adsabs/SciX_UAT_keywords huggingface dataset:
The Parsec-scale Jet of the Neutrino-emitting Blazar TXS 0506+056

Recently the IceCube Collaboration detected very high energy (VHE) neutrinos and associated them with the blazar TXS 0506+056, raising a possible association of VHE neutrinos with this and other individual blazars. Very long baseline interferometry (VLBI) is so far the only technique enabling the imaging of the innermost jet at milliarcsec resolution (parsec scale), where the high-energy emission possibly originates from. Here, we report on the radio properties of the parsec-scale jet in TXS 0506+056 derived from the analysis of multiepoch, multifrequency archive VLBI data. The half opening angle of the jet beam is about 3°8, and the jet inclination angle is about 20°. The overall jet structure shows a helical trajectory with a precessing period of 5-6 yr, likely originating from instabilities operating at parsec scales. The calculated beaming parameters (Doppler boosting factor, bulk Lorentz factor) suggest a moderately relativistic jet. The parsec-scale magnetic field strength is estimated in the contexts of core shift and variability, and is in general agreement in the range of 0.2-0.7 G. And it is found to decrease from a relatively larger value during the quiescent period before the ongoing flare. This suggests a conversion of magnetic field energy density to particle energy density that helps accelerate injected particles at the jet base and results in variable shocked emission. The neutrino event could be associated with the onset of energetic particle injection into the jet. This scenario then supports the lepto-hadronic origin of the VHE neutrinos and γ-ray emission owing to a cospatial origin.

Keywords: blazars; radio active galactic nuclei; neutrino astronomy; radio jets; gamma-ray sources; non-thermal radiation sources
Scarlet Spectra: Two Red L Dwarfs Revealed by SOAR

We present the analysis of two unusually red L dwarfs, CWISE J075554.14-325956.3 (W0755-3259) and CWISE J165909.91-351108.5 (W1659-3511), confirmed by their newly obtained near-infrared spectra collected with the TripleSpec4 spectrograph on the Southern Astrophysical Research Telescope. We classify W0755-3259 as an L7 very low-gravity dwarf, exhibiting extreme redness with a characteristic peaked H-band and spectral indices typical of low-gravity late-type L dwarfs. We classify W1659-3511 as a red L7 field-gravity dwarf, with a more rounded H-band peak and spectral indices that support a normal gravity designation. W1659-3511 is noticeably fainter than W0755-3259, and the rounded H-band of W1659-3511 may be evidence of CH4 absorption.

Keywords: l dwarfs; brown dwarfs; spectroscopy; near infrared astronomy
Discovery of a Variable Multiphase Outflow in the X-Ray-emitting Tidal Disruption Event ASASSN-20qc

Tidal disruption events (TDEs) are exotic transients that can lead to temporary super-Eddington accretion onto a supermassive black hole. Such an accretion mode is naturally expected to result in powerful outflows of ionized matter. However, to date such an outflow has only been directly detected in the X-ray band in a single TDE, ASASSN-14li. This outflow has a low velocity of just a few 100 km s-1, although there is also evidence for a second, ultrafast phase. Here we present the detection of a low-velocity outflow in a second TDE, ASASSN-20qc. The high-resolution X-ray spectrum reveals an array of narrow absorption lines, each blueshifted by a few 100 km s-1, which cannot be described by a single photoionization phase. For the first time, we confirm the multiphase nature of a TDE outflow, with at least two phases and two distinct velocity components. One highly ionized phase is outflowing at ${910}_{-80}^{+90}$ km s-1, while a lower ionization component is blueshifted by ${400}_{-120}^{+100}$ km s-1. We perform a time-resolved analysis of the X-ray spectrum and detect that, surprisingly, the ionization parameter of the mildly ionized absorber strongly varies over the course of a single 60 ks observation, indicating that its distance from the black hole may be as low as 400 gravitational radii. We discuss these findings in the context of TDEs and compare this newly detected outflow with that of ASASSN-14li.

Keywords: accretion; supermassive black holes; tidal disruption
Satellites around Milky Way Analogs: Tension in the Number and Fraction of Quiescent Satellites Seen in Observations versus Simulations

We compare the star-forming properties of satellites around Milky Way (MW) analogs from the Stage II release of the Satellites Around Galactic Analogs Survey (SAGA-II) to those from the APOSTLE and Auriga cosmological zoom-in simulation suites. We use archival GALEX UV imaging as a star formation indicator for the SAGA-II sample and derive star formation rates (SFRs) to compare with those from APOSTLE and Auriga. We compare our detection rates from the NUV and FUV bands to the SAGA-II Hα detections and find that they are broadly consistent with over 85% of observed satellites detected in all three tracers. We apply the same spatial selection criteria used around SAGA-II hosts to select satellites around the MW-like hosts in APOSTLE and Auriga. We find very good overall agreement in the derived SFRs for the star-forming satellites as well as the number of star-forming satellites per host in observed and simulated samples. However, the number and fraction of quenched satellites in the SAGA-II sample are significantly lower than those in APOSTLE and Auriga below a stellar mass of M* ~ 108 M⊙, even when the SAGA-II incompleteness and interloper corrections are included. This discrepancy is robust with respect to the resolution of the simulations and persists when alternative star formation tracers are employed. We posit that this disagreement is not readily explained by vagaries in the observed or simulated samples considered here, suggesting a genuine discrepancy that may inform the physics of satellite populations around MW analogs.

Keywords: dwarf galaxies; galaxy evolution; galaxy quenching; quenched galaxies; star formation
Constraining the Properties of Black Hole Seeds from the Farthest Quasars

Over 60 yr after the discovery of the first quasar, more than 275 such sources are identified in the epoch of reionization at z > 6. JWST is now exploring higher redshifts (z ≳ 8) and lower-mass (≲107 M ⊙) ranges. The discovery of progressively farther quasars is instrumental to constraining the properties of the first population of black holes (BHs), or BH seeds, formed at z ~ 20-30. For the first time, we use Bayesian analysis of the most comprehensive catalog of quasars at z > 6 to constrain the distribution of BH seeds. We show that the mass distribution of BH seeds can be effectively described by combining a power law and a lognormal function tailored to the mass ranges associated with light and heavy seeds, assuming Eddington-limited growth and early seeding time. Our analysis reveals a power-law slope of $-{0.70}_{-0.46}^{+0.46}$ and a lognormal mean of ${4.44}_{-0.30}^{+0.30}$ . The inferred values of the Eddington ratio, the duty cycle, and the mean radiative efficiency are ${0.82}_{-0.10}^{+0.10}$ , ${0.66}_{-0.23}^{+0.23}$ , and ${0.06}_{-0.02}^{+0.02}$ , respectively. Models that solely incorporate a power law or a lognormal distribution within the specific mass range corresponding to light and heavy seeds are statistically strongly disfavored, unlike models not restricted to this specific range. Our results suggest that including both components is necessary to comprehensively account for the masses of high-redshift quasars, and that both light and heavy seeds formed in the early Universe and grew to form the population of quasars we observe.

Keywords: active galaxies; early universe; quasars; galaxy evolution; bayesian statistics
The Early Discovery of SN 2017ahn: Signatures of Persistent Interaction in a Fast-declining Type II Supernova

We present high-cadence, comprehensive data on the nearby (D ≃ 33 Mpc) Type II supernova (SN II) 2017ahn, discovered within about one day of the explosion, from the very early phases after explosion to the nebular phase. The observables of SN 2017ahn show a significant evolution over the ≃470 days of our follow-up campaign, first showing prominent, narrow Balmer lines and other high-ionization features purely in emission (i.e., flash spectroscopy features), which progressively fade and lead to a spectroscopic evolution similar to that of more canonical SNe II. Over the same period, the decline of the light curves in all bands is fast, resembling the photometric evolution of linearly declining H-rich core-collapse SNe. The modeling of the light curves and early flash spectra suggests that a complex circumstellar medium surrounds the progenitor star at the time of explosion, with a first dense shell produced during the very late stages of its evolution that is swept up by the rapidly expanding ejecta within the first ∼6 days of the SN evolution, while signatures of interaction are observed also at later phases. Hydrodynamical models support the scenario in which linearly declining SNe II are predicted to arise from massive yellow super- or hypergiants depleted of most of their hydrogen layers.

Keywords: supernovae; core-collapse supernovae; type ii supernovae
Rigorous Theory for Secondary Cosmic-Ray Ionization

The energy spectrum of electrons produced in molecular gas by interstellar cosmic rays (CRs) is rigorously calculated as a function of gas column density N traversed by the CRs. This allows us to accurately compute the local value of the secondary ionization rate of molecular hydrogen, ${\zeta }_{\sec }(N)$ , as a function of the local primary ionization rate, ζp(N). The ratio ${\zeta }_{\sec }/{\zeta }_{p}$ increases monotonically with N, and can considerably exceed the value of ≈0.67 commonly adopted in the literature. For sufficiently soft interstellar spectra, the dependence ${\zeta }_{\sec }/{\zeta }_{p}$ versus N is practically insensitive to their particular shape and thus is a general characteristic of the secondary CR ionization in dense gas.

Keywords: secondary cosmic rays; molecular clouds
Improved Companion Mass Limits for Sirius A with Thermal Infrared Coronagraphy Using a Vector-apodizing Phase Plate and Time-domain Starlight-subtraction Techniques

We use observations with the infrared-optimized Magellan Adaptive Optics (MagAO) system and Clio camera in 3.9 μm light to place stringent mass constraints on possible undetected companions to Sirius A. We suppress the light from Sirius A by imaging it through a grating vector-apodizing phase plate coronagraph with a 180° dark region (gvAPP-180). To remove residual starlight in postprocessing, we apply a time-domain principal-components-analysis-based algorithm we call PCA-Temporal, which uses eigen time series rather than eigenimages to subtract starlight. By casting the problem in terms of eigen time series, we reduce the computational cost of postprocessing the data, enabling the use of the fully sampled data set for improved contrast at small separations. We also discuss the impact of retaining fine temporal sampling of the data on final contrast limits. We achieve postprocessed contrast limits of 1.5 × 10-6-9.8 × 10-6 outside of 0.″75, which correspond to planet masses of 2.6-8.0 M J. These are combined with values from the recent literature of high-contrast imaging observations of Sirius to synthesize an overall completeness fraction as a function of mass and separation. After synthesizing these recent studies and our results, the final completeness analysis rules out 99% of ≥9 M J planets from 2.5 to 7 au.

Keywords: coronagraphic imaging; high contrast techniques; direct imaging; exoplanet detection methods; exoplanet astronomy
The Origin of Binary Black Hole Mergers

Recently Venumadhav et al. proposed a new pipeline to analyze LIGO-Virgo Collaboration's O1-O2 data, and discovered eight new binary black hole (BBH) mergers, including one with a high effective spin, χeff. This discovery helps to clarify the origin of the observed BBHs and the dynamical capture versus field binaries debate. Using a tide-wind model that characterizes the late phases of binary evolution and captures the essence of field binary spin evolution, we show that the observed χeff distribution favors this model over capture. However, given the current limited sample size, capture scenarios (isotropic models) cannot be ruled out. Observations of roughly 100 merges will enable us to distinguish between the different formation scenarios. However, if as expected, both formation channels operate, it may be difficult to resolve their exact fraction.

Keywords: gravitational waves; gravitational wave sources
Following up TESS Single Transits with Archival Photometry and Radial Velocities

NASA's Transiting Exoplanet Survey Satellite (TESS) mission is expected to discover hundreds of planets via single transits first identified in their light curves. Determining the orbital period of these single-transit candidates typically requires a significant amount of follow-up work to observe a second transit or measure a radial velocity (RV) orbit. In Yao et al., we developed simulations that demonstrated the ability to use archival photometric data in combination with TESS to "precover" the orbital period for these candidates with a precision of several minutes, assuming circular orbits. In this work, we incorporate updated models for TESS single transits, allowing for eccentric orbits, along with an updated methodology to improve the reliability of the results. Additionally, we explore how RV observations can be used to follow up single-transit events, using strategies distinct from those employed when the orbital period is known. We find that the use of an estimated period based on a circular orbit to schedule reconnaissance RV observations can efficiently distinguish eclipsing binaries from planets. For candidates that pass reconnaissance RV observations, we simulate RV monitoring campaigns that enable one to obtain an approximate orbital solution. We find that this method can regularly determine the orbital periods for planets more massive than 0.5 MJ with orbital periods as long as 100 days.

Keywords: transit photometry; radial velocity; ground-based astronomy; exoplanet detection methods; astronomy data analysis
Statistical Study of the Optimal Local Sources for Cosmic Ray Nuclei and Electrons

Local sources, such as the Geminga supernova remnant (SNR), may have played an important role in the anomaly of protons, electrons, and anisotropy in past works. In fact, there exist 12 SNRs around the solar system within 1 kpc. One question is whether other SNRs also possibly contribute to the spectra of nuclei and electrons, and explain the special structure of the anisotropy. In this work, under spatial-dependent propagation, we systematically study the contribution of all local SNRs, within 1 kpc around the solar system, to the spectra of nuclei and electrons, as well as the energy dependence of the anisotropy. As a result, only the Geminga, the Monogem, and the Vela SNRs have quantitative contributions to the nuclei and electron spectra, and the anisotropy. Here, the Geminga SNR is the sole optimal candidate and the Monogem SNR is controversial due to the tension of the anisotropy between the model calculation and the observations. The Vela SNR contributes to a new spectral structure beyond TeV energy, hinted by the HESS, the VERITAS, the DAMPE, and the CALET measurements. More interestingly, the electron anisotropy satisfies the Fermi-LAT limit below TeV energy, but rises greatly and reaches 10% at several TeV. This novel structure will shed new light on verifying our model. We hope that the new structure of the electron spectrum and anisotropy can be observed by the spaceborne DAMPE and HERD, and the ground-based HAWC and LHAASO experiments in the near future.

Keywords: cosmic anisotropy; galactic cosmic rays; supernova remnants
Dust Temperature of Compact Star-forming Galaxies at z ∼ 1-3 in 3D-HST/CANDELS

Recent simulation studies suggest that the compaction of star-forming galaxies (SFGs) at high redshift might be a critical process, during which the central bulge is being rapidly built, followed by quenching of the star formation. To explore dust properties of SFGs with compact morphology, we investigate the dependence of dust temperature, Tdust, on their size and star formation activity, using a sample of massive SFGs with $\mathrm{log}({M}_{* }/{M}_{\odot })\gt 10$ at 1 < z < 3, drawn from the 3D-HST/CANDELS database in combination with deep Herschel observations. Tdust is derived via fitting the mid-to-far-infrared photometry with a mid-infrared power law and a far-infrared modified blackbody. We find that both extended and compact SFGs generally follow a similar Tdust - z evolutionary track as that of the main-sequence galaxies. The compact SFGs seem to share similar dust temperature with extended SFGs. Despite the frequent occurrence of active galactic nuclei (AGNs) in compact SFGs, we do not observe any effect on dust caused by the presence of AGNs in these galaxies during the compaction. Our results disfavor different ISM properties between compact and extended SFGs, suggesting that a rapid and violent compaction process might be not necessary for the formation of compact SFGs.

Keywords: galaxy evolution; high-redshift galaxies; galaxy structure; star formation
On the Origin of Late-time X-Ray Flares in UV/optically Selected Tidal Disruption Events

We propose a model to explain the time delay between the peak of the optical and X-ray luminosity, ΔtO-X hereafter, in UV/optically selected tidal disruption events (TDEs). The following picture explains the observed ΔtO-X in several TDEs as a consequence of the circularization and disk accretion processes as long as the sub-Eddington accretion. At the beginning of the circularization, the fallback debris is thermalized by the self-crossing shock caused by relativistic precession, providing the peak optical emission. During the circularization process, the mass fallback rate decreases with time to form a ring around the supermassive black hole (SMBH). The formation timescale corresponds to the circularization timescale of the most tightly bound debris, which is less than a year to several decades, depending mostly on the penetration factor, the circularization efficiency, and the black hole mass. The ring will subsequently evolve viscously over the viscous diffusion time. We find that it accretes onto the SMBH on a fraction of the viscous timescale, which is 2 years for the typical given parameters, leading to X-ray emission at late times. The resultant ΔtO-X is given by the sum of the circularization timescale and the accretion timescale and significantly decreases with increasing penetration factor to several to ~10 yr typically. Since the X-ray luminosity substantially decreases as the viewing angle between the normal to the disk plane and line of sight increases from 0° to 90°, a low late-time X-ray luminosity can be explained by an edge-on view. We also discuss the super-Eddington accretion scenario, where ΔtO-X is dominated by the circularization timescale.

Keywords: astrophysical black holes; black hole physics; supermassive black holes; accretion; galaxy accretion disks; tidal disruption; transient sources; high energy astrophysics
AGILE Gamma-Ray Detection of the Exceptional GRB 221009A

Gamma-ray emission in the MeV-GeV range from explosive cosmic events is of invaluable relevance to understanding physical processes related to the formation of neutron stars and black holes. Here we report on the detection by the AGILE satellite in the MeV-GeV energy range of the remarkable long-duration gamma-ray burst GRB 221009A. The AGILE onboard detectors have good exposure to GRB 221009A during its initial crucial phases. Hard X-ray/MeV emission in the prompt phase lasted hundreds of seconds, with the brightest radiation being emitted between 200 and 300 s after the initial trigger. Very intense GeV gamma-ray emission is detected by AGILE in the prompt and early afterglow phase up to 10,000 s. Time-resolved spectral analysis shows time-variable MeV-peaked emission simultaneous with intense power-law GeV radiation that persists in the afterglow phase. The coexistence during the prompt phase of very intense MeV emission together with highly nonthermal and hardening GeV radiation is a remarkable feature of GRB 221009A. During the prompt phase, the event shows spectrally different MeV and GeV emissions that are most likely generated by physical mechanisms occurring in different locations. AGILE observations provide crucial flux and spectral gamma-ray information regarding the early phases of GRB 221009A during which emission in the TeV range was reported.

Keywords: gamma-ray bursts; gamma-ray astronomy; gamma-ray observatories
Small-scale Dynamical Coherence Accompanied with Galaxy Conformity

The discovery of the coherence between galaxy rotation and neighbor motion in 1 Mpc scales has recently been reported. Following up on the discovery, we investigate whether the neighbors in such dynamical coherence also present galaxy conformity, using the Calar Alto Legacy Integral Field Area Survey (CALIFA) data and the NASA-Sloan Atlas catalog. We measure the correlation coefficient of g - r colors between the CALIFA galaxies and their neighbors, as a quantitative indicator of galaxy conformity. The neighbors are divided into coherently moving and anticoherently moving ones, the correlation coefficients from which are compared with each other, in various bins of relative luminosity and projected distance. In most cases, the CALIFA galaxies and their neighbors show positive correlation coefficients in g - r color, even for the anticoherent neighbors. However, we find a statistically significant (2.6σ) difference between coherent and anticoherent neighbors, when the neighbor galaxies are bright ( ${\rm{\Delta }}{M}_{r}\leqslant -1.0$ ) and close (D ≤ 400 kpc). That is, when they are bright and close to the CALIFA galaxies, the coherently moving neighbors show stronger conformity with the CALIFA galaxies than the anticoherently moving neighbors. This result supports that the small-scale dynamical coherence may originate from galaxy interactions as galaxy conformity is supposed to do, which agrees with the conclusion of the previous study.

Keywords: galaxy environments; interacting galaxies; companion galaxies; galaxy kinematics; galaxy rotation; galaxy dynamics
Construction of Explicit Symplectic Integrators in General Relativity. III. Reissner-Nordström-(anti)-de Sitter Black Holes

We give a possible splitting method to a Hamiltonian for the description of charged particles moving around the Reissner-Nordström-(anti)-de Sitter black hole with an external magnetic field. This Hamiltonian can be separated into six analytical solvable pieces, whose solutions are explicit functions of proper time. In this case, second- and fourth-order explicit symplectic integrators are easily available. They exhibit excellent long-term behavior in maintaining the boundness of Hamiltonian errors regardless of ordered or chaotic orbits if appropriate step sizes are chosen. Under some circumstances, an increase of the positive cosmological constant gives rise to strengthening the extent of chaos from the global phase space; namely, chaos of charged particles occurs easily for the accelerated expansion of the universe. However, an increase of the magnitude of the negative cosmological constant does not. The different contributions to chaos are because the cosmological constant acts as a repulsive force in the Reissner-Nordström-de Sitter black hole, but an attractive force in the Reissner-Nordström-anti-de Sitter black hole.

Keywords: celestial mechanics; computational astronomy; computational methods; black hole physics