adsabs/SciX_UAT_keywords huggingface dataset:
Signatures of Strangeness in Neutron Star Merger Remnants

Neutron star (NS) mergers provide us with information rich in physics using multimessenger astrophysical observations. One of the probable remnants of such a merger is a differentially rotating hot hypermassive NS. The stability of the merger remnant crucially depends on the underlying equation of state and thus provides a method to probe the nature of dense matter in NSs. In this work, we search for possible signatures of strangeness-containing matter in NS interiors on the secular stability of the merger remnant. We also use recently proposed methods to make a rough estimate of the collapse time of the merger remnant and the threshold mass above which the merger promptly collapses to a black hole.

Keywords: neutron star cores; neutron stars; relativistic stars
Gravitational Instability of a Magnetic Rotating Disk with Ohmic Dissipation and Ambipolar Diffusion

We perform a linear analysis of the stability of isothermal, rotating, magnetic, self-gravitating sheets that are weakly ionized. We include a self-consistent treatment of thermal pressure, gravitational, rotational, and magnetic (pressure and tension) forces together with two nonideal magnetohydrodynamic (MHD) effects: Ohmic dissipation and ambipolar diffusion. Our results show that there is always a preferred lengthscale and associated minimum timescale for gravitational instability. The addition of rotation leads to a generalized Toomre criterion (that includes a magnetic dependence) and modified lengthscales and timescales for collapse. We show that both the nonideal MHD effects qualitatively behave in a similar way but have quantitative differences. We apply our results to protostellar disk properties in the early embedded phase and find that the preferred scale of instability can significantly exceed the thermal (Jeans) scale and the peak preferred fragmentation mass is likely to be ∼10-90MJup.

Keywords: magnetohydrodynamics; interstellar magnetic fields; circumstellar disks; interstellar clouds; gravitational instability
On the Evolution of the Globular Cluster System in NGC 1052-DF2: Dynamical Friction, Globular-Globular Interactions, and Galactic Tides

The ultradiffuse galaxy NGC 1052-DF2 has an overabundance of luminous globular clusters (GCs), and its kinematics is consistent with the presence of little to no dark matter. As the velocity dispersion among the GCs is comparable to the expected internal dispersions of the individual GCs, the galaxy might be highly conducive to GC-GC merging. If true, this could explain the puzzling luminosity function of its GCs. Here we examine this possibility by resimulating three of our earlier simulations of the GC system, where the GCs were modeled as single particles, with live GCs. Somewhat surprisingly, we infer a low merger rate of ∼0.03 Gyr-1. The main reason is that the GCs are too dense for tidal shock capture, caused by impulsive encounters among them, to operate efficiently (we infer a tidal capture rate of only ∼0.002 Gyr-1). Therefore, whatever mergers occur are driven by other mechanisms, which we find to be captures induced by dynamical friction and compressive tides from other GCs. The low merger rate inferred here makes it unlikely that the unusually large luminosities of the GCs can be explained as a result of past GC-GC mergers. Our simulations also indicate that, if NGC 1052-DF2 is indeed largely devoid of dark matter, its tidal field is too weak to induce any significant mass loss from the GCs. Therefore, in such a scenario, we predict that it is improbable for the GCs to reveal tidal features, something that can be tested with future deep observations.

Keywords: globular star clusters; dynamical friction; n-body simulations
A Relationship between Stellar Age and Spot Coverage

We investigate starspot distributions consistent with space-based photometry of F, G, and K stars in six stellar associations ranging in age from 10 Myr to 4 Gyr. We show that a simple light-curve statistic called the "smoothed amplitude" is proportional to stellar age as t-1/2, following a Skumanich-like spin-down relation. We marginalize over the unknown stellar inclinations by forward modeling the ensemble of light curves for direct comparison with the Kepler, K2, and TESS photometry. We sample the posterior distributions for spot coverage with approximate Bayesian computation. We find typical spot coverages in the range 1%-10%, which decrease with increasing stellar age. The spot coverage is proportional to tn where n = -0.37 ± 0.16, also statistically consistent with a Skumanich-like t-1/2 decay of starspot coverage with age. We apply two techniques to estimate the spot coverage of young exoplanet-hosting stars likely to be targeted for transmission spectroscopy with the James Webb Space Telescope, and estimate the bias in exoplanet radius measurements due to varying starspot coverage.

Keywords: stellar photospheres; starspots; stellar rotation; bayesian statistics
The CO(3-2)/CO(1-0) Luminosity Line Ratio in Nearby Star-forming Galaxies and Active Galactic Nuclei from xCOLD GASS, BASS, and SLUGS

We study the ${r}_{31}={L}_{\mathrm{CO}(3\mbox{--}2)}^{{\prime} }/{L}_{\mathrm{CO}(1\mbox{--}0)}^{{\prime} }$ luminosity line ratio in a sample of nearby (z < 0.05) galaxies: 25 star-forming galaxies (SFGs) from the xCOLD GASS survey, 36 hard X-ray-selected active galactic nucleus (AGN) host galaxies from the BAT AGN Spectroscopic Survey, and 37 infrared-luminous galaxies from the SCUBA Local Universe Galaxy Survey. We find a trend for r31 to increase with star formation efficiency (SFE). We model r31 using the UCL-PDR code and find that the gas density is the main parameter responsible for the variation of r31, while the interstellar radiation field and cosmic-ray ionization rate play only a minor role. We interpret these results to indicate a relation between SFE and gas density. We do not find a difference in the r31 value of SFGs and AGN host galaxies, when the galaxies are matched in SSFR (<r31> = 0.52 ± 0.04 for SFGs and <r31> = 0.53 ± 0.06 for AGN hosts). According to the results of the UCL-PDR models, the X-rays can contribute to the enhancement of the CO line ratio, but only for strong X-ray fluxes and for high gas density (nH > 104 cm-3). We find a mild tightening of the Kennicutt-Schmidt relation when we use the molecular gas mass surface density traced by CO(3-2) (Pearson correlation coefficient R = 0.83), instead of the molecular gas mass surface density traced by CO(1-0) (R = 0.78), but the increase in correlation is not statistically significant (p-value = 0.06). This suggests that the CO(3-2) line can be reliably used to study the relation between SFR and molecular gas for normal SFGs at high redshift and to compare it with studies of low-redshift galaxies, as is common practice.

Keywords: interstellar medium; star formation; active galactic nuclei; galaxies; seyfert galaxies
Eruption of a Million-Kelvin Warm Magnetic Flux Rope on the Sun

Solar magnetic flux rope (MFR) plays a central role in the physics of coronal mass ejections (CMEs). It mainly includes a cold filament at typical chromospheric temperatures (∼10,000 K) and a hot channel at high coronal temperatures (∼10 MK). The warm MFR at quiescent coronal temperatures of a million Kelvin is, however, rarely reported. In this study, using multiwavelength images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory and Extreme Ultraviolet Imager (EUVI) on board the Solar Terrestrial Relations Observatory-A, we present an eruption of a warm channel that represents an MFR with quiescent coronal temperatures (∼0.6–2.5 MK). On 2022 May 8, we observed the failed eruption of a hot channel, with the average temperature and emission measure (EM) of 10 MK and 1.1 × 1028 cm‑5, using AIA high-temperature images in the active region (AR) 13007. This failed eruption was associated with a C8.2 flare, with no CME. Subsequently, we observed a warm channel that appeared in AIA and EUVI low-temperature images rather than in AIA high-temperature images. It then erupted and transformed into a semicircular shape. An associated C2.1 flare, along with the signatures of magnetic reconnection in AIA high-temperature images, were identified. Additionally, we observed a CME associated with this event. Compared with the hot channel, the warm channel is cooler and rarer with the average temperature and EM of 1.7 (1.6) MK and 2.0 × 1026 (2.3 × 1026) cm‑5. All the results suggest an unambiguous observation of the million-Kelvin warm MFR that erupted as a CME and fill a gap in the temperature domain of coronal MFRs.

Keywords: solar filaments; solar coronal mass ejections; solar flares; plasma physics; solar extreme ultraviolet emission; solar corona
Particles in Relativistic MHD Jets. I. Role of Jet Dynamics in Particle Acceleration

Relativistic jets from (supermassive) black holes are typically observed in nonthermal emission, caused by highly relativistic electrons. Here, we study the interrelation between three-dimensional (special) relativistic magnetohydrodynamics, and particle acceleration in these jets. We inject Lagrangian particles into the jet that are accelerated through diffusive shock acceleration and radiate energy via synchrotron and inverse Compton processes. We investigate the impact of different injection nozzles on the jet dynamics, propagation, and the spectral energy distribution of relativistic particles. We consider three different injection nozzles-injecting steady, variable, and precessing jets. These jets evolve with substantially different dynamics, driving different levels of turbulence and shock structures. The steady jet shows a strong, stationary shock feature, resulting from a head-on collision with an inner back-flow along the jet axis-a jet inside a jet. This shock represents a site for highly efficient particle acceleration for electrons up to a few tens of TeV and should be visible in emission as a jet knot. Overall, we find that the total number of shocks is more essential for particle acceleration than the strength of the shocks. The precessing jet is most efficient in accelerating electrons to high energies reaching even few hundred TeVs, with power-law index ranging from 2.3 to 3.1. We compare different outflow components, such as the jet and the entrained material concerning particle acceleration. For the precessing nozzle, the particle acceleration in the entrained material is as efficient as that in the jet stream. This is due to the higher level of turbulence induced by the precession motion.

Keywords: active galactic nuclei; relativistic jets; magnetohydrodynamics; high energy astrophysics; particle astrophysics; shocks
RelSIM: A Relativistic Semi-implicit Method for Particle-in-cell Simulations

We present a novel Relativistic Semi-Implicit Method (RelSIM) for particle-in-cell (PIC) simulations of astrophysical plasmas, implemented in a code framework ready for production runs. While explicit PIC methods have gained widespread recognition in the astrophysical community as a reliable tool to simulate plasma phenomena, implicit methods have been seldom explored. This is partly due to the lack of a reliable relativistic implicit PIC formulation that is applicable to state-of-the-art simulations. We propose the RelSIM to fill this gap: our new method is relatively simple, being free of nonlinear iterations and only requiring a global linear solve of the field equations. With a set of one- and two-dimensional tests, we demonstrate that the RelSIM produces more accurate results with much smaller numerical errors in the total energy than standard explicit PIC, in particular when characteristic plasma scales (skin depth and plasma frequency) are heavily underresolved on the numerical grid. By construction, the RelSIM also performs much better than the relativistic implicit-moment method, originally proposed for semi-implicit PIC simulations in the relativistic regime. Our results are promising to conduct large-scale (in terms of duration and domain size) PIC simulations of astrophysical plasmas, potentially reaching physical regimes inaccessible by standard explicit PIC codes.

Keywords: computational methods; special relativity; plasma physics
Estimating Lifetimes of UV-selected Massive Galaxies at 0.5 ≤ z ≤ 2.5 in the COSMOS/UltraVISTA Field through Clustering Analyses

To investigate the lifetimes of red sequence (RS), blue cloud (BC), and green valley (GV) galaxies, we derive their lifetimes using clustering analyses at 0.5 ≤ z ≤ 2.5 in the COSMOS/UltraVISTA field. Several essentials that may influence the lifetime estimation have been explored, including the dark matter (DM) halo mass function (HMF), the width of the redshift bin, the growth of DM halos within each redshift bin, and the stellar mass. We find that the HMF difference results in scatters of ∼0.2 dex on the lifetime estimation, adopting a redshift bin width of Δz = 0.5 is good enough to estimate the lifetime, and no significant effect on lifetime estimation is found due to the growth of DM halos within each redshift bin. The galaxy subsamples with higher stellar masses generally have shorter lifetimes, but the lifetimes in different subsamples at z > 1.5 tend to be independent of stellar mass. Consistently, the clustering-based lifetime for each galaxy subsample agrees well with that inferred using the spectral energy distribution modeling. Moreover, the lifetimes of the RS and BC galaxies also coincide well with their typical gas-depletion timescales attributed to the consumption of star formation. Interestingly, the distinct lifetime behaviors of the GV galaxies at z ≤ 1.5 and z > 1.5 cannot be fully accounted for by their gas-depletion timescales. Instead, this discrepancy between the lifetimes and gas-depletion timescales of the GV galaxies suggests that there are additional physical processes, such as feedback of active galactic nuclei, which accelerates the quenching of GV galaxies at high redshifts.

Keywords: red sequence galaxies; high-redshift galaxies; galaxy evolution; galaxy formation; galaxy quenching
A Study of Dimmings, CMEs, and Flares during the STEREO-SOHO Quadrature

During the quadrature period (2010 December-2011 August) the STEREO-A and B satellites were approximately at right angles to the SOHO satellite. This alignment was particularly advantageous for determining the coronal mass ejection (CME) properties, since the closer a CME propagates to the plane of sky, the smaller the measurement inaccuracies are. Our primary goal was to study dimmings and their relationship to CMEs and flares during this time. We identified 53 coronal dimmings using STEREO/EUVI 195 Å observations, and linked 42 of the dimmings to CMEs (observed with SOHO/LASCO/C2) and 23 to flares. Each dimming in the catalog was processed with the Coronal Dimming Tracker which detects transient dark regions in extreme ultraviolet images directly, without the use of difference images. This approach allowed us to observe footpoint dimmings: the regions of mass depletion at the footpoints of erupting magnetic flux rope structures. Our results show that the CME mass has a linear, moderate correlation with dimming total EUV intensity change, and a monotonic, moderate correlation with dimming area. These results suggest that the more the dimming intensity drops and the larger the erupting region is, the more plasma is evacuated. We also found a strong correlation between the flare duration and the total change in EUV intensity. The correlation between dimming properties showed that larger dimmings tend to be brighter; they go through more intensity loss and generally live longer-supporting the hypothesis that larger transient open regions release more plasma and take longer to close down and refill with plasma.

Keywords: solar flares; solar coronal mass ejections; solar ultraviolet emission
A Statistical Analysis of Galactic Radio Supernova Remnants

We present a revised table of 390 Galactic radio supernova remnants (SNRs) and their basic parameters. Statistical analyses are performed on SNR diameters, ages, spectral indices, Galactic heights, and spherical symmetries. Furthermore, the accuracy of distances estimated using the Σ-D relation is examined. The arithmetic mean of the Galactic SNR diameters is 30.5 pc with standard error 1.7 pc and standard deviation 25.4 pc. The geometric mean and geometric standard deviation factor of Galactic SNR diameters is 21.9 pc and 2.4, respectively. We estimate ages of 97 SNRs and find a supernova (SN) birth rate lower than, but within 2σ of, currently accepted values for the SN birth rate. The mean spectral index of shell-type SNRs is -0.51 ± 0.01 and no correlations are found between spectral indices and the SNR parameters of molecular cloud association, SN type, diameter, Galactic height, and surface brightness. The Galactic height distribution of SNRs is best described by an exponential distribution with a scale height of 48 ± 4 pc. The spherical symmetry measured by the ovality of radio SNRs is not correlated to any other SNR parameters considered here or to explosion type.

Keywords: supernova remnants; radio astronomy
The Distant, Galaxy Cluster Environment of the Short GRB 161104A at z ∼ 0.8 and a Comparison to the Short GRB Host Population

We present optical observations of the Swift short-duration gamma-ray burst (GRB) GRB 161104A and its host galaxy at z = 0.793 ± 0.003. We model the multiband photometry and spectroscopy with the stellar population inference code Prospector and explore the posterior using nested sampling. We find a mass-weighted age of tm = 2.12+0.23-0.21 Gyr, stellar mass of $\mathrm{log}(M/{M}_{\odot })=10.21\pm 0.04$ , metallicity of $\mathrm{log}(Z/{Z}_{\odot })={0.08}_{-0.06}^{+0.05}$ , dust extinction of AV = 0.08+0.08-0.05, and low star formation rate of 9.9 × 10-2 M⊙ yr-1. These properties, along with a prominent 4000 Å break and optical absorption lines, classify this host as an early-type, quiescent galaxy. Using Dark Energy Survey galaxy catalogs, we demonstrate that the host of GRB 161104A resides on the outskirts of a galaxy cluster at z ≈ 0.8, situated ≈1 Mpc from the likely brightest cluster galaxy. We also present new modeling for 20 additional short GRB hosts (≈33% of which are early-type galaxies), finding population medians of $\mathrm{log}(M/{M}_{\odot })={9.94}_{-0.98}^{+0.88}$ and tm = 1.07+1.98-0.67 Gyr (68% confidence). We further find that the host of GRB 161104A is more distant, less massive, and younger than the four other short GRB hosts known to be associated with galaxy clusters. Cluster short GRBs have faint afterglows, in the lower ≈11% (≈30%) of observed X-ray (optical) luminosities. We place a lower limit on the fraction of short GRBs in galaxy clusters versus those in the field of ≈5%-13%, consistent with the fraction of stellar mass of ≈10%-20% in galaxy clusters at redshifts 0.1 ≤ z ≤ 0.8. Future studies that take advantage of wider-field and deeper cluster surveys are needed to understand the true rate of short GRBs in clusters and their effect on heavy-element enrichment in the intracluster medium.

Keywords: gamma-ray bursts; galaxy clusters; galaxy environments; high energy astrophysics
Mushroom-instability-driven Magnetic Reconnections in Collisionless Relativistic Jets

We study the kinetic plasma dynamics in collisionless relativistic jets with velocity shear, by carrying out particle-in-cell simulations in the transverse plane of a jet. It is discovered that intermittent magnetic reconnections (MRs) are driven by mushroom instability (MI), which is an important kinetic-scale plasma instability in the plasma shear flows with relativistic bulk speed. We refer to this sequence of kinetic plasma phenomena as "MI-driven MR." The MI-driven MRs intermittently occur with moving the location of the reconnection points from the vicinity of the initial velocity-shear surface toward the center of the jet. As a consequence, the number density of high-energy electrons that are accelerated by MI-driven MRs increases with time in the region inside the initial velocity-shear surface with the accompanying generation and subsequent amplification of magnetic fields by MI. The maximum Lorentz factor of electrons increases with initial bulk Lorentz factor of the jet. A possible relation of MI-driven MR to the bright synchrotron emission in the jet spine of an active galactic nucleus jet is also discussed.

Keywords: relativistic jets; plasma astrophysics; plasma physics; plasma jets; high energy astrophysics; radio jets; active galactic nuclei
Amplitude and Frequency Modulation of Super-Nyquist Frequency from Kepler Photometric Sampling

We present a simulation showing that super-Nyquist frequencies may have periodic amplitude and frequency modulations, even if actually stable, in time series sampled like the Kepler data. These modulations are caused by the barycentric time correction, which destroys the evenly spaced time measurements, making the Nyquist frequency variable over the spacecraft orbit around the Sun. These modulations can easily be identified in pulsating stars from Kepler's photometric data.

Keywords: pulsation frequency method; pulsating variable stars
Coronal Dimmings Associated with Coronal Mass Ejections on the Solar Limb

We present a statistical analysis of 43 coronal dimming events associated with Earth-directed coronal mass ejections (CMEs) that occurred during the period of quasi-quadrature of the Solar Dynamics Observatory (SDO) and Solar Terrestrial Relations Observatory (STEREO) satellites. We studied coronal dimmings that were observed above the limb by STEREO Extreme Ultraviolet Imager and compared their properties with the mass and speed of the associated CMEs. The unique position of the satellites allowed us to compare our findings with the results from Dissauer et al., who studied the same events observed against the solar disk by the SDO Atmospheric Imaging Assembly. Such statistics is done for the first time and confirms the relation of coronal dimmings and CME parameters for the off-limb viewpoint. The observations of dimming regions from different lines of sight reveal a similar decrease in the total extreme ultraviolet intensity (c = 0.60 ± 0.14). We find that the (projected) dimming areas are typically larger for off-limb observations (mean value of 1.24 ± 1.23 × 1011 km2 against 3.51 ± 0.71 × 1010 km2 for on-disk), with a correlation of c = 0.63 ± 0.10. This systematic difference can be explained by the (weaker) contributions to the dimming regions higher up in the corona that cannot be detected in the on-disk observations. The off-limb dimming areas and brightnesses show very strong correlations with the CME mass (c = 0.82 ± 0.06 and 0.75 ± 0.08), whereas the dimming area and brightness change rate correlate with the CME speed (c ∼ 0.6). Our findings suggest that coronal dimmings have the potential to provide early estimates of the mass and speed of Earth-directed CMEs, relevant for space weather forecasts, for satellite locations at both L1 and L5.

Keywords: solar coronal mass ejections; the sun; active sun