Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Two states of the slow solar wind are identified from in situ measurements by the Parker Solar Probe (PSP) inside 50 solar radii from the Sun. At such distances the wind measured by PSP has not yet undergone significant transformation related to the expansion and propagation of the wind. We focus in this study on the properties of the quiet solar wind with no magnetic switchbacks. The two states differ by their plasma beta, flux, and magnetic pressure. PSP’s magnetic connectivity established with potential field source surface reconstructions, tested against extreme ultraviolet and white-light imaging, reveals the two states correspond to a transition from a streamer to an equatorial coronal hole. The expansion factors of magnetic field lines in the streamer are 20 times greater than those rooted near the center of the coronal hole. The very different expansion rates of the magnetic field result in different magnetic pressures measured by PSP in the two plasma states. Solar wind simulations run along these differing flux tubes reproduce the slower and denser wind measured in the streamer and the more tenuous wind measured in the coronal hole. Plasma heating is more intense at the base of the streamer field lines rooted near the boundary of the equatorial hole than those rooted closer to the center of the hole. This results in a higher wind flux driven inside the streamer than deeper inside the equatorial hole.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using the Insight-HXMT observations of GRS 1915+105 when it exhibits low-frequency quasiperiodic oscillations (QPOs), we measure the evolution of the QPO frequency along with disk inner radius and mass accretion rate. We find a tight positive correlation between the QPO frequency and mass accretion rate. Our results extend the finding of previous work with AstroSat to a larger range of accretion rates with independent instruments and observations. Treating the QPO frequency of GRS 1915+105 as the relativistic dynamic frequency of a truncated disk, we are able to confirm the high spin nature of the black hole in GRS 1915+105. We also address the potential of our finding to test general relativity in the future.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Basing our analysis on ROGUE I, a catalog of over 32,000 radio sources associated with optical galaxies, we provide two diagnostics to select the galaxies where the radio emission is dominated by an active galactic nucleus (AGN), referred to in the paper as radio-AGNs. Each of these diagnostics can be applied independently. The first one, dubbed MIRAD, compares the flux <jats:italic>F</jats:italic> <jats:sub> <jats:italic>W</jats:italic>3</jats:sub> in the <jats:italic>W</jats:italic>3 mid-infrared band of the Wide-field Infrared Survey Explorer telescope, with the radio flux at 1.4 GHz, <jats:italic>F</jats:italic> <jats:sub>1.4</jats:sub>. MIRAD requires no optical spectra. The second diagnostic, dubbed DLM, compares the 4000 Å break strength, <jats:italic>D</jats:italic> <jats:sub>n</jats:sub>(4000), with the radio luminosity per unit stellar mass. The DLM diagram has already been used in the past, but not as stand-alone. For these two diagrams, we propose simple, empirical dividing lines that result in the same classification for the objects in common. These lines correctly classify as radio-AGN 99.5% of the extended radio sources in the ROGUE I catalog, and as star-forming galaxies 98%–99% of the galaxies identified as such by their emission-line ratios. Both diagrams clearly show that radio-AGNs are preferentially found among elliptical galaxies and among galaxies hosting the most massive black holes. Most of the radio sources classified as radio-AGNs in the MIRAD or DLM diagrams are either optically weak AGNs or retired galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This is the third sequel in a series discussing the discovery of various types of extragalactic transients with the James Webb Space Telescope (JWST) in a narrow-field (∼0.1 deg<jats:sup>2</jats:sup>), moderately deep (<jats:italic>m</jats:italic> <jats:sub>AB</jats:sub> ∼ 27 mag) survey. In this part we focus on the detectability and observational characteristics of direct-collapse black holes (DCBHs) and tidal disruption events (TDEs) around them. We use existing models for DCBH accretion luminosities and spectra, as well as for TDE light curves, and find that accreting DCBH seeds may be bright enough for detection up to <jats:italic>z</jats:italic> ∼ 7 with JWST NIRCam imaging. TDEs of massive (<jats:italic>M</jats:italic> ≳ 50<jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub>) stars around them can enhance the chance for discovering them as transient objects, although the rate of such events is low, a few per survey time. TDEs around nonaccreting black holes of <jats:italic>M</jats:italic> ∼ 10<jats:sup>6</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> may also be detected at <jats:italic>z</jats:italic> &lt; 7 redshifts in the redder NIRCam bands between 3 and 5 <jats:italic>μ</jats:italic>s. It is also shown that accreting DCBHs appear separate from supernovae on the NIRCam color–color plot, but TDEs from quiescent black holes fall in nearly the same color range as superluminous supernovae, which makes them more difficult to identify.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Gravitationally lensed Type Ia supernovae (SNe Ia) may be the next frontier in cosmic probes, able to deliver independent constraints on dark energy, spatial curvature, and the Hubble constant. Measurements of time delays between the multiple images become more incisive due to the standardized candle nature of the source, monitoring for months rather than years, and partial immunity to microlensing. While currently extremely rare, hundreds of such systems should be detected by upcoming time domain surveys. Others will have the images spatially unresolved, with the observed lightcurve a superposition of time-delayed image fluxes. We investigate whether unresolved images can be recognized as lensed sources given only lightcurve information, and whether time delays can be extracted robustly. We develop a method that we show can identify these systems for the case of lensed SNe Ia with two images and time delays exceeding ten days. When tested on such an ensemble, without microlensing, the method achieves a false-positive rate of ≲5%, and measures the time delays with a completeness of ≳93% and with a bias of ≲0.5% for Δ<jats:italic>t</jats:italic> <jats:sub>fit</jats:sub> ≳ 10 days. Since the method does not assume a template of any particular type of SN, the method has the (untested) potential to work on other types of lensed SNe systems and possibly on other transients as well.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>After the prediction of many sub- and super-Chandrasekhar (at least a dozen for the latter) limiting-mass white dwarfs (WDs), hence apparently a peculiar class of WDs, from the observations of luminosity of Type Ia supernovae, researchers have proposed various models to explain these two classes of WD separately. We earlier showed that these two peculiar classes of WD, along with the regular WD, can be explained by a single form of the <jats:italic>f</jats:italic>(<jats:italic>R</jats:italic>) gravity, whose effect is significant only in the high-density regime, and it almost vanishes in the low-density regime. However, since there is no direct detection of such a WD, it is difficult to single out one specific theory from the zoo of modified theories of gravity. We discuss the possibility of direct detection of such a WD in gravitational wave (GW) astronomy. It is well known that in <jats:italic>f</jats:italic>(<jats:italic>R</jats:italic>) gravity more than two polarization modes are present. We estimate the amplitudes of all the relevant modes for the peculiar and the regular WD. We further discuss the possibility of their detections through future-based GW detectors, such as LISA, ALIA, DECIGO, BBO, or the Einstein Telescope, and thereby put constraints on or rule out various modified theories of gravity. This exploration links the theory with possible observations through GW in <jats:italic>f</jats:italic>(<jats:italic>R</jats:italic>) gravity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We analyze magnetic field data from two magnetosheath crossings, representative of a larger collection of similar cases in the database of the Cluster spacecraft. We apply a novel data analysis method to identify the power-law behavior of the structure functions and to find the validity range of the power-law scaling. We validate the technique with solar wind magnetic field data and a synthetic magnetic field signal. This approach grants a rigorous determination of the scale range for a linear fit of the structure function in the log–log representation, which most often is chosen arbitrarily. The fitting allows an estimation of the power spectral index from the scale variation of the second-order structure function exponent. Data recorded during the first Cluster magnetosheath crossing, called <jats:italic>Event 1,</jats:italic> indicate three different power-law scaling regimes (injection, inertial, and kinetic) separated by two spectral breaks, consistent with the scenario of fully developed turbulence. However, data from the second Cluster magnetosheath crossing, called <jats:italic>Event 2,</jats:italic> depict a different scenario with only two power-law scaling regimes determined from the fit. A spectral slope shallower than the Kolmogorovian solar wind power-law index is determined at magnetohydrodynamic scales, spanning more than three frequency decades, which is separated by a spectral break from the kinetic regime. An analysis of simultaneous solar wind data from the Advanced Composition Explorer suggests that the scale behavior of the magnetosheath fluctuations might be controlled by the structure of the bow shock; solar wind turbulent fluctuations are only partially destroyed while they are carried across the bow shock. Both events are recorded in a quasi-perpendicular magnetosheath.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Helioseismic waves observable at the solar surface can be used to probe the properties of the Sun’s interior. By measuring helioseismic travel times between different location on the surface, flows and other interior properties can be inferred using so-called sensitivity kernels that relate the amount of travel-time shift with variations in interior properties. In particular, sensitivity kernels for flows have been developed in the past, using either ray or Born approximation, and have been used to infer solar interior flows such as the meridional circulation, which is of particular interest for understanding the structure and dynamics of the Sun. Here we introduce a new method for deriving three-dimensional sensitivity kernels for large-scale horizontal flows in the solar interior. We perform global-Sun wave-propagation simulations through 784 small flow perturbations placed individually in the interior of a simulated Sun, and measure the shifts in helioseismic travel times caused by these perturbations. Each measurement corresponds to a linear equation connecting the flow perturbation velocities and the sensitivity kernels. By solving the resulting large set of coupled linear equations, we derive three-dimensional sensitivity kernels for horizontal flows, which have a longitudinal component (parallel to the wave’s travel direction) and a transverse component (perpendicular to the wave’s travel direction). The kernels exhibit a “banana” shape, similar to kernels derived using Born-approximation methods, and show that transverse components are not negligible in inversions for interior flows.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>An accretion disk in an Active Galactic Nucleus harbors and shields dust from external illumination. Our model shows that, at the midplane of the disk around an <jats:italic>M</jats:italic> <jats:sub>BH</jats:sub> = 10<jats:sup>7</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> black hole, dust can exist at 0.1 pc from the black hole, compared to 0.5 pc outside of the disk where such self-shielding is constrained. We construct a physical model of a disk region approximately located between the radius of dust sublimation at the disk midplane and the radius at which dust sublimes at the disk surface. Our main conclusion is that, for a wide range of model parameters such as local accretion rate and/or opacity, the accretion disk’s own radiation pressure on dust significantly influences its vertical structure. In this region, convection plays important role in the vertical transport of energy. When the local accretion rate exceeds 2.5<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr, the 10<jats:sup>−2</jats:sup> pc scale disk is supercritical with respect to dust opacity. Such a disk puffs up and transforms from geometrically thin to slim. Our model fits into the narrative of a “failed wind” scenario of Czerny &amp; Hryniewicz and the “compact torus” model of Baskin &amp; Laor, incorporating them as variations of the radiative dusty disk model.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present FANTASY (Finally A Numerical Trajectory Algorithm both Straightforward and sYmplectic), a user-friendly, open-source symplectic geodesic integrator written in Python. FANTASY is designed to work “out of the box” and does not require anything from the user aside from the metric and the initial conditions for the geodesics. FANTASY efficiently computes derivatives up to machine precision using automatic differentiation, allowing the integration of geodesics in arbitrary space(times) without the need for the user to manually input Christoffel symbols or any other metric derivatives. Further, FANTASY utilizes a Hamiltonian integration scheme that doubles the phase space, where two copies of the particle phase space are evolved together. This technique allows for an integration scheme that is both explicit and symplectic, even when the Hamiltonian is not separable. FANTASY comes prebuilt with second- and fourth-order schemes, and is easily extendable to higher-order schemes. FANTASY also includes an automatic Jacobian calculator that allows for coordinate transformations to be done automatically.</jats:p>