Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Light bridges (LBs) are among the most striking substructures in sunspots, where various activities have been revealed by recent high-resolution observations from the Interface Region Imaging Spectrograph (IRIS). Based on the variety of their physical properties, we classified these activities into four distinct categories: transient brightening (TB), intermittent jet (IJ), type-I light wall (LW-I), and type-II light wall (LW-II). In IRIS 1400/1330 Å observations, TBs are characterized by abrupt emission enhancements, and IJs appear as collimated plasma ejections with a width of 1–2 Mm at some LB sites. Most observed TBs are associated with IJs and show superpositions of some chromosphere absorption lines on enhanced and broadened wings of C <jats:sc>ii</jats:sc> and Si <jats:sc>iv</jats:sc> lines, which could be driven by intermittent magnetic reconnection in the lower atmosphere. LW-I and LW-II are wall-shaped structures with bright fronts above the whole LB. An LW-I has a continuous oscillating front with a typical height of several Mm and an almost stationary period of 4–5 minutes. On the contrary, an LW-II has an indented front with a height of over 10 Mm, which has no stable period and is accompanied by recurrent TBs in the entire LB. These results support that LW-IIs are driven by frequent reconnection occurring along the entire LB due to large-scale magnetic flux emergence or intrusion, rather than the leakage of waves producing LW-Is. Our observations reveal a highly dynamical scenario of activities above LBs driven by different basic physical processes, including magnetoconvection, magnetic reconnection, and wave leakage.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Prestellar cores represent the initial conditions in the process of star and planet formation. Their low temperatures (&lt;10 K) allow the formation of thick icy dust mantles, which will be partially preserved in future protoplanetary disks, ultimately affecting the chemical composition of planetary systems. Previous observations have shown that carbon- and oxygen-bearing species, in particular CO, are heavily depleted in prestellar cores due to the efficient molecular freeze-out onto the surface of cold dust grains. However, N-bearing species such as NH<jats:sub>3</jats:sub> and, in particular, its deuterated isotopologues appear to maintain high abundances where CO molecules are mainly in the solid phase. Thanks to ALMA, we present here the first clear observational evidence of NH<jats:sub>2</jats:sub>D freeze-out toward the L1544 prestellar core, suggestive of the presence of a “complete depletion zone” within a ≃1800 au radius, in agreement with astrochemical prestellar core model predictions. Our state-of-the-art chemical model coupled with a non-LTE radiative transfer code demonstrates that NH<jats:sub>2</jats:sub>D becomes mainly incorporated in icy mantles in the central 2000 au and starts freezing out already at ≃7000 au. Radiative transfer effects within the prestellar core cause the NH<jats:sub>2</jats:sub>D(1<jats:sub>11</jats:sub> − 1<jats:sub>01</jats:sub>) emission to appear centrally concentrated, with a flattened distribution within the central ≃3000 au, unlike the 1.3 mm dust continuum emission, which shows a clear peak within the central ≃1800 au. This prevented NH<jats:sub>2</jats:sub>D freeze-out from being detected in previous observations, where the central 1000 au cannot be spatially resolved.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The flat-spectrum radio quasar B2 1633+382 (4C 38.41) has been monitored for several years and has presented correlated variability in multiple wavelengths. In this article, we are performing different analyses for multiple frequencies, from gamma rays to radio, as well as the C <jats:sc>iv</jats:sc> <jats:italic>λ</jats:italic>1549 Å emission line and the <jats:italic>λ</jats:italic>1350 Å continuum. Using the nonthermal dominance parameter, we separated the C <jats:sc>iv</jats:sc> and the continuum light curves for when the dominant source of continuum is the accretion disk or the jet. We found a correlation at a delay consistent with zero between the line and the continuum dominated by disk emission indicating a very small broad-line region (BLR). From the resulting delay between the 15 GHz and gamma rays, we estimated the distance of the gamma-ray emission region from the jet apex to be ∼37 pc. The C <jats:sc>iv</jats:sc> flux decreases when the continuum and gamma rays increase at some of the high-activity periods. The C <jats:sc>iv</jats:sc> profile presents a larger variable component in its blue wing. The relation between the luminosities of C <jats:sc>iv</jats:sc> and the continuum does not completely follow the relation for a quasar sample. Our results lead us to propose an outflow of BLR material in the jet flow direction, a gamma-ray production through magnetic reconnection for the flaring event of mid-2011, and that there is not enough BLR material close to the radio core to be easily ionized by the nonthermal continuum.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The global 21 cm H <jats:sc>i</jats:sc> emission-line profile of a galaxy encodes valuable information on the spatial distribution and kinematics of the neutral atomic gas. Galaxy interactions significantly influence the H <jats:sc>i</jats:sc> disk and imprint observable features on the integrated H <jats:sc>i</jats:sc> line profile. In this work, we study the neutral atomic gas properties of galaxy mergers selected from the Great Observatories All-sky LIRG Survey. The H <jats:sc>i</jats:sc> spectra come from new observations with the Five-hundred-meter Aperture Spherical Telescope and from a collection of archival data. We quantify the H <jats:sc>i</jats:sc> profile of the mergers with a newly developed method that uses the curve of growth of the line profile. Using a control sample of non-merger galaxies carefully selected to match the stellar mass of the merger sample, we show that mergers have a larger proportion of single-peaked H <jats:sc>i</jats:sc> profiles, as well as a greater tendency for the H <jats:sc>i</jats:sc> central velocity to deviate from the systemic optical velocity of the galaxy. By contrast, the H <jats:sc>i</jats:sc> profiles of mergers are not significantly more asymmetric than those of non-mergers.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present coordinated observations of GRB 170202A carried out by the Zadko and the Virgin Island Robotic Telescopes. The observations started 59 s after the event trigger, and provided nearly continuous coverage for two days, due to the unique locations of these telescopes. We clearly detected an early rise in optical emission, followed by late optical flares. By complementing these data with archival observations, we show that GRB 170202A is well described by the standard fireball model if multiple reverse shocks are taken into account. Its fireball is evidenced as expanding within a constant-density interstellar medium, with most burst parameters being consistent with the usual ranges found in the literature. The electron and magnetic energy parameters (<jats:italic>ϵ</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub>, <jats:italic>ϵ</jats:italic> <jats:sub> <jats:italic>B</jats:italic> </jats:sub>) are orders of magnitude smaller than the commonly assumed values. We argue that the global fit of the fireball model achieved by our study should be possible for any burst, pending the availability of a sufficiently comprehensive data set. This conclusion emphasizes the crucial importance of coordinated observation campaigns of gamma-ray bursts, such as the one central to this work, to answer outstanding questions about the underlying physics driving these phenomena.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The very careful Event Horizon Telescope estimate of the mass of the supermassive black hole at the center of the giant cD galaxy M87, allied with recent high-quality photometric and spectroscopic measurements, yields a proper dark/luminous mass decomposition from the galaxy center to its virial radius. That provides us with decisive information on crucial cosmological and astrophysical issues. The dark and the standard matter distributions in a wide first time detected galaxy region under the supermassive black hole gravitational control. The well-known supermassive black hole mass versus stellar dispersion velocity relationship at the highest galaxy masses implies an exotic growth of the former. This may be the first case in which one can argue that the supermassive black hole mass growth was also contributed by the dark matter component. A huge dark matter halo core in a galaxy with inefficient baryonic feedback is present and consequently constrains the nature of the dark halo particles. The unexplained entanglement between dark/luminous structural properties, already emerged in disk systems, also appears.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The radiation energy of X-ray pulsars is mainly concentrated in the high-energy ray bands, so processing high-energy photon signals is helpful for discovering some young and active pulsars. To quickly and accurately detect effective pulsar signals from a large number of samples within a finite observation time, an automatic identification algorithm for pulsar candidates based on X-ray observations is developed in this paper. First, the autocorrelation operation is used to improve the signal-to-noise ratio of the profile and solve the initial phase misalignment problem. Then, the candidate frequency range is expanded, and the output signal is folded according to these frequencies to obtain a series of profiles. The six statistical features of these profiles are extracted to generate frequency-feature curves. Compared with the traditional epoch folding method, the frequency-feature curves show more consistent characteristics. To improve the classification accuracy, the frequency-feature curves are converted into two-dimensional images, and ConvNets are used for deep feature extraction and classification. A simulation method based on the nonhomogeneous Poisson process is utilized to create the training set, and generative adversarial networks are used for data augmentation to solve the class imbalance problem caused by limited pulsar samples. Finally, the RXTE observation data of PSR B0531+21, PSR B0540-69, and PSR B1509-58 are selected for testing. The experimental results show that the highest recall and precision reached 0.996 and 0.983, respectively. Demonstrating the considerable potential of this method for identifying pulsar candidates based on X-ray observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We compile a sample of 92 active galactic nuclei (AGNs) at <jats:italic>z</jats:italic> &lt; 0.75 with <jats:italic>gri</jats:italic> photometric light curves from the archival data of the Zwicky Transient Facility and measure the accretion disk sizes via continuum reverberation mapping. We employ Monte Carlo simulation tests to assess the influences of data sampling and broad emission lines and select out the sample with adequately high sampling cadences (3 days apart in average) and minimum contaminations of broad emission lines. The interband time delays of individual AGNs are calculated using the interpolated cross-correlation function, and then these delays are fitted with a generalized accretion disk model, in which interband time delays are a power function of wavelength, black hole mass, and luminosity. A Markov Chain Monte Carlo method is adopted to determine the best parameter values. Overall the interband time delays can be fitted with the <jats:italic>τ</jats:italic> ∝ <jats:italic>λ</jats:italic> <jats:sup>4/3</jats:sup> relation as predicted from a steady-state, optically thick, geometrically thin accretion disk; however, the yielded disk size is systematically larger than expected, although the ratio of the measured to theoretical disk sizes depends on using the emissivity- or responsivity-weighted disk radius. These results are broadly consistent with previous studies, all together raising a puzzle about the “standard” accretion disk model.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Transmission spectroscopy is one of the premier methods used to probe the temperature, composition, and cloud properties of exoplanet atmospheres. Recent studies have demonstrated that the multidimensional nature of exoplanet atmospheres—due to nonuniformities across the day–night transition and between the morning and evening terminators—can strongly influence transmission spectra. However, the computational demands of 3D radiative-transfer techniques have precluded their usage within atmospheric retrievals. Here we introduce TRIDENT, a new 3D radiative-transfer model which rapidly computes transmission spectra of exoplanet atmospheres with day–night, morning–evening, and vertical variations in temperature, chemical abundances, and cloud properties. We also derive a general equation for transmission spectra, accounting for 3D atmospheres, refraction, multiple scattering, ingress/egress, grazing transits, stellar heterogeneities, and nightside thermal emission. After introducing TRIDENT’s linear-algebra-based approach to 3D radiative transfer, we propose new parametric prescriptions for 3D temperature and abundance profiles and 3D clouds. We show that multidimensional transmission spectra exhibit two significant observational signatures: (i) day–night composition gradients alter the relative amplitudes of absorption features; and (ii) morning–evening composition gradients distort the peak-to-wing contrast of absorption features. Finally, we demonstrate that these signatures of multidimensional atmospheres incur residuals &gt;100 ppm compared to 1D models, rendering them potentially detectable with the James Webb Space Telescope. TRIDENT’s rapid radiative transfer, coupled with parametric multidimensional atmospheres, unlocks the final barrier to 3D atmospheric retrievals.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We examine the contribution of high-redshift (<jats:italic>z</jats:italic> &gt; 6) active galactic nuclei (AGNs) to cosmic hydrogen reionization, by tracing the growth and ionizing output of the first generation of supermassive black holes (SMBHs). Our calculations are anchored to the observed population of <jats:italic>z</jats:italic> ≃ 6 quasars, and trace back the evolving spectral energy distributions (SEDs) of the accretion flows that power these early AGNs and consider a variety of growth histories, including super-Eddington accretion. Compared to a fixed-shape SED, the evolving thin disks produce ionizing radiation that is higher by up to ∼80%. Across a variety of SMBH growth scenarios, the contribution of AGNs to reionization is limited to late epochs (<jats:italic>z</jats:italic> &lt; 7), and remains subdominant compared to star-forming galaxies. This conclusion holds irrespective of the (still unknown) space density of low-luminosity <jats:italic>z</jats:italic> = 6 AGNs, and for growth scenarios that allow super-Eddington accretion. The contribution of AGNs to reionization can extend to earlier epochs (<jats:italic>z</jats:italic> ≳ 8) in scenarios with relatively slow SMBH mass growth, i.e., for low accretion rates and/or high spins. We finally demonstrate that our framework can reproduce the observed quasar proximity-zone sizes, and that compact proximity zones around <jats:italic>z</jats:italic> = 6 quasars can be explained by the late onset of super-Eddington accretion.</jats:p>