Sazuna/UAT_keywords huggingface dataset:
The Halo Mass Function of Late-type Galaxies from H I Kinematics. We present an empirical method to measure the halo mass function (HMF) of galaxies. We determine the relation between the H I line width from single-dish observations and the dark matter halo mass (M 200) inferred from rotation-curve fits in the Spitzer Photometry and Accurate Rotation Curves (SPARC) database, then we apply this relation to galaxies from the H I Parkes All Sky Survey (HIPASS) to derive the HMF. This empirical HMF is well fit by a Schechter function, and matches that expected in the Λ Cold Dark Matter (ΛCDM) model over the range 1010.5 &lt; M 200 &lt; 1012 M ⊙. More massive halos must be poor in neutral gas to maintain consistency with the power law predicted by ΛCDM. We detect no discrepancy at low masses. The lowest halo mass probed by HIPASS, however, is just greater than the mass scale where the Local Group missing satellite problem sets in. The integrated mass density associated with the dark matter halos of H I-detected galaxies sums to Ωm,gal ≈ 0.03 over the probed mass range.

Keywords: Galaxy dark matter halos, Galaxy formation, Cold dark matter, H I line emission, Dark matter density, Stellar mass functions, Galaxy abundances, Galaxy kinematics, Galaxy evolution, Galaxy counts, Galaxy masses, Galaxy rotation curves
Orbital Decay in a 20 Minute Orbital Period Detached Binary with a Hydrogen-poor Low-mass White Dwarf. We report the discovery of a detached double white dwarf binary with an orbital period of ≈20.6 minutes, PTF J053332.05+020911.6. The visible object in this binary, PTF J0533+0209B, is a ≈0.17 M ⊙ mass white dwarf with a helium-dominated atmosphere containing traces of hydrogen. This object exhibits ellipsoidal variations due to tidal deformation, and is the visible component in a single-lined spectroscopic binary with a velocity semi-amplitude of K  B  = 618.7 ± 6.9 km s-1. We have detected significant orbital decay due to the emission of gravitational radiation, and we expect that the Laser Interferometer Space Antenna (LISA) will detect this system with a signal to noise of {8.4}-3.0+4.2 after four years of operation. Because this system already has a well-determined orbital period, radial velocity semi-amplitude, temperature, atmospheric composition, surface gravity, and orbital decay rate, a LISA signal will help fully constrain the properties of this system by providing a direct measurement of its inclination. Thus, this binary demonstrates the synergy between electromagnetic and gravitational radiation for constraining the physical properties of an astrophysical object.

Keywords: High energy astrophysics, Relativistic binary stars, White dwarf stars, Compact binary stars, Gravitational wave sources, Spectroscopic binary stars, Ellipsoidal variable stars, Detached binary stars
Small-scale H I Channel Map Structure Is Cold: Evidence from Na I Absorption at High Galactic Latitudes. The spatial distribution of neutral hydrogen (H I) emission is a powerful probe of interstellar medium physics. The small-scale structure in H I channel maps is often assumed to probe the velocity field rather than real density structures. In this work we directly test this assumption, using high-resolution GALFA-H I observations and 50,985 quasar spectra from the Sloan Digital Sky Survey. We measure the equivalent widths of interstellar Na I D1 and Na I D2 absorption, and robustly conclude that together they depend nearly four times as strongly on the column density of small-scale structure in H I than on either the large-scale H I structure or the total H I column. This is inconsistent with the hypothesis that small-scale channel map structure is driven by velocity crowding. Instead, the data favor the interpretation that this emission structure predominantly originates in cold, dense interstellar material, consistent with a clumpy cold neutral medium.

Keywords: Quasar absorption line spectroscopy, Interstellar atomic gas, Interstellar magnetic fields, Interstellar absorption, Interstellar medium
Infrared Spectroscopy of the Recent Outburst in V1047 Cen (Nova Centauri 2005). Fourteen years after its eruption as a classical nova (CN), V1047 Cen (Nova Cen 2005) began an unusual re-brightening in 2019 April. The amplitude of the brightening suggests that this is a dwarf nova (DN) eruption in a CN system. Very few CNe have had DN eruptions within decades of the main CN outburst. The 14 yr separating the CN and DN eruptions of V1047 Cen is the shortest of all instances recorded thus far. Explaining this rapid succession of CN and DN outbursts in V1047 Cen may be challenging within the framework of standard theories for DN outbursts. Following a CN eruption, the mass accretion rate is believed to remain high (\dot{M}∼ {10}-8 {M}☉  {yr}}-1) for a few centuries, due to the irradiation of the secondary star by the still-hot surface of the white dwarf. Thus a DN eruption is not expected to occur during this high mass accretion phase as DN outbursts, which result from thermal instabilities in the accretion disk, and arise during a regime of low mass accretion rate (\dot{M}∼ {10}-10 {M}☉  {yr}}-1). Here we present near-infrared spectroscopy to show that the present outburst is most likely a DN eruption, and discuss the possible reasons for its early occurrence. Even if the present re-brightening is later shown to be due to a cause other than a DN outburst, the present study provides invaluable documentation of this unusual event.

Keywords: Cataclysmic variable stars, Infrared sources
Low-frequency Variability in Massive Stars: Core Generation or Surface Phenomenon?. Bowman et al. reported low-frequency photometric variability in 164 O- and B-type stars observed with K2 and TESS. They interpret these motions as internal gravity waves, which could be excited stochastically by convection in the cores of these stars. The detection of internal gravity waves in massive stars would help distinguish between massive stars with convective or radiative cores, determine core size, and would provide important constraints on massive star structure and evolution. In this work, we study the observational signature of internal gravity waves generated by core convection. We calculate the wave transfer function, which links the internal gravity wave amplitude at the base of the radiative zone to the surface luminosity variation. This transfer function varies by many orders of magnitude for frequencies ≲1 days-1, and has regularly spaced peaks near 1 days-1 due to standing modes. This is inconsistent with the observed spectra that have smooth “red noise” profiles, without the predicted regularly spaced peaks. The wave transfer function is only meaningful if the waves stay predominately linear. We next show that this is the case: low-frequency traveling waves do not break unless their luminosity exceeds the radiative luminosity of the star; the observed luminosity fluctuations at high frequencies are so small that standing modes would be stable to nonlinear instability. These simple calculations suggest that the observed low-frequency photometric variability in massive stars is not due to internal gravity waves generated in the core of these stars. We finish with a discussion of (sub)surface convection that produces low-frequency variability in low-mass stars; this is very similar to that observed in Bowman et al. in higher-mass stars.

Keywords: Internal waves, Massive stars, Stellar oscillations, Asteroseismology, Astrophysical fluid dynamics
Comet 240P/NEAT Is Stirring. Comets are primitive objects that formed in the protoplanetary disk, and have been largely preserved over the history of the solar system. However, they are not pristine, and surfaces of cometary nuclei do evolve. In order to understand the extent of their primitive nature, we must define the mechanisms that affect their surfaces and comae. We examine the lightcurve of comet 240P/NEAT over three consecutive orbits, and investigate three events of significant brightening (Δm ∼ -2 mag). Unlike typical cometary outbursts, each of the three events are long-lived, with enhanced activity for at least 3-6 months. The third event, observed by the Zwicky Transient Facility, occurred in at least two stages. The anomalous behavior appears to have started after the comet was perturbed by Jupiter in 2007, reducing its perihelion distance from 2.53 to 2.12 au. We suggest that the brightening events are temporary transitions to a higher baseline activity level, brought on by the increased insolation, which has warmed previously insulated sub-surface layers. The new activity is isolated to one or two locations on the nucleus, indicating that the surface or immediate sub-surface is heterogeneous. Further study of this phenomenon may provide insight into cometary outbursts, the structure of the near-surface nucleus, and cometary nucleus mantling.

Keywords: Light curves
Two Years of Nonthermal Emission from the Binary Neutron Star Merger GW170817: Rapid Fading of the Jet Afterglow and First Constraints on the Kilonova Fastest Ejecta. We present Chandra and Very Large Array observations of GW170817 at ∼521-743 days post-merger, and a homogeneous analysis of the entire Chandra data set. We find that the late-time nonthermal emission follows the expected evolution of an off-axis relativistic jet, with a steep temporal decay {F}ν \propto {t}-1.95+/- 0.15 and power-law spectrum {F}ν \propto {ν }-0.575+/- 0.007. We present a new method to constrain the merger environment density based on diffuse X-ray emission from hot plasma in the host galaxy and find n≤slant 9.6× {10}-3 {cm}}-3. This measurement is independent from inferences based on jet afterglow modeling and allows us to partially solve for model degeneracies. The updated best-fitting model parameters with this density constraint are a fireball kinetic energy {E}0={1.5}-1.1+3.6× {10}49 {erg} ({E}iso}={2.1}-1.5+6.4× {10}52 {erg}) and jet opening angle {θ }0={5.9}-0.7+1.0 \deg with characteristic Lorentz factor {{{Γ }}}j={163}-43+23, expanding in a low-density medium with {n}0={2.5}-1.9+4.1× {10}-3 {cm}}-3 and viewed {θ }obs}={30.4}-3.4+4.0 \deg off-axis. The synchrotron emission originates from a power-law distribution of electrons with index p={2.15}-0.02+0.01. The shock microphysics parameters are constrained to {∊ }{{e}}={0.18}-0.13+0.30 and {∊ }{{B}}={2.3}-2.2+16.0× {10}-3. Furthermore, we investigate the presence of X-ray flares and find no statistically significant evidence of ≥2.5σ of temporal variability at any time. Finally, we use our observations to constrain the properties of synchrotron emission from the deceleration of the fastest kilonova ejecta with energy {E}kKN}\propto {({{Γ }}β )}-α  into the environment, finding that shallow stratification indexes α ≤ 6 are disfavored. Future radio and X-ray observations will refine our inferences on the fastest kilonova ejecta properties.

Keywords: Neutron stars, Gamma-ray bursts, X-ray transient sources, Diffuse x-ray background, Radio transient sources
Large- and Medium-scale Anisotropies in the Arrival Directions of Cosmic Rays Observed with KASCADE-Grande. We search for anisotropies in the arrival directions of cosmic rays (CRs) observed by the KASCADE-Grande air shower experiment. The analysis is based on public data of about 23.7 million events with reconstructed primary energies above 1 PeV. We apply a novel maximum-likelihood reconstruction method for the CR anisotropy that compensates for spurious anisotropies induced by local detector effects. We find no evidence for a large-scale dipole anisotropy in the data, consistent with official results based on the conventional east-west derivative method. On the other hand, a subset of CRs with a median energy of 33 PeV shows strong evidence for a medium-scale feature with an angular diameter of 40°. After accounting for the look-elsewhere effect, the post-trial significance of this medium-scale feature is at the level of 4σ.

Keywords: Astronomy data analysis, Cosmic rays
Can Kilonova Light Curves Be Standardized?. Binary neutron star (NS) mergers have been recently confirmed to be the progenitors of the optical transients kilonovae (KNe). KNe are powered by the radioactive decay of neutron-rich elements (r-process elements), which are believed to be the product of disruption of NSs during their merger. KNe exhibit interesting parallels with SNe Ia, whose light curves show specific correlations that allow them to be used as standardizable candles. In this Letter, we investigate whether KNe light curves could exhibit similar correlations. While a satisfactory answer to this question can only be provided by future KNe observations, employing theoretical models we explore whether there is any ground for harboring such expectations. Using semi-analytic models of KNe light curves in conjunction with results from numerical relativity simulations of binary NS mergers, we obtain the maximum bolometric luminosity ({L}Bol}\max ) and decline from peak luminosity ({{Δ }}{log}{L}Bol}) for a simulated population of mergers. We find that theoretical light curves of KNe show remarkable correlations despite the complex physics governing their behavior. This presents a possibility of future observations to uncover such correlations in the observed light curves, eventually allowing observers to standardize these light curves and to use them for local distance measurements.

Keywords: Neutron stars, Relativistic stars, Explosive nucleosynthesis, Relativistic binary stars, Distance measure, Transient sources, Gravitational wave sources, Hubble constant, Radiative transfer equation, Gravitational waves, Compact objects
J0453+1559: A Neutron Star-White Dwarf Binary from a Thermonuclear Electron-capture Supernova?. The compact binary radio pulsar system J0453+1559 consists of a recycled pulsar as primary component of 1.559(5) M ⊙ and an unseen companion star of 1.174(4) M ⊙. Because of the relatively large orbital eccentricity of e = 0.1125, it was argued that the companion is a neutron star (NS), making it the NS with the lowest accurately determined mass to date. However, a direct observational determination of the nature of the companion is currently not feasible. Moreover, state-of-the-art stellar evolution and supernova modeling are contradictory concerning the possibility of producing such a low-mass NS remnant. Here we challenge the NS interpretation by reasoning that the lower-mass component could instead be a white dwarf born in a thermonuclear electron-capture supernova (tECSN) event, in which oxygen-neon deflagration in the degenerate stellar core of an ultra-stripped progenitor ejects several 0.1 M ⊙ of matter and leaves a bound ONeFe white dwarf as the second-formed compact remnant. We determine the ejecta mass and remnant kick needed in this scenario to explain the properties of PSR J0453+1559 by a NS-white dwarf system. More work on tECSNe is needed to assess the viability of this scenario.

Keywords: Neutron stars, Late stellar evolution, White dwarf stars, Compact binary stars, Supernova remnants, Binary pulsars, Supernovae
Spontaneous Generation of δ-sunspots in Convective Magnetohydrodynamic Simulation of Magnetic Flux Emergence. Observations reveal that strong solar flares and coronal mass ejections tend to occur in complex active regions characterized by δ-sunspots, spot rotation, sheared polarity inversion lines (PILs), and magnetic flux ropes. Here we report on the first modeling of spontaneous δ-spot generation as a result of flux emergence from the turbulent convection zone. Utilizing state-of-the-art radiative magnetohydrodynamics code R2D2, we simulate the emergence of a force-free flux tube in the convection zone that stretches down to -140 Mm. Elevated by large-scale convective upflows, the tube appears on the photosphere as two emerging bipoles. The opposite polarities collide against each other due to the subsurface connectivity, and they develop into a pair of closely packed δ-spots. The Lorentz force drives the spot rotation and a strong counter-streaming flow of 10 km s-1 at the PIL in δ-spots, which, in tandem with local convection, strengthens the horizontal field to 4 kG and builds up a highly sheared PIL. In the atmosphere above the PIL, a flux rope structure is created. All these processes follow the multi-buoyant segment theory of the δ-spot formation, and they occur as a natural consequence of interaction between magnetic flux and turbulent convection, suggesting that the generation of δ-spots and the resultant flare eruptions may be a stochastically determined process.

Keywords: Magnetohydrodynamics, Solar flares, Solar interior, Sunspots, Solar magnetic fields, Solar coronal mass ejections
A Bright Electromagnetic Counterpart to Extreme Mass Ratio Inspirals. The extreme mass ratio inspiral (EMRI), defined as a stellar-mass compact object inspiraling into a supermassive black hole (SMBH), has been widely argued to be a low-frequency gravitational-wave (GW) source. Providing accurate measurements of the black hole mass and spin of EMRIs is one of the primary interests for the Laser Interferometer Space Antenna (LISA). However, it is currently understood that there are no electromagnetic (EM) counterparts to EMRIs. Here we show a new formation channel of EMRIs with tidal disruption flares as EM counterparts. In this scenario, flares can be produced from the tidal stripping of the helium (He) envelope of a massive star by an SMBH. The remaining compact core of the massive star then evolves into an EMRI. We find that, under a certain initial eccentricity and semimajor axis, the GW frequency of the inspiral can enter the LISA band within 10 ∼ 20 yr, which makes the tidal disruption flare an EM precursor to an EMRI. Although the event rate is just 2× {10}-4 {Gpc}}-3 {yr}}-1, this association not only improves the localization accuracy of LISA and helps us to find the host galaxy of EMRI, but it also serves as a new GW standard siren for cosmology.

Keywords: Accretion, Tidal disruption, Gravitational wave sources
A Model-independent Determination of the Hubble Constant from Lensed Quasars and Supernovae Using Gaussian Process Regression. Strongly lensed quasar systems with time delay measurements provide “time delay distances,” which are a combination of three angular diameter distances and serve as powerful tools to determine the Hubble constant H 0. However, current results often rely on the assumption of the ΛCDM model. Here we use a model-independent method based on Gaussian process to directly constrain the value of H 0. By using Gaussian process regression, we can generate posterior samples of unanchored supernova distances independent of any cosmological model and anchor them with strong lens systems. The combination of a supernova sample with large statistics but no sensitivity to H 0 with a strong lens sample with small statistics but H 0 sensitivity gives a precise H 0 measurement without the assumption of any cosmological model. We use four well-analyzed lensing systems from the state-of-art lensing program H0LiCOW and the Pantheon supernova compilation in our analysis. Assuming the universe is flat, we derive the constraint H 0 = 72.2 ± 2.1 km s-1 Mpc-1, a precision of 2.9%. Allowing for cosmic curvature with a prior of Ω k  = [-0.2, 0.2], the constraint becomes {H}0={73.0}-3.0+2.8 {km} {{{s}}}-1 {Mpc}}-1.

Keywords: Hubble constant, Strong gravitational lensing, Dark energy, Cosmological parameters
First Results from TESS Observations of Comet 46P/Wirtanen. We report on initial results from 20 days’ worth of Transiting Exoplanet Survey Satellite spacecraft observations of comet 46P/Wirtanen. The long-duration, high-cadence measurements show a 2018 September 26 outburst that exhibited a two-phase, 0.5 mag brightening profile, and may be the best temporally characterized natural outburst ever recorded. Gas velocities from the outburst peaked at 800 {{m}} {{{s}}}-1, while dust expanded at only 10s of {{m}} {{{s}}}-1. Coadded images also revealed a previously unreported dust trail that extends beyond the 24° field of view.

Keywords: Comets, Short period comets
A Compact Source for Quasi-periodic Pulsation in an M-class Solar Flare. Quasi-periodic pulsations (QPPs) are usually found in the light curves of solar and stellar flares; they carry the features of time characteristics and plasma emission of the flaring core, and could be used to diagnose the coronas of the Sun and remote stars. In this study, we combined the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory and the Nobeyama Radioheliograph (NoRH) to observe an M7.7 class flare that occurred at active region 11520 on 2012 July 19. A QPP was detected both in the AIA 131 \mathringA bandpass and the NoRH 17 {GHz} channel; it had a period of about four minutes. In the spatial distribution of Fourier power, we found that this QPP originated from a compact source and that it overlapped with the X-ray source above the loop top. The plasma emission intensities in the AIA 131 \mathringA bandpass were highly correlated within this region. The source region is further segmented into stripes that oscillated with distinctive phases. Evidence in this event suggests that this QPP was likely to be generated by intermittent energy injection into the reconnection region.

Keywords: Active solar corona, Magnetohydrodynamics, Solar flares
Particle Acceleration in Shearing Flows: Efficiencies and Limits. We examine limits to the efficiency for particle acceleration in shearing flows, showing that relativistic flow speeds are required for efficient gradual shear acceleration. We estimate maximum achievable particle energies for parameters applicable to the relativistic jets of active galactic nuclei. The implications of our estimates is that if large-scale jets are relativistic, then efficient electron acceleration up to several PeV and proton acceleration up to several EeV energies appears feasible. This suggests that shear particle acceleration could lead to a continued energization of synchrotron X-ray emitting electrons, and be of relevance for the production of ultra-high-energy cosmic-ray particles.

Keywords: High energy astrophysics, Relativistic jets, Radio jets, Ultra-high-energy cosmic radiation
An Improved Distance to NGC 4258 and Its Implications for the Hubble Constant. NGC 4258 is a critical galaxy for establishing the extragalactic distance scale and estimating the Hubble constant ({H}0). Water masers in the nucleus of the galaxy orbit about its supermassive black hole, and very long baseline interferometric observations of their positions, velocities, and accelerations can be modeled to give a geometric estimate of the angular-diameter distance to the galaxy. We have improved the technique to obtain model parameter values, reducing both statistical and systematic uncertainties compared to previous analyses. We find the distance to NGC 4258 to be 7.576 ± 0.082 (stat.) ± 0.076 (sys.) Mpc. Using this as the sole source of calibration of the Cepheid-SN Ia distance ladder results in {H}0=72.0+/- 1.9 km s-1 Mpc-1, and in concert with geometric distances from Milky Way parallaxes and detached eclipsing binaries in the LMC we find {H}0=73.5 +/- 1.4 km s-1 Mpc-1. The improved distance to NGC 4258 also provides a new calibration of the tip of the red giant branch of {M}F814W=-4.01+/- 0.04 mag, with reduced systematic errors for the determination of {H}0 compared to the LMC-based calibration, because it is measured on the same Hubble Space Telescope (HST) photometric system and through similarly low extinction as SN Ia host halos. The result is {H}0=71.1+/- 1.9 km s-1 Mpc-1, in good agreement with the result from the Cepheid route, and there is no difference in {H}0 when using the same calibration from NGC 4258 and the same SN Ia Hubble diagram intercept to start and end both distance ladders.

Keywords: Galaxy distances, Observational cosmology