Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We report a Giant Metrewave Radio Telescope <jats:sc /> 21 cm mapping study of the neutral atomic hydrogen (H<jats:sc>i</jats:sc>) in the host galaxy of the fast radio burst (FRB) FRB 20180916B at <jats:italic>z</jats:italic> ≈ 0.03399. We find that the FRB host has an H<jats:sc>i</jats:sc> mass of <jats:italic>M</jats:italic> <jats:sub>H<jats:sc>i</jats:sc> </jats:sub> = (2.74 ± 0.33) × 10<jats:sup>9</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and a high H<jats:sc>i </jats:sc>to stellar mass ratio, ≈1.3. The FRB host is thus a gas-rich but near-quiescent galaxy that is likely to have acquired a significant mass of H<jats:sc>i</jats:sc> in the recent past. The H<jats:sc>i</jats:sc> distribution is disturbed, with extended H<jats:sc>i</jats:sc> 21 cm emission detected in a northeastern tail, a counter-tail toward the south, an H<jats:sc>i</jats:sc> hole between the galaxy center and the FRB location, and a high H<jats:sc>i</jats:sc> column density measured close to the FRB position. The FRB host is part of a group with four companions detected in their H<jats:sc>i</jats:sc> 21 cm emission, the nearest of which is only 22 kpc from the FRB location. The gas richness and disturbed H<jats:sc>i</jats:sc> distribution indicate that the FRB host has recently undergone a minor merger, which increased its H<jats:sc>i</jats:sc> mass, disturbed the H<jats:sc>i</jats:sc> in the galaxy disk, and compressed the H<jats:sc>i</jats:sc> near the FRB location to increase its surface density. We propose that this merger caused the burst of star formation in the outskirts of the galaxy that gave rise to the FRB progenitor. The evidence for a minor merger is consistent with scenarios in which the FRB progenitor is a massive star, formed due to the merger event.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We searched through the entire Gaia EDR3 candidate white dwarf catalog for stars with proper motions and positions that are consistent with them having escaped from the Alpha Persei cluster within the past 81 Myr, the age of the cluster. In this search we found five candidate white dwarf escapees from Alpha Persei and obtained spectra for all of them. We confirm that three are massive white dwarfs sufficiently young to have originated in the cluster. All these are more massive than any white dwarf previously associated with a cluster using Gaia astrometry, and possess some of the most massive progenitors. In particular, the white dwarf Gaia EDR3 4395978097863572, which lies within 25 pc of the cluster center, has a mass of about 1.20 solar masses and evolved from an 8.5 solar-mass star, pushing the upper limit for white dwarf formation from a single massive star, while still leaving a substantial gap between the resulting white dwarf mass and the Chandrasekhar mass.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the role of coronal mass ejection (CME) driven shocks in the acceleration of solar energetic electrons. Using observations by the two STEREO spacecraft, we correlate electron peak intensities of solar energetic particle events measured in situ with various parameters of the associated coronal shocks. These shock parameters were derived by combining 3D shock reconstructions with global modeling of the corona. This modeling technique provides also shock properties in the specific shock regions that are magnetically connected to the two STEREO spacecraft. We find significant correlations between the peak intensities and the Mach number of the shock with correlation coefficients of about 0.7, which are similar for electrons at ∼1 MeV and protons at &gt;60 MeV. Lower-energy electrons with &lt;100 keV show a smaller correlation coefficient of 0.47. The causal relationship between electron intensities and the shock properties is supported by the vanishing correlations when peak intensities at STEREO A are related with the Alfvénic Mach number at the magnetic footpoint of STEREO B and vice versa, which yields correlation coefficients of 0.03 and −0.13 for ∼1 MeV and &lt;100 keV electron peak intensities, respectively. We conclude that the high-energy electrons are accelerated mainly by the shock, while the low-energy electrons are likely produced by a mixture of flare and shock-related acceleration processes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present three new spectra of the nearby Type Ia supernova (SN Ia) 2011fe covering ≈480–850 days after maximum light and show that the ejecta undergoes a rapid ionization shift at ∼500 days after explosion. The prominent Fe <jats:sc>iii</jats:sc> emission lines at ≈4600 Å are replaced with Fe <jats:sc>i</jats:sc>+Fe <jats:sc>ii</jats:sc> blends at ∼4400 Å and ∼5400 Å. The ≈7300 Å feature, which is produced by [Fe <jats:sc>ii</jats:sc>]+[Ni <jats:sc>ii</jats:sc>] at ≲400 days after explosion, is replaced by broad (≈±15,000 km s<jats:sup>−1</jats:sup>) symmetric [Ca <jats:sc>ii</jats:sc>] emission. Models predict this ionization transition occurring ∼100 days later than what is observed, which we attribute to clumping in the ejecta. Finally, we use the nebular-phase spectra to test several proposed progenitor scenarios for SN 2011fe. Nondetections of H and He exclude nearby nondegenerate companions, [O <jats:sc>i</jats:sc>] nondetections disfavor the violent merger of two white dwarfs, and the symmetric emission-line profiles favor a symmetric explosion.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the first ever discovery of a short-period and unusually helium-deficient dwarf nova KSP-OT-201701a by the Korea Microlensing Telescope Network Supernova Program. The source shows three superoutbursts, each led by a precursor outburst, and several normal outbursts in <jats:italic>BVI</jats:italic> during the span of ∼2.6 yr with supercycle and normal cycle lengths of about 360 and 76 days, respectively. Spectroscopic observations near the end of a superoutburst reveal the presence of strong double-peaked H <jats:sc>i</jats:sc> emission lines together with weak He <jats:sc>i</jats:sc> emission lines. The helium-to-hydrogen intensity ratios measured by He <jats:sc>i</jats:sc> <jats:sub> <jats:italic>λ</jats:italic>5876</jats:sub> and H<jats:italic>α</jats:italic> lines are 0.10 ± 0.01 at a quiescent phase and 0.26 ± 0.04 at an outburst phase, similar to the ratios found in long-period dwarf novae, while significantly lower than those in helium cataclysmic variables (He CVs). Its orbital period of 51.91 ± 2.50 minutes, which is estimated based on time-series spectroscopy, is a bit shorter than the superhump period of 56.52 ± 0.19 minutes, as expected from the gravitational interaction between the eccentric disk and the secondary star. We measure its mass ratio to be <jats:inline-formula> <jats:tex-math> <?CDATA ${0.37}_{-0.21}^{+0.32}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>0.37</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.21</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.32</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac4c41ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> using the superhump period excess of 0.089 ± 0.053. The short orbital period, which is under the period minimum, the unusual helium deficiency, and the large mass ratio suggest that KSP-OT-201701a is a transition object evolving to an He CV from a long-period dwarf nova with an evolved secondary star.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We analyze the micro-kinetic stability of the electron strahl in the solar wind depending on heliocentric distance. The oblique fast-magnetosonic/whistler (FM/W) instability has emerged in the literature as a key candidate mechanism for the effective scattering of the electron strahl into the electron halo population. Using data from the Parker Solar Probe (PSP) and Helios, we compare the measured strahl properties with the analytical thresholds for the oblique FM/W instability in the low- and high-<jats:italic>β</jats:italic> <jats:sub>∥<jats:italic>c</jats:italic> </jats:sub> regimes, where <jats:italic>β</jats:italic> <jats:sub>∥<jats:italic>c</jats:italic> </jats:sub> is the ratio of the core parallel thermal pressure to the magnetic pressure. Our PSP and Helios data show that the electron strahl is on average stable against the oblique FM/W instability in the inner heliosphere. Our analysis suggests that the instability, if at all, can only be excited sporadically and on short timescales. We discuss the caveats of our analysis and potential alternative explanations for the observed scattering of the electron strahl in the solar wind. Furthermore, we recommend the numerical evaluation of the stability of individual distributions in the future to account for any uncertainties in the validity of the analytical expressions for the instability thresholds.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We analyze the recent astrophysical constraints in the context of a hadronic equation of state (EoS) in which the baryonic matter is subject to chiral symmetry restoration. We show that with such EoS it is possible to reconcile the modern constraints on the neutron star (NS) mass, radius, and tidal deformability (TD). We find that the softening of the EoS, required by the TD constraint of a canonical 1.4 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> NS, followed by a subsequent stiffening, required by the 2 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> constraint, is driven by the appearance of Δ matter due to partial restoration of chiral symmetry. Consequently, a purely hadronic EoS that accounts for the fundamental properties of quantum chromodynamics linked to the dynamical emergence of parity doubling with degenerate masses of nucleons and Δ resonances can be fully consistent with multi-messenger data. Therefore, with the present constraints on the EoS, the conclusion about the existence of quark matter in the stellar core may still be premature.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The structure of the electron diffusion region (EDR) is essential for determining how fast the magnetic energy converts to plasma energy during magnetic reconnection. Conventional knowledge of the diffusion region assumes that the EDR is a single layer embedded within the ion diffusion region (IDR). This paper reports the first observation of two EDRs that stack in parallel within an IDR by the Magnetospheric Multiscale mission. The oblique tearing modes can result in these stacked EDRs. Intense electron flow shear in the vicinity of two EDRs induced electron Kelvin–Helmholtz vortices, which subsequently generated kinetic-scale magnetic peak and holes, which may effectively trap electrons. Our analyses show that both the oblique tearing instability and electron Kelvin–Helmholtz instability are important in three-dimensional reconnection since they can control the electron dynamics and structure of the diffusion region through cross-scale coupling.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Time-dependent energy spectra of galactic cosmic rays (GCRs) carry fundamental information regarding their origin and propagation. When observed at the Earth, these spectra are significantly affected by the solar wind and the embedded solar magnetic field that permeates the heliosphere, changing significantly over an 11 yr solar cycle. Energy spectra of GCRs measured during different epochs of solar activity provide crucial information for a thorough understanding of solar and heliospheric phenomena. The PAMELA experiment collected data for almost 10 years (2006 June 15–2016 January 23), including the minimum phase of solar cycle 23 and the maximum phase of solar cycle 24. In this paper, we present new spectra for helium nuclei measured by the PAMELA instrument from 2010 January to 2014 September over a three-Carrington-rotation time basis. These data are compared to the PAMELA spectra measured during the previous solar minimum, providing a picture of the time dependence of the helium-nuclei fluxes over a nearly full solar cycle. Time and rigidity dependencies are observed in the proton-to-helium flux ratios. The force-field approximation of the solar modulation was used to relate these dependencies to the shapes of the local interstellar proton and helium-nuclei spectra.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>If a significant fraction of dark matter is in the form of compact objects, they will cause microlensing effects in the gravitational wave signals observable by LIGO and Virgo. From the nonobservation of microlensing signatures in the binary black hole events from the first two observing runs and the first half of the third observing run, we constrain the fraction of compact dark matter in the mass range 10<jats:sup>2</jats:sup>–10<jats:sup>5</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> to be less than ≃50%–80% (details depend on the assumed source population properties and the Bayesian priors). These modest constraints will be significantly improved in the next few years with the expected detection of thousands of binary black hole events, providing a new avenue to probe the nature of dark matter.</jats:p>