Sazuna/UAT_keywords huggingface dataset:
Arecibo Investigations of Pulsar B0823+26. I. Plasma Source Changes Configure Its Bright and Quiet Modes. The recently discovered 100X weaker quiescent (Q) mode in pulsar B0823+26 is X-ray quiet, unlike its usual bright (B) mode. Arecibo polarimetric observations were conducted to confirm the pulsar's orthogonal geometry and investigate the emission associated with its main pulse (MP), interpulse (IP), and postcursor (PC) components. Main results: (1) the pulsar's MP, PC, and IP are present in both modes and exhibit a two-pole orthogonal geometry. (2) The B-mode MP is dominated by core emission with weak conal outriders, whereas, the Q-mode double profile shows mainly residual conal emission with little core. The IP is conal in both modes. (3) Sporadic intrapulse emission trailing the PC is detected in the Q mode. (4) B0823+26 falls close to an $\dot{E}$ boundary of 1032.5 erg s-1 (or B12/P2 ∼ 2.5) between core- and conal-dominated profiles—which also represents a boundary between pair-plasma source configurations above the polar cap. For larger energies, the pair-formation front is central, flat, and generates backflow heating, whereas for smaller energies it is peripheral, lower, and produces little heating. (5) Apparently, the pulsar is able to assume both core- and conal-dominated "states" corresponding to its bright and weak modes. These circumstances appear to explain B0823+26's B-mode X-ray bright/core-dominated radio emission or Q-mode X-ray faint/conal radio emission—and why the IP is X-ray quiet in both modes. (6) These same considerations applied to B0943+10 may explain why its brighter radio mode was conal and X-ray quiet, while the weaker one was X-ray bright—because its peripheral sightline would miss most core radiation.

Keywords: Non-thermal radiation sources, Polarimetry, Proper motions, Pulsars
Modeling the Strongest Silicate Emission Features of Local Type 1 AGNs. We measure the 10 and 18 μm silicate features in a sample of 67 local (z &lt; 0.1) type 1 active galactic nuclei (AGN) with available Spitzer spectra dominated by nonstellar processes. We find that the 10 μm silicate feature peaks at ${10.3}_{-0.9}^{+0.7}\,\mu {\rm{m}}$ with a strength (Sip = ln fp(spectrum)/fp(continuum)) of ${0.11}_{-0.36}^{+0.15}$ , while the 18 μm one peaks at ${17.3}_{-0.7}^{+0.4}\,\mu {\rm{m}}$ with a strength of ${0.14}_{-0.06}^{+0.06}$ . We select from this sample sources with the strongest 10 μm silicate strength ( ${\sigma }_{{\mathrm{Si}}_{10\mu {\rm{m}}}}\gt 0.28$ , 10 objects). We carry out a detailed modeling of the infrared spectrometer/Spitzer spectra by comparing several models that assume different geometries and dust composition: a smooth torus model, two clumpy torus models, a two-phase medium torus model, and a disk+outflow clumpy model. We find that the silicate features are well modeled by the clumpy model of Nenkova et al., and among all models, those including outflows and complex dust composition are the best. We note that even in AGN-dominated galaxies, it is usually necessary to add stellar contributions to reproduce the emission at the shortest wavelengths.

Keywords: Infrared astronomy, Dust continuum emission, Active galaxies, Active galactic nuclei
Bayesian Revisit of the Relationship between the Total Field Strength and the Volume Density of Interstellar Clouds. The Zeeman effect has been the only method to directly probe the magnetic field strength in molecular clouds. The Bayesian analysis of Zeeman measurements carried out by Crutcher et al. is the only reference for cloud magnetic field strength. Here we extended their model and Bayesian analysis of the relation between field strength (B) and volume density (n) in the following three directions based on the recent observational and theoretical development. First, we take R, the observational uncertainty of n, as a parameter to be estimated from data. Second, the restriction of α, the index of the B-n relationship, is relieved from [0, 0.75] to [0, 1]. Third, we allow f, the minimum-to-maximum B ratio, to vary with n. Our results show that taking R as a parameter provides a better fitting to the B-n relationship and much more reliable estimates on R, f, and the changing point of α. Arguably our most important finding is that α cannot be reliably estimated by any of the models studied here, either from us or Crutcher et al., if R &gt; 2, which is indeed the case from our estimate. This is the so-called errors-in-variables bias, a well known problem for statisticians.

Keywords: Bayesian statistics, Star formation, Molecular clouds, Magnetic fields
Chemistry Along Accretion Streams in a Viscously Evolving Protoplanetary Disk. The composition of a protoplanetary disk is set by a combination of interstellar inheritance and gas and grain surface chemical reactions within the disk. The survival of inherited molecules, as well as the disk in situ chemistry depends on the local temperature, density and irradiation environment, which can change over time due to stellar and disk evolution, as well as transport in the disk. We address one aspect of this coupling between the physical and chemical evolution in disks by following accretion streamlines of gas and small grains in the disk midplane, while simultaneously taking the evolving star into account. This approach is computationally efficient and enables us to take into account changing physical conditions without reducing the chemical network. We find that many species are enhanced in the inner disk midplane in the dynamic model due to inward transport of cosmic-ray driven chemical products, resulting in, e.g., orders of magnitude hydrocarbon enhancements at 1 au, compared to a static disk. For several other chemical families, there is no difference between the static and dynamic models, indicative of a robust chemical reset, while yet others show differences between static and dynamic models that depend on complex interactions between physics and chemistry during the inward track. The importance of coupling dynamics and chemistry when modeling the chemical evolution of protoplanetary disks thus depends on what chemistry is of interest.

Keywords: Stellar accretion disks, Protoplanetary disks, Astrochemistry
Simulating Metal Mixing of Both Common and Rare Enrichment Sources in a Low-mass Dwarf Galaxy. One-zone models constructed to match observed stellar abundance patterns have been used extensively to constrain the sites of nucleosynthesis with sophisticated libraries of stellar evolution and stellar yields. The metal mixing included in these models is usually highly simplified, although it is likely to be a significant driver of abundance evolution. In this work we use high-resolution hydrodynamics simulations to investigate how metals from individual enrichment events with varying source energies Eej mix throughout the multiphase interstellar medium (ISM) of a low-mass (Mgas = 2 × 106 M⊙), low-metallicity, isolated dwarf galaxy. These events correspond to the characteristic energies of both common and exotic astrophysical sites of nucleosynthesis, including asymptotic giant branch winds (Eej ∼ 1046 erg), neutron star-neutron star mergers (Eej ∼ 1049 erg), supernovae (Eej ∼ 1051 erg), and hypernovae (Eej ∼ 1052 erg). We find the mixing timescales for individual enrichment sources in our dwarf galaxy to be long (100 Myr-1 Gyr), with a clear trend of increasing homogeneity for the more energetic events. Given these timescales, we conclude that the spatial distribution and frequency of events are important drivers of abundance homogeneity on large scales; rare, low-Eej events should be characterized by particularly broad abundance distributions. The source energy Eej also correlates with the fraction of metals ejected in galactic winds, ranging anywhere from 60% at the lowest energy to 95% for hypernovae. We conclude by examining how the radial position, local ISM density, and global star formation rate influence these results.

Keywords: Chemical enrichment, Dwarf galaxies, Hydrodynamics, Galaxy chemical evolution
SZ Scaling Relations of Galaxy Groups and Clusters Near the North Ecliptic Pole. Sunyaev-Zel'dovich (SZ) scaling relations have been used to test the self-similar prediction for massive galaxy clusters, but little attention has been given to individual galaxy groups. We investigate the scaling relations of galaxy groups and clusters near the North Ecliptic Pole using X-ray and SZ observations. This region of the sky is where both the ROSAT and Planck satellites achieved their deepest observations, permitting the investigation of lower mass systems. Our sample consists of 62 X-ray detected groups and clusters, spanning a mass range of ${10}^{13.4}{M}_{\odot }\lt \,{M}_{500}\lt {10}^{15}{M}_{\odot }$ and redshifts of 0.03 ≲ z ≲ 0.82. We extract the total SZ flux from unresolved Planck data and estimate the fraction of the SZ flux within R500 assuming two different pressure profiles. The SZ scaling relations were derived using a Bayesian technique that accounts for censored data. We find a power law slope of ${1.73}_{-0.18}^{+0.19}$ for the YSZ-M500 relation that is consistent with the self-similar prediction of 5/3. The slope of ${0.89}_{-0.08}^{+0.09}$ for the ${Y}_{\mathrm{SZ}}\mbox{--}{L}_{{\rm{X}},500}$ relation is in agreement with other observational studies but not the self-similar prediction of 5/4, and the ${Y}_{\mathrm{SZ}}\mbox{--}{Y}_{{\rm{X}}}$ relation lies below the 1:1 relation when the slope is fixed to unity. The determined scaling relations are dependent on the selected pressure profile, so resolved data are needed to determine the effects of active galactic nucleus feedback. In addition, we find a number of potential cluster candidates in the Planck Compton maps that were not identified in our X-ray sample.

Keywords: Galaxy clusters, Intracluster medium, Sunyaev-Zeldovich effect, Galaxy groups
Turbulence in a Self-gravitating Molecular Cloud Core. Externally driven interstellar turbulence plays an important role in shaping the density structure in molecular clouds. Here we study the dynamical role of internally driven turbulence in a self-gravitating molecular cloud core. Depending on the initial conditions and evolutionary stages, we find that a self-gravitating core in the presence of gravity-driven turbulence can undergo constant, decelerated, and accelerated infall, and thus has various radial velocity profiles. In the gravity-dominated central region, a higher level of turbulence results in a lower infall velocity, a higher density, and a lower mass accretion rate. As an important implication of this study, efficient reconnection diffusion of magnetic fields against the gravitational drag naturally occurs due to the gravity-driven turbulence, without invoking externally driven turbulence.

Keywords: Interstellar magnetic fields, Astrophysical fluid dynamics, Star formation
Extreme-ultraviolet Late Phase of Solar Flares. A second peak in the extreme ultraviolet sometimes appears during the gradual phase of solar flares, which is known as the EUV late phase (ELP). Stereotypically ELP is associated with two separated sets of flaring loops with distinct sizes, and it has been debated whether ELP is caused by additional heating or extended plasma cooling in the longer loop system. Here we carry out a survey of 55 M-and-above GOES-class flares with ELP during 2010-2014. Based on the flare-ribbon morphology, these flares are categorized as circular-ribbon (19 events), two-ribbon (23 events), and complex-ribbon (13 events) flares. Among them, 22 events (40%) are associated with coronal mass ejections, while the rest are confined. An extreme ELP, with the late-phase peak exceeding the main-phase peak, is found in 48% of two-ribbon flares, 37% of circular-ribbon flares, and 31% of complex-ribbon flares, suggesting that additional heating is more likely present during ELP in two-ribbon than in circular-ribbon flares. Overall, cooling may be the dominant factor causing the delay of the ELP peak relative to the main-phase peak, because the loop system responsible for the ELP emission is generally larger than, and well separated from, that responsible for the main-phase emission. All but one of the circular-ribbon flares can be well explained by a composite "dome-plate" quasi-separatrix layer (QSL). Only half of these show a magnetic null point, with its fan and spine embedded in the dome and plate, respectively. The dome-plate QSL, therefore, is a general and robust structure characterizing circular-ribbon flares.

Keywords: Solar active region magnetic fields, Solar flares, Solar extreme ultraviolet emission, Active sun, Solar active regions, Solar physics, Solar activity, Active solar corona
The Deepest Radio Observations of Nearby SNe Ia: Constraining Progenitor Types and Optimizing Future Surveys. We report deep radio observations of nearby Type Ia supernovae (SNe Ia) with the electronic Multi-Element Radio Linked Interferometer Network and the Australia Telescope Compact Array. No detections were made. With standard assumptions for the energy densities of relativistic electrons going into a power-law energy distribution and the magnetic field strength (ɛe = ɛB = 0.1), we arrive at upper limits on mass-loss rate for the progenitor system of SN 2013dy (SN 2016coj, SN 2018gv, SN 2018pv, SN 2019np) of $\dot{M}\lesssim 12\,(2.8,1.3,2.1,1.7)\times {10}^{-8}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}({V}_{w}/100\,\mathrm{km}\,{{\rm{s}}}^{-1})$ , where Vw is the wind speed of the mass loss. To SN 2016coj, SN 2018gv, SN 2018pv, and SN 2019np we add radio data for 17 other nearby SNe Ia and model their nondetections. With the same model as described, all 21 SNe Ia have $\dot{M}\lesssim 4\times {10}^{-8}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}({V}_{w}/100\,\mathrm{km}\,{{\rm{s}}}^{-1})$ . We compare those limits with the expected mass-loss rates in different single-degenerate progenitor scenarios. We also discuss how information on ɛe and ɛB can be obtained from late observations of SNe Ia and the youngest SN Ia remnant detected in radio, G1.9+0.3, as well as stripped-envelope core-collapse SNe. We highlight SN 2011dh and argue for ɛe ≈ 0.1 and ɛB ≈ 0.0033. Finally, we discuss strategies to observe at radio frequencies to maximize the chance of detection, given the time since explosion, the distance to the SN, and the telescope sensitivity.

Keywords: White dwarf stars, Stellar mass loss, Supernova remnants, Type Ia supernovae, Radio continuum emission
Halo Counts-in-cells for Cosmological Models with Different Dark Energy. We examine the counts-in-cells (CiC) probability distribution functions (PDFs) that describe dark matter halos in the Dark Energy Universe Simulations (DEUS). We describe the measurements between redshifts z = 0 to z = 4 on both linear and nonlinear scales. The best fits of the gravitational quasi-equilibrium distribution (GQED), the negative binomial distribution (NBD), the Poisson-Lognormal distribution (PLN), and the Poisson-Lognormal distribution with a bias parameter (PLNB) are compared to simulations. The fits agree reasonably consistently over a range of redshifts and scales. To distinguish quintessence (RPCDM) and phantom (wCDM) dark energy from Λ dark energy, we present a new method that compares the model parameters of the CiC PDFs. We find that the mean and variance of the halo CiC on 2-25h-1 Mpc scales between redshifts 0.65 &lt; z &lt; 4 show significant percentage differences for different dark energy cosmologies. On 15-25 h-1 Mpc scales, the g parameter in NBD, ω parameter in PLN, and b and Cb parameters in PLNB show larger percentage differences for different dark energy cosmologies than on smaller scales. On 2-6 h-1 Mpc scales, the kurtosis and the b parameter in the GQED show larger percentage differences for different dark energy cosmologies than on larger scales. For cosmologies explored in the DEUS, the percentage differences between these statistics for the RPCDM and wCDM dark energy cosmologies relative to ΛCDM generally increases with redshift from a few percent to significantly larger percentages at z = 4. Applying our method to simulations and galaxy surveys can provide a useful way to distinguish among dark energy models and cosmologies in general.

Keywords: Cosmology, Theoretical models, Large-scale structure of the universe, Dark matter, Dark energy
Heating of Heavy Ions in Low-beta Compressible Turbulence. Enhancement of minor ions such as 3He and heavy ions in flare-associated solar energetic particle (SEP) events remains one of the major puzzles in heliophysics. In this work, we use 3D hybrid simulations (kinetic protons and fluid electrons) to investigate particle energization in a turbulent low-beta environment similar to solar flares. It is shown that in this regime the injected large-amplitude Alfvén waves develop into compressible and anisotropic turbulence, which efficiently heats thermal ions of different species. We find that temperature increase of heavy ions is inversely proportional to the charge-to-mass ratio, which is consistent with observations of impulsive SEP events. Further analysis reveals that ions are energized by interacting with nearly perpendicular magnetosonic waves near a proton inertial scale.

Keywords: Space plasmas, Solar energetic particles, Interplanetary turbulence, Alfven waves, N-body simulations
Periodic Fast Radio Bursts from Young Neutron Stars. Fast radio bursts (FRBs) are highly energetic radio pulses from cosmological origins. Despite an abundance of detections, their nature remains elusive. At least a subset of FRBs is expected to repeat, as the volumetric FRB rate surpasses that of any known cataclysmic event, which has been confirmed by observations. One of the proposed mechanisms to generate repeating FRBs is supergiant pulses from young and highly spinning neutron stars (NSs), in which case FRBs could inherit the periodicity of their parent NS. Here we examine the consequences of such a population of periodic fast radio bursts (PFRBs). We calculate the rate and lifetime of PFRB progenitors, and find that each newly born highly spinning NS has to emit a number ${N}_{\mathrm{PFRB}}\sim {10}^{2}$ of detectable bursts during its active lifetime of $\tau \sim 100$ yr, after which it becomes too dim and crosses a PFRB "death line" analogous to the pulsar one. We propose several tests of this hypothesis. First, the period of PFRBs would increase over time, and their luminosity would decrease, due to the NS spin-down. Second, PFRBs may show modest amounts of rotation measure, given the lack of expelled matter from the pulsar, as opposed to the magnetar-sourced FRBs proposed to explain the first repeater FRB 121102. As an example, we study whether the second confirmed repeater (FRB 180814) is a PFRB, given the preference for an inter-pulse separation of 13 ms within its sub-bursts. We show that, if confirmed, this period would place FRB 180814 in a different category as FRB 121102. We develop tests that would identify—and characterize—the prospective population of PFRBs.

Keywords: Neutron stars, Transient sources, Pulsars, Radio bursts, Radio transient sources
Constraining Screened Modified Gravity with Spaceborne Gravitational-wave Detectors. Screened modified gravity (SMG) is a unified theoretical framework that describes scalar-tensor gravity with a screening mechanism. Based on the gravitational-wave (GW) waveform derived in our previous work, in this article we investigate the potential constraints on SMG theory through GW observation by future spaceborne GW detectors, including the Laser Interferometer Space Antenna (LISA), TianQin, and Taiji. We find that, for the extreme-mass-ratio inspirals (EMRIs) consisting of a massive black hole and a neutron star, if the EMRIs are at the Virgo cluster, the GW signals can be detected by the detectors at quite high significance level, and the screened parameter ɛNS can be constrained at about ${ \mathcal O }({10}^{-5})$ , which is more than one order of magnitude tighter than the potential constraint given by a ground-based Einstein telescope. However, for the EMRIs consisting of a massive black hole and a white dwarf, it is more difficult to detect them than in the previous case. For the specific SMG models, including chameleon, symmetron, and dilaton, we find these constraints are complementary to that from the Cassini experiment, but weaker than those from lunar laser ranging observations and binary pulsars, due to the strong gravitational potentials on the surface of neutron stars. By analyzing the deviation of the GW waveform in SMG from that in general relativity, as anticipated, we find the dominant contribution of the SMG constraint comes from the correction terms in the GW phases, rather than the extra polarization modes or the correction terms in the GW amplitudes.

Keywords: Non-standard theories of gravity, Gravitational wave detectors, Gravitational waves
Broadband Variability and Correlation Study of 3C 279 during Flares of 2017-2018. A multiwavelength temporal and spectral analysis of flares of 3C 279 during 2017 November-2018 July are presented in this work. Three bright gamma-ray flares were observed simultaneously in X-ray and optical/UV along with a prolonged quiescent state. A "harder-when-brighter" trend is observed in both gamma-rays and X-rays during the flaring period. The gamma-ray light curve for all the flares is binned in one day time bins and a day-scale variability is observed. Variability time constrains the size and location of the emission region to 2.1 × 1016 cm and 4.4 × 1017 cm, respectively. The fractional variability reveals that the source is more than 100% variable in gamma-rays and it decreases toward the lower energy. A cross-correlation study of the emission from different wavebands is done using the discrete correlations function method, which shows a strong correlation between them without any time lags. The zero time lag between different wavebands suggests their cospatial origin. This is the first time 3C 279 has shown a strong correlation between gamma-ray and X-ray emission with zero time lag. A single-zone emission model was adopted to model the multiwavelength spectral energy distributions by using the publicly available code GAMERA. The study reveals that a higher jet power in electrons is required to explain the gamma-ray flux during the flaring state, as much as 10 times that required for the quiescent state. However, more jet power in the magnetic field has been observed during the quiescent state compared to the flaring state.

Keywords: Jets, Quasars, Blazars, Active galaxies, Galactic and extragalactic astronomy, Gamma-rays
A Massive Young Runaway Star in W49 North. We analyzed high-angular resolution 45.5 GHz images of the W49 North massive star-forming region obtained in 1998 and 2016 with the Very Large Array. Most of the ultracompact H II regions show no detectable changes over the time interval of the observations. However, subcomponents B1, B2, G2a, and G2c have increased its peak flux densities by values in the range of 3.8%-21.4%. Most interestingly, the cometary region C clearly shows proper motions that at the distance of the region are equivalent to a velocity of 76 ± 6 km s-1 in the plane of the sky. We interpret this region as the ionized bowshock produced by a runaway O6 ZAMS star that was ejected from the eastern edge of Welch's ring about 6400 yr ago.

Keywords: Extragalactic radio sources, Radio astrometry, Proper motions