Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We present the results of a detailed investigation of the poorly studied X-ray pulsar (XRP) XTE J1858+034 based on the data obtained with the NuSTAR observatory during the outburst of the source in 2019. The spectral analysis resulted in the discovery of a cyclotron absorption feature in the source spectrum at ∼48 keV in both the pulse phase-averaged and resolved spectra. Accurate X-ray localization of the source using the NuSTAR and Chandra observatories allowed us to accurately determine the position of the X-ray source and identify the optical companion of the pulsar. The analysis of the counterpart properties suggested that the system is likely a symbiotic binary hosting an XRP and a late-type companion star of the K-M classes rather than a Be X-ray binary as previously suggested.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Solar flares and plasma eruptions are sudden releases of magnetic energy stored in the plasma atmosphere. To understand the physical mechanisms governing their occurrences, three-dimensional magnetic fields from the photosphere up to the corona must be studied. The solar photospheric magnetic fields are observable, whereas the coronal magnetic fields cannot be measured. One method for inferring coronal magnetic fields is performing data-driven simulations, which involves time-series observational data of the photospheric magnetic fields with the bottom boundary of magnetohydrodynamic simulations. We developed a data-driven method in which temporal evolutions of the observational vector magnetic field can be reproduced at the bottom boundary in the simulation by introducing an inverted velocity field. This velocity field is obtained by inversely solving the induction equation and applying an appropriate gauge transformation. Using this method, we performed a data-driven simulation of successive small eruptions observed by the Solar Dynamics Observatory and the Solar Magnetic Activity Telescope in 2017 November. The simulation well reproduced the converging motion between opposite-polarity magnetic patches, demonstrating successive formation and eruptions of helical flux ropes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Taking into account the terrestrial experiments and the recent astrophysical observations of neutron stars and gravitational-wave signals, we impose restrictions on the equation of state (EoS) for isospin-asymmetric nuclear matter. Using the relativistic mean-field model with SU(3) flavor symmetry, we investigate the impacts of effective nucleon mass, nuclear incompressibility, and slope parameter of nuclear symmetry energy on the nuclear and neutron star properties. It is found that the astrophysical information of massive neutron stars and tidal deformabilities, as well as the nuclear experimental data, plays an important role to restrict the EoS for neutron stars. In particular, the softness of the nuclear EoS due to the existence of hyperons in the core gives stringent constraints on those physical quantities. Furthermore, it is possible to put limits on the curvature parameter of nuclear symmetry energy by means of nuclear and astrophysical calculations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Observations at intermediate redshifts reveal the presence of numerous compact, weak Mg <jats:sc>ii</jats:sc> absorbers with near to supersolar metallicities, often surrounded by extended regions that produce C <jats:sc>iv</jats:sc> and/or O <jats:sc>vi</jats:sc> absorption, in the circumgalactic medium at large impact parameters from luminous galaxies. Their origin and nature remain unclear. We hypothesize that undetected satellite dwarf galaxies are responsible for producing some of these weak Mg <jats:sc>ii</jats:sc> absorbers. We test our hypothesis using gas dynamical simulations of galactic outflows from a dwarf galaxy with a halo mass of 5 × 10<jats:sup>9</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, as might be falling into a larger <jats:italic>L</jats:italic>* halo at <jats:italic>z</jats:italic> = 2. We find that thin, filamentary, weak Mg <jats:sc>ii</jats:sc> absorbers (≲100 pc) are produced in two stages: (1) when shocked core-collapse supernova (SN II)–enriched gas descending in a galactic fountain gets shock compressed by upward flows driven by subsequent SN II and cools (phase 1) and, later, (2) during an outflow driven by Type Ia supernovae that shocks and sweeps up pervasive SN II–enriched gas, which then cools (phase 2). The Mg <jats:sc>ii</jats:sc> absorbers in our simulations are continuously generated by shocks and cooling with moderate metallicity ∼0.1–0.2 <jats:italic>Z</jats:italic> <jats:sub>⊙</jats:sub> but low column density &lt;10<jats:sup>12</jats:sup> cm<jats:sup>−2</jats:sup>. They are also surrounded by larger (0.5–1 kpc) C <jats:sc>iv</jats:sc> absorbers that seem to survive longer. Larger-scale (&gt;1 kpc) C <jats:sc>iv</jats:sc> and O <jats:sc>vi</jats:sc> clouds are also produced in both expanding and shocked SN II–enriched gas. Observable ion distributions from our models appear well converged at our standard resolution (12.8 pc). Our simulation highlights the possibility of dwarf galactic outflows producing highly enriched multiphase gas.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Large-scale magnetic field is believed to play a key role in launching and collimating jets/outflows. It was found that advection of the external field by a geometrically thin disk is rather inefficient, while the external weak field may be dragged inwards by fast radially moving tenuous and/or hot gas above the thin disk. We investigate the field advection in a thin (cold) accretion disk covered with hot corona, in which turbulence is responsible for the angular momentum transfer of the gas in the disk and corona. The radial velocity of the gas in the corona is significantly higher than that in the thin disk. Our calculations show that the external magnetic flux is efficiently transported inwards by the corona, and the field line is strongly inclined toward the disk surface, which helps to launch outflows. The field configurations are consistent with those observed in the numerical simulations. The strength of the field is substantially enhanced in the inner region of the disk (usually several orders of magnitude higher than the external field strength), which is able to drive a fraction of gas in the corona into outflows. This mechanism may be useful in explaining the observational features in X-ray binaries and active galactic nuclei. Our results may help in understanding the physics of the magnetohydrodynamic simulations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present results of spectroscopic monitoring observations of the ultraluminous infrared galaxy F01004−2237. This galaxy was observed to undergo changes in its optical spectrum, detected by comparing a spectrum from 2015 with one from 2000. These changes were coincident with photometric brightening. The main changes detected in the optical spectrum are enhanced He <jats:sc>ii</jats:sc> <jats:italic>λ</jats:italic>4686 emission and the appearance of He <jats:sc>i</jats:sc> <jats:italic>λ</jats:italic>3898,<jats:italic>λ</jats:italic>5876 emission lines. The favored interpretation of these changes was that of a tidal disruption event (TDE) happening in 2010. However, subsequent work suggested that these changes are caused by another hitherto unknown effect related to variations in the accretion rate in the active galactic nucleus (AGN). Our optical spectroscopic monitoring observations show that the evolution of the He lines is in line with the evolution seen in TDEs and opposite of what is observed from reverberation-mapping studies of AGNs, renewing the discussion of the interpretation of the flare as a TDE.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This work presents results from simulations of the 2000 July 14 (“Bastille Day”) solar proton event. We used the Energetic Particle Radiation Environment Model (EPREM) and the CORona-HELiosphere (CORHEL) software suite within the SPE Threat Assessment Tool (STAT) framework to model proton acceleration to GeV energies due to the passage of a CME through the low solar corona, and we compared the model results to GOES-08 observations. The coupled simulation models particle acceleration from 1 to 20 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub>, after which it models only particle transport. The simulation roughly reproduces the peak event fluxes and the timing and spatial location of the energetic particle event. While peak fluxes and overall variation within the first few hours of the simulation agree well with observations, the modeled CME moves beyond the inner simulation boundary after several hours. The model therefore accurately describes the acceleration processes in the low corona and resolves the sites of most rapid acceleration close to the Sun. Plots of integral flux envelopes from multiple simulated observers near Earth further improve the comparison to observations and increase potential for predicting solar particle events. Broken power-law fits to fluence spectra agree with diffusive acceleration theory over the low energy range. Over the high energy range, they demonstrate the variability in acceleration rate and mirror the interevent variability observed in solar cycle 23 ground-level enhancements. We discuss ways to improve STAT predictions, including using corrected GOES energy bins and computing fits to the seed spectrum. This paper demonstrates a predictive tool for simulating low-coronal solar energetic particle acceleration.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Binary millisecond pulsars (MSPs) are believed to have descended from low-mass X-ray binaries (LMXBs), which have experienced substantial mass transfer and tidal circularization. Therefore, they should have very circular orbits. However, the discovery of several eccentric binary MSPs (with eccentricity <jats:italic>e</jats:italic> ∼ 0.01–0.1) challenges this standard picture. Three models have been proposed thus far based on accretion-induced collapse of massive white dwarfs (WDs), neutron star–strange star transition, and formation of circumbinary disks. All of them are subject to various uncertainties and are not entirely consistent with observations. Here, we propose an alternative model that takes into account the influence of thermonuclear flashes on proto-WDs. We assume that the flashes lead to asymmetrical mass ejection, which imparts a mild kick to the proto-WDs. By simulating orbital changes of binary MSPs with multiple shell flashes, we show that it is possible to reproduce the observed eccentricities, provided that the kick velocities are around a few km s<jats:sup>−1</jats:sup>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Although the standard cosmological model, the so-called Λ cold dark matter (ΛCDM), appears to fit well observations at the cosmological level, it is well known that it possesses several inconsistencies at the galactic scales. In order to address the problems of the ΛCDM on a small scale, some alternative models have been proposed. Among the most popular candidates, the proposal that dark matter in the universe is made of ultralight bosons is a strong candidate today. For this work, we study through an analytical approach the consequences arising from comparing the Spitzer Photometry and Accurate Rotation Curves catalog observed-baryon acceleration correlation with the scalar field dark matter model. We carry out such analysis either considering the features of galactic halos extracted from structure-formation simulations or considering the existence of other non-dark-matter elements in the whole system (such as baryons or a supermassive black hole). Specifically, we address a recent claim that the model is not capable of reproducing a constant surface density in the core, in contrast to what observations suggest for a host of galaxies with different sizes and morphologies. In this direction, we show that this discrepancy can be alleviated once the contributions of non-dark-matter constituents in the whole galactic system are taken into account. Additionally, we find that a mass of <jats:italic>m</jats:italic> ≃ 1.41 × 10<jats:sup>−22</jats:sup> eV/<jats:italic>c</jats:italic> <jats:sup>2</jats:sup> is capable of reproducing all of our findings and correctly adjusting the rotation curves coming from the Milky Way galaxy.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The origin of hard X-rays and <jats:italic>γ</jats:italic>-rays emitted from the solar atmosphere during occulted solar flares is still debated. The hard X-ray emissions could come from flaring loop tops rising above the limb or coronal mass ejection shock waves, two by-products of energetic solar storms. For the shock scenario to work, accelerated particles must be released on magnetic field lines rooted on the visible disk and precipitate. We present a new Monte Carlo code that computes particle acceleration at shocks propagating along large coronal magnetic loops. A first implementation of the model is carried out for the 2014 September 1 event, and the modeled electron spectra are compared with those inferred from Fermi Gamma-ray Burst Monitor (GBM) measurements. When particle diffusion processes are invoked, our model can reproduce the hard electron spectra measured by GBM nearly 10 minutes after the estimated on-disk hard X-rays appear to have ceased from the flare site.</jats:p>