adsabs/SciX_UAT_keywords huggingface dataset:
Opacity of the Highly Ionized Lanthanides and the Effect on the Early Kilonova

We investigate the effect of the presence of lanthanides (Z = 57-71) on the kilonova at t ~ 1 hr after the neutron star merger for the first time. For this purpose, we calculate the atomic structures and the opacities for selected lanthanides: Nd (Z = 60), Sm (Z = 62), and Eu (Z = 63). We consider the ionization degree up to 10th (XI), applicable for the ejecta at t ~ a few hours after the merger, when the temperature is T ~ 105 K. We find that the opacities for the highly ionized lanthanides are exceptionally high, reaching ${\kappa }_{\exp }\sim 1000\,{\mathrm{cm}}^{2}\,{{\rm{g}}}^{-1}$ for Eu, due to the highly dense energy levels. Using the new opacity, we perform radiative transfer simulations to show that the early light curves become fainter by a (maximum) factor of four, in comparison to lanthanide-free ejecta at t ~ 0.1 days. However, the period at which the light curves are affected is relatively brief owing to the rapid time evolution of the opacity in the outermost layer of the ejecta. We predict that for a source at a distance of ~100 Mpc, UV brightness for lanthanide-rich ejecta shows a drop to ~21-22 mag at t ~ 0.1 days and the UV peaks around t ~ 0.2 days with a magnitude of ~19 mag. Future detection of such a kilonova by an existing UV satellite like Swift or the upcoming UV satellite ULTRASAT will provide useful constraints on the abundance in the outer ejecta and the corresponding nucleosynthesis conditions in the neutron star mergers.

Keywords: neutron stars; stellar atmospheric opacity; radiative transfer; gravitational waves; nucleosynthesis; r-process
Earth as an Exoplanet. III. Using Empirical Thermal Emission Spectra as an Input for Atmospheric Retrieval of an Earth-twin Exoplanet

In this study, we treat Earth as an exoplanet and investigate our home planet by means of a potential future mid-infrared space mission called the Large Interferometer For Exoplanets (LIFE). We combine thermal spectra from an empirical data set of disk-integrated Earth observations with a noise model for LIFE to create mock observations. We apply a state-of-the-art atmospheric retrieval framework to characterize the planet, assess the potential for detecting the known bioindicators, and investigate the impact of viewing geometry and seasonality on the characterization. Our key findings reveal that we are observing a temperate habitable planet with significant abundances of CO2, H2O, O3, and CH4. Seasonal variations in the surface and equilibrium temperature, as well as in the Bond albedo, are detectable. Furthermore, the viewing geometry and the spatially and temporally unresolved nature of our observations only have a minor impact on the characterization. Additionally, Earth's variable abundance profiles and patchy cloud coverage can bias retrieval results for the atmospheric structure and trace-gas abundances. Lastly, the limited extent of Earth's seasonal variations in biosignature abundances makes the direct detection of its biosphere through atmospheric seasonality unlikely. Our results suggest that LIFE could correctly identify Earth as a planet where life could thrive, with detectable levels of bioindicators, a temperate climate, and surface conditions allowing liquid surface water. Even if atmospheric seasonality is not easily observed, our study demonstrates that next generation space missions can assess whether nearby temperate terrestrial exoplanets are habitable or even inhabited.

Keywords: astrobiology; earth (planet); infrared spectroscopy; biosignatures; exoplanet atmospheric variability; space vehicle instruments
Localizing Quasiperiodic Pulsations in Hard X-Ray, Microwave, and Lyα Emissions of an X6.4 Flare

We report the simultaneous observations of quasiperiodic pulsations (QPPs) in wavelengths of hard X-ray (HXR), microwave, Lyα, and ultraviolet (UV) emissions during the impulsive phase of an X6.4 flare on 2024 February 22 (SOL2024-02-22T22:08). The X6.4 flare shows three repetitive and successive pulsations in HXR and microwave wavebands, and they have an extremely large modulation depth. The onset of flare QPPs is almost simultaneous with the start of magnetic cancellation between positive and negative fields. The wavelet power spectra suggest the presence of double periods, which are centered at ∼200 and ∼95 s, respectively. The long-period QPP can also be detected in Lyα and UV wavebands at the flare area, and it could be observed in the adjacent sunspot. Our observations indicate that the flare QPPs are most likely triggered by accelerated electrons that are associated with periodic magnetic reconnections. The long period at ∼200 s is probably modulated by the slow magnetoacoustic wave originating from the neighboring sunspot, while the short period at ∼95 s could be regarded as its second harmonic mode.

Keywords: solar flares; solar oscillations; solar x-ray emission; solar radio emission; solar ultraviolet emission; sunspots
Insight-HXMT Detections of Hard X-Ray Tails in Scorpius X-1

Using the observations of the high-energy detector of the Hard X-ray Modulation Telescope (Insight-HXMT) for Scorpius X-1 from 2017 to 2020, we search for hard X-ray tails in the X-ray spectra in ~30-200 keV. The hard X-ray tails are found throughout the Z-track on the hardness-intensity diagram, and the detected hard X-ray tails become hard and weak from the horizontal branch (HB), through the normal branch (NB), to the flaring branch (FB). Comparing the hard X-ray spectra of Insight-HXMT between Cyg X-1 and Sco X-1, it is concluded that the hard X-ray spectrum of Cyg X-1 shows a high-energy cutoff, implying a hot corona in it, but the high-energy cutoff is not seen in the hard X-ray spectrum of Sco X-1. From fitting the broadband spectrum of Sco X-1 in ~2-200 keV, it is proposed that the hard X-ray tails in the HB and NB can be explained by the overall Comptonization COMPTB model, suggesting that the hard X-ray tails could have resulted from the Comptonization of the photons from the neutron star (NS) surface by the thermal electrons in the region between the NS and the disk and the energetic electrons in the freefall toward the NS in the converging flow onto the NS. However, this model cannot be responsible for the hard X-ray tails in the FB. Further study on the FB hard X-ray tails is needed.

Keywords: neutron stars; x-ray binary stars; low-mass x-ray binary stars; non-thermal radiation sources
Detection of Rubidium and Samarium in the Atmosphere of the Ultrahot Jupiter MASCARA-4b

Ultrahot Jupiters (UHJs) possess the most extreme environments among various types of exoplanets, making them ideal laboratories to study the chemical composition and kinetics properties of exoplanet atmosphere with high-resolution spectroscopy. It has the advantage of resolving the tiny Doppler shift and weak signal from exoplanet atmosphere and has helped to detect dozens of heavy elements in UHJs including KELT-9b, WASP-76b, and WASP-121b. MASCARA-4b is a 2.8 days UHJ with an equilibrium temperature of ~2250 K, which is expected to contain heavy elements detectable with the Very Large Telescope (VLT). In this letter, we present a survey of atoms/ions in the atmosphere of the MASCARA-4b, using the two VLT/ESPRESSO transits data. Cross-correlation analyses are performed on the obtained transmission spectra at each exposure with the template spectra generated by petitRADTRANS for atoms/ions from element Li to U. We confirm the previous detection of Mg, Ca, Cr, and Fe, and report the detection of Rb, Sm, Ti+, and Ba+ with peak signal-to-noise ratios (S/Ns) > 5. We report a tentative detection of Sc+, with peak S/Ns ~ 6 but deviating from the estimated position. The most interesting discovery is the first-time detection of elements Rb and Sm in an exoplanet. Rb is an alkaline element like Na and K, while Sm is the first lanthanide series element and is by far the heaviest one detected in exoplanets. Detailed modeling and acquiring more data are required to yield abundance ratios of the heavy elements and to understand better the common presence of them in UHJ's atmospheres.

Keywords: exoplanet atmospheric composition; high resolution spectroscopy; exoplanet atmospheres
The Luminosity Function of Tidal Disruption Events from Fallback-powered Emission: Implications for the Black Hole Mass Function

Tidal disruption events (TDEs), in which a star is destroyed by the gravitational field of a supermassive black hole (SMBH), are being observed at a high rate owing to the advanced state of survey science. One of the properties of TDEs that is measured with increasing statistical reliability is the TDE luminosity function, $d{\dot{N}}_{\mathrm{TDE}}/{dL}$ , which is the TDE rate per luminosity (i.e., how many TDEs are within a given luminosity range). Here we show that if the luminous emission from a TDE is directly coupled to the rate of return of tidally destroyed debris to the SMBH, then the TDE luminosity function is in good agreement with observations and scales as ∝L -2.5 for high luminosities, provided that the SMBH mass function ${{dN}}_{\bullet }/{{dM}}_{\bullet }$ -the number of SMBHs (N •) per SMBH mass (M •)-is approximately flat in the mass range over which we observe TDEs. We also show that there is a cutoff in the luminosity function at low luminosities that is a result of direct captures, and this cutoff has been tentatively observed. If ${{dN}}_{\bullet }/{{dM}}_{\bullet }$ is flat, which is in agreement with some observational campaigns, these results suggest that the fallback rate feeds the accretion rate in TDEs. Contrarily, if ${{dN}}_{\bullet }/d\mathrm{log}{M}_{\bullet }$ is flat, which has been found theoretically and is suggested by other observational investigations, then the emission from TDEs is likely powered by another mechanism. Future observations and more TDE statistics, provided by the Rubin Observatory/LSST, will provide additional evidence as to the reality of this tension.

Keywords: black hole physics; event horizons; tidal disruption
Precision Modeling of JWST's First Cluster Lens SMACS J0723.3-7327

Exploiting the fundamentally achromatic nature of gravitational lensing, we present a lens model for the massive galaxy cluster SMACS J0723.3-7323 (SMACS J0723; z = 0.388) that significantly improves upon earlier work. Building on strong-lensing constraints identified in prior Hubble Space Telescope (HST) observations, the mass model utilizes 21 multiple-image systems, 17 of which were newly discovered in Early Release Observation data from the JWST. The resulting lens model maps the cluster mass distribution to an rms spatial precision of 0.″32, and is publicly available. Consistent with previous analyses, our study shows SMACS J0723.3 to be well described by a single large-scale component centered on the location of the brightest cluster galaxy. However, satisfying all lensing constraints provided by the JWST data, the model points to the need for the inclusion of an additional, diffuse component west of the cluster. A comparison of the galaxy, mass, and gas distributions in the core of SMACS J0723 based on HST, JWST, and Chandra data reveals a concentrated regular elliptical profile along with tell-tale signs of a recent merger, possibly proceeding almost along our line of sight. The exquisite sensitivity of JWST's NIRCam reveals in spectacular fashion both the extended intracluster light distribution and numerous star-forming clumps in magnified background galaxies. The high-precision lens model derived here for SMACS J0723 demonstrates the unprecedented power of combining HST and JWST data for studies of structure formation and evolution in the distant universe. *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs GO-11103, GO-12166, GO-12884, GO-1409; and on observations made with the NASA/ESA/CSA James Webb Space Telescope, under NASA contract NAS 5-03127 for JWST. These observations are associated with program #2736.

Keywords: galaxy clusters; strong gravitational lensing
The Luminosity Distribution of Short Gamma-Ray Bursts under a Structured Jet Scenario

The joint detection of gravitational wave (GW) and electromagnetic radiation from the binary neutron star merger event GW170817 marks a breakthrough in the field of multi-messenger astronomy. The short gamma-ray burst (sGRB) GRB 170817A, associated with this binary neutron star merger event, has an isotropic-equivalent gamma-ray radiation luminosity of 1.6 × 1047 erg s-1, which is much lower than that of other sGRBs. The measurement of the superluminal movement of the radio afterglow emission confirms the presence of the relativistic jet, and the emission features can be well explained by the structured jet model. In this paper, we calculate the luminosity distribution of sGRBs and its evolution with redshift based on the structured (Gaussian) jet model, and find that the typical luminosity increase with redshift, for nearby sGRBs (such as for luminosity distance less than 200 Mpc) the typical gamma-ray luminosity is just around 1047-1048 erg s-1, which naturally explains the very low radiation luminosity of GRB 170817A. We derived the detection probability of sGRBs by Fermi-GBM and found that the expected detection rate of sGRBs is only about 1 yr-1 within the distance of several hundred Mpc. We explored the effect of the power-law index α of the merger time distribution on the observed characteristics and found that it had little effect on the observed luminosity and viewing-angle distributions. However, it is very interesting that, for different values of α, the distributions of the number of observed sGRBs are quite different, so it is possible to determine the value of α through observed distributions of the number of sGRBs. We used the Bayesian method to make a quantitative analysis and found that the value of α may be identified when the number of observed sGRBs with known redshifts is more than 200. Finally, we compare our results of gamma-ray luminosity distribution with sGRBs with known redshifts, and found that our results are consistent with the observation, which implies that our simulation results can reproduce the observed luminosity distribution well.

Keywords: gamma-ray bursts; gamma-ray astronomy; astronomical methods
Note on Fundamental Physics Tests from Black Hole Imaging: Comment on "Hunting for Extra Dimensions in the Shadow of Sagittarius A*"

Several recent works have tested fundamental physics with horizon-scale black hole (BH) images, using the size r sh and deviation from circularity ${\rm{\Delta }}{ \mathcal C }$ of the BH shadow. For the Event Horizon Telescope image of Sgr A*, limits on ${\rm{\Delta }}{ \mathcal C }$ are not available due to the sparse interferometric coverage of the 2017 observations, alongside the short variability timescale of Sgr A* compared to M87*. We comment on the results of a recent preprint which purports to have derived new limits on extra dimensions using the deviation from circularity of Sgr A*'s shadow. The latter is quoted to be ≲10% as with M87*, based on the "similarity" of the two shadows, which however is an incorrect assumption. In the immediate future, the simplest tests of fundamental physics from Sgr A*'s image will mostly have to rely on r sh.

Keywords: astrophysical processes; black hole physics
Gemini-LIGHTS: Herbig Ae/Be and Massive T Tauri Protoplanetary Disks Imaged with Gemini Planet Imager

We present the complete sample of protoplanetary disks from the Gemini- Large Imaging with the Gemini Planet Imager Herbig/T Tauri Survey, which observed bright Herbig Ae/Be stars and T Tauri stars in near-infrared polarized light to search for signatures of disk evolution and ongoing planet formation. The 44 targets were chosen based on their near- and mid-infrared colors, with roughly equal numbers of transitional, pre-transitional, and full disks. Our approach explicitly did not favor well-known, "famous" disks or those observed by the Atacama Large Millimeter/submillimeter Array, resulting in a less-biased sample suitable to probe the major stages of disk evolution during planet formation. Our optimized data reduction allowed polarized flux as low as 0.002% of the stellar light to be detected, and we report polarized scattered light around 80% of our targets. We detected point-like companions for 47% of the targets, including three brown dwarfs (two confirmed, one new), and a new super-Jupiter-mass candidate around V1295 Aql. We searched for correlations between the polarized flux and system parameters, finding a few clear trends: the presence of a companion drastically reduces the polarized flux levels, far-IR excess correlates with polarized flux for nonbinary systems, and systems hosting disks with ring structures have stellar masses <3 M⊙. Our sample also included four hot, dusty "FS CMa" systems, and we detected large-scale ( >100 au) scattered light around each, signs of extreme youth for these enigmatic systems. Science-ready images are publicly available through multiple distribution channels using a new FITS file standard that has been jointly developed with members of the Very Large Telescope Spectro-polarimetric High-contrast Exoplanet Research team.

Keywords: protoplanetary disks; direct imaging; exoplanets; herbig ae/be stars; circumstellar dust
Unveiling the Architecture of a Pulsar-Binary Black Hole Triple System with Pulsar Arrival Time Analysis

A large number of binary black holes (BBHs) with longer orbital periods are supposed to exist as progenitors of BBH mergers recently discovered with gravitational wave (GW) detectors. In our previous papers, we proposed to search for such BBHs in triple systems through the radial velocity modulation of the tertiary orbiting star. If the tertiary is a pulsar, high-precision and high-cadence observations of its arrival time enable an unambiguous characterization of the pulsar-BBH triples located at several kiloparsecs, which are inaccessible with the radial velocity of stars. The present paper shows that such inner BBHs can be identified through the short-term Rømer delay modulation, on the order of 10 ms for our fiducial case, a triple consisting of a 20 M⊙ BBH and 1.4 M⊙ pulsar with Pin = 10 days and Pout = 100 days. If the relativistic time delays are measured as well, one can determine basically all the orbital parameters of the triple. For instance, this method is applicable to inner BBHs of down to ∼1 hr orbital periods if the orbital period of the tertiary pulsar is around several days. Inner BBHs with ≲1 hr orbital period emit the GW detectable by future space-based GW missions, including LISA, DECIGO, and BBO, and very short inner BBHs with subsecond orbital period can be even probed by the existing ground-based GW detectors. Therefore, our proposed methodology provides a complementary technique to search for inner BBHs in triples, if they exist at all, in the near future.

Keywords: pulsar timing method; celestial mechanics; three-body problem; multiple stars; black holes; compact binary stars; pulsars; gravitational waves
Orbital Decay in M82 X-2

M82 X-2 is the first pulsating ultraluminous X-ray source discovered. The luminosity of these extreme pulsars, if isotropic, implies an extreme mass transfer rate. An alternative is to assume a much lower mass transfer rate, but with an apparent luminosity boosted by geometrical beaming. Only an independent measurement of the mass transfer rate can help discriminate between these two scenarios. In this paper, we follow the orbit of the neutron star for 7 yr, measure the decay of the orbit ( ${\dot{P}}_{\mathrm{orb}}/{P}_{\mathrm{orb}}\approx -8\cdot {10}^{-6}\,{\mathrm{yr}}^{-1}$ ), and argue that this orbital decay is driven by extreme mass transfer of more than 150 times the mass transfer limit set by the Eddington luminosity. If this is true, the mass available to the accretor is more than enough to justify its luminosity, with no need for beaming. This also strongly favors models where the accretor is a highly magnetized neutron star.

Keywords: pulsars; ultraluminous x-ray sources; pulsar timing method; orbital evolution
Quasi-perpendicular Shock Acceleration and Tidal Disruption Event Radio Flares

Delayed radio flares of optical tidal disruption events (TDEs) indicate the existence of nonrelativistic outflows accompanying TDEs. The interaction of TDE outflows with the surrounding circumnuclear medium creates quasi-perpendicular shocks in the presence of toroidal magnetic fields. Because of the large shock obliquity and large outflow velocity, we find that the shock acceleration induced by TDE outflows generally leads to a steep particle energy spectrum, with the power-law index significantly larger than the "universal" index for a parallel shock. The measured synchrotron spectral indices of recently detected TDE radio flares are consistent with our theoretical expectation. It suggests that the particle acceleration at quasi-perpendicular shocks can be the general acceleration mechanism accounting for the delayed radio emission of TDEs.

Keywords: radio transient sources; shocks
QUOTAS: A New Research Platform for the Data-driven Discovery of Black Holes

We present QUOTAS, a novel research platform for the data-driven investigation of supermassive black hole (SMBH) populations. While SMBH data-observations and simulations-have grown in complexity and abundance, our computational environments and tools have not matured commensurately to exhaust opportunities for discovery. To explore the BH, host galaxy, and parent dark matter halo connection-in this pilot version-we assemble and colocate the high-redshift, z > 3 quasar population alongside simulated data at the same cosmic epochs. As a first demonstration of the utility of QUOTAS, we investigate correlations between observed Sloan Digital Sky Survey (SDSS) quasars and their hosts with those derived from simulations. Leveraging machine-learning algorithms (ML), to expand simulation volumes, we show that halo properties extracted from smaller dark-matter-only simulation boxes successfully replicate halo populations in larger boxes. Next, using the Illustris-TNG300 simulation that includes baryonic physics as the training set, we populate the larger LEGACY Expanse dark-matter-only box with quasars, and show that observed SDSS quasar occupation statistics are accurately replicated. First science results from QUOTAS comparing colocated observational and ML-trained simulated data at z3 are presented. QUOTAS demonstrates the power of ML, in analyzing and exploring large data sets, while also offering a unique opportunity to interrogate theoretical assumptions that underpin accretion and feedback models. QUOTAS and all related materials are publicly available at the Google Kaggle platform. (The full data set-observational data and simulation data-are available at: https://www.kaggle.com/ and the codes are available at:https://www.kaggle.com/datasets/quotasplatform/quotas)

Keywords: quasars