bluuebunny/crossref_metadata_2025_split huggingface dataset:
The abacus cosmological N-body code
Authors: Garrison Lehman H , Eisenstein Daniel J , Ferrer Douglas , Maksimova Nina A , Pinto Philip A 
Published: September 2021

ABSTRACT
We present abacus, a fast and accurate cosmological N-body code based on a new method for calculating the gravitational potential from a static multipole mesh. The method analytically separates the near- and far-field forces, reducing the former to direct 1/r2 summation and the latter to a discrete convolution over multipoles. The method achieves 70 million particle updates per second per node of the Summit supercomputer, while maintaining a median fractional force error of 10−5. We express the simulation time-step as an event-driven ‘pipeline’, incorporating asynchronous events such as completion of co-processor work, input/output, and network communication. abacus has been used to produce the largest suite of N-body simulations to date, the abacussummit suite of 60 trillion particles, incorporating on-the-fly halo finding. abacus enables the production of mock catalogues of the volume and resolution required by the coming generation of cosmological surveys.
Broad-band study of BL Lac during flare of 2020: spectral evolution and emergence of HBL component
Authors: Prince Raj 
Published: September 2021

ABSTRACT
BL Lacertae (BL Lac) is categorized as TeV blazar and considered as a possible source of astrophysical neutrinos. In 2020, the brightest X-ray flare ever detected from it. A detailed study can answer many puzzling questions related to multiband emissions and fast-flux variability often seen in this kind of source. We have performed the temporal and spectral analysis of the brightest flare. The variability is characterized by the fractional variability amplitude and the variability time. We found that the source has crossed all its previous limits of flux and reached to a maximum ever seen from it in optical and X-rays. It is highly variable in X-rays with fractional variability above 100 per cent (1.8397 ± 0.0181) and the fastest variability time of 11.28 h within a day. The broad-band light-curves correlation with X-ray suggest a time lag of one day. A broad-band SED modelling is pursued to understand the possible physical mechanisms responsible for broad-band emission. Modelling requires two emission regions located at two different sites to explain the low and high flux states. A significant spectral change is observed in the optical-UV and X-ray spectrum during the high state, which eventually leads to shifts in the location of the synchrotron peak towards higher energy, suggesting an emergence of a new HBL component.
A broad-band radio study of PSR J0250+5854: the slowest spinning radio pulsar known
Authors: Agar C H , Weltevrede P , Bondonneau L , Grießmeier J-M , Hessels J W T , Huang W J , Karastergiou A , Keith M J , Kondratiev V I , Künsemöller J , Li D , Peng B , Sobey C , Stappers B W , Tan C M , Theureau G , Wang H G , Zhang C M , Cecconi B , Girard J N , Loh A , Zarka P 
Published: September 2021

ABSTRACT
We present radio observations of the most slowly rotating known radio pulsar PSR J0250+5854. With a 23.5-s period, it is close, or even beyond, the P-$\dot{P}$ diagram region thought to be occupied by active pulsars. The simultaneous observations with the Five-hundred-metre Aperture Spherical radio Telescope (FAST), the Chilbolton and Effelsberg Low Frequency Array (LOFAR) international stations, and New Extension in Nançay Upgrading loFAR (NenuFAR) represent a five-fold increase in the spectral coverage of this object, with the detections at 1250 (FAST) and 57 MHz (NenuFAR) being the highest and lowest frequency published, respectively, to date. We measure a flux density of 4 ± 2 $\mu$Jy at 1250 MHz and an exceptionally steep spectral index of $-3.5^{+0.2}_{-1.5}$, with a turnover below ∼95 MHz. In conjunction with observations of this pulsar with the Green Bank Telescope and the LOFAR Core, we show that the intrinsic profile width increases drastically towards higher frequencies, contrary to the predictions of conventional radius-to-frequency mapping. We examine polarimetric data from FAST and the LOFAR Core and conclude that its polar cap radio emission is produced at an absolute height of several hundreds of kilometres around 1.5 GHz, similar to other rotation-powered pulsars across the population. Its beam is significantly underfilled at lower frequencies, or it narrows because of the disappearance of conal outriders. Finally, the results for PSR J0250+5854 and other slowly spinning rotation-powered pulsars are contrasted with the radio-detected magnetars. We conclude that magnetars have intrinsically wider radio beams than the slow rotation-powered pulsars, and that consequently the latter’s lower beaming fraction is what makes objects such as PSR J0250+5854 so scarce.
Searching for Fermi GRB optical counterparts with the prototype Gravitational-wave Optical Transient Observer (GOTO)
Authors: Mong Y-L , Ackley K , Galloway D K , Dyer M , Cutter R , Brown M J I , Lyman J , Ulaczyk K , Steeghs D , Dhillon V , O’Brien P , Ramsay G , Noysena K , Kotak R , Breton R , Nuttall L , Pallé E , Pollacco D , Thrane E , Awiphan S , Burhanudin U , Chote P , Chrimes A , Daw E , Duffy C , Eyles-Ferris R , Gompertz B , Heikkilä T , Irawati P , Kennedy M , Killestein T , Levan A , Littlefair S , Makrygianni L , Marsh T , Mata-Sanchez D , Mattila S , Maund J , McCormac J , Mkrtichian D , Mullaney J , Rol E , Sawangwit U , Stanway E , Starling R , Strøm P , Tooke S , Wiersema K 
Published: September 2021

ABSTRACT
The typical detection rate of ∼1 gamma-ray burst (GRB) per day by the Fermi Gamma-ray Burst Monitor (GBM) provides a valuable opportunity to further our understanding of GRB physics. However, the large uncertainty of the Fermi localization typically prevents rapid identification of multiwavelength counterparts. We report the follow-up of 93 Fermi GRBs with the Gravitational-wave Optical Transient Observer (GOTO) prototype on La Palma. We selected 53 events (based on favourable observing conditions) for detailed analysis, and to demonstrate our strategy of searching for optical counterparts. We apply a filtering process consisting of both automated and manual steps to 60 085 candidates initially, rejecting all but 29, arising from 15 events. With ≈3 GRB afterglows expected to be detectable with GOTO from our sample, most of the candidates are unlikely to be related to the GRBs. Since we did not have multiple observations for those candidates, we cannot confidently confirm the association between the transients and the GRBs. Our results show that GOTO can effectively search for GRB optical counterparts thanks to its large field of view of ≈40 deg2 and its depth of ≈20 mag. We also detail several methods to improve our overall performance for future follow-up programmes of Fermi GRBs.
Strong scatterings of cold Jupiters and their influence on inner low-mass planet systems: theory and simulations
Authors: Pu Bonan , Lai Dong 
Published: September 2021

ABSTRACT
Recent observations have indicated a strong connection between compact (a ≲ 0.5 au) super-Earth and mini-Neptune systems and their outer (a ≳ a few au) giant planet companions. We study the dynamical evolution of such inner systems subject to the gravitational effect of an unstable system of outer giant planets, focusing on systems whose end configurations feature only a single remaining outer giant. In contrast to similar studies which used on N-body simulations with specific (and limited) parameters or scenarios, we implement a novel hybrid algorithm which combines N-body simulations with secular dynamics with aims of obtaining analytical understanding and scaling relations. We find that the dynamical evolution of the inner planet system depends crucially on Nej, the number of mutual close encounters between the outer planets prior to eventual ejection/merger. When Nej is small, the eventual evolution of the inner planets can be well described by secular dynamics. For larger values of Nej, the inner planets gain orbital inclination and eccentricity in a stochastic fashion analogous to Brownian motion. We develop a theoretical model, and compute scaling laws for the final orbital parameters of the inner system. We show that our model can account for the observed eccentric super-Earths/mini-Neptunes with inclined cold Jupiter companions, such as HAT-P-11, Gliese 777, and π Men.
Radiative MHD simulations of photon bubbles in radiation-supported magnetized atmospheres of neutron stars with isotropic Thomson scattering
Authors: (张力中) Lizhong Zhang , Blaes Omer , (姜燕飞) Yan-Fei Jiang 
Published: September 2021

ABSTRACT
A major uncertainty in the structure and dynamics of magnetized, radiation pressure dominated neutron star accretion columns in X-ray pulsars and pulsating ultraluminous X-ray sources is that they are thought to be subject to the photon bubble instability. We present the results of two-dimensional radiation relativistic magnetohydrodynamic simulations of a non-accreting, static atmosphere to study the development of this instability assuming isotropic Thomson scattering in the slow diffusion regime that is relevant to neutron star accretion columns. Photon bubbles generally grow faster towards shorter wavelengths, until a maximum growth rate is achieved at the radiation viscosity length-scale, which is generally quite small and requires high numerical resolution to simulate. We confirm the consistency between our simulation results and linear theory in detail, and show that the non-linear evolution inevitably leads to collapse of the atmosphere with the higher resolution simulation collapsing faster due to the presence of shorter length-scale non-linear structures. At least in static atmospheres with horizontally periodic boundary conditions, this resolution dependence may make simulations of the non-linear dynamics of photon bubble instability in neutron star accretion columns challenging. It remains to be seen whether these difficulties will persist upon inclusion of an accretion flow through the top and magnetically confined horizontal boundaries through which photons can escape. Our results here provide a foundation for such future work.
Using in situ solar-wind observations to generate inner-boundary conditions to outer-heliosphere simulations – I. Dynamic time warping applied to synthetic observations
Authors: Owens Mathew J , Nichols Jonathan D 
Published: September 2021

ABSTRACT
The structure and dynamics of the magnetospheres of the outer planets, particularly Saturn and Jupiter, have been explored through both remote and in situ observations. Interpreting these observations often necessitates simultaneous knowledge of the solar-wind conditions impinging on the magnetosphere. Without an available upstream monitor, solar-wind context is typically provided using models initiated with either the output of magnetogram-constrained coronal models or, more commonly, in situ observations from 1 au. While 1-au observations provide a direct measure of solar-wind conditions, they are single-point observations and thus require interpolation to provide inputs to outer-heliosphere solar-wind models. In this study, we test the different interpolation methods using synthetic 1-au observations of time-evolving solar-wind structure. The simplest method is ‘corotation’, which assumes solar-wind structure is a steady state and rotates with the Sun. This method of reconstruction produces discontinuities in the solar-wind inputs as new observations become available. This can be reduced by corotating both backwards and forwards in time, but this still introduces large errors in the magnitude and timing of solar-wind streams. We show how the dynamic time warping (DTW) algorithm can provide around an order-of-magnitude improvement in solar-wind inputs to the outer-heliosphere model from in situ observations near 1 au. This is intended to build the foundation for further work demonstrating and validating methods to improve inner-boundary conditions of outer-heliosphere solar-wind models, including dealing with solar-wind transients and quantifying the improvements at Saturn and Jupiter.
GRMHD simulations of BH activation by small scale magnetic loops: formation of striped jets and active coronae
Authors: Chashkina Anna , Bromberg Omer , Levinson Amir 
Published: September 2021

ABSTRACT
We have performed a series of numerical experiments aimed at studying the activation of Kerr black holes (BHs) by advection of small scale magnetic fields. Such configurations may potentially give rise to the formation of quasi-striped Blandford-Znajek jets. It can also lead to enhanced dissipation and generation of plasmoids in current sheets formed in the vicinity of the BH horizon, which may constitute a mechanism to power the hard X-ray emission seen in many accreting BH systems (a la lamppost models). Our analysis suggests that formation of quasi-striped jets with significant power may be possible provided loops with alternating polarity having sizes larger than ∼10rg or so can be maintained (either form sporadically or advected from outside) at a radius ≲ 102rg. This conclusion is consistent with recent results of general relativistic force-free simulations. We also find that the accretion dynamics exhibits cyclic behaviour in Magnetically Arrested Disc states, alternating between high accretion phases and quenched accretion phases during which the magnetosphere becomes force-free out to radii ≳ 10rg. We suggest that such a behaviour should lead to notable variations of the observed luminosity and image of the inner disc (BH shadow image). Finally, we find that the transition between accreted loops on the BH gives rise to the formation of current sheets and energetic plasmoids on the jet boundary during intermittent periods when the jet becomes inactive, in addition to an equatorial current sheet that forms during peaks in the jet activity.
On the initial mass–radius relation of stellar clusters
Authors: Choksi Nick , Kruijssen J M Diederik 
Published: September 2021

ABSTRACT
Young stellar clusters across nearly five orders of magnitude in mass appear to follow a power-law mass–radius relationship (MRR), $R_{\star }\propto M_{\star }^{\alpha }$, with α ≈ 0.2–0.33. We develop a simple analytic model for the cluster mass–radius relation. We consider a galaxy disc in hydrostatic equilibrium, which hosts a population of molecular clouds that fragment into clumps undergoing cluster formation and feedback-driven expansion. The model predicts a mass–radius relation of $R_{\star }\propto M_{\star }^{1/2}$ and a dependence on the kpc-scale gas surface density $R_{\star }\propto \Sigma _{\rm g}^{-1/2}$, which results from the formation of more compact clouds (and cluster-forming clumps within) at higher gas surface densities. This environmental dependence implies that the high-pressure environments in which the most massive clusters can form also induce the formation of clusters with the smallest radii, thereby shallowing the observed MRR at high-masses towards the observed $R_{\star }\propto M_{\star }^{1/3}$. At low cluster masses, relaxation-driven expansion induces a similar shallowing of the MRR. We combine our predicted MRR with a simple population synthesis model and apply it to a variety of star-forming environments, finding good agreement. Our model predicts that the high-pressure formation environments of globular clusters at high redshift naturally led to the formation of clusters that are considerably more compact than those in the local Universe, thereby increasing their resilience to tidal shock-driven disruption and contributing to their survival until the present day.
Parameters of the X-ray binary system Scorpius X-1
Authors: Cherepashchuk A M , Khruzina T S , Bogomazov A I 
Published: September 2021

ABSTRACT
We modelled optical light curves of Sco X-1 obtained by the Kepler Space Telescope during the K2 mission. Modelling was performed for the case of strong heating of the optical star and accretion disc by X-rays. In the model considered, the optical star fully filled its Roche lobe. We investigated the inverse problem in wide ranges of values of model parameters and estimated the following parameters of Sco X-1: the mass ratio of components q = Mx/Mv = 3.6 (3.5–3.8), where Mx and Mv are the masses of the neutron and optical stars correspondingly; the orbital inclination was i = 30° (25–34°). In the brackets the uncertainties of parameters q and i are shown; these originated due to uncertainties of characteristics of the physical model of Sco X-1. The temperature of the non-heated optical star was T2 = 2500–3050 K, its radius was R2 = 1.25R⊙ = 8.7 × 1010 cm, and its bolometric luminosity was Lbol = (2.1–4.6) × 1032 erg s−1. The mass of the star was $M_v\simeq 0.4\, \mathrm{M}_{\odot }$. The contribution of the X-ray-heated accretion disc dominated in the total optical emission of Sco X-1. The transition between low and high states occurred due to the increase of X-ray luminosity by a factor of 2–3.
Global 3D radiation hydrodynamic simulations of proto-Jupiter’s convective envelope
Authors: Zhu Zhaohuan , Jiang Yan-Fei , Baehr Hans , Youdin Andrew N , Armitage Philip J , Martin Rebecca G 
Published: September 2021

ABSTRACT
The core accretion model of giant planet formation has been challenged by the discovery of recycling flows between the planetary envelope and the disc that can slow or stall envelope accretion. We carry out 3D radiation hydrodynamic simulations with an updated opacity compilation to model the proto-Jupiter’s envelope. To isolate the 3D effects of convection and recycling, we simulate both isolated spherical envelopes and envelopes embedded in discs. The envelopes are heated at given rates to achieve steady states, enabling comparisons with 1D models. We vary envelope properties to obtain both radiative and convective solutions. Using a passive scalar, we observe significant mass recycling on the orbital time-scale. For a radiative envelope, recycling can only penetrate from the disc surface until ∼0.1–0.2 planetary Hill radii, while for a convective envelope, the convective motion can ‘dredge up’ the deeper part of the envelope so that the entire convective envelope is recycled efficiently. This recycling, however, has only limited effects on the envelopes’ thermal structure. The radiative envelope embedded in the disc has identical structure as the isolated envelope. The convective envelope has a slightly higher density when it is embedded in the disc. We introduce a modified 1D approach which can fully reproduce our 3D simulations. With our updated opacity and 1D model, we recompute Jupiter’s envelope accretion with a 10 M⊕ core, and the time-scale to runaway accretion is shorter than the disc lifetime as in prior studies. Finally, we discuss the implications of the efficient recycling on the observed chemical abundances of the planetary atmosphere (especially for super-Earths and mini-Neptunes).
State transitions of GX 339-4 during its outburst rising phase
Authors: Shui Q C , Yin H X , Zhang S , Qu J L , Chen Y P , Kong L D , Wang P J , Zhang H F , Song J X , Ning B , Wang Y F , Chang Z , Zhang P 
Published: September 2021

ABSTRACT
We investigate systematically four outbursts of black hole system GX 339-4 observed by the Rossi X-ray Timing Explorer (RXTE) in both spectral and timing domains and find that these outbursts have some common properties, although they experience different ‘q’ tracks in the hardness–intensity diagram (HID). While the spectral indices are around 1.5 in the low/hard state (LHS) and 2.4 in the soft intermediate state (SIMS) and high/soft state (HSS), the spectral parameters of thermal, non-thermal, and reflection components vary significantly in transitions from the LHS to HIMS. Also, the quasi-periodic oscillation (QPO) shows a peculiar behaviour during the state transition between the LHS and HIMS: the RMS drop of the type C fundamental QPO is accompanied by the appearance of the second harmonic. Interestingly, the QPO RMS is found to have a similar linear relationship with the non-thermal fraction of emission in different outbursts. These findings provide more clues to aid our understanding of the outbursts of a black hole X-ray binary system.
Morphology of solar system scale plasma lenses in the interstellar medium: a test from pulsar scintillation parabolic arcs
Authors: Shi Xun 
Published: September 2021

ABSTRACT
Scintillation spectra of some pulsars have suggested the existence of ≲ AU scale density structures in the ionized interstellar medium, whose astrophysical correspondence is still a mystery. The detailed study of Brisken et al. suggested two possible morphologies for these structures: A parallel set of filaments or sheets (the ‘parallel stripes model’), or a filament broken up into denser knots (the ‘threaded beads model’). Here, we propose a straightforward test that can distinguish these two morphologies: Whether the apex of the main parabolic arc created by the scattered images deviates from the origin of the scintillation spectrum or not. In the ‘parallel stripes’ model, the scattered images move along the stripes as the relative position of the pulsar moves. As a result, the pulsar is always co-linear with the scattered images, and thus, the apex of the main parabolic arc stays at the origin of the scintillation spectrum. In the ‘threaded beads’ model, the scattered images remain at almost fixed positions relative to the density structures, and thus, the pulsar is not co-linear with the scattered images at most times, leading to an offset between the apex and the origin. Looking for this possible offset in a large sample of pulsar scintillation spectra, or monitoring the evolution of parabolic arcs will help pin down the morphology of these tiny density structures and constrain their astrophysical origin.
Exploring the possibility of Peter Pan discs across stellar mass
Authors: Wilhelm Martijn J C , Portegies Zwart Simon 
Published: September 2021

ABSTRACT
Recently, several accreting M dwarf stars have been discovered with ages far exceeding the typical protoplanetary disc lifetime. These ‘Peter Pan discs’ can be explained as primordial discs that evolve in a low-radiation environment. The persistently low masses of the host stars raise the question whether primordial discs can survive up to these ages around stars of higher mass. In this work we explore the way in which different mass loss processes in protoplanetary discs limit their maximum lifetimes, and how this depends on host star mass. We find that stars with masses ≲0.6 M⊙ can retain primordial discs for ∼50 Myr. At stellar masses ≳0.8 M⊙, the maximum disc lifetime decreases strongly to below 50 Myr due to relatively more efficient accretion and photoevaporation by the host star. Lifetimes up to 15 Myr are still possible for all host star masses up to ∼2 M⊙. For host star masses between 0.6 and 0.8 M⊙, accretion ceases and an inner gap forms before 50 Myr in our models. Observations suggest that such a configuration is rapidly dispersed. We conclude that Peter Pan discs can only occur around M dwarf stars.