Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Using neural networks, we integrate the ability to account for Doppler smearing due to a pulsar’s orbital motion with the pulsar population synthesis package <jats:sc>psrpoppy</jats:sc> to develop accurate modeling of the observed binary pulsar population. As a first application, we show that binary neutron star systems where the two components have highly unequal mass are, on average, easier to detect than systems that are symmetric in mass. We then investigate the population of ultracompact (1.5 minutes ≤ <jats:italic>P</jats:italic> <jats:sub>b</jats:sub> ≤ 15 minutes) neutron star–white dwarf (NS–WD) and double neutron star (DNS) systems, which are promising sources for the Laser Interferometer Space Antenna gravitational-wave detector. Given the nondetection of these systems in radio surveys thus far, we estimate a 95% confidence upper limit of ∼1450 and ∼1100 ultracompact NS–WD and DNS systems in the Milky Way that are beaming toward the Earth, respectively. We also show that using survey integration times in the range 20 s–200 s with time-domain resampling will maximize the signal-to-noise ratio as well as the probability of detection of these ultracompact binary systems. Among all the large-scale radio pulsar surveys, those that are currently being carried out using archival data collected with the Arecibo radio telescope have a ∼50%–80% chance of detecting at least one of these systems using current integration integration times and ∼80%–95% using optimal integration times in the next several years.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We measure chemical abundances for over 20 elements of 15 N-rich field stars with high-resolution (<jats:italic>R</jats:italic> ∼ 30,000) optical spectra. We find that Na, Mg, Al, Si, and Ca abundances of our N-rich field stars are mostly consistent with those of stars from globular clusters (GCs). Seven stars are estimated to have [Al/Fe ] &gt; 0.5, which is not found in most GC “first generation” stars. On the other hand, <jats:italic>α</jats:italic> element abundances (especially Ti) could show distinguishable differences between in situ stars and accreted stars. We discover that one interesting star, with consistently low [Mg/Fe], [Si/Fe], [Ca/Fe], [Ti/Fe], [Sc/Fe], [V/Fe], and [Co/Fe], show similar kinematics and [Ba/Eu] as other stars from the dissolved dwarf galaxy “Gaia–Sausage–Enceladus.” The <jats:italic>α</jats:italic>-element abundances and the iron-peak element abundances of the N-rich field stars with metallicities − 1.25 ≤ [Fe/H] ≤ − 0.95 show consistent values with Milky Way field stars (we refer to Milky Way field stars as Milky Way halo field stars unless otherwise specified in this paper) rather than stars from dwarf galaxies, indicating that they were formed in situ. In addition, the neutron-capture elements of N-rich field stars show that most of them could be enriched by asymptotic giant branch stars with masses around 3–5 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The progenitors of Type Ia supernovae (SNe Ia) are debated, particularly the evolutionary state of the binary companion that donates mass to the exploding carbon–oxygen white dwarf. In our previous work, we presented hydrodynamic models and optically thin radio synchrotron light curves of SNe Ia interacting with detached, confined shells of CSM, representing CSM shaped by novae. In this work, we extend these light curves to the optically thick regime, considering both synchrotron self-absorption and free–free absorption. We obtain simple formulae to describe the evolution of optical depth seen in the simulations, allowing optically thick light curves to be approximated for arbitrary shell properties. We then demonstrate the use of this tool by interpreting published radio data. First, we consider the nondetection of PTF11kx—an SN Ia known to have a detached, confined shell—and we find that the nondetection is consistent with current models for its CSM, and that observations at a later time would have been useful for this event. Second, we statistically analyze an ensemble of radio nondetections for SNe Ia with no signatures of interaction. We find that shells with masses (10<jats:sup>−4</jats:sup>–0.3) <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> located (10<jats:sup>15</jats:sup>–10<jats:sup>16</jats:sup>) cm from the progenitor are currently not well constrained by radio datasets, due to their dim, rapidly evolving light curves.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Whether or not dark energy evolves with time may be determined by the nonparametric method. In order to avoid instability of the derivative for the functional data, we linearize the luminosity-distance integral formula in near-flat space by adopting Lagrange interpolation for the numerical integral, and proposing a method of combining principal component analysis (PCA) and biased estimation on the basis of ridge regression analysis to reconstruct the regression parameters. We also present a principal component selection criterion to better distinguish between ΛCDM and <jats:italic>w</jats:italic>(<jats:italic>z</jats:italic>) ≠ −1 models by reconstruction. We define the type I error as the situation where <jats:italic>w</jats:italic> <jats:sub>true</jats:sub> = −1 but <jats:italic>w</jats:italic> <jats:sub>recon</jats:sub> ≠ −1, and the type II error as the situation where <jats:italic>w</jats:italic> <jats:sub>true</jats:sub> ≠ −1 but <jats:italic>w</jats:italic> <jats:sub>recon</jats:sub> = −1; we use the various <jats:italic>w</jats:italic>(<jats:italic>z</jats:italic>) functions to test the method. The preliminary test results demonstrate that the PCA-biased method can be used to determine the most probable behavior of <jats:italic>w</jats:italic>(<jats:italic>z</jats:italic>). Finally, we apply this method to recent supernova measurements, reconstructing the continuous history of <jats:italic>w</jats:italic>(<jats:italic>z</jats:italic>) out to redshift <jats:italic>z</jats:italic> = 1.5.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent studies of gamma-ray, cosmic-ray, and radio data put stringent constraints on the fraction of primordial black holes (PBHs) in our universe. In this article, we propose a new indirect method in using the X-ray luminosity data of cool-core clusters to constrain the evaporating PBH fraction for the monochromatic, log-normal and power-law mass distributions. The present results show that the amount of evaporating PBHs only constitutes a minor component of dark matter for a large parameter space. The constraints are consistent with and close to that obtained from other cosmic-ray and multiwavelength observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Ultralight dark matter (ULDM) is currently one of the most popular classes of cosmological dark matter. The most important advantage is that ULDM with mass <jats:italic>m</jats:italic> ∼ 10<jats:sup>−22</jats:sup> eV can account for the small-scale problems encountered in the standard cold dark matter model like the core–cusp problem, missing satellite problem, and the too-big-to-fail problem in galaxies. In this paper, we formulate a new simple model-independent analysis using the Spitzer Photometry and Accurate Rotation Curves data to constrain the range of ULDM mass. In particular, the most stringent constraint comes from the data of a galaxy ESO563–G021, which can conservatively exclude a ULDM mass range <jats:italic>m</jats:italic> = (0.14–3.11) × 10<jats:sup>−22</jats:sup> eV. This model-independent excluded range is consistent with many bounds obtained by recent studies and it suggests that the ULDM proposal may not be able to alleviate the small-scale problems.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Chromospheric condensation is a brief episode of downflow often accompanying energy release and evaporation in a solar flare. While this component of a flare reflects the energy release process only indirectly, it can be observed at high spatial and temporal resolution, even from the ground. It appears in spectroscopic observations of cooler lines, formed below ∼10<jats:sup>5</jats:sup> K, as a redshift that peaks and decays after less than 1 minute. In order to use this signature to infer characteristics of solar flare energy release, it is important to establish quantitative relationships with properties of the condensation. The initial investigation reported here does so after restricting consideration to energy transport via thermal conduction into a simplified, stratified chromosphere. We develop an analytical expression for the decay of a condensation propagating into a stratified atmosphere. This model provides a relationship between shock velocity and preshock density structure. We also use one-dimensional gasdynamic simulations to explore the dynamics of these shocks as they penetrate into the stratified chromosphere. We find that the peak downflow speed primarily reflects the energy flux into the chromosphere, while the product of this velocity and the redshift duration is proportional to the preshock density scale height as <jats:italic>H</jats:italic> ≃ 0.6<jats:italic>u</jats:italic> <jats:sub>0</jats:sub> <jats:italic>τ</jats:italic>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Binary neutron star (NS) mergers have been expected to synthesize <jats:italic>r</jats:italic>-process elements and emit radioactively powered radiation, called kilonovae. Although <jats:italic>r</jats:italic>-process nucleosynthesis was confirmed by the observations of GW170817/AT2017gfo, no trace of individual elements has been identified except for strontium. In this paper, we perform systematic calculations of line strength for bound–bound transitions and radiative transfer simulations in NS merger ejecta toward element identification in kilonova spectra. We find that Sr <jats:sc>ii</jats:sc> triplet lines appear in the spectrum of a lanthanide-poor model, which is consistent with the absorption feature observed in GW170817/AT2017gfo. The synthetic spectrum also shows the strong Ca <jats:sc>ii</jats:sc> triplet lines. This is natural because Ca and Sr are coproduced in the material with relatively high electron fraction and their ions have similar atomic structures with only one <jats:italic>s</jats:italic>-electron in the outermost shell. The line strength, however, highly depends on the abundance distribution and temperature in the ejecta. For our lanthanide-rich model, the spectra show the features of doubly ionized heavy elements, such as Ce, Tb, and Th. Our results suggest that the line-forming region of GW170817/AT2017gfo was lanthanide-poor. We show that the Sr <jats:sc>ii</jats:sc> and Ca <jats:sc>ii</jats:sc> lines can be used as a probe of physical conditions in NS merger ejecta. Absence of the Ca <jats:sc>ii</jats:sc> line features in GW170817/AT2017gfo implies that the Ca/Sr ratio is &lt;0.002 in mass fraction, which is consistent with nucleosynthesis for electron fraction ≥0.40 and entropy per nucleon (in units of Boltzmann constant) ≥25.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Future microcalorimeter X-ray observations will resolve spectral features in unmatched detail. Understanding of line formation processes in X-rays deserves much attention. The purpose of this paper is to discuss such processes in the presence of a photoionizing source. Line formation processes in one- and two-electron species are broadly categorized into four cases. Case A occurs when the Lyman line optical depths are very small and photoexcitation does not occur. Line photons escape the cloud without any scattering. Case B occurs when the Lyman line optical depths are large enough for photons to undergo multiple scatterings. Case C occurs when a broadband continuum source strikes an optically thin cloud. The Lyman lines are enhanced by induced radiative excitation of the atoms/ions by continuum photons, also known as continuum pumping. A fourth, less studied scenario, where the Case B spectrum is enhanced by continuum pumping, is called Case D. Here, we establish the mathematical foundation of Cases A, B, C, and D in an irradiated cloud with Cloudy. We also show the total X-ray emission spectrum for all four cases within the energy range 0.1–10 keV at the resolving power of XRISM around 6 keV. Additionally, we show that the combined effect of electron scattering and partial blockage of continuum pumping reduces the resonance line intensities. Such reduction increases with column density and can serve as an important tool to measure the column density/optical depth of the cloud.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We perform a Bayesian analysis of the maximum mass <jats:italic>M</jats:italic> <jats:sub>TOV</jats:sub> of neutron stars with a quark core, incorporating the observational data from tidal deformability of the GW170817 binary neutron star merger as detected by LIGO/Virgo and the mass and radius of PSR J0030+0451 as detected by the Neutron Star Interior Composition Explorer. The analysis is performed under the assumption that the hadron–quark phase transition is of first order, where the low-density hadronic matter described in a unified manner by the soft QMF or the stiff DD2 equation of state (EOS) transforms into a high-density phase of quark matter modeled by the generic “constant-sound-speed” parameterization. The mass distribution measured for the 2.14 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> pulsar MSP J0740+6620 is used as the lower limit on <jats:italic>M</jats:italic> <jats:sub>TOV</jats:sub>. We find the most probable values of the hybrid star maximum mass are <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{\mathrm{TOV}}={2.36}_{-0.26}^{+0.49}\,{\text{}}{M}_{\odot }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>TOV</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>2.36</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.26</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.49</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em" /> <mml:mtext mathvariant="italic" /> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf355ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> (<jats:inline-formula> <jats:tex-math> <?CDATA ${2.39}_{-0.28}^{+0.47}\,{\text{}}{M}_{\odot }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>2.39</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.28</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.47</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em" /> <mml:mtext mathvariant="italic" /> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf355ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>) for QMF (DD2), with an absolute upper bound around 2.85 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, to the 90% posterior credible level. Such results appear robust with respect to the uncertainties in the hadronic EOS. We also discuss astrophysical implications of this result, especially on the postmerger product of GW170817, short gamma-ray bursts, and other likely binary neutron star mergers.</jats:p>