Brown Michael L 
Published: September 2021

ABSTRACT
Upcoming cosmological intensity mapping surveys will open new windows on the Universe, but they must first overcome a number of significant systematic effects, including polarization leakage. We present a formalism that uses scan strategy information to model the effect of different instrumental systematics on the recovered cosmological intensity signal for ‘single-dish’ (autocorrelation) surveys. This modelling classifies different systematics according to their spin symmetry, making it particularly relevant for dealing with polarization leakage. We show how to use this formalism to calculate the expected contamination from different systematics as a function of the scanning strategy. Most importantly, we show how systematics can be disentangled from the intensity signal based on their spin properties via map-making. We illustrate this, using a set of toy models, for some simple instrumental systematics, demonstrating the ability to significantly reduce the contamination to the observed intensity signal. Crucially, unlike existing foreground removal techniques, this approach works for signals that are non-smooth in frequency, e.g. polarized foregrounds. These map-making approaches are simple to apply and represent an orthogonal and complementary approach to existing techniques for removing systematics from upcoming 21 cm intensity mapping surveys.
On the impact of the numerical method on magnetic reconnection and particle acceleration – I. The MHD case
Authors: Puzzoni E , Mignone A , Bodo G 
Published: September 2021

ABSTRACT
We present 2D magnetohydrodynamics numerical simulations of tearing-unstable current sheets coupled to a population of non-thermal test particles, in order to address the problem of numerical convergence with respect to grid resolution, numerical method, and physical resistivity. Numerical simulations are performed with the pluto code for astrophysical fluid dynamics through different combinations of Riemann solvers, reconstruction methods, and grid resolutions at various Lundquist numbers. The constrained transport method is employed to control the divergence-free condition of magnetic field. Our results indicate that the reconnection rate of the background tearing-unstable plasma converges only for finite values of the Lundquist number and for sufficiently large grid resolutions. In general, it is found that (for a second-order scheme) the minimum threshold for numerical convergence during the linear phases requires the number of computational zones covering the initial current sheet width to scale roughly as $\sim \sqrt{\bar{S}}$, where $\bar{S}$ is the Lundquist number defined on the current sheet width. On the other hand, the process of particle acceleration is found to be nearly independent of the underlying numerical details inasmuch as the system becomes tearing-unstable and enters in its non-linear stages. In the limit of large $\bar{S}$, the ensuing power-law index quickly converge to p ≈ 1.7, consistently with the fast reconnection regime.
The origin of a universal filament width in molecular clouds
Authors: Priestley F D , Whitworth A P 
Published: September 2021

ABSTRACT
Filamentary structures identified in far-infrared observations of molecular clouds are typically found to have full widths at half-maximum $\sim 0.1\, {\rm pc}$. However, the physical explanation for this phenomenon is currently uncertain. We use hydrodynamic simulations of cylindrically symmetric converging flows to show that the full width at half-maximum of the resulting filament’s surface density profile, $\rm{\small FWHM}{_\Sigma }$, is closely related to the location of the accretion shock, where the inflow meets the boundary of the filament. For inflow Mach number, ${\cal M}$, between 1 and 5, filament $\rm{\small FWHM}{_\Sigma }$s fall in the range $0.03\, {\rm pc}\lesssim \rm{\small FWHM}{_\Sigma }\lesssim 0.3\, {\rm pc}$, with higher ${\cal M}$ resulting in narrower filaments. A large sample of filaments, seen at different evolutionary stages and with different values of ${\cal M}$, naturally results in a peaked distribution of $\rm{\small FWHM}{_\Sigma }$s similar in shape to that obtained from far-infrared observations of molecular clouds. However, unless the converging flows are limited to ${\cal M} \lesssim 3$, the peak of the distribution of $\rm{\small FWHM}{_\Sigma }$s is below the observed $\sim 0.1 \, {\rm pc}$.
Fast estimation of aperture-mass statistics – II. Detectability of higher order statistics in current and future surveys
Authors: Porth Lucas , Smith Robert E 
Published: September 2021

ABSTRACT
We explore an alternative method to the usual shear correlation function approach for the estimation of aperture mass statistics in weak-lensing survey data. Our approach builds on the direct estimator method. In this paper, we extend our analysis to statistics of arbitrary order and to the multiscale aperture mass statistics. We show that there always exists a linear order algorithm to retrieve any of these generalized aperture mass statistics from shape catalogues when the direct estimator approach is adopted. We validate our approach through application to a large number of Gaussian mock-lensing surveys where the true answer is known and we do this up to 10th-order statistics. We then apply our estimators to an ensemble of real-world mock catalogues obtained from N-body simulations – the SLICS mocks, and show that one can expect to retrieve detections of higher order clustering up to fourth order in a KiDS-1000 like survey. We expect that these methods will be of most utility for future wide-field surveys like Euclid and the Rubin Telescope.