adsabs/SciX_UAT_keywords huggingface dataset:
Optical Spectropolarimetric Variability Properties in Blazars PKS 0637–75 and PKS 1510–089

Spectropolarimetry is a powerful tool to investigate the central regions of active galactic nuclei (AGNs) as polarization signatures are key to probing magnetic field structure, evolution, and the physics of particle acceleration in jets. Optical linear polarization of blazars is typically greater than a few percent, indicating the emission is dominated by nonthermal synchrotron radiation, while polarization less than a few percent is common for other type 1 AGNs. We present a spectropolarimetric study of PKS 0637–75 and PKS 1510–089 to determine how the head-on orientation of a jet and dominant emission processes influence polarimetric variations in the broad lines and continuum. Observations were obtained biweekly from the Robert Stobie Spectrograph on the Southern African Large Telescope. Variability in the continuum polarization is detected for both PKS 0637–75 and PKS 1510–089, with a total average level of 2.5% ± 0.1% and 7.5% ± 0.1%, respectively. There is no clear polarization in the broad Balmer emission lines and weak polarization in Mg II as the average level across all observations is 0.2% ± 0.1% for Hβ, 0.2% ± 0.3% for Hγ, and 0.6% ± 0.2% for Mg II. We find that polarization measurements confirm the conclusions drawn from spectral energy distribution modeling of the disk–jet contributions to the emission as optical polarization and time variability for PKS 0637–75 are shown to be dominated by accretion disk emission while those of PKS 1510–089 are due to both disk and jet emission, with greater jet contribution during flaring states.

Keywords: blazars; flat-spectrum radio quasars; spectropolarimetry; active galactic nuclei; relativistic jets
Formation of the Cosmic-Ray Halo: The Role of Nonlinear Landau Damping

We present a nonlinear model of a self-consistent Galactic halo, where the processes of cosmic-ray (CR) propagation and excitation/damping of MHD waves are included. The MHD turbulence that prevents CR escape from the Galaxy is entirely generated by the resonant streaming instability. The key mechanism controlling the halo size is the nonlinear Landau (NL) damping, which suppresses the amplitude of MHD fluctuations and, thus, makes the halo larger. The equilibrium turbulence spectrum is determined by a balance of CR excitation and NL damping, which sets the regions of diffusive and advective propagation of CRs. The boundary z cr(E) between the two regions is the halo size, which slowly increases with the energy. For the vertical magnetic field of ~1 μG, we estimate z cr ~ 1 kpc for GeV protons. The derived proton spectrum is in a good agreement with observational data.

Keywords: cosmic rays
Contribution of Secondary Neutrinos from Line-of-sight Cosmic-Ray Interactions to the IceCube Diffuse Astrophysical Flux

In 10 years of observations, the IceCube neutrino observatory has revealed a neutrino sky in tension with previous expectations for neutrino point-source emissions. Astrophysical objects associated with hadronic processes might act as production sites for neutrinos, observed as point sources at Earth. Instead, a nearly isotropic flux of astrophysical neutrinos is observed up to PeV energies, prompting a reassessment of the assumed transport and production physics. This work applies a new physical explanation for neutrino production from populations of active galactic nuclei and starburst galaxies to three years of public IceCube point-source data. Specifically, cosmic rays produced at such sources might interact with extragalactic background light and gas along the line of sight, generating a secondary neutrino flux. This model is tested alongside a number of typical flux weighting schemes, in all cases the all-sky flux contribution being constrained to percent levels of the reported IceCube diffuse astrophysical flux.

Keywords: neutrino astronomy; active galactic nuclei; blazars; starburst galaxies; extragalactic magnetic fields; intergalactic medium; cosmic rays; gamma-rays; particle astrophysics
Turbulent Gas in Lensed Planck-selected Starbursts at z ∼ 1-3.5

Dusty star-forming galaxies at high redshift (1 < z < 3) represent the most intense star-forming regions in the universe. Key aspects to these processes are the gas heating and cooling mechanisms, and although it is well known that these galaxies are gas-rich, little is known about the gas excitation conditions. Only a few detailed radiative transfer studies have been carried out owing to a lack of multiple line detections per galaxy. Here we examine these processes in a sample of 24 strongly lensed star-forming galaxies identified by the Planck satellite (LPs) at z ∼ 1.1-3.5. We analyze 162 CO rotational transitions (ranging from Jup = 1 to 12) and 37 atomic carbon fine-structure lines ([C I]) in order to characterize the physical conditions of the gas in the sample of LPs. We simultaneously fit the CO and [C I] lines and the dust continuum emission, using two different non-LTE, radiative transfer models. The first model represents a two-component gas density, while the second assumes a turbulence-driven lognormal gas density distribution. These LPs are among the most gas-rich, IR-luminous galaxies ever observed (μL ${L}_{\mathrm{IR}(8-1000\mu {\rm{m}})}\sim {10}^{13-14.6}$ L⊙; $\langle $ μLMISM $\rangle $ = (2.7 ± 1.2) × 1012 M⊙, with μL ∼ 10-30 the average lens magnification factor). Our results suggest that the turbulent interstellar medium present in the LPs can be well characterized by a high turbulent velocity dispersion ( $\langle $ ΔVturb $\rangle $ ∼ 100 km s-1) and ratios of gas kinetic temperature to dust temperature $\langle $ Tkin/Td $\rangle $ ∼ 2.5, sustained on scales larger than a few kiloparsecs. We speculate that the average surface density of the molecular gas mass and IR luminosity, ${{\rm{\Sigma }}}_{{M}_{\mathrm{ISM}}}$ ∼ 103-4 M⊙ pc-2 and ${{\rm{\Sigma }}}_{{L}_{\mathrm{IR}}}$ ∼ 1011-12 L⊙ kpc-2, arise from both stellar mechanical feedback and a steady momentum injection from the accretion of intergalactic gas.

Keywords: starburst galaxies; strong gravitational lensing; high-redshift galaxies; interstellar medium
Disentangling the Entangled Linkages of Relative Magnetic Helicity

Magnetic helicity, H, measures magnetic linkages in a volume. The early theoretical development of helicity focused on magnetically closed systems in ${ \mathcal V }$ bounded by $\partial { \mathcal V }$ . For magnetically closed systems, ${ \mathcal V }\in {{\mathbb{R}}}^{3}={ \mathcal V }+{{ \mathcal V }}^{\ast }$ , no magnetic flux threads the boundary, $\hat{{\boldsymbol{n}}}\cdot {\boldsymbol{B}}{| }_{\partial { \mathcal V }}=0$ . Berger & Field and Finn & Antonsen extended the definition of helicity to relative helicity, ${ \mathcal H }$ , for magnetically open systems where magnetic flux may thread the boundary. Berger expressed this relative helicity as two gauge-invariant terms that describe the self-helicity of the magnetic field that closes inside ${ \mathcal V }$ and the mutual helicity between the magnetic field that threads the boundary $\partial { \mathcal V }$ and the magnetic field that closes inside ${ \mathcal V }$ . The total magnetic field that permeates ${ \mathcal V }$ entangles magnetic fields that are produced by current sources J in ${ \mathcal V }$ with magnetic fields that are produced by current sources J ∗ in ${{ \mathcal V }}^{\ast }$ . Building on this fact, we extend Berger's expressions for relative magnetic helicity to eight gauge-invariant quantities that simultaneously characterize both of these self and mutual helicities and attribute their origins to currents J in ${ \mathcal V }$ and/or J ∗ in ${{ \mathcal V }}^{\ast }$ , thereby disentangling the domain of origin for these entangled linkages. We arrange these eight terms into novel expressions for internal and external helicity (self) and internal-external helicity (mutual) based on their domain of origin. The implications of these linkages for interpreting magnetic energy are discussed and new boundary observables are proposed for tracking the evolution of the field that threads the boundary.

Keywords: analytical mathematics; astrophysical magnetism; stellar magnetic fields; solar magnetic fields; solar magnetic reconnection; magnetohydrodynamics; magnetohydrodynamical simulations
Probing the Nature of Rotation in the Pleiades, Alpha Persei, and Hyades Clusters

Unraveling the internal kinematics of open clusters is crucial for understanding their formation and evolution. However, there is a dearth of research on this topic, primarily due to the lack of high-quality kinematic data. Using the exquisite-precision astrometric parameters and radial velocities provided by Gaia data release 3, we investigate the internal rotation in three of the most nearby and best-studied open clusters, namely the Pleiades, Alpha Persei, and Hyades clusters. Statistical analyses of the residual motions of the member stars clearly indicate the presence of three-dimensional rotation in the three clusters. The mean rotation velocities of the Pleiades, Alpha Persei, and Hyades clusters within their tidal radii are estimated to be 0.24 ± 0.04, 0.43 ± 0.08, and 0.09 ± 0.03 km s‑1, respectively. Similar to the Praesepe cluster that we have studied before, the rotation of the member stars within the tidal radii of these three open clusters can be well interpreted by Newton's theorem. No expansion or contraction is detected in the three clusters either. Furthermore, we find that the mean rotation velocity of open clusters may be positively correlated with the cluster mass, and the rotation is likely to diminish as open clusters age.

Keywords: open star clusters; stellar kinematics
Tidal Deformability of Neutron Stars in Scalar-tensor Theories of Gravity

Gravitational waves from compact binary coalescences are valuable for testing theories of gravity in the strong field regime. By measuring neutron star tidal deformability using gravitational waves from binary neutron stars, stringent constraints were placed on the equation of state of matter at extreme densities. Tidal Love numbers in alternative theories of gravity may differ significantly from their general relativistic counterparts. Understanding exactly how the tidal Love numbers change will enable scientists to untangle physics beyond general relativity from the uncertainty in the equation of state measurement. In this work, we explicitly calculate the fully relativistic l ≥ 2 tidal Love numbers for neutron stars in scalar-tensor theories of gravitation. We use several realistic equations of state to explore how the mass, radius, and tidal deformability relations differ from those of general relativity. We find that tidal Love numbers and tidal deformabilities can differ significantly from those in general relativity in certain regimes. The electric tidal deformability can differ by ~200%, and the magnetic tidal deformability differs by ~300%. These deviations occur at large compactnesses (C = M/r ≳ 0.2) and vary slightly depending on the equation of state. This difference suggests that using the tidal Love numbers from general relativity could lead to significant errors in tests of general relativity using the gravitational waves from binary neutron star and neutron star black hole mergers.

Keywords: neutron stars; non-standard theories of gravity; gravitation; gravitational wave astronomy
SDSS-IV MaNGA: Modeling the Spectral Line-spread Function to Subpercent Accuracy

The Sloan Digital Sky Survey IV Mapping Nearby Galaxies at APO (MaNGA) program has been operating from 2014 to 2020, and has now observed a sample of 9269 galaxies in the low redshift universe (z ∼ 0.05) with integral-field spectroscopy. With rest-optical (λλ0.36-1.0 μm) spectral resolution R ∼ 2000 the instrumental spectral line-spread function (LSF) typically has 1σ width of about 70 km s-1, which poses a challenge for the study of the typically 20-30 km s-1 velocity dispersion of the ionized gas in present-day disk galaxies. In this contribution, we present a major revision of the MaNGA data pipeline architecture, focusing particularly on a variety of factors impacting the effective LSF (e.g., under-sampling, spectral rectification, and data cube construction). Through comparison with external assessments of the MaNGA data provided by substantially higher-resolution R ∼ 10,000 instruments, we demonstrate that the revised MPL-10 pipeline measures the instrumental LSF sufficiently accurately (≤0.6% systematic, 2% random around the wavelength of Hα) that it enables reliable measurements of astrophysical velocity dispersions σHα ∼ 20 km s-1 for spaxels with emission lines detected at signal-to-noise ratio > 50. Velocity dispersions derived from [O II], Hβ, [O III], [N II], and [S II] are consistent with those derived from Hα to within about 2% at σHα > 30 km s-1. Although the impact of these changes to the estimated LSF will be minimal at velocity dispersions greater than about 100 km s-1, scientific results from previous data releases that are based on dispersions far below the instrumental resolution should be reevaluated.

Keywords: spectroscopy; galaxy kinematics; astronomy data analysis
The Isaac Newton Telescope Monitoring Survey of Local Group Dwarf Galaxies. V. The Star Formation History of Sagittarius Dwarf Irregular Galaxy Derived from Long-period Variable Stars

We conducted an optical monitoring survey of the Sagittarius dwarf irregular galaxy (SagDIG) during the period of 2016 June-2017 October, using the 2.5 m Isaac Newton Telescopeat La Palama. Our goal was to identify long-period variable stars (LPVs), namely, asymptotic giant branch stars (AGBs) and red supergiant stars, to obtain the star formation history of isolated, metal-poor SagDIG. For our purpose, we used a method that relies on evaluating the relation between luminosity and the birth mass of these most evolved stars. We found 27 LPV candidates within 2 half-light radii of SagDIG. 10 LPV candidates were in common with previous studies, including one extreme-AGB (x-AGB). By adopting the metallicity Z = 0.0002 for older populations and Z = 0.0004 for younger ages, we estimated that the star formation rate changes from 0.0005 ± 0.0002 M ⊙ yr-1 kpc-2 (13 Gyr ago) to 0.0021 ± 0.0010 M ⊙ yr-1 kpc-2 (0.06 Gyr ago). Like many dwarf irregular galaxies, SagDIG has had continuous star formation activity across its lifetime, though with different rates, and experiences an enhancement of star formation since z ≃ 1. We also evaluated the total stellar mass within 2 half-light radii of SagDIG for three choices of metallicities. For metallicity Z = 0.0002 and 0.0004, we estimated the stellar mass M* = (5.4 ± 2.3) × 106 and (3.0 ± 1.3) × 106 M ⊙, respectively. Additionally, we determined a distance modulus of μ = 25.27 ± 0.05 mag, using the tip of the red giant branch.

Keywords: dwarf galaxies
The Central 300 pc of the Galaxy Probed by Infrared Spectra of H3+ and CO. II. Expansion and Morphology of the Warm Diffuse Gas

Velocity profiles of a line of ${{\rm{H}}}_{3}^{+}$ at 3.7 μm produced in warm diffuse gas have been observed toward 18 stars in the Central Molecular Zone (CMZ) of the Galaxy. Their longitude-velocity diagram indicates that the gas is radially expanding within the CMZ at speeds up to a maximum of ∼150 km s-1. The current momentum and energy in the gas are ∼5 × 108 M⊙ km s-1 and ∼5 × 1053 erg. The motion is similar to that of the Expanding Molecular Ring discovered in 1972 by Kaifu et al. and by Scoville. We propose that the expanding gas seen in ${{\rm{H}}}_{3}^{+}$ is part of the same phenomenon, despite differences in estimates of density, morphology, and degree of rotation. The outward motion suggests that one or more ejection events occurred near the center of the CMZ (0.5-1) × 106 yr ago, which may be related to creation of the recently observed microwave bubble. These observations revive the circular face-on view of the CMZ proposed in 1972, which fell out of favor after 1991 when Binney et al. proposed that a face-on view of the CMZ would show it to have an elliptical shape, with high eccentricity. While that model may apply on kiloparsec scales, we argue that it is incorrect to apply it to the much smaller CMZ. We discuss the fate of the expanding gas, which appears to be eventual infall into the center, leading to episodes of star formation and violent events associated with accretion onto Sgr A*.

Keywords: astrochemistry; cosmic rays; galactic center; interstellar line absorption; interstellar molecules; interstellar clouds
X-Ray Observations of the Isolated Black Hole Candidate OGLE-2011-BLG-0462 and Other Collapsed Objects Discovered through Gravitational Microlensing

Isolated black holes and neutron stars can be revealed through the observation of long-duration gravitational microlensing events. A few candidates have been found in surveys of stars in the direction of the Galactic bulge. Recently, thanks to the addition of astrometric information at milliarcsecond level, it has been possible to reduce the uncertainties in the masses and distances for some of these "dark" gravitational lenses and select the most promising candidates. These isolated compact objects might emit X-rays powered by accretion from the interstellar medium. Using data of the Chandra, XMM-Newton, and INTEGRAL satellites, we searched for X-ray emission in the isolated black hole candidate OGLE-2011-BLG-0462, and in several other putative collapsed objects found with gravitational microlensing. OGLE-2011-BLG-0462 has been recently interpreted as a 7.1 M ⊙ black hole at a distance of 1.6 kpc, although a different group obtained a mass range (1.6-4.4 M ⊙) that cannot exclude a massive neutron star. We have derived upper limits on the flux from OGLE-2011-BLG-0462 of 9 × 10-15 erg cm-2 s-1 in the 0.5-7 keV range and ~2 × 10-12 erg cm-2 s-1 in the 17-60 keV range. The implied X-ray luminosity is consistent with the small radiative efficiency expected for a black hole and disfavors a neutron star interpretation. Limits down to a factor of about five lower are obtained for the soft X-ray flux of other candidates, but their interpretation is affected by larger uncertainties in the masses, distances, and spatial velocities.

Keywords: gravitational lensing; stellar mass black holes; bondi accretion; x-ray sources
Point-spread Function Estimation for Adaptive Optics Imaging of Astronomical Extended Objects

This paper focuses on point-spread function (PSF) estimation for astronomical images containing only single extended objects captured by adaptive optics systems. The problem is very different from, and much more challenging than, PSF estimation with point-like source images. We propose a new PSF estimation framework based on deep-learning technology. In this framework, PSFs can be estimated “end-to-end” using the original degraded images. Moreover, such a framework can precisely address different sources of blur without requiring accurate prior information about the PSF, image or imaging system. Therefore, the method is practical. We test the proposed method on both simulated and real data, and the favorable results show that the method is valid and performs much better than classical methods do.

Keywords: optical telescopes
GRB 101225A as Orphan Dipole Radiation of a Newborn Magnetar with Precession Rotation in an Off-axis Gamma-ray Burst

The unusual multiwavelength lightcurves of GRB 101225A are revisited by assuming that they are from an off-axis GRB powered by a newborn magnetar. We show that GRB 101225A's optical afterglow lightcurve is fitted with the forward shock model by parameterizing its jet structure as a Gaussian function with a half-opening angle of the jet core as 1°67. The derived initial Lorentz factor (Γ0) is 120, and the viewing angle to the jet axis is θv = 3°7. Tentative QPO signatures of P = 488 s and P = 250 ~ 300 s are found with a confidence level of 90% by analyzing its X-ray flares observed in the time interval of [4900, 7500] s. Its global gamma-ray/X-ray lightcurve and the QPO signatures are represented with the magnetar dipole radiation (DR) model by considering the magnetar precession motion, assuming that the magnetar spindown is dominated by GW emission. The bulk Lorentz factor of the DR ejecta is limited to 8, being much lower than Γ0. Comparing GRB 101225A with the extremely off-axis GRB 170817A, we suspect that the nature of the two-component jet in GRB 170817A is a combination of a co-axial GRB jet and a DR ejecta. GRB 101225A would be among the brightest ones of the CDF-S XT2-like X-ray transient population driven by newborn magnetars. A discussion of the detectability of its gravitational wave emission is also presented.

Keywords: gamma-ray bursts; magnetars
Wind-powered Ultraluminous X-ray Sources

Although ultraluminous X-ray sources (ULX) are important for astrophysics because of their extreme apparent super-Eddington luminosities, their nature is still poorly known. Theoretical and observational studies suggest that ULXs could be a diversified group of objects that are composed of low-mass X-ray binaries, high-mass X-ray binaries and marginally also systems containing intermediate-mass black holes. Observational data on the ULX donors could significantly boost our understanding of these systems, but only a few have been detected. There are several candidates, mostly red supergiants (RSGs), but surveys are typically biased toward luminous near-infrared objects. In ULXs harbouring RSGs matter accreted onto the compact body would have to be provided by the stellar wind of the companion because a Roche-lobe overflow could be unstable for relevant mass-ratios. We present a comprehensive study of the evolution and population of wind-fed ULXs, and we provide a theoretical support for the link between RSGs and ULXs. Assuming a minimal model of stellar-wind emission, our estimated upper limit on contribution of wind-fed ULX to the overall ULX population is ~75%-96% for young (<100 Myr) star-forming environments, ~49%-87% for prolonged constant star formation (e.g., disk of Milky Way), and ≲1% for environments in which star formation ceased long time (>2 Gyr) ago. We show also that some wind-fed ULXs (up to 6%) may evolve into merging double compact objects (DCOs). We demonstrate that the exclusion of wind-fed ULXs from population studies of ULXs might have lead to systematic errors in their conclusions.

Keywords: black holes; gravitational waves; binary stars; x-ray binary stars; astrostatistics; astronomy databases
KMT-2019-BLG-2073: Fourth Free-floating Planet Candidate with θE < 10 μas

We analyze the very short Einstein timescale (tE ≃ 7 hr) event KMT-2019-BLG-2073. Making use of the pronounced finite-source effects generated by the clump giant source, we measure the Einstein radius θE ≃ 4.8 μas and so infer a mass $M=59\,{M}_{\oplus }{({\pi }_{\mathrm{rel}}/16\mu \mathrm{as})}^{-1}$ , where πrel is the lens-source relative parallax. We find no significant evidence for a host of this planetary-mass object, though one could be present at sufficiently wide separation. If so, it would be detectable after about 10 yr. This is the fourth isolated microlens with a measured Einstein radius θE < 10 μas, which we argue is a useful threshold for a "likely free-floating planet (FFP)" candidate. We outline a new approach to constructing a homogeneous sample of giant-star finite-source/point-lens (FSPL) events, within which the subsample of FFP candidates can be statistically analyzed. We illustrate this approach using 2019 KMTNet data and show that there appears to be a large θE gap between the two FFP candidates and the 11 other FSPL events. We argue that such sharp features are more identifiable in a sample selected on θE compared to the traditional approach of identifying candidates based on short tE.

Keywords: gravitational microlensing exoplanet detection