Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The attenuation produced by extragalactic background light (EBL) in <jats:italic>γ</jats:italic>-ray spectra of blazars has been used to constrain the Hubble constant (<jats:italic>H</jats:italic> <jats:sub>0</jats:sub>) and matter density (Ω<jats:sub>m</jats:sub>) of the universe. We propose to estimate <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> and Ω<jats:sub>m</jats:sub> using the well-measured &gt;10 GeV extragalactic <jats:italic>γ</jats:italic>-ray background (EGB). This suggestion is based on the fact that the &gt;10 GeV EGB is totally explained by the emissions from blazars, and an EBL-absorption cutoff occurs at ∼50 GeV in the EGB spectrum. We fit the &gt;10 GeV EGB data with modeled EGB spectrum. This results in <jats:inline-formula> <jats:tex-math> <?CDATA ${H}_{0}={64.9}_{-4.3}^{+4.6}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab35e3ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Omega }}}_{{\rm{m}}}={0.31}_{-0.14}^{+0.13}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab35e3ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. Note that the uncertainties may be underestimated due to the limit of our realization for EBL model. <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> and Ω<jats:sub>m</jats:sub> are degenerate in our method. Independent determination of Ω<jats:sub>m</jats:sub> by other methods would improve the constraint on <jats:italic>H</jats:italic> <jats:sub>0</jats:sub>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Coronal mass ejections (CMEs) are responsible for most severe space weather events, such as solar energetic particle events and geomagnetic storms at Earth. Type II radio bursts are slow drifting emissions produced by beams of suprathermal electrons accelerated at CME-driven shock waves propagating through the corona and interplanetary medium. Here, we report a statistical study of 153 interplanetary type II radio bursts observed by the two <jats:italic>STEREO</jats:italic> spacecraft between 2008 March and 2014 August. The shock associated radio emission was compared with CME parameters included in the Heliospheric Cataloguing, Analysis and Techniques Service catalog. We found that faster CMEs are statistically more likely to be associated with the interplanetary type II radio bursts. We correlate frequency drifts of interplanetary type II bursts with white-light observations  to localize radio sources with respect to CMEs. Our results suggest that interplanetary type II bursts are more likely to have a source region situated closer to CME flanks than  CME leading edge regions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Type II white-light flares (WLFs) have weak Balmer line emission and no Balmer jump. We carried out a set of radiative hydrodynamic simulations to understand how the hydrogen radiative losses vary with the electron-beam parameters and more specifically with the low-energy cutoff. Our results have revealed that for low-energy beams, the excess flare Lyman emission diminishes with increasing low-energy cutoff as the energy deposited into the top chromosphere is low compared to the energy deposited into the deeper layers. Some Balmer excess emission is always present and is driven primarily by direct heating from the beam with a minor contribution from Lyman continuum backwarming. The absence of Lyman excess emission in electron-beam driven models with high low-energy cutoff is a prominent spectral signature of type II WLFs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>It is widely accepted that stars in a spiral disk, like the Milky Way’s, can radially migrate on the order of a scale length over the disk’s lifetime. With the exception of cold torquing, also known as “churning,” processes that contribute to the radial migration of stars are necessarily associated with kinematic heating. Additionally, it is an open question as to whether or not an episode of cold torquing is kinematically cold over long radial distances. This study uses a suite of analytically based simulations to investigate the dynamical response when stars are subject to cold torquing and are also resonant with an ultraharmonic. Model results demonstrate that these populations are kinematically heated and have rms changes in orbital angular momentum around corotation that can exceed those of populations that do not experience resonant overlap. Thus, kinematic heating can occur during episodes of cold torquing. In a case study of a Milky Way-like disk with an exponential surface density profile and flat rotation curve, up to 40% of cold torqued stars in the solar cylinder experience resonant overlap. This fraction increases toward the galactic center. To first approximation, the maximum radial excursions from cold torquing depend only on the strength of the spiral pattern and the underlying rotation curve. This work places an upper limit to these excursions to be the distance between the ultraharmonics, otherwise radial migration near corotation can kinematically heat. The diffusion rate for kinematically cold radial migration is thus constrained by limiting the step size in the random walk approximation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>SNe Ia play key roles in revealing the accelerating expansion of the universe, but our knowledge of their progenitors is still very limited. Here we report the discovery of a rigid dichotomy in circumstellar (CS) environments around two subclasses of SNe Ia as defined by their distinct photospheric velocities. For the SNe Ia with high photospheric velocities (HVs), we found a significant excess flux in blue light 60–100 days past maximum, while this phenomenon is absent for SNe with normal photospheric velocity. This blue excess can be attributed to light echoes by circumstellar dust located at a distance of about (1–2) × 10<jats:sup>17</jats:sup> cm from the HV subclass. Moreover, we also found that the HV SNe Ia show systematically evolving Na <jats:sc>i</jats:sc> absorption line by performing a systematic search of variable Na <jats:sc>i</jats:sc> absorption lines in spectra of all SNe Ia, whereas this evolution is rarely seen in normal ones. The evolving Na <jats:sc>i</jats:sc> absorption can be modeled in terms of photoionization model, with the location of the gas clouds at a distance of about 2 × 10<jats:sup>17</jats:sup> cm, in striking agreement with the location of CS dust inferred from <jats:italic>B</jats:italic>-band light-curve excess. These observations show clearly that the progenitors of HV subclass are likely from single-degenerate progenitor system (i.e., symbiotic binary), while the NV subclass may arise from double-degenerate system.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Interchange reconnection is thought to play an important role in driving the dynamics of the slow solar wind. To understand the details of this process, it is important to catalog the various magnetic structures that are present at the boundary between open and closed magnetic flux. To this end we have developed a numerical method for partitioning the coronal volume into individual flux domains using volume segmentation along layers of high magnetic squashing degree (<jats:italic>Q</jats:italic>). Our publicly available implementation of this method is able to identify the different magnetic structures within a coronal magnetic field model that define the open-closed boundary and comprise the so-called Separatrix-Web (S-Web). With this we test previous predictions of how different configurations of high-<jats:italic>Q</jats:italic> arcs within the S-Web are related to coronal magnetic field structures. Here we present our findings from a survey of 11 different potential field source surface models, spanning from 2008 to 2017, which offer a representative sample of the coronal magnetic field across nearly a complete solar cycle. Two key findings of our analysis are that (i) “vertex” structures—where arcs of the S-Web meet away from the heliospheric current sheet—are associated with underlying magnetic dome structures, and (ii) that any given arc of the S-Web is almost equally as likely to be formed by a narrow corridor of open flux (corresponding to a hyperbolic flux tube) as by the separatrix surface of a magnetic null. Together, these findings highlight the importance of a variety of topological configurations for future studies of interchange reconnection and the acceleration of the solar wind.</jats:p>