Sazuna/UAT_keywords huggingface dataset:
Access of Energetic Particles to a Magnetic Flux Rope from External Magnetic Field Lines. Cosmic-ray (CR) fluxes in the heliosphere are affected by the transient interplanetary coronal mass ejections (ICMEs), causing so-called Forbush decreases (FDs), characterized by a decline of up to 25% in the neutron monitor counts at the Earth's surface, lasting up to over a week. FDs are thought to be caused by the ICME shock wave or the magnetic flux rope embedded in the ICME inhibiting CR propagation through the ICME structure. FDs are typically modeled as enhanced diffusion within the ICME structure. However, so far modeling has not considered the access of the CRs from the interplanetary field lines into the isolated magnetic field lines of the ICME flux rope. We study the effect of an ICME flux rope on particle propagation by using full-orbit particle simulations, with the interface between the external interplanetary magnetic field and the isolated flux rope field lines modeled analytically. We find that the particles can access the flux rope through the x-point region, where the external magnetic fields cancel the azimuthal component of the rope field. The transport through this region is fast compared to diffusive radial propagation within the rope. As a result, the propagation of CRs into the flux rope can be modeled as diffusion into a cylinder. The density cavity within the rope is asymmetric, and limited to the magnetic field lines isolated from the external field. Thus, in order to evaluate the role of the flux rope in FDs, one must analyze the extent of the region where the flux rope magnetic field lines are separated from the interplanetary magnetic fields.

Keywords: Interplanetary turbulence, Forbush effect, Galactic cosmic rays, Interplanetary magnetic fields, Solar coronal mass ejections, Interplanetary physics
Investigating the Mini and Giant Radio Flare Episodes of Cygnus X-3. The microquasar Cygnus X-3 underwent a giant radio flare in 2017 April, reaching a maximum flux of ∼16.5 Jy at 8.5 GHz. We present results from a long monitoring campaign carried out with Medicina at 8.5, 18.6, and 24.1 GHz, parallel to the Metsähovi radio telescope at 37 GHz, from 2017 April 4 to 11. We observe a spectral steepening from $\alpha =0.2$ to 0.5 (with ${S}_{\nu }\propto {\nu }^{-\alpha }$ ) within 6 hr of the epoch of the flare's peak maximum, and rapid changes in the spectral slope in the following days during brief enhanced emission episodes while the general trend of the radio flux density indicated the decay of the giant flare. We further study the radio orbital modulation of Cyg X-3 emission associated with the 2017 giant flare and with six mini-flares observed in 1983, 1985, 1994, 1995, 2002, and 2016. The enhanced emission episodes observed during the decline of the giant flare at 8.5 GHz coincide with the orbital phase $\phi \sim 0.5$ (orbital inferior conjunction). On the other hand, the light curves of the mini-flares observed at 15-22 GHz peak at $\phi \sim 0$, except for the 2016 light curve, which is shifted 0.5 w.r.t. the other ones. We attribute the apparent phase shift to the variable location of the emitting region along the bent jet. This might be explained by the different accretion states of the flaring episodes (the 2016 mini-flare occurred in the hypersoft X-ray state).

Keywords: High mass x-ray binary stars, Radio jets
A Variable Ionized Disk Wind in the Black Hole Candidate EXO 1846-031. After 34 yr, the black hole candidate EXO 1846-031 went into outburst again in 2019. We investigate its spectral properties in the hard intermediate and the soft states with NuSTAR and Insight-HXMT. A reflection component has been detected in the two spectral states but possibly originating from different illumination spectra: in the intermediate state, the illuminating source is attributed to a hard coronal component, which has been commonly observed in other X-ray binaries, whereas in the soft state, the reflection is probably produced by disk self-irradiation. Both cases support EXO 1846-031 as a low-inclination system of $\sim 40^\circ $ . An absorption line is clearly detected at ∼7.2 keV in the hard intermediate state, corresponding to a highly ionized disk wind ( $\mathrm{log}\,\xi \gt 6.1$ ) with a velocity of up to 0.06c. Meanwhile, quasi-simultaneous radio emissions have been detected before and after the X-rays, implying the coexistence of disk winds and jets in this system. If only the high-flux segment of the NuSTAR observation is considered, the observed wind appears to be magnetically driven. The absorption line disappeared in the soft state and a narrow emission line appeared at ∼6.7 keV on top of the reflection component, which may be evidence for disk winds, but data with higher spectral resolution are required to examine this.

Keywords: Accretion, X-ray transient sources, High energy astrophysics
A Closer Look at Two of the Most Luminous Quasars in the Universe. Ultraluminous quasars (M1450 ≤ -29) provide us with a rare view into the nature of the most massive and most rapidly accreting supermassive black holes (SMBHs). Following the discovery of two of these extreme sources, J0341+1720 (M1450 = -29.56, z = 3.71) and J2125-1719 (M1450 = -29.39, z = 3.90), in the Extremely Luminous Quasar Survey (ELQS) and its extension to the Pan-STARRS 1 footprint (PS-ELQS), we herein present an analysis of their rest-frame UV to optical spectroscopy. Both quasars harbor very massive SMBHs with ${M}_{\mathrm{BH}}={6.73}_{-0.83}^{+0.75}\times {10}^{9}\,{M}_{\odot }$ and ${M}_{\mathrm{BH}}={5.45}_{-0.55}^{+0.60}\times {10}^{9}\,{M}_{\odot }$, respectively, showing evidence of accretion above the Eddington limit ( ${L}_{\mathrm{bol}}/{L}_{\mathrm{Edd}}={2.74}_{-0.27}^{+0.39}$ and ${L}_{\mathrm{bol}}/{L}_{\mathrm{Edd}}={3.01}_{-0.30}^{+0.34}$ ). NOEMA 3 millimeter observations of J0341+1720 reveal a highly star-forming (SFR ≍ 1500 M☉ yr-1), ultraluminous infrared galaxy (LIR ≍ 1.0 × 1013 L☉) host, which, based on an estimate of its dynamical mass, is only ∼30 times more massive than the SMBH it harbors at its center. As examples of luminous super-Eddington accretion, these two quasars provide support for theories that explain the existence of billion solar mass SMBHs ∼700 million years after the Big Bang by moderate super-Eddington growth from standard SMBH seeds.

Keywords: AGN host galaxies, Supermassive black holes, Quasars, Millimeter astronomy, Active galaxies, Active galactic nuclei, Spectroscopy, Ultraluminous infrared galaxies, Astrophysical black holes
Superorbital Modulation in the High-mass X-Ray Binary 4U 1538-52 and Possible Modulation in IGR J16393-4643. Hard X-ray observations with the Neil Gehrels Swift Observatory Burst Alert Telescope (BAT) reveal superorbital modulation in the wind-accreting supergiant high-mass X-ray binary (HMXB) 4U 1538-52 at a period of 14.9130 ± 0.0026 days that is consistent with four times the 3.73 day orbital period. These periods agree with a previously suggested correlation between superorbital and orbital periods in similar HMXBs. During the ∼14 yr of observations the superorbital modulation changes amplitude, and since ∼MJD 57,650 it was no longer detected in the power spectrum, although a peak near the second harmonic of this was present for some time. Measurements of the spin period of the neutron star in the system with the Fermi Gamma-ray Burst Monitor show a long-term spin-down trend, which halted toward the end of the light curve, suggesting a connection between ${\dot{P}}_{\mathrm{spin}}$ and superorbital modulation, as proposed for 2S 0114+650. However, an earlier torque reversal from INTEGRAL observations was not associated with superorbital modulation changes. B- and V-band photometry from the Las Cumbres Observatory reveals orbital ellipsoidal photometric variability, but no superorbital optical modulation. However the photometry was obtained when the 14.9130 day period was no longer detected in the BAT power spectrum. We revisit possible superorbital modulation in BAT observations of IGR J16393-4643 but cannot conclusively determine whether this is present, although it is not persistent. We consider superorbital modulation mechanisms, and suggest that the corotating interaction region model, with small deviations from orbital synchronization, appears promising.

Keywords: Neutron stars, Accretion, X-ray binary stars, Bondi accretion, High mass x-ray binary stars, OB supergiant stars
Space Telescope and Optical Reverberation Mapping Project. XIII. An Atlas of UV and X-Ray Spectroscopic Signatures of the Disk Wind in NGC 5548. The unusual behavior of the spectral lines of NGC5548 during the STORM campaign demonstrated a missing piece in the structure of AGNs. For a two-month period in the middle of the campaign, the spectral lines showed a deficit in flux and a reduced response to the variations of the UV continuum. This was the first time that this behavior was unequivocally observed in an AGN. Our previous papers explained this as being due to a variable disk wind that acts as a shield and alters the SED. Here, we use Cloudy to create an atlas of photoionization models for a variety of disk winds, in order to study their effects on the SED. We show that the winds have three different cases: Case 1 winds are transparent, fully ionized, and have minimal effects on the intrinsic SED, although they can produce some line emission, especially He II or FeKα. We propose that this is the situation in most of the AGNs. Case 2 winds, which have a He++-He+ ionization front, block part of the XUV continuum but transmit much of the Lyman continuum. They lead to the observed abnormal behavior. Case 3 winds have a H+ ionization front and block much of the Lyman continuum. The results show that the presence of these winds has important effects on the spectral lines of AGNs. They will thus have an effect on the measurements of the black hole mass and the geometry of the AGN. This atlas of spectral simulations can serve as a guide to future reverberation campaigns.

Keywords: AGN host galaxies
Supernova Explosions in Accretion Disks in Active Galactic Nuclei: Three-dimensional Models. Supernova (SN) explosions can potentially affect the structure and evolution of circumnuclear disks in active galactic nuclei (AGN). Some previous studies have suggested that a relatively low rate of SN explosions can provide an effective value of alpha viscosity between 0.1 and 1 in AGN accretion disks within a 1 pc scale. In order to test this possibility, we provide some analytic scalings of the evolution of an SN remnant embedded in a differentially rotating smooth disk. We calibrate our estimates using three-dimensional hydrodynamical simulations where the gas is modeled as adiabatic with index γ. Our simulations are suited to include the fact that a fraction of the momentum injected by the SN escapes from the disk into the corona. Based on these results, we calculate the contribution of SN explosions to the effective alpha viscosity, denoted by αSNe, in a model AGN accretion disk, where accretion is driven by the local viscosity α. We find that for AGN galaxies with a central black hole of $\sim {10}^{8}{M}_{\odot }$ and a disk with viscosity α = 0.1, the contribution of SN explosions may be as large as ${\alpha }_{\mathrm{SNe}}\simeq 0.02$ , provided that $\gamma \gtrsim 1.1$ . On the other hand, in the momentum conservation limit, which is valid when the push by the internal pressure of the SN remnant is negligible, we find ${\alpha }_{\mathrm{SNe}}\lesssim 6\times {10}^{-4}$ .

Keywords: Accretion, Black hole physics, Hydrodynamics, Quasars, Active galaxies, Galaxy accretion disks
A New Feedback Cycle in the Archetypal Cooling Flow Group NGC 5044. The fate of cooling gas in the centers of galaxy clusters and groups is still not well understood, as is also the case for the complex process of triggering active galactic nucleus (AGN) outbursts in their central dominant galaxies and the consequent reheating of the gas by the AGN jets. With the largest known reservoir of cold molecular gas of any group-dominant galaxy and three epochs of AGN activity visible as cavities in its hot gas, NGC 5044 is an ideal system in which to study the cooling/AGN feedback cycle at the group scale. We present VLBA observations of NGC 5044 to ascertain the current state of the central AGN. We find a compact core and two small jets aligned almost in the plane of the sky and in the orthogonal direction to the location of cavities. We construct the radio/submillimeter spectral energy distribution over more than 3 orders of magnitude. We find that below 5 GHz, the spectrum is best fit by a self-absorbed continuous injection model representing emission coming from the jets, while the higher frequencies show clear signs of an advection-dominated accretion flow. We derive a black hole mass and accretion rate consistent with independent measurements. We conclude that the age of the jets is much younger than the innermost cavities, marking the start of a new feedback cycle.

Keywords: Accretion, Jets, Radio jets, Active galactic nuclei, Galaxy groups
Excitation of Spin-Orbit Misalignments in Stellar Binaries with Circumbinary Disks: Application to DI Herculis. The large spin-orbit misalignments in the DI Herculis stellar binary system have resolved the decades-long puzzle of the anomalously slow apsidal precession rate, but raise new questions regarding the origin of the obliquities. This paper investigates obliquity evolution in stellar binaries hosting modestly inclined circumbinary disks. As the disk and binary axes undergo mutual precession, each oblate star experiences a torque from its companion star, so that the spin and orbital axes undergo mutual precession. As the disk loses mass through a combination of winds and accretion, the system may be captured into a high-obliquity Cassini state (a spin-orbit resonance). The final obliquity depends on the details of the disk dispersal. We construct a simple disk model to emulate disk dispersal due to viscous accretion and photoevaporation, and identify the necessary disk properties for producing the observed obliquities in DI Herculis. The disk must be massive (at least 10% of the binary mass). If accretion onto the binary is suppressed, the observed high stellar obliquities are reproduced with a binary-disk inclination of ∼5°-10°, but if substantial accretion occurs, the inclination must be larger, ∼20°-30°. If moderate accretion occurs, initially the disk must lose its mass slowly, but eventually lose its remaining mass abruptly, analogous to the observed two-timescale behavior for disks around T-Tauri stars. The spin feedback on the binary orbit causes the binary-disk inclination to decay as the obliquity evolves, a feature that is absent from the standard Cassini state treatment.

Keywords: Binary stars
Monte Carlo Applications for Partially Polarized Inverse External-Compton Scattering (MAPPIES). I. Description of the Code and First Results. The radiation mechanisms responsible for the multiwavelength emission from relativistic jet sources are poorly understood. The modeling of the spectral energy distributions and light curves alone is not adequate to distinguish between existing models. Polarization in the X-ray and γ-ray regime of these sources may provide new and unique information about the jet physics and radiation mechanisms. Several upcoming projects will be able to deliver polarimetric measurements of the brightest X-ray sources, including active galactic nuclei jets and γ-ray bursts. This article describes the development of a new Monte Carlo code—MAPPIES (Monte Carlo Applications for Partially Polarized Inverse External-Compton Scattering)—for polarization-dependent Compton scattering in relativistic jet sources. Generic results for Compton polarization in the Thomson and Klein-Nishina regimes are presented.

Keywords: Blazars, Active galaxies, Relativistic jets, Active galactic nuclei, X-ray active galactic nuclei, Non-thermal radiation sources, Polarimeters, Polarimetry, Gamma-rays
Global Spiral Density Wave Modes in Protoplanetary Disks: Morphology of Spiral Arms. We analyze two-armed global spiral density wave modes generated by gravitational instability in razor-thin, nonviscous, self-gravitating protoplanetary disks to understand the dependence of spiral arm morphology (pitch angle α and amplitude) on various disk conditions. The morphologies of the resulting spiral density wave modes closely resemble observations. Their pitch angles and pattern speeds are insensitive to the boundary conditions adopted. Gaussian disks exhibit more tightly wound spirals (smaller pitch angle) than power-law disks under the same conditions. We find that at a fixed disk-to-star mass ratio (Md/M*), the pitch angle increases with average Toomre's stability parameter ( $\overline{Q}$ ) or average disk aspect ratio ( $\overline{h}$ ). For a given $\overline{Q}$ , density wave modes with higher Md/M* have larger pitch angles, while the behavior reverses for a given $\overline{h}$ . The interdependence between pitch angle and disk properties can be roughly approximated by $\alpha \propto {c}_{s}^{2}/{M}_{d}$ , where cs is the sound speed. Our gravitational instability-excited spiral density waves can be distinguished from planet-launched spirals: (1) massive cool disks have spiral pitch angle falling with radius, while low-mass hot disks have spiral pitch angle rising with radius; (2) the profile of spiral amplitude presents several dips and bumps. We propose that gravitational instability-excited density waves can serve as an alternative scenario to explain the observed spiral arms in self-gravitating protoplanetary disks.

Keywords: Gravitational instability, Spiral arms, Density wave model, Protoplanetary disks, Spiral pitch angle
The Formation of Glycolonitrile (HOCH<SUB>2</SUB>CN) from Reactions of C<SUP>+</SUP> with HCN and HNC on Icy Grain Mantles. Quantum chemical cluster calculations show that reactions of C+ with HCN or HNC embedded in the surface of an icy grain mantle can account for the formation of a recently detected molecule, glycolonitrile, which is considered to be an important precursor to ribonucleic compounds. Reactions of cations deposited on ice mantles with minimal kinetic energy have been found theoretically to result in previously unknown pathways to significant organic compounds in protostellar systems and the interstellar medium. In density functional theory cluster calculations involving up to 24H2O, C+ reacts consistently with HCN embedded in ice to yield the neutral HOCHNC radical with no barrier, along with H3O+ as a byproduct. If HOCHNC then reacts with H, three species can be formed: HOCH2NC (isocyanomethanol), HOCH2CN (glycolonitrile), and HOCHNCH. For the C++ HNC reaction on ice, the HOCHCN and H2OCCN radicals form as intermediates, the first of which is another direct precursor to glycolonitrile via H addition. In addition to characterizing reaction pathways, predictions are provided of the vibrational and electronic spectra of the HCN and HNC starting clusters and the HOCHNC ice-bound intermediate.

Keywords: Interstellar dust, Theoretical models, Protoplanetary nebulae, Molecular spectroscopy, Astrochemistry, Protoplanetary disks
The Dust-to-gas Ratio and the Role of Radiation Pressure in Luminous, Obscured Quasars. The absence of high-Eddington-ratio, obscured active galactic nuclei (AGNs) in local (z ≲ 0.1) samples of moderate-luminosity AGNs has generally been explained to result from radiation pressure on the dusty gas governing the level of nuclear (≲10 pc) obscuration. However, very high accretion rates are routinely reported among obscured quasars at higher luminosities and may require a different feedback mechanism. We compile constraints on obscuration and Eddington ratio for samples of X-ray, optical, infrared, and submillimeter selected AGNs at quasar luminosities. Whereas moderate-luminosity, obscured AGNs in the local universe have a range of lower Eddington ratios (fEdd ∼ 0.001-0.1), the most luminous (Lbol ≳ 1046 erg s-1) IR/submillimeter-bright, obscured quasars out to z ∼ 3 commonly have very high Eddington ratios (fEdd ∼ 0.11). This apparent lack of radiation-pressure feedback in luminous, obscured quasars is likely coupled with AGN timescales, such that a higher fraction of luminous, obscured quasars are seen because of the short timescale for which quasars are most luminous. When adopting quasar evolutionary scenarios, extended (∼102-3 pc) obscuration may work together with the shorter timescales to explain the observed fraction of obscured, luminous quasars, while outflows driven by radiation pressure will slowly clear this material over the AGN lifetime.

Keywords: Active galaxies, Galaxy evolution, Interstellar medium, Quasars
Gravitomagnetic Instabilities of Relativistic Magnetohydrodynamics. We study gravitomagnetic instabilities of a static homogeneous medium with an aligned magnetic field in the two contexts of relativistic magnetohydrodynamics (MHD): first, MHD with post-Newtonian (PN) corrections, and second, special relativistic (SR) MHD with weak gravity. The analysis in the PN MHD is made without taking the temporal gauge condition, thus results are gauge-invariant. The PN corrections of the internal energy, pressure, sound velocity, and the Alfvén velocity lower the critical (Jeans) wavelength. All relativistic effects tend to destabilize the system. Although the SR MHD with weak gravity is presented in the harmonic gauge, in the presence of gravity the stability analysis is strictly valid to Newtonian order. In the absence of gravity, the SR MHD is independent of the gauge condition. We present the plane wave velocities and the stability criteria in both cases.

Keywords: Gravitation, Relativity, Gravitational instability, Magnetohydrodynamics
A VLBA Survey of Radio Stars in the Orion Nebula Cluster. I. The Nonthermal Radio Population. We present first results of a four-epoch VLBA survey for nonthermal emission toward all 556 compact radio sources previously identified in a deep VLA survey of the Orion Nebula Cluster (ONC). We identify VLBA counterparts toward an unprecedented 123 sources. Of these, 41 do not have X-ray counterparts, of which 34 also do not display near-infrared counterparts. Since these cannot be explained by extragalactic background sources, this suggests a component of the ONC population of young stellar objects that are too deeply embedded for even X-rays to be detectable. We find pervasive variability and detect even most of the highest-S/N sources in only one out of four epochs. Neither a negative spectral index nor extreme variability in the VLA data is a good predictor of a VLBA detection.

Keywords: Star formation, Non-thermal radiation sources, Radio astrometry
A VLBA Survey of Radio Stars in the Orion Nebula Cluster. II. Astrometry. From Very Long Baseline Array (VLBA) observations we previously identified a population of 123 young stellar systems with nonthermal radio emission toward the core of the Orion Nebula Cluster (ONC). We find optical sources in the Gaia DR2 catalog for 34 of them within 0"2 of the radio positions. Most of the radio sources are likely companions of Gaia detections. However, there are 11 stars whose VLBA positions differ from Gaia by &lt;1.6 mas, and some of these radio sources probably are the direct counterparts of the optical stars. We are able to obtain radio proper motions for 23 stars. Combining the stellar proper motions derived from the VLBA and Gaia DR2 data we find the global motion and velocity dispersion of the ONC to be (μα∗, μδ) = (1.20 ± 0.09, 0.18 ± 0.09) mas yr-1 and ( ${\sigma }_{{\mu }_{\alpha }}\ast ,{\sigma }_{{\mu }_{\delta }}$ ) = (0.84 ± 0.09, 1.30 ± 0.09) mas yr-1. Finally, we looked for ordered motions by estimating the means of scalar and vectorial products, which results in $\overline{{\boldsymbol{v}}\cdot \hat{{\boldsymbol{r}}}}=-0.61\pm 1.00$ km s-1 and $\overline{{\boldsymbol{v}}\times \hat{{\boldsymbol{r}}}}=0.57\pm 0.95$ km s-1. These do not show indications that the young stellar cluster is in expansion, contraction, or rotation.

Keywords: Non-thermal radiation sources, Star formation, Radio astrometry