adsabs/SciX_UAT_keywords huggingface dataset:
Constraints on UHECR Sources and Extragalactic Magnetic Fields from Directional Anisotropies

A dipole anisotropy in ultra–high-energy cosmic ray (UHECR) arrival directions, of extragalactic origin, is now firmly established at energies E > 8 EeV. Furthermore, the UHECR angular power spectrum shows no power at smaller angular scales than the dipole, apart from hints of possible individual hot or warm spots for energy thresholds ≳40 EeV. Here we exploit the magnitude of the dipole and the limits on smaller-scale anisotropies to place constraints on two quantities: the extragalactic magnetic field (EGMF) and the number density of UHECR sources or the volumetric event rate if UHECR sources are transient. We also vary the bias between the extragalactic matter and the UHECR source densities, reflecting whether UHECR sources are preferentially found in over- or underdense regions, and find that little or no bias is favored. We follow Ding et al. (2021) in using the CosmicFlows-2 density distribution of the local universe as our baseline distribution of UHECR sources, but we improve and extend that work by employing an accurate and self-consistent treatment of interactions and energy losses during propagation. Deflections in the Galactic magnetic field are treated using either the full JF12 magnetic field model, with both random and coherent components, or just the coherent part, to bracket the impact of the GMF on the dipole anisotropy. This large-scale structure model gives good agreement with both the direction and magnitude of the measured dipole anisotropy and forms the basis for simulations of discrete sources and the inclusion of EGMF effects.

Keywords: cosmic ray astronomy; cosmic ray sources; ultra-high-energy cosmic radiation; extragalactic magnetic fields; milky way magnetic fields; cosmic anisotropy; large-scale structure of the universe
High-frequency Decayless Waves with Significant Energy in Solar Orbiter/EUI Observations

High-frequency wave phenomena present a great deal of interest as one of the possible candidates to contribute to the energy input required to heat the corona as a part of the alternating current heating theory. However, the resolution of imaging instruments up until the Solar Orbiter has made it impossible to resolve the necessary time and spatial scales. The present paper reports on high-frequency transverse motions in a small loop located in a quiet-Sun region of the corona. The oscillations were observed with the High Resolution Imager in the Extreme Ultraviolet telescope (17.4 nm) of the Extreme Ultraviolet Imager instrument on board the Solar Orbiter. We detect two transverse oscillations in short loops with lengths of 4.5 and 11 Mm. The shorter loop displays an oscillation with a 14 s period and the longer a 30 s period. Despite the high resolution, no definitive identification as propagating or standing waves is possible. The velocity amplitudes are found to be equal to 72 and 125 km s-1, respectively, for the shorter and longer loops. Based on that, we also estimated the values of the energy flux contained in the loops-the energy flux of the 14 s oscillation is 1.9 kW m-2 and that of the 30 s oscillation is 6.5 kW m-2. While these oscillations have been observed in the quiet Sun, their energy fluxes are of the same order as the energy input required to heat the active solar corona. Numerical simulations were performed in order to reproduce the observed oscillations. The correspondence of the numerical results to the observations provides support to the estimates of energy content for the observations. Such high energy densities have not yet been observed in decayless coronal waves, and this is promising for coronal heating models based on wave damping.

Keywords: the sun; active solar corona; solar coronal waves
The Unusual Brightness Phase Curve of (65803) Didymos

On 2022 September 26, NASA's Double Asteroid Redirection Test (DART) successfully hit Dimorphos, the smaller companion of the binary system formed with the asteroid (65803) Didymos. Both the binary system and the impact event were imaged by the Light Italian Cubesat for Imaging of Asteroids, detached from DART 15 days before the impact. Images from the onboard LUKE red, green, and blue camera together with ground-based observations enabled the reconstruction of Didymos's brightness phase curve, with phase angles ranging from 2.35° to 107.7°. The opposition effect regime was studied using the exponential-linear equation, the "Shevchenko" function and the linear-by-parts model while the IAU-official HG1G2 magnitude system was applied to the full phase curve. The opposition effect indicates an unusual asteroid surface for an S type, with characteristics similar to M-type asteroids. While the HG1G2 parameters from the full phase curve place Didymos well among asteroids of the taxonomic C complex. Didymos's phase curve parameters when compared to near-Earth asteroids are very close to the Q type (1862) Apollo, indicating possible depletion of fine submicrometric grains through resurfacing. Didymos's geometric albedo (0.15 ± 0.01) is reported to be 30%–45% smaller than the average geometric albedo for near-Earth S types (0.26 ± 0.04). We propose that Didymos might be an LL ordinary chondrite analog containing albedo-suppressing, shock-darkened/impact melt minerals that have undergone resurfacing processes in the past. A comparison with meteorites indicates that, less likely, Didymos could also contain materials analog to carbon-bearing brecciated L3 ordinary chondrites.

Keywords: asteroids; asteroid surfaces; phase angle; near-earth objects; photometry; rgb photometry
Charged Particle Circular Orbits around Weakly Charged and Magnetized Kerr Black Holes

We study the circular orbits of charged particles around a weakly charged Kerr black hole immersed in a weak, axisymmetric magnetic field. First, we review the circular orbits of neutral particles. We then review the circular orbits of charged particles around a weakly charged Kerr black hole and weakly magnetized Kerr black hole. The case of a weakly magnetized and charged black hole is investigated thereafter. We investigate, in particular, the effect of the electromagnetic forces on the charged particles' innermost stable circular orbits. We examine the conditions for the existence of negative-energy stable circular orbits and the possibility of the emergence of a gap or double orbit in thin accretion disks. Some of the interesting astrophysical consequences of our findings are discussed as well.

Keywords: black hole physics; charged black holes; kerr black holes; black holes; classical black holes; rotating black holes; astrophysical black holes
The Multiwavelength Environment of Second Bologna Catalog Sources

We present the first results of the Chandra Cool Targets (CCT) survey of the Second Bologna Catalog (B2CAT) of powerful radio sources, aimed at investigating the extended X-ray emission surrounding these sources. For the first 33 sources observed in the B2CAT CCT survey, we performed both imaging and spectral X-ray analysis, producing multiband Chandra images, and compared these images with radio observations. To evaluate the presence of extended emission in the X-rays, we extracted surface flux profiles comparing them with simulated ACIS point-spread functions. We detected X-ray nuclear emission for 28 sources. In addition, we detected eight regions of increased X-ray flux originating from radio hot spots or jet knots, and a region of decreased flux, possibly associated with an X-ray cavity. We performed X-ray spectral analysis for 15 nuclei and found intrinsic absorption significantly larger than the Galactic values in four of them. We detected significant extended X-ray emission in five sources, and fitted their spectra with thermal models with gas temperatures ~2 keV. In the case of B2.1 0742+31, the surrounding hot gas is compatible with the intracluster medium of low-luminosity clusters of galaxies, while the X-ray diffuse emission surrounding the highly disturbed wide-angle-tailed radio galaxy B2.3 2254+35 features a luminosity similar to those of relatively bright galaxy groups, although its temperature is similar to those of low-luminosity galaxy clusters. These results highlight the power of low-frequency radio selection, combined with short Chandra snapshot observations, for investigating the properties of X-ray emission from radio sources.

Keywords: active galaxies; galaxy jets; galaxy clusters
History of Ceres's Cold Traps Based on Refined Shape Models

Permanently shadowed regions (PSRs) in the north polar region of Ceres have been previously mapped by the Dawn spacecraft. Putative ice deposits are found in some of these PSRs, whereas most PSRs host no bright deposits, which is thought to be due to oscillations of the axis tilt with a ∼25 ka period. We use stereophotoclinometry to construct refined topographic models of PSR-hosting craters. Ray-tracing calculations reveal that no PSRs remain at the maximum axis tilt, which implies that the ice deposits are remarkably young. The bright ice deposits do not extend beyond PSRs at an axis tilt of 10°, which last occurred about 6 ka ago. This suggests that water is delivered to the polar regions or exposed within the craters by frequent and short-lived events. Surface temperatures are calculated with a terrain irradiance model to delineate cold traps. Based on maximum equilibrium temperatures, Cerean PSRs are too warm to trap supervolatiles.

Keywords: ceres; planetary polar regions; surface ices
SN 2019ehk: A Double-peaked Ca-rich Transient with Luminous X-Ray Emission and Shock-ionized Spectral Features

We present panchromatic observations and modeling of the Calcium-rich supernova (SN) 2019ehk in the star-forming galaxy M100 (d ≈ 16.2 Mpc) starting 10 hr after explosion and continuing for ∼300 days. SN 2019ehk shows a double-peaked optical light curve peaking at t = 3 and 15 days. The first peak is coincident with luminous, rapidly decaying Swift-XRT-discovered X-ray emission ( ${L}_{{\rm{x}}}\approx {10}^{41}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ at 3 days; Lx ∝ t-3), and a Shane/Kast spectral detection of narrow Hα and He II emission lines (v ≈ 500 $\mathrm{km}\,{{\rm{s}}}^{-1}$ ) originating from pre-existent circumstellar material (CSM). We attribute this phenomenology to radiation from shock interaction with extended, dense material surrounding the progenitor star at r < 1015 cm and the resulting cooling emission. We calculate a total CSM mass of ∼7 × 10-3 ${M}_{\odot }$ (MHe/MH ≈6) with particle density n ≈ 109 cm-3. Radio observations indicate a significantly lower density n < 104 cm-3 at larger radii r > (0.1-1) × 1017 cm. The photometric and spectroscopic properties during the second light-curve peak are consistent with those of Ca-rich transients (rise-time of tr = 13.4 ± 0.210 days and a peak B-band magnitude of MB = -15.1 ± 0.200 mag). We find that SN 2019ehk synthesized (3.1 ± 0.11) × 10-2 ${M}_{\odot }$ of ${}^{56}\mathrm{Ni}$ and ejected Mej = (0.72 ± 0.040) ${M}_{\odot }$ total with a kinetic energy Ek = (1.8 ± 0.10) × 1050 erg. Finally, deep HST pre-explosion imaging at the SN site constrains the parameter space of viable stellar progenitors to massive stars in the lowest mass bin (∼10 ${M}_{\odot }$ ) in binaries that lost most of their He envelope or white dwarfs (WDs). The explosion and environment properties of SN 2019ehk further restrict the potential WD progenitor systems to low-mass hybrid HeCO WD+CO WD binaries.

Keywords: supernovae; white dwarf stars; core-collapse supernovae; x-ray telescopes; stellar mass loss; stellar phenomena; transient sources
An ALMA Study of the Massive Molecular Clump N159W-North in the Large Magellanic Cloud: A Possible Gas Flow Penetrating One of the Most Massive Protocluster Systems in the Local Group

Massive dense clumps in the Large Magellanic Cloud can be an important laboratory to explore the formation of populous clusters. We report multiscale ALMA observations of the N159W-North clump, which is the most CO-intense region in the galaxy. High-resolution CO isotope and 1.3 mm continuum observations with an angular resolution of ~0.″25 (~0.07 pc) revealed more than five protostellar sources with CO outflows within the main ridge clump. One of the thermal continuum sources, MMS-2, shows an especially massive/dense nature whose total H2 mass and peak column density are ~104 M ⊙ and ~1024 cm-2, respectively, and harbors massive (~100 M ⊙) starless core candidates identified as its internal substructures. The main ridge containing this source can be categorized as one of the most massive protocluster systems in the Local Group. The CO high-resolution observations found several distinct filamentary clouds extending southward from the star-forming spots. The CO (1-0) data set with a larger field of view reveals a conical, ~30 pc long complex extending toward the northern direction. These features indicate that a large-scale gas compression event may have produced the massive star-forming complex. Based on the striking similarity between the N159W-North complex and the other two previously reported high-mass star-forming clouds in the nearby regions, we propose a "teardrops inflow model" that explains the synchronized, extreme star formation across >50 pc, including one of the most massive protocluster clumps in the Local Group.

Keywords: interstellar medium; interstellar clouds; interstellar filaments; protostars; giant molecular clouds; local group; large magellanic cloud; star formation
Observations of Small-scale Magnetic Reconnections within a Magnetic Flux Rope in Earth's Magnetosheath

The small-scale magnetic reconnection, which has been observed in turbulent plasma, is detected in the interior regions of an ion-scale flux rope in the magnetosheath. Reconnecting current sheets are configured with a nearly symmetric inflow boundary condition and a large guide field of six times the asymptotic field. The evidence of ongoing reconnection is consistent with the standard reconnection model, except no ion flow is detected. In this study, the electron shear flow near the current sheets allows the reconnections to occur. Strong dissipation with these reconnections indicate that electromagnetic energy can be effectively transformed into electron heating and kinetic energy. In particular, the small-scale reconnections do not result in an increase in high-energy electrons, but are responsible for an increase in electron flux over a lower energy range of 100-200 eV. Observations indicate that small-scale reconnection is very common and provides an important channel for energy dissipation in the magnetosheath plasma.

Keywords: space plasmas
Unveiling the Initiation Route of Coronal Mass Ejections through Their Slow Rise Phase

Understanding the early evolution of coronal mass ejections (CMEs), in particular their initiation, is the key to forecasting solar eruptions and induced disastrous space weather. Although many initiation mechanisms have been proposed, a full understanding of CME initiation, which is identified as a slow rise of CME progenitors in kinematics before impulsive acceleration, remains elusive. Here, with a state-of-the-art thermal magnetohydrodynamics simulation, we determine a complete CME initiation route in which multiple mainstream mechanisms occur in sequence yet are tightly coupled. The slow rise is first triggered and driven by the developing hyperbolic flux tube (HFT) reconnection. Subsequently, the slow rise continues as driven by the coupling of the HFT reconnection and the early development of torus instability. The end of the slow rise, i.e., the onset of the impulsive acceleration, is induced by the start of the fast magnetic reconnection coupled with the torus instability. These results unveil that CME initiation is a complicated process involving multiple physical mechanisms, thus being hardly resolved by a single initiation mechanism.

Keywords: solar coronal mass ejections; solar flares; solar magnetic reconnection
TOI 4201 b and TOI 5344 b: Discovery of Two Transiting Giant Planets around M-dwarf Stars and Revised Parameters for Three Others

We present the discovery from the TESS mission of two giant planets transiting M-dwarf stars: TOI 4201 b and TOI 5344 b. We also provide precise radial velocity measurements and updated system parameters for three other M dwarfs with transiting giant planets: TOI 519, TOI 3629, and TOI 3714. We measure planetary masses of 0.525 ± 0.064 M J, 0.243 ± 0.020 M J, 0.689 ± 0.030 M J, 2.57 ± 0.15 M J, and 0.412±0.040 M J for TOI 519 b, TOI 3629 b, TOI 3714 b, TOI 4201 b, and TOI 5344 b, respectively. The corresponding stellar masses are 0.372 ± 0.018 M ☉, 0.635 ± 0.032 M ☉, 0.522 ± 0.028 M ☉, 0.626 ± 0.033 M ☉, and 0.612 ± 0.034 M ☉. All five hosts have supersolar metallicities, providing further support for recent findings that, like for solar-type stars, close-in giant planets are preferentially found around metal-rich M-dwarf host stars. Finally, we describe a procedure for accounting for systematic errors in stellar evolution models when those models are included directly in fitting a transiting planet system.

Keywords: exoplanet systems
A Toy Model for the Electromagnetic Output of Neutron-star Merger Prompt Collapse to a Black Hole: Magnetized Neutron-star Collisions

We present a systematic study of magnetized neutron star head-on collisions. We investigate the resulting magnetic field geometries as the two neutron stars merge. Furthermore, we analyze the luminosity produced in these collisions and monitor the evolution of the magnetic fields from the time of merger until the subsequent production of a black hole. At the time of black hole formation, the luminosity peaks and rings down following the decay of the electromagnetic fields. A comparison is presented for three different cases: one where the initial magnetic field in both neutron stars is aligned, one where they are anti-aligned, and one where they initially have unequal magnetic field strength. We identify regions and set limits so that pair creation and magnetic reconnection would occur in this scenario and further discuss limits and differences in the radiated energy. This study should be regarded as a toy model of the case where the remnant of a binary neutron star merger undergoes a prompt collapse to a black hole with a negligible surrounding disk. We note that the generated electromagnetic pulses resemble the fast radio burst phenomenology. We consider implications of the high-mass mergers leading to a fast prompt collapse to a black hole and the expected flux to be observed at a distance similar to the binary neutron star gravitational wave detection GW190425.

Keywords: neutron stars; compact objects; gravitational waves; magnetohydrodynamical simulations
Magnetic Fields in the Central Molecular Zone Influenced by Feedback and Weakly Correlated with Star Formation

Magnetic fields of molecular clouds in the central molecular zone (CMZ) have been relatively under-observed at sub-parsec resolution. Here, we report JCMT/POL2 observations of polarized dust emission in the CMZ, which reveal magnetic field structures in dense gas at ∼0.5 pc resolution. The 11 molecular clouds in our sample include two in the western part of the CMZ (Sgr C and a farside cloud candidate), four around the Galactic longitude 0 (the 50 km s‑1 cloud, CO 0.02‑0.02, the Stone, and the Sticks and Straw among the Three Little Pigs), and five along the Dust Ridge (G0.253+0.016, clouds b, c, d, and e/f), for each of which we estimate the magnetic field strength using the angular dispersion function method. The morphologies of magnetic fields in the clouds suggest potential imprints of feedback from expanding H II regions and young massive star clusters. A moderate correlation between the total viral parameter versus the star formation rate (SFR) and the dense gas fraction of the clouds is found. A weak correlation between the mass-to-flux ratio and the SFR, and a weak anticorrelation between the magnetic field and the dense gas fraction are also found. Comparisons between magnetic fields and other dynamic components in clouds suggest a more dominant role of self-gravity and turbulence in determining the dynamical states of the clouds and affecting star formation at the studied scales.

Keywords: interstellar magnetic fields; molecular clouds; galactic center; star formation
Why Do M Dwarfs Have More Transiting Planets?

We propose a planet formation scenario to explain the elevated occurrence rates of transiting planets around M dwarfs compared to Sun-like stars discovered by Kepler. We use a pebble drift and accretion model to simulate the growth of planet cores inside and outside of the snow line. A smaller pebble size interior to the snow line delays the growth of super-Earths, allowing giant planet cores in the outer disk to form first. When those giant planets reach pebble isolation mass they cut off the flow of pebbles to the inner disk and prevent the formation of close-in super-Earths. We apply this model to stars with masses between 0.1 and 2 M⊙ and for a range of initial disk masses. We find that the masses of hot super-Earths and of cold giant planets are anticorrelated. The fraction of our simulations that form hot super-Earths is higher around lower-mass stars and matches the exoplanet occurrence rates from Kepler. The fraction of simulations forming cold giant planets is consistent with the stellar mass dependence from radial-velocity surveys. A key testable prediction of the pebble accretion hypothesis is that the occurrence rates of super-Earths should decrease again for M dwarfs near the substellar boundary like Trappist-1.

Keywords: exoplanets; exoplanet formation; planet formation; planetary system formation; protoplanetary disks
Sub-ion Scale Compressive Turbulence in the Solar Wind: MMS Spacecraft Potential Observations

Compressive plasma turbulence is investigated at sub-ion scales in the solar wind using both the Fast Plasma Investigation (FPI) instrument on the Magnetospheric MultiScale mission (MMS), as well as using calibrated spacecraft potential data from the Spin Plane Double Probe (SDP) instrument. The data from FPI allow the sub-ion scale region (fsc ≳ 1 Hz) to be investigated before the instrumental noise becomes significant at a spacecraft frame frequency of fsc ≈ 3 Hz. Whereas the calibrated spacecraft potential allows a measurement up to fsc ≈ 40 Hz. In this work, we give a detailed description of density estimation in the solar wind using the spacecraft potential measurement from the SDP instrument on MMS. Several intervals of solar wind plasma have been processed using the methodology described and are made available. One of the intervals is investigated in more detail and the power spectral density of the compressive fluctuations is measured from the inertial range to the sub-ion range. The morphology of the density spectra can be explained by either a cascade of Alfvén waves and slow waves at large scales and kinetic Alfvén waves at sub-ion scales or more generally by the Hall effect. Using electric field measurements, the two hypotheses are discussed.

Keywords: interplanetary turbulence; space plasmas; plasma physics; solar wind