Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>As the standard gamma-ray burst (GRB) prompt-emission model, the internal shock (IS) model can reproduce the fast-rise and slow-decay features of the pulses in the GRB light curve. The time- and energy-dependent polarization can deliver important physical information on the emission region and can be used to test models. Polarization predictions for the GRB prompt phase with the magnetized IS model should be investigated carefully. The magnetic field of the magnetized IS model is very likely to be mixed and decays with radius. The synchrotron emission in the presence of such a decaying magnetic field can recover the Band-like spectrum of the GRB prompt phase. We investigate the dependence of the polarization of GRB prompt emission on both time and energy in the framework of the magnetized IS model. Due to the large range of parameters, it is hard to distinguish the magnetized IS model and the magnetic-reconnection model through polarization degree (PD) curves. The energy-dependent PD could increase toward the high-energy band for the magnetized IS model, while it decreases to zero above the megaelectronvolt band for the dissipative photosphere model. Therefore, we conclude that the energy dependence of PD can be used to distinguish these two models for the GRB prompt emission. Finally, we find that, independent of the observational energy band, the profiles of the <jats:italic>ξ</jats:italic> <jats:sub> <jats:italic>B</jats:italic> </jats:sub> − PD curve for the time-integrated and time-resolved PDs are very similar, where <jats:italic>ξ</jats:italic> <jats:sub> <jats:italic>B</jats:italic> </jats:sub> is the magnetic field strength ratio of the ordered component to the random component.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We have discovered a new candidate redback millisecond pulsar binary near the center of the error ellipse of the bright unassociated Fermi-LAT <jats:italic>γ</jats:italic>-ray source 4FGL J0940.3–7610. The candidate counterpart is a variable optical source that also shows faint X-ray emission. Optical photometric and spectroscopic monitoring with the SOAR telescope indicates that the companion is a low-mass star in a 6.5 hr orbit around an invisible primary, showing both ellipsoidal variations and irradiation and consistent with the properties of known redback millisecond pulsar binaries. Given the orbital parameters, preliminary modeling of the optical light curves suggests an edge-on inclination and a low-mass (∼1.2–1.4 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) neutron star, along with a secondary mass somewhat more massive than the typical ≳0.4 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. This combination of inclination and secondary properties could make radio eclipses more likely for this system, explaining its previous nondiscovery in radio pulsation searches. Hence, 4FGL J0940.3–7610 may be a strong candidate for a focused search for <jats:italic>γ</jats:italic>-ray pulsations to enable the future detection of a millisecond pulsar.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a broadband X-ray timing study of the variations in pulse behavior with the superorbital cycle in the low-mass X-ray binary Her X-1. This source shows a 35 day superorbital modulation in X-ray flux that is likely caused by occultation by a warped, precessing accretion disk. Our data set consists of four joint XMM-Newton and NuSTAR observations of Her X-1 which sample a complete superorbital cycle. We focus our analysis on the first and fourth observations, which occur during the bright “main-on” phase, because these observations have strongly detected pulsations. We added an archival XMM-Newton observation during the “short-on” phase of the superorbital cycle because our observations at that phase are lower in signal to noise. We find that the energy-resolved pulse profiles show the same shape at similar superorbital phases, and the profiles are consistent with expectations from a precessing disk. We demonstrate that a simple precessing accretion disk model is sufficient to reproduce the observed pulse profiles. The results of this model suggest that the similarities in the observed pulse profiles are due to reprocessing by a precessing disk that has returned to its original precession phase. We determine that the broadband spectrum is well fit by an absorbed power law with a soft blackbody component and show that the spectral continuum also exhibits a dependence on the superorbital cycle. We also present a brief analysis of the energy-resolved light curves of a pre-eclipse dip, which shows soft X-ray absorption and hard X-ray variability during the dip.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In the past few years, approximate Bayesian Neural Networks (BNNs) have demonstrated the ability to produce statistically consistent posteriors on a wide range of inference problems at unprecedented speed and scale. However, any disconnect between training sets and the distribution of real-world objects can introduce bias when BNNs are applied to data. This is a common challenge in astrophysics and cosmology, where the unknown distribution of objects in our universe is often the science goal. In this work, we incorporate BNNs with flexible posterior parameterizations into a hierarchical inference framework that allows for the reconstruction of population hyperparameters and removes the bias introduced by the training distribution. We focus on the challenge of producing posterior PDFs for strong gravitational lens mass model parameters given Hubble Space Telescope–quality single-filter, lens-subtracted, synthetic imaging data. We show that the posterior PDFs are sufficiently accurate (statistically consistent with the truth) across a wide variety of power-law elliptical lens mass distributions. We then apply our approach to test data sets whose lens parameters are drawn from distributions that are drastically different from the training set. We show that our hierarchical inference framework mitigates the bias introduced by an unrepresentative training set’s interim prior. Simultaneously, we can precisely reconstruct the population hyperparameters governing our test distributions. Our full pipeline, from training to hierarchical inference on thousands of lenses, can be run in a day. The framework presented here will allow us to efficiently exploit the full constraining power of future ground- and space-based surveys (https://github.com/swagnercarena/ovejero).</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the relation of black hole mass versus host stellar mass and that of mass accretion rate versus star formation rate (SFR) in moderately luminous (<jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}{L}_{\mathrm{bol}}\sim 44.5\mbox{--}46.5\ \mathrm{erg}\,{{\rm{s}}}^{-1}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabdf55ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>), X-ray selected broad-line active galactic nuclei (AGNs) at <jats:italic>z</jats:italic> = 1.18–1.68 in the Subaru/XMM-Newton Deep Field. The far-infrared to far-ultraviolet spectral energy distributions of 85 AGNs are reproduced with the latest version of Code Investigating GALaxy Emission (<jats:monospace>CIGALE</jats:monospace>), where the AGN clumpy torus model <jats:monospace>SKIRTOR</jats:monospace> is implemented. Most of their hosts are confirmed to be main-sequence star-forming galaxies. We find that the mean ratio of the black hole mass (<jats:italic>M</jats:italic> <jats:sub>BH</jats:sub>) to the total stellar mass (<jats:italic>M</jats:italic> <jats:sub>stellar</jats:sub>) is <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}{M}_{\mathrm{BH}}/{M}_{\mathrm{stellar}}=-2.2$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabdf55ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, which is similar to the local black hole–to–bulge mass ratio. This suggests that if the host galaxies of these moderately luminous AGNs at <jats:italic>z</jats:italic> ∼ 1.4 are dominated by bulges, they already established the local black hole mass–bulge mass relation; if they are disk dominant, their black holes are overmassive relative to the bulges. The AGN bolometric luminosities and SFR show a good correlation with ratios higher than that expected from the local black hole-to-bulge mass relation, suggesting that these AGNs are in a SMBH-growth dominant phase.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this paper the author applies the scalaron gravity field and corresponding Yukawa coupling (derived by Kalita from the consideration of quantum vacuum fluctuations with UV and IR scales) to examine the scales of stellar orbits near the Galactic Center black hole, which can be probed by upcoming astrometric facilities for constraining modified gravity. Through the assumption that the pericenter shift of stellar orbits becomes of the order of spin and quadrupole moment effects of the black hole, it is found that for semimajor axes bounded below by time scales of gravitational wave emission and stellar age and above by S-2 like orbits (<jats:italic>a</jats:italic> = 990 au) the black hole spin with 0.1 ≤ <jats:italic>χ</jats:italic> ≤ 0.980 is eligible to probe scalaron masses within (10<jats:sup>−22</jats:sup>–10<jats:sup>−18</jats:sup>) eV and also the scalaron coupling, <jats:italic>α</jats:italic> = 2.73 × 10<jats:sup>−4</jats:sup> derived earlier from quantum vacuum fluctuations. The orbital eccentricities are considered as <jats:italic>e</jats:italic> = 0.1, 0.5, and 0.9. Astrometric categories with <jats:italic>σ</jats:italic> = 10, 50, and 100 <jats:italic>μ</jats:italic>as are used to probe the time scales and number of observing campaigns required for simultaneously constraining scalaron mass and black hole spin. It is found that extraction of black hole spin is possible within <jats:italic>a</jats:italic> = (74–433) au through 10 <jats:italic>μ</jats:italic>as facilities. The present analysis is realized to be an independent opportunity to simultaneously constrain scalaron coupling, black hole spin, and tidal charge and hence to reveal the true nature of the spacetime structure of our nearest supermassive black hole.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>There is increasing evidence that magnetohydrodynamic waves play an important role in the propagation and dissipation of energy in the solar atmosphere. Here we investigate how torsional Alfvén waves driven at the photosphere can transport energy to an overlying coronal magnetic loop and explore their ability to heat the plasma. We consider a coronal loop whose feet are embedded in the partially ionized chromosphere. A broadband driver at the photosphere excites torsional Alfvén waves that propagate upward to the coronal loop. By means of numerical computations under the stationary-state assumption, we study the transmission of wave energy to the loop and the heating associated with ohmic diffusion and ion–neutral collisions. We find that wave transmission to the loop is heavily affected by the presence of cavity resonances when the frequency of the driver matches an eigenfrequency of the loop. A tremendous amount of wave energy is channeled to the coronal loop for those particular frequencies. The transmitted energy surpasses by many orders of magnitude the requirements to balance thermal radiation. However, dissipation is so weak in the coronal plasma that only a tiny percentage of the energy budget is converted into heat, which is not enough to compensate for radiative losses. Most of the energy simply leaks back to the chromosphere. Conversely, dissipation is much more efficient in the lower atmosphere, and wave heating can locally balance a significant fraction of radiation in the chromosphere. We argue that nonlinear effects such as turbulence triggered by the Kelvin–Helmholtz instability should enhance the heating efficiency at coronal heights.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The discovery of a planet orbiting around Proxima Centauri, the closest star to the Sun, opens new avenues for the remote observations of the atmosphere and surface of an exoplanet, Proxima b. To date, three-dimensional (3D) general circulation models (GCMs) are the best available tools to investigate the properties of the exo-atmospheres, waiting for the next generation of space- and ground-based telescopes. In this work, we use the Planet Simulator (PlaSim), an intermediate-complexity, flexible and fast 3D GCM, suited to handle all the orbital and physical parameters of a planet and to study the dynamics of its atmosphere. Assuming an Earth-like atmosphere and a 1:1 spin/orbit configuration (tidal locking), our simulations of Proxima b are consistent with a dayside open ocean planet with a superrotating atmosphere. Moreover, because of the limited representation of the radiative transfer in PlaSim, we compute the spectrum of the exoplanet with an offline radiative transfer code with a spectral resolution of 1 nm. This spectrum is used to derive the thermal phase curves for different orbital inclination angles. In combination with instrumental detection sensitivities, the different thermal phase curves are used to evaluate observation conditions at ground level (e.g., ELT) or in space (e.g., James Webb Space Telescope (JWST)). We estimated the exposure time to detect the Proxima b (assuming an Earth-like atmosphere) thermal phase curve in the far-IR with JWST with signal-to-noise ratio ≃1. Under the hypothesis of total noise dominated by shot noise, neglecting other possible extra contribution producing a noise floor, the exposure time is equal to 5 hr for each orbital epoch.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Eridanus II (Eri II) is an ultrafaint dwarf (UFD) galaxy (<jats:italic>M</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> = −7.1) located at a distance close to the Milky Way virial radius. Early shallow color–magnitude diagrams (CMDs) indicated that it possibly hosted an intermediate-age or even young stellar population, which is unusual for a galaxy of this mass. In this paper, we present new Hubble Space Telescope/Advanced Camera for Surveys CMDs reaching the oldest main-sequence turnoff with excellent photometric precision and derive a precise star formation history (SFH) for this galaxy through CMD fitting. This SFH shows that the bulk of the stellar mass in Eri II formed in an extremely short star formation burst at the earliest possible time. The derived star formation rate profile has a width at half maximum of 500 Myr and reaches a value compatible with null star formation 13 Gyr ago. However, tests with mock stellar populations and with the CMD of the globular cluster M92 indicate that the star formation period could be shorter than 100 Myr. From the quantitative determination of the amount of mass turned into stars in this early star formation burst ( ∼2 × 10<jats:sup>5</jats:sup> <jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub>) we infer the number of supernova (SN) events and the corresponding energy injected into the interstellar medium. For reasonable estimates of the Eri II virial mass and values of the coupling efficiency of the SN energy, we conclude that Eri II could be quenched by SN feedback alone, thus casting doubts on the need to invoke cosmic reionization as the preferred explanation for the early quenching of old UFD galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Brightness-weighted differential source counts <jats:italic>S</jats:italic> <jats:sup>2</jats:sup> <jats:italic>n</jats:italic>(<jats:italic>S</jats:italic>) spanning the eight decades of flux density between 0.25 <jats:italic>μ</jats:italic>Jy and 25 Jy at 1.4 GHz were measured from (1) the confusion brightness distribution in the MeerKAT DEEP2 image below 10 <jats:italic>μ</jats:italic>Jy, (2) counts of DEEP2 sources between 10 <jats:italic>μ</jats:italic>Jy and 2.5 mJy, and (3) counts of NVSS sources stronger than 2.5 mJy. We present our DEEP2 catalog of 1.7 × 10<jats:sup>4</jats:sup> discrete sources complete above <jats:italic>S</jats:italic> = 10 <jats:italic>μ</jats:italic>Jy over Ω = 1.04 deg<jats:sup>2</jats:sup>. The brightness-weighted counts converge as <jats:italic>S</jats:italic> <jats:sup>2</jats:sup> <jats:italic>n</jats:italic>(<jats:italic>S</jats:italic>) ∝ <jats:italic>S</jats:italic> <jats:sup>1/2</jats:sup> below <jats:italic>S</jats:italic> = 10 <jats:italic>μ</jats:italic>Jy, so &gt;99% of the Δ<jats:italic>T</jats:italic> <jats:sub>b</jats:sub> ∼ 0.06 K sky brightness produced by active galactic nuclei and ≈96% of the Δ<jats:italic>T</jats:italic> <jats:sub>b</jats:sub> ∼ 0.04 K added by star-forming galaxies has been resolved into sources with <jats:italic>S</jats:italic> ≥ 0.25 <jats:italic>μ</jats:italic>Jy. The Δ<jats:italic>T</jats:italic> <jats:sub>b</jats:sub> ≈ 0.4 K excess brightness measured by ARCADE 2 cannot be produced by faint sources smaller than ≈50 kpc if they cluster like galaxies.</jats:p>