adsabs/SciX_UAT_keywords huggingface dataset:
The Weakness of Soft X-Ray Intensity: Possible Physical Reason for Weak-line Quasars

Weak-line quasars (WLQs) are a notable group of active galactic nuclei (AGNs) that show unusually weak UV lines even though their optical-UV continuum shapes are similar to those of typical quasars. The physical mechanism for WLQs is an unsolved puzzle in the AGN unified model. We explore the properties of UV emission lines by performing extensive photoionization calculations based on Cloudy simulations with different spectral energy distributions (SEDs) of AGNs. The AGN continua are built from several observational empirical correlations, where the blackbody emission from the cold disk, the power-law emission from the hot corona, and a soft X-ray excess component are considered. We find that the equivalent width (EW) of C IV from our models is systematically lower than observational values if the component of soft X-ray excess is neglected. The EW will increase several times and is roughly consistent with the observations after considering the soft X-ray excess component as constrained from normal type I AGNs. We find that the UV lines are weak for QSOs with quite large black hole mass (e.g., M BH > 109 M ⊙) and weak soft X-ray emission due to the deficit of ionizing photons. As an example, we present the strength of C IV based on the multiband SEDs for three nearby weak-line AGNs, where the weaker soft X-ray emission normally predicts the weaker lines.

Keywords: active galactic nuclei; supermassive black holes; quasars; x-ray active galactic nuclei; accretion; line intensities
BYORP and Dissipation in Binary Asteroids: Lessons from DART

The near-Earth binary asteroid Didymos was the target of the planetary defense demonstration mission DART in 2022 September. The smaller binary component, Dimorphos, was impacted by the spacecraft in order to measure momentum transfer in kinetic impacts into rubble piles. DART and associated Earth-based observation campaigns have provided a wealth of scientific data on the Didymos–Dimorphos binary. DART revealed the largely oblate and ellipsoidal shape of Dimorphos before the impact, while the postimpact observations suggest that Dimorphos now has a prolate shape. Here we add those data points to the known properties of small binary asteroids and propose new paradigms of the radiative binary Yarkovsky–O'Keefe–Radzievskii–Paddack (BYORP) effect as well as tidal dissipation in small binaries. We find that relatively spheroidal bodies like Dimorphos made of small debris may experience a weaker and more size-dependent BYORP effect than previously thought. This could explain the observed values of period drift in several well-characterized binaries. We also propose that energy dissipation in small binaries is dominated by relatively brief episodes of large-scale movement of (likely surface) materials, rather than long-term steady-state tidal dissipation. We propose that one such episode was triggered on Dimorphos by the DART impact. Depending on the longevity of this high-dissipation regime, it is possible that Dimorphos will be more dynamically relaxed in time for the Hera mission than it was in the weeks following the impact.

Keywords: asteroid dynamics; asteroid satellites; tidal friction
Exploring Bistability in the Cycles of the Solar Dynamo through Global Simulations

The calling card of solar magnetism is the sunspot cycle, during which sunspots regularly reverse their polarity sense every 11 yr. However, a number of more complicated time-dependent behaviors have also been identified. In particular, there are temporal modulations associated with active longitudes and hemispheric asymmetry, when sunspots appear at certain solar longitudes or else in one hemisphere preferentially. So far, a direct link between this asymmetric temporal behavior and the underlying solar dynamo has remained elusive. In this work, we present results from global 3D magnetohydrodynamic simulations, which display both behavior reminiscent of the sunspot cycle (regular polarity reversals and equatorward migration of internal magnetic field) and asymmetric, irregular behavior which we interpret as active longitudes and hemispheric asymmetry in the simulations. The simulations are thus bistable, in that the turbulent convection can stably support two distinct flavors of magnetism at different times, in superposition or with smooth transitions from one state to the other. We discuss this new family of dynamo models in the context of the extensive observations of the Sun's surface magnetic field with the Solar and Heliospheric Observatory and the Solar Dynamics Observatory, as well as earlier observations of sunspot number and synoptic maps. We suggest that the solar dynamo itself may be bistable in nature, exhibiting two types of temporal behavior in the magnetic field.

Keywords: solar interior; solar magnetic fields; solar dynamo; solar convective zone; magnetohydrodynamical simulations
Difference of Photometric Properties between Regular and Nonregular Miras in the Magellanic Clouds

Mira variables are asymptotic giant-branch pulsating stars with long pulsation periods and large amplitudes in optical bands. By applying the random forest algorithm to the I-band light curves for the Miras in the Magellanic Clouds, we have classified these Miras into regular Miras and nonregular Miras. Nonregular Miras exhibit a long-term variation in addition to their primary pulsation periods. Our results confirm that the period-luminosity relation for maximum light has a small dispersion, but only occurs on the regular oxygen-rich Miras, which we recommend to be applied in future distance-scale work. We have also collected multiband photometry for these Miras to perform a spectral energy distribution fitting with stellar and dust components, showing that a significant fraction of dust is present around the nonregular Miras. According to our results, we believe that the periodic long-term variations seen in the nonregular Miras might be due to the presence of dust.

Keywords: mira variable stars; periodic variable stars; pulsating variable stars; long period variable stars
Multi-messenger Observations of Binary Neutron Star Mergers in the O4 Run

We present realistic expectations for the number and properties of neutron star binary mergers to be detected as multi-messenger sources during the upcoming fourth observing run (O4) of the LIGO-Virgo-KAGRA gravitational-wave (GW) detectors, with the aim of providing guidance for the optimization of observing strategies. Our predictions are based on a population synthesis mode, which includes the GW signal-to-noise ratio, the kilonova (KN) optical and near-infrared light curves, the relativistic jet gamma-ray burst (GRB) prompt emission peak photon flux, and the afterglow light curves in radio, optical, and X-rays. Within our assumptions, the rate of GW events to be confidently detected during O4 is ${7.7}_{-5.7}^{+11.9}$ yr-1 (calendar year), 78% of which will produce a KN, and a lower 52% will also produce a relativistic jet. The typical depth of current optical electromagnetic search and follow-up strategies is still sufficient to detect most of the KNæ in O4, but only for the first night or two. The prospects for detecting relativistic jet emission are not promising. While closer events (within z ≲ 0.02) will likely still have a detectable cocoon shock breakout, most events will have their GRB emission (both prompt and afterglow) missed unless seen under a small viewing angle. This reduces the fraction of events with detectable jets to 2% (prompt emission, serendipitous) and 10% (afterglow, deep radio monitoring), corresponding to detection rates of ${0.17}_{-0.13}^{+0.26}$ and ${0.78}_{-0.58}^{+1.21}$ yr-1, respectively. When considering a GW subthreshold search triggered by a GRB detection, our predicted rate of joint GW+GRB prompt emission detections increases up to a more promising ${0.75}_{-0.55}^{+1.16}$ yr-1.

Keywords: transient sources; gravitational waves; gravitational wave astronomy; neutron stars
A SPectroscopic Survey of Biased Halos in the Reionization Era (ASPIRE): JWST Discovers an Overdensity around a Metal Absorption-selected Galaxy at z 5.5

The launch of JWST opens a new window for studying the connection between metal-line absorbers and galaxies at the end of the Epoch of Reionization. Previous studies have detected absorber-galaxy pairs in limited quantities through ground-based observations. To enhance our understanding of the relationship between absorbers and their host galaxies at z > 5, we utilized the NIRCam wide-field slitless spectroscopy to search for absorber-associated galaxies by detecting their rest-frame optical emission lines (e.g., [O III] + Hβ). We report the discovery of a Mg II-associated galaxy at z = 5.428 using data from the JWST ASPIRE program. The Mg II absorber is detected on the spectrum of quasar J0305-3150 with a rest-frame equivalent width of 0.74 Å. The associated galaxy has an [O III] luminosity of 1042.5 erg s-1 with an impact parameter of 24.9 pkpc. The joint Hubble Space Telescope-JWST spectral energy distribution (SED) implies a stellar mass and star formation rate of M * ≈ 108.8 M ⊙, star-formation rate ≈ 10 M ⊙ yr-1. Its [O III] equivalent width and stellar mass are typical of [O III] emitters at this redshift. Furthermore, connecting the outflow starting time to the SED-derived stellar age, the outflow velocity of this galaxy is ~300 km s-1, consistent with theoretical expectations. We identified six additional [O III] emitters with impact parameters of up to ~300 pkpc at similar redshifts (∣dv∣ < 1000 km s-1). The observed number is consistent with that in cosmological simulations. This pilot study suggests that systematically investigating the absorber-galaxy connection within the ASPIRE program will provide insights into the metal-enrichment history in the early Universe.

Keywords: quasar absorption line spectroscopy; circumgalactic medium; high-redshift galaxies
X3: A High-mass Young Stellar Object Close to the Supermassive Black Hole Sgr A*

To date, the proposed observation of young stellar objects (YSOs) in the Galactic center still raises the question of where and how these objects could have formed due to the violent vicinity of Sgr A*. Here, we report the multiwavelength detection of a highly dynamic YSO close to Sgr A* that might be a member of the IRS 13 cluster. We observe the beforehand known coreless bow-shock source X3 in the near- and mid-infrared (NIR/MIR) with SINFONI (VLT), NACO (VLT), ISAAC (VLT), VISIR (VLT), SHARP (NTT), and NIRCAM2 (KECK). In the radio domain, we use CO continuum and H30α ALMA observations to identify system components at different temperatures and locations concerning the central stellar source. It is suggested that these radio/submillimeter observations in combination with the NIR Brγ line can be associated with a protoplanetary disk of the YSO, which is consistent with manifold VISIR observations that reveal complex molecules and elements such as PAH, S IV, Ne II, and Ar III in a dense and compact region. Based on the photometric multiwavelength analysis, we infer the mass of ${15}_{-5}^{+10}{M}_{\odot }$ for the YSO with a related age of a few 104 yr. Due to this age estimate and the required relaxation timescales for high-mass stars, this finding is an indication of ongoing star formation in the inner parsec. The proper motion and 3D distance imply a relation between X3 and IRS 13. We argue that IRS 13 may serve as a birthplace for young stars that are ejected due to the evaporation of the cluster.

Keywords: galactic center; young stellar objects; massive stars; star formation; young massive clusters; stellar bow shocks; supermassive black holes
Non-Newtonian Gravity in Strange Quark Stars and Constraints from the Observations of PSR J0740+6620 and GW170817

We investigate the effects of non-Newtonian gravity on the properties of strange quark stars (QSs) and constrain the parameters of the standard MIT bag model used to describe strange quark matter (SQM) by employing the mass of PSR J0740+6620 and the tidal deformability of GW170817. We find that, for the standard MIT bag model, these mass and tidal deformability observations would rule out the existence of QSs if non-Newtonian gravity effects are ignored. For a strange quark mass of ms = 95 MeV, we find that QSs can exist for values of the non-Newtonian gravity parameter g2/μ2 in the range of 1.37 GeV-2 ≤ g2/μ2 ≤ 7.28 GeV-2 and limits on the bag constant and the strong interaction coupling constant of the SQM model given by 141.3 MeV ≤ B1/4 ≤ 150.9 MeV and αS ≤ 0.56. For a strange quark mass of ms = 150 MeV, QSs can exist for 1.88 GeV-2 ≤ g2/μ2 ≤ 6.27 GeV-2 and limits on the parameters of the SQM model given by 139.7 MeV ≤ B1/4 ≤ 147.3 MeV and αS ≤ 0.49.

Keywords: neutron stars; non-standard theories of gravity; gravitational waves
Pixel Centroid Characterization with Laser Speckle and Application to the Nancy Grace Roman Space Telescope Detector Arrays

The Nancy Grace Roman Space Telescope will use its wide-field instrument to carry out a suite of sky surveys in the near-infrared. Several of the science objectives of these surveys, such as the measurement of the growth of cosmic structure using weak gravitational lensing, require exquisite control of instrument-related distortions of the images of astronomical objects. Roman will fly new large-format (4 × 4 k) Teledyne H4RG-10 infrared detector arrays. This paper investigates whether the pixel centroids are located on a regular grid by projecting laser speckle patterns through a double slit aperture onto a non-flight detector array. We develop a method to reconstruct the pixel centroid offsets from the stochastic speckle pattern. Due to the orientation of the test setup, only x-offsets are measured here. We test the method both on simulations, and by injecting artificial offsets into the real images. We use cross-correlations of the reconstructions from different speckle realizations to determine how much of the variance in the pixel offset maps is signal (fixed to the detector) and how much is noise. After performing this reconstruction on 64 × 64 pixel patches, and fitting out the best-fit linear mapping from pixel index to position, we find that there are residual centroid offsets in the x (column) direction from a regular grid of 0.0107 pixels rms (excluding shifts of an entire row relative to another, which our speckle patterns cannot constrain). This decreases to 0.0097 pix rms if we consider residuals from a quadratic rather than linear mapping. These rms offsets include both the physical pixel offsets, as well as any apparent offsets due to crosstalk and remaining systematic errors in the reconstruction. We comment on the advantages and disadvantages of speckle scene measurements as a tool for characterizing the pixel-level behavior in astronomical detectors.

Keywords: weak gravitational lensing; astrometry; infrared observatories
The Variable and Non-variable X-Ray Absorbers in Compton-thin Type II Active Galactic Nuclei

We have conducted an extensive X-ray spectral variability study of a sample of 20 Compton-thin type II galaxies using broadband spectra from XMM-Newton, Chandra, and Suzaku. The aim is to study the variability of the neutral intrinsic X-ray obscuration along the line of sight and investigate the properties and location of the dominant component of the X-ray-obscuring gas. The observations are sensitive to absorption columns of ${N}_{{\rm{H}}}$ ∼ 1020.5-24 cm-2 of fully and partially covering neutral and/or lowly ionized gas on timescales spanning days to well over a decade. We detected variability in the column density of the full-covering absorber in 7/20 sources, on timescales of months to years, indicating a component of compact-scale X-ray-obscuring gas lying along the line of sight of each of these objects. Our results imply that torus models incorporating clouds or over-dense regions should account for line-of-sight column densities as low as ∼a few ×1021 cm-2. However, 13/20 sources yielded no detection of significant variability in the full-covering obscurer, with upper limits of ΔNH spanning 1021-23 cm-2. The dominant absorbing media in these systems could be distant, such as kiloparsec-scale dusty structures associated with the host galaxy, or a homogeneous medium along the line of sight. Thus, we find that overall, strong variability in full-covering obscurers is not highly prevalent in Compton-thin type IIs, at least for our sample, in contrast to previous results in the literature. Finally, 11/20 sources required a partial-covering, obscuring component in all or some of their observations, consistent with clumpy near-Compton-thick compact-scale gas.

Keywords: active galaxies; interstellar medium; quasar absorption line spectroscopy; supermassive black holes
On Measuring Divergence for Magnetic Field Modeling

A physical magnetic field has a divergence of zero. Numerical error in constructing a model field and computing the divergence, however, introduces a finite divergence into these calculations. A popular metric for measuring divergence is the average fractional flux $\left\langle | {f}_{i}| \right\rangle $ . We show that $\left\langle | {f}_{i}| \right\rangle $ scales with the size of the computational mesh, and may be a poor measure of divergence because it becomes arbitrarily small for increasing mesh resolution, without the divergence actually decreasing. We define a modified version of this metric that does not scale with mesh size. We apply the new metric to the results of DeRosa et al., who measured $\left\langle | {f}_{i}| \right\rangle $ for a series of nonlinear force-free field models of the coronal magnetic field based on solar boundary data binned at different spatial resolutions. We compute a number of divergence metrics for the DeRosa et al. data and analyze the effect of spatial resolution on these metrics using a nonparametric method. We find that some of the trends reported by DeRosa et al. are due to the intrinsic scaling of $\left\langle | {f}_{i}| \right\rangle $ . We also find that different metrics give different results for the same data set and therefore there is value in measuring divergence via several metrics.

Keywords: solar corona; magnetic fields; computational methods
Nonequilibrium Flux Rope Formation by Confined Flares Preceding a Solar Coronal Mass Ejection

We present evidence that a magnetic flux rope was formed before a coronal mass ejection (CME) and its associated long-duration flare during a pair of preceding confined eruptions and associated impulsive flares in a compound event in NOAA Active Region 12371. Extreme-ultraviolet images and the extrapolated nonlinear force-free field show that the first two (impulsive) flares, SOL2015-06-21T01:42, result from the confined eruption of highly sheared low-lying flux, presumably a seed flux rope. The eruption spawns a vertical current sheet, where magnetic reconnection creates flare ribbons and loops, a nonthermal microwave source, and a sigmoidal hot channel that can only be interpreted as a magnetic flux rope. Until the subsequent long-duration flare, SOL2015-06-21T02:36, the sigmoid's elbows expand, while its center remains stationary, suggesting nonequilibrium but not yet instability. The "flare reconnection" during the confined eruptions acts like "tether-cutting reconnection" whose flux feeding of the rope leads to instability. The subsequent full eruption is seen as an accelerated rise of the entire hot channel, seamlessly evolving into the fast halo CME. Both the confined and ejective eruptions are consistent with the onset of the torus instability in the dipped decay index profile that results from the region's two-scale magnetic structure. We suggest that the formation or enhancement of a nonequilibrium but stable flux rope by confined eruptions is a generic process occurring prior to many CMEs.

Keywords: active solar corona; solar coronal mass ejections; solar flares; solar magnetic fields; solar magnetic reconnection
Constraining a Companion of the Galactic Center Black Hole Sgr A*

We use 23 yr of astrometric and radial velocity data on the orbit of the star S0-2 to constrain a hypothetical intermediate-mass black hole orbiting the massive black hole Sgr A* at the Galactic center. The data place upper limits on variations of the orientation of the stellar orbit at levels between 0.°02 and 0.°07 per year. We use a combination of analytic estimates and full numerical integrations of the orbit of S0-2 in the presence of a black hole binary. For a companion intermediate-mass black hole outside the orbit of S0-2 (1020 au), we find that a companion black hole with mass m c between 103 and 105 M ⊙ is excluded, with a boundary behaving as ${a}_{c}\sim {m}_{c}^{1/3}$ . For a companion with a c < 1020 au, a black hole with mass between 103 and 105 M ⊙ is excluded, with ${a}_{c}\sim {m}_{c}^{-1/2}$ . These bounds arise from quadrupolar perturbations of the orbit of S0-2. Significantly stronger bounds on an inner companion arise from the fact that the location of S0-2 is measured relative to the bright emission of Sgr A* and that separation is perturbed by the "wobble" of Sgr A* about the center of mass between it and the companion. The result is a set of bounds as small as 400 M ⊙ at 200 au; the numerical simulations suggest a bound from these effects varying as ${a}_{c}\sim {m}_{c}^{-1}$ . We compare and contrast our results with those from a recent analysis by the GRAVITY collaboration.

Keywords: supermassive black holes; astrophysical black holes; galactic center; gravitation; three-body problem; milky way dynamics
Self-modulation of Cosmic Rays in Molecular Clouds: Imprints in the Radio Observations

We analyze properties of nonthermal radio emission from the Central Molecular Zone (CMZ) and from individual molecular clouds, and argue that the observed features can be interpreted in the framework of our recent theory of self-modulation of cosmic rays (CRs) penetrating dense molecular regions. For clouds with gas column densities of ~1023 cm-2, the theory predicts depletion of sub-GeV CR electrons, occurring due to self-modulation of CR protons and leading to harder synchrotron spectra in the sub-GHz range. The predicted imprints of electron depletion in the synchrotron spectra agree well with the spectral hardening seen in available radio observations of the CMZ. A similar, but even stronger, effect on the synchrotron emission is predicted for individual (denser) CMZ clouds, such as the Sgr B2. However, the emission at frequencies above ~GHz, where observational data are available, is completely dominated by the thermal component, and therefore new observations at lower frequencies are needed to verify the predictions.

Keywords: galactic cosmic rays; radio continuum emission; non-thermal radiation sources; galactic center
Discovery of a Damped Lyα Galaxy at z ∼ 3 toward the Quasar SDSS J011852+040644

We report the detection of the host galaxy of a damped Lyα system (DLA) with log N(H I) [cm-2] = 21.0 ± 0.10 at z ≈ 3.0091 toward the background quasar SDSS J011852+040644 using the Palomar Cosmic Web Imager at the Hale (P200) telescope. We detect Lyα emission in the dark core of the DLA trough at a 3.3σ confidence level, with Lyα luminosity of LLyα = (3.8 ± 0.8) × 1042 erg s-1, corresponding to a star formation rate of ≳2 M⊙ yr-1 (considering a lower limit on Lyα escape fraction ${f}_{\mathrm{esc}}^{\mathrm{Ly}\alpha }\sim 2 \% $ ) as typical for Lyman break galaxies at these redshifts. The Lyα emission is blueshifted with respect to the systemic redshift derived from metal absorption lines by 281 ± 43 km s-1. The associated galaxy is at very small impact parameter of ≲12 kpc from the background quasar, which is in line with the observed anticorrelation between column density and impact parameter in spectroscopic searches tracing the large-scale environments of DLA host galaxies.

Keywords: quasar absorption line spectroscopy; star formation