adsabs/SciX_UAT_keywords huggingface dataset:
Does Gravity Fall Down? Evidence for Gravitational-wave Deflection along the Line of Sight to GW170817

We present a novel test of general relativity (GR): measuring the geometric component of the time delay due to gravitational lensing. GR predicts that photons and gravitational waves follow the same geodesic paths and thus experience the same geometric time delay. We show that for typical systems, the time delays are tens of seconds, and thus can dominate over astrophysical delays in the timing of photon emission. For the case of GW170817, we use a multi-plane lensing code to evaluate the time delay due to four massive halos along the line of sight. From literature mass and distance measurements of these halos, we establish at high confidence (significantly greater than $5\sigma $ ) that the gravitational waves of GW170817 underwent gravitational deflection to arrive within 1.7 s of the photons.

Keywords: weak gravitational lensing; gravitational waves; gravitational deflection; gravitational wave sources; gravitational wave astronomy
The Complex Organic Molecular Content in the L1498 Starless Core

Observations carried out toward starless and prestellar cores have revealed that complex organic molecules are prevalent in these objects, but it is unclear what chemical processes are involved in their formation. Recently, it has been shown that complex organics are preferentially produced at an intermediate-density shell within the L1544 prestellar core at radial distances of ~4000 au with respect to the core center. However, the spatial distribution of complex organics has only been inferred toward this core, and it remains unknown whether these species present a similar behavior in other cores. We report high-sensitivity observations carried out toward two positions in the L1498 starless core, the dust peak and a position located at a distance of ~11,000 au from the center of the core where the emission of CH3OH peaks. Similarly to L1544, our observations reveal that small O-bearing molecules and N-bearing species are enhanced by factors of ~4-14 toward the outer shell of L1498. However, unlike L1544, large O-bearing organics such as CH3CHO, CH3OCH3, or CH3OCHO are not detected within our sensitivity limits. For N-bearing organics, these species are more abundant toward the outer shell of the L1498 starless core than toward the one in L1544. We propose that the differences observed between O-bearing and N-bearing species in L1498 and L1544 are due to the different physical structure of these cores, which in turn is a consequence of their evolutionary stage, with L1498 being younger than L1544.

Keywords: interstellar medium; interstellar molecules; astrochemistry; molecular clouds
Stereophotoclinometry for OSIRIS-REx Spacecraft Navigation

We summarize a decade of effort by the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission team to build up the unique capabilities, processes, and procedures required to accomplish the unprecedented navigation performance required during proximity operations at asteroid (101955) Bennu. Stereophotoclinometry was a key technology used for digital terrain model (DTM) generation and landmark navigation, enabling estimation of spacecraft trajectories and Bennu's geophysical parameters. We outline the concept of operations for OSIRIS-REx landmark navigation and the wide array of testing and verification efforts leading up to OSIRIS-REx's arrival at Bennu. We relate the outcome of these efforts to the experiences during proximity operations. We discuss navigation and DTM performance during operations, including detailed lessons learned to carry forward for future missions.

Keywords: asteroid dynamics; asteroid surfaces; near-earth objects; asteroids; astrodynamics; orbits; astronomy data modeling; orbit determination; astronomical methods; optical astronomy; astronomical models; astronomical simulations
Complex Structure of the Eastern Lobe of the Pictor A Radio Galaxy: Spectral Analysis and X-Ray/Radio Correlations

Here we present detailed analysis of the distinct X-ray emission features present within the eastern radio lobe of the Pictor A galaxy, around the jet termination region, utilizing the data obtained from the Chandra X-ray Observatory. Various emission features have been selected for the study based on their enhanced X-ray surface brightness, including five sources that appear pointlike, as well as three extended regions, one characterized by a filamentary morphology. For those, we perform a basic spectral analysis within the 0.5-7 keV range. We also investigate various correlations between the X-ray emission features and the nonthermal radio emission, utilizing the high-resolution radio maps from the Very Large Array at gigahertz frequencies. The main novel findings following from our analysis concern the newly recognized bright X-ray filament located upstream of the jet termination region, extending for at least 30 kpc (projected), and inclined with respect to the jet axis. For this feature, we observe a clear anticorrelation between the X-ray surface brightness and the polarized radio intensity, as well as a decrease in the radio rotation measure with respect to the surroundings. We speculate on the nature of the filament, in particular addressing a possibility that it is related to the presence of a hot X-ray-emitting thermal gas, only partly mixed with the nonthermal radio/X-ray-emitting electrons within the lobe, combined with the reversals in the lobe's net magnetic field.

Keywords: non-thermal radiation sources; radio galaxies; relativistic jets; x-ray active galactic nuclei
Influence of the Gravitational Darkening Effect on the Spectrum of a Hot, Rapidly Rotating Neutron Star. II. Iron Lines

Rapidly rotating neutron stars are similar to highly flattened ellipsoids. Observed spectra of flattened stars must exhibit effects of nonspherical shape and gravitational darkening. We examined in detail the influence of both effects on the observed central energies and profiles of lines of highly ionized iron, Fe XXV and Fe XXVI. We note that the gravitational darkening effect does not change the central energy of lines. Most importantly, spectra of neutron stars that rotate with different frequencies and are seen at various inclination angles differ significantly. The appearance and the depth of lines strongly depend on the parameters, like the inclination angle of the star or the frequency of the star rotation. In this paper we clearly show that the gravitational darkening effect should be included in realistic models of the atmospheres of the neutron stars.

Keywords: neutron stars; radiative transfer equation
The BAT AGN Spectroscopic Survey. XVIII. Searching for Supermassive Black Hole Binaries in X-Rays

Theory predicts that a supermassive black hole binary (SMBHB) could be observed as a luminous active galactic nucleus (AGN) that periodically varies on the order of its orbital timescale. In X-rays, periodic variations could be caused by mechanisms including relativistic Doppler boosting and shocks. Here we present the first systematic search for periodic AGNs using 941 hard X-ray light curves (14-195 keV) from the first 105 months of the Swift Burst Alert Telescope (BAT) survey (2004-2013). We do not find evidence for periodic AGNs in Swift-BAT, including the previously reported SMBHB candidate MCG+11-11-032. We find that the null detection is consistent with the combination of the upper-limit binary population in AGNs in our adopted model, their expected periodic variability amplitudes, and the BAT survey characteristics. We have also investigated the detectability of SMBHBs against normal AGN X-ray variability in the context of the extended ROentgen Survey with an Imaging Telescope Array (eROSITA) survey. Under our assumptions of a binary population and the periodic signals they produce, which have long periods of hundreds of days, up to 13% true periodic binaries can be robustly distinguished from normal variable AGNs with the ideal uniform sampling. However, we demonstrate that realistic eROSITA sampling is likely to be insensitive to long-period binaries because longer observing gaps reduce their detectability. In contrast, large observing gaps do not diminish the prospect of detecting binaries of short, few-day periods, as 19% can be successfully recovered, the vast majority of which can be identified by the first half of the survey.

Keywords: active galaxies; surveys; x-ray sources
Environmental Dependence of Galactic Properties Traced by Lyα Forest Absorption: Diversity among Galaxy Populations

In order to shed light on how galactic properties depend on the intergalactic medium (IGM) environment traced by the Lyα forest, we observationally investigate the IGM-galaxy connection using the publicly available 3D IGM tomography data (CLAMATO) and several galaxy catalogs in the COSMOS field. We measure the cross-correlation function (CCF) for 570 galaxies with spec-z measurements and detect a correlation with the IGM up to 50 h-1 comoving Mpc. We show that galaxies with stellar masses of 109-1010 M⊙ are the dominant contributor to the total CCF signal. We also investigate CCFs for several galaxy populations: Lyα emitters (LAEs), Hα emitters (HAEs), [O III] emitters (O3Es), active galactic nuclei (AGNs), and submillimeter galaxies (SMGs), and we detect the highest signal in AGNs and SMGs at large scales (r ≥ 5 h-1 Mpc), but in LAEs at small scales (r < 5 h-1 Mpc). We find that they live in various IGM environments—HAEs trace the IGM in a similar manner to the continuum-selected galaxies, but LAEs and O3Es tend to reside in higher-density regions. Additionally, LAEs' CCF is flat up to r ∼ 3 h-1 Mpc, indicating that they tend to avoid the highest-density regions. For AGNs and SMGs, the CCF peak at r = 5-6 h-1 Mpc implies that they tend to be in locally lower-density regions. We suspect that it is due to the photoionization of IGM H I by AGNs, i.e., the proximity effect.

Keywords: galaxy formation; galaxy evolution; lyman alpha forest; intergalactic medium; large-scale structure of the universe; emission line galaxies; agn host galaxies
Optical Observations and Modeling of the Superluminous Supernova 2018lfe

We present optical imaging and spectroscopy of SN 2018lfe, which we classify as a Type I superluminous supernova (SLSN-I) at a redshift of z = 0.3501 ± 0.0004 with a peak absolute magnitude of M r = -22.1 ± 0.1 mag, one of the brightest SLSNe discovered. SN 2018lfe was identified for follow-up using our FLEET machine-learning pipeline. Both the light curve and the spectra of SN 2018lfe are consistent with the broad population of SLSNe. We fit the light curve with a magnetar central engine model and find an ejecta mass of M ej ≈ 3.8 M ⊙, a magnetar spin period of P ≈ 2.9 ms, and a magnetic field strength of B ⊥ ≈ 2.8 × 1014 G. The magnetic field strength is near the top of the distribution for SLSNe, while the spin period and ejecta mass are near the median values of the distribution for SLSNe. From late-time imaging and spectroscopy we find that the host galaxy of SN 2018lfe has an absolute magnitude of M r = -17.85 ± 0.24, (L B = 0.029 ± 0.007L*), and an inferred metallicity of Z ≈ 0.3 Z ⊙ and star formation rate of ≈0.8 M ⊙ yr-1.

Keywords: supernovae; core-collapse supernovae
The Effect of Cosmic Rays on Cometary Nuclei. II. Impact on Ice Composition and Structure

Since their formation in the protosolar nebula some ∼4.5 billion years ago, comets are in storage in cold distant regions of the solar system, the Kuiper Belt/scattered disk or Oort Cloud. Therefore, they have been considered as mostly unaltered samples of the protosolar nebula. However, a significant dose of energy is deposited by galactic cosmic rays (GCRs) into the outermost tens of meters of cometary nuclei during their stay in the Oort Cloud or Kuiper Belt. We investigate the impact of energy deposition by GCRs on cometary nuclei. We use experimental results from laboratory experiments and the energy deposition by GCRs estimated by Gronoff et al. (2020), to discuss the depth down to which the cometary nucleus is altered by GCRs. We show that GCRs do not significantly change the isotopic composition of cometary material but modify the chemical composition and the ice structure in the outer layers of the nucleus, which cannot be considered as pristine solar nebula material. We discuss the effect of the collisional history of comets on the distribution of processed material inside the nucleus and its implication on the observation of comets.

Keywords: comet interiors; galactic cosmic rays; comets; high-energy cosmic radiation; cosmic rays
Hunt for Starspots in HARPS Spectra of G and K Stars

We present a method for detecting starspots on cool stars using the cross-correlation function (CCF) of high-resolution molecular spectral templates applied to archival high-resolution spectra of G and K stars observed with the High Accuracy Radial Velocity Planet Searcher (HARPS)/HARPS-N. We report nondetections of starspots on the Sun even when the Sun was spotted, the solar twin 18 Scorpii, and the very spotted Sun-like star HAT-P-11, suggesting that Sun-like starspot distributions will be invisible to the CCF technique, and should not produce molecular absorption signals that might be confused for signatures of exoplanet atmospheres. We detect strong TiO absorption in the T Tauri K-dwarfs LkCa 4 and AA Tau, consistent with significant coverage by cool regions. We show that despite the nondetections, the technique is sensitive to relatively small spot coverages on M dwarfs and large starspot areas on Sun-like stars.

Keywords: high resolution spectroscopy; stellar magnetic fields; stellar activity; starspots
On the Spatial Distribution of Polarization and Color of a Distant Comet C/2017 K2 (PanSTARRS)

Comet C/2017 K2 (PanSTARRS) was observed at two wavelengths using two different-sized apertures in two measurement campaigns. We find that all the observations can be interpreted using a two-component mixture of dust composed of Mg-rich silicates and amorphous carbon. The modeling suggests a slight increase in the absorption of the refractory component at shorter wavelengths, which is consistent with the optical properties of Mg-rich silicates, and a change in the size distribution as a function of distance from the cometary nucleus, a result of smaller particles accelerating more rapidly from the expanding-gas and radiative-pressure forces.

Keywords: comets; comae; long period comets; coma dust
Narrowband Observations of Comet 46P/Wirtanen during Its Exceptional Apparition of 2018/19. I. Apparent Rotation Period and Outbursts

We obtained broad- and narrowband images of the hyperactive comet 46P/Wirtanen on 33 nights during its 2018/2019 apparition, when the comet made a historic close approach to the Earth. With our extensive coverage, we investigated the temporal behavior of the comet on both seasonal and rotational timescales. We used CN observations to explore the coma morphology, revealing that there are two primary active areas that produce spiral structures. The direction of rotation of these structures changes from pre- to postperihelion, indicating that the Earth crossed the comet's equatorial plane sometime around perihelion. We also used the CN images to create photometric light curves that consistently show two peaks in the activity, confirming the two source regions. We measured the nucleus's apparent rotation period at a number of epochs using both the morphology and the light curves. These results all show that the rotation period is continuously changing throughout our observation window, increasing from 8.98 hr in early November to 9.14 hr around perihelion and then decreasing again to 8.94 hr in February. Although the geometry changes rapidly around perihelion, the period changes cannot be primarily due to synodic effects. The repetition of structures in the coma, both within a night and from night to night, strongly suggests that the nucleus is in a near-simple rotation state. We also detected two outbursts, one on December 12 and the other on January 28. Using the apparent velocities of the ejecta in these events, 68 ± 5 and 162 ± 15 m s-1, respectively, we derived start times of 2018 December 12 at 00:13 UT ± 7 minutes and 2019 January 27 at 20:01 UT ± 30 minutes.

Keywords: comets; short period comets; comet nuclei; comae; near-earth objects
Broad Emission Lines in Optical Spectra of Hot, Dust-obscured Galaxies Can Contribute Significantly to JWST/NIRCam Photometry

Selecting the first galaxies at z > 7 - 10 from JWST surveys is complicated by z < 6 contaminants with degenerate photometry. For example, strong optical nebular emission lines at z < 6 may mimic JWST/NIRCam photometry of z > 7-10 Lyman-break galaxies (LBGs). Dust-obscured 3 < z < 6 galaxies in particular are potentially important contaminants, and their faint rest-optical spectra have been historically difficult to observe. A lack of optical emission line and continuum measures for 3 < z < 6 dusty galaxies now makes it difficult to test their expected JWST/NIRCam photometry for degenerate solutions with NIRCam dropouts. Toward this end, we quantify the contribution by strong emission lines to NIRCam photometry in a physically motivated manner by stacking 21 Keck II/NIRES spectra of hot, dust-obscured, massive ( $\mathrm{log}{M}_{* }/{M}_{\odot }\gtrsim 10\mbox{--}11$ ) and infrared (IR) luminous galaxies at z ~ 1-4. We derive an average spectrum and measure strong narrow (broad) [O III]5007 and Hα features with equivalent widths of 130 ± 20 Å (150 ± 50 Å) and 220 ± 30 Å (540 ± 80 Å), respectively. These features can increase broadband NIRCam fluxes by factors of 1.2 - 1.7 (0.2-0.6 mag). Due to significant dust attenuation (A V ~ 6), we find Hα+[N II] to be significantly brighter than [O III]+Hβ and therefore find that emission-line dominated contaminants of high -z galaxy searches can only reproduce moderately blue perceived UV continua of S λ ∝ λ β with β > - 1.5 and z > 4. While there are some redshifts (z ~ 3.75) where our stack is more degenerate with the photometry of z > 10 LBGs at λ rest ~ 0.3-0.8 μm , redder filter coverage beyond λ obs > 3.5 μm and far-IR/submillimeter follow-up may be useful for breaking the degeneracy and making a crucial separation between two fairly unconstrained populations, dust-obscured galaxies at z ~ 3-6 and LBGs at z > 10.

Keywords: high-redshift galaxies; luminous infrared galaxies; lyman-break galaxies
Investigation of Periodic Modulation Behaviors from Pulsar J2022+5154

We have carried out a detailed study of individual pulse emission from the pulsar J2022+5154 (B2021+51), observed at 2250 MHz using the Jiamusi 66 m radio telescope. We have investigated the modulations in single-pulse behavior using fluctuation spectral analysis, which shows the presence of two prominent periodicities, around 5 and 40 rotation periods, respectively. The shorter periodicity is associated with the phenomenon of subpulse drifting. In the absence of aliasing, the emission pattern is demonstrated to consist of eight subbeams, which rotate around the magnetic axis in about 45 periods. In addition to subpulse drifting, the pulsar also shows the presence of periodic amplitude modulation with a longer periodicity in the single-pulse sequence. The pulsar joins a select group that shows the presence of periodic phase-modulated drifting as well as amplitude-modulated drifting. This provides further evidence for the two phenomena being distinct from each other with different physical origins.

Keywords: radio pulsars
Neptune's Pole-on Magnetosphere: Dayside Reconnection Observations by Voyager 2

The "pole-on" configuration occurs when the polar magnetosphere of a planet is directed into the solar wind velocity vector. Such magnetospheric configurations are unique to the ice giant planets. This means that magnetic reconnection, a process that couples a magnetosphere to the solar wind, will be different at the ice giants when they are pole-on compared to other planets. The only available in situ measurements of a pole-on magnetosphere are from the Neptune flyby by Voyager 2, which we analyze in this paper. We show that dayside magnetopause conditions were conducive to magnetic reconnection. A plasma depletion layer in the magnetosheath adjacent to the magnetopause was observed. Plasma measurements inside the magnetospheric cusp show evidence of multiple reconnection taking place at the magnetopause before the spacecraft crossed the open-closed field line boundary. A possible traveling compression region from a nearby passing flux rope was also observed, providing further supporting evidence that multiple X-line reconnection occurred during the flyby. During a perfectly pole-on configuration, reconnection will not depend on the orientation of the interplanetary magnetic field, as is the case at other planetary magnetospheres. The rate of reconnection will not vary because the area of the dayside magnetopause where antiparallel shears occur will be approximately equal for all interplanetary magnetic field orientations. Therefore, we suggest that rotating into and out of the pole-on configuration will likely drive the "on-off"/"switch-like" dynamics observed in simulations. Consequently, the pole-on configuration is most likely an important rotational phase for driving ice giant magnetospheric dynamics.

Keywords: neptune; planetary magnetospheres; space plasmas; planetary polar regions
On the Orbital Spacing Pattern of Kepler Multiple-planet Systems

The Kepler space mission has detected a large number of exoplanets in multiple transiting planet systems. Previous studies found that these Kepler multiple-planet systems exhibit an intra-system uniformity, namely planets in the same system have similar sizes and correlated orbital spacings. However, it is important to consider the possible role of selection effects due to observational biases. In this paper, we revisit the orbital spacing aspect of the pattern after taking observational biases into account using a forward modeling method. We find that orbital spacings, in terms of period ratios, of Kepler multiple-planet systems are significantly correlated only for those tightly packed systems, and the transition from correlation to noncorrelation is abrupt with a boundary at mean period ratio $\overline{\mathrm{PR}}$ ∼ 1.5-1.7. In this regard, the pattern of orbital spacing is more like a dichotomy rather than a global correlation. Furthermore, we find that such an apparent orbital spacing dichotomy could be essentially a projection of a dichotomy that related to mean motion resonance (MMR), which we dub as MMR dichotomy, and itself could be a natural result of planet migration and dynamical evolution.

Keywords: exoplanet astronomy; astrostatistics