Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We have measured the gas temperature in the IC 63 photodissociation region (PDR) using the S(1) and S(5) pure rotation lines of molecular hydrogen with SOFIA/EXES. We divide the PDR into three regions for analysis based on the illumination from <jats:italic>γ</jats:italic> Cas: sunny, ridge, and shady. Constructing rotation diagrams for the different regions, we obtain temperatures of <jats:italic>T</jats:italic> <jats:sub>ex</jats:sub> = <jats:inline-formula> <jats:tex-math> <?CDATA ${562}_{-43}^{+52}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>562</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>43</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>52</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2eb7ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> K toward the ridge and <jats:italic>T</jats:italic> <jats:sub>ex</jats:sub> = <jats:inline-formula> <jats:tex-math> <?CDATA ${495}_{-25}^{+28}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>495</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>25</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>28</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2eb7ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> K in the shady side. The H<jats:sub>2</jats:sub> emission was not detected on the sunny side of the ridge, likely due to the photodissociation of H<jats:sub>2</jats:sub> in this gas. Our temperature values are lower than the value of <jats:italic>T</jats:italic> <jats:sub>ex</jats:sub> = 685 ± 68 K using the S(1), S(3), and S(5) pure rotation lines, derived by Thi et al. using lower spatial resolution ISO-SWS data at a different location of the IC 63 PDR. This difference indicates that the PDR is inhomogeneous and illustrates the need for high-resolution mapping of such regions to fully understand their physics. The detection of a temperature gradient correlated with the extinction into the cloud, points to the ability of using H<jats:sub>2</jats:sub> pure rotational line spectroscopy to map the gas temperature on small scales. We used a PDR model to estimate the FUV radiation and corresponding gas densities in IC 63. Our results shows the capability of SOFIA/EXES to resolve and provide detailed information on the temperature in such regions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Depression in magnetic field strength with a scale below one proton gyroradius is referred to as a kinetic-size magnetic hole (KSMH). KSMHs are frequently observed near Earth’s space environments and are thought to play an important role in electron energization and energy dissipation in space plasmas. Recently, KSMHs have been evidenced in the Venusian magnetosheath. However, observations of KSMHs in other planetary environments are still lacking. In this study, we present the in situ detection of KSMHs in the Martian magnetosheath using Mars Atmosphere and Volatile EvolutioN (MAVEN) for the first time. The distribution of KSMHs is asymmetry in the southern–northern hemisphere and no obvious asymmetry in the dawn–dusk hemisphere. The observed KSMHs are accompanied by increases in the electron fluxes in the perpendicular direction, indicating the cues of trapped electrons and the formation of electron vortices inside KSMHs. These features are similar to the observations in the Earth’s magnetosheath and magnetotail plasma sheet and the Venusian magnetosheath. This implies that KSMHs are a universal magnetic structure in space.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We revisit the short-term post-glitch relaxation of the Vela 2000 glitch in the simple two-component model of the pulsar glitch by making use of the latest realistic equations of states from the microscopic Brueckner and the relativistic Brueckner theories for neutron stars, which can reconcile with the available astrophysical constraints. We show that to fit both the glitch size and the post-glitch jumps in frequency derivatives approximately 1 minute after the glitch, the mass of the Vela pulsar is necessarily small, and there may be demands for a stiff equation of state (which results in a typical stellar radius larger than ∼12.5 km) and a strong suppression of the pairing gap in the nuclear medium. We discuss the implications of this result on the understanding of pulsar glitches.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present both the observation and the magnetohydrodynamics (MHD) simulation of the M2.4 flare (SOL2017-07-14T02:09) of NOAA active region (AR) 12665 with a goal to identify its initiation mechanism. The observation by the Atmospheric Image Assembly (AIA) on board the Solar Dynamics Observatory (SDO) shows that the major topology of the AR is a sigmoidal configuration associated with a filament/flux rope. A persistent emerging magnetic flux and the rotation of the sunspot in the core region were observed with Magnetic Imager (HMI) on board the SDO on the timescale of hours before and during the flare, which may provide free magnetic energy needed for the flare/coronal mass ejection (CME). A high-lying coronal loop is seen moving outward in AIA EUV passbands, which is immediately followed by the impulsive phase of the flare. We perform an MHD simulation using the potential magnetic field extrapolated from the measured pre-flare photospheric magnetic field as initial conditions and adopting the observed sunspot rotation and flux emergence as the driving boundary conditions. In our simulation, a sigmoidal magnetic structure and an overlying magnetic flux rope (MFR) form as a response to the imposed sunspot rotation, and the MFR rises to erupt like a CME. These simulation results in good agreement with the observation suggest that the formation of the MFR due to the sunspot rotation and the resulting torus and kink instabilities were essential to the initiation of this flare and the associated coronal mass ejection.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on the observations of four well-localized binary black hole (BBH) mergers by the High Energy Stereoscopic System (H.E.S.S.) during the second and third observing runs of Advanced LIGO and Advanced Virgo, O2 and O3. H.E.S.S. can observe 20 deg<jats:sup>2</jats:sup> of the sky at a time and follows up gravitational-wave (GW) events by “tiling” localization regions to maximize the covered localization probability. During O2 and O3, H.E.S.S. observed large portions of the localization regions, between 35% and 75%, for four BBH mergers (GW170814, GW190512_180714, GW190728_064510, and S200224ca). For these four GW events, we find no significant signal from a pointlike source in any of the observations, and we set upper limits on the very high energy (&gt;100 GeV) <jats:italic>γ</jats:italic>-ray emission. The 1–10 TeV isotropic luminosity of these GW events is below 10<jats:sup>45</jats:sup> erg s<jats:sup>−1</jats:sup> at the times of the H.E.S.S. observations, around the level of the low-luminosity GRB 190829A. Assuming no changes are made to how follow-up observations are conducted, H.E.S.S. can expect to observe over 60 GW events per year in the fourth GW observing run, O4, of which eight would be observable with minimal latency.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Much of our understanding of the state of coronal plasmas comes from observations that are optically thin. This means that light travels freely through the corona without being materially affected by it, which allows it to be easily seen through, but also results in a line-of-sight degeneracy that has previously thwarted attempts to recover the three-dimensional structure of the coronal plasma. However, although the corona is disorganized in the line-of-sight direction, it is highly organized in the field-aligned direction. This paper demonstrates how to exploit this organization to resolve the line-of-sight degeneracy in the plasma properties using a suitable magnetic field structure. This allows, for the first time, the two-dimensional optically thin plasma observations to directly drive the three-dimensional plasma reconstruction throughout an entire active region (or larger). A preliminary investigation with a potential field is shown, finding a solution which clearly resembles the real solar data, even with a single perspective. The results indicate that there is ample information in the resulting residuals that can be used to refine the magnetic field structure, suggesting that these residuals can in turn be used to directly constrain the magnetic field extrapolations used in the reconstruction. The paper concludes with a discussion of how these residuals can in turn be used to directly drive the magnetic field extrapolations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Modeling the evolution of the number density distribution of quasars through the quasar luminosity function (QLF) is critical to improving our understanding of the connection between black holes, galaxies, and their halos. Here we present a novel semiempirical model for the evolution of the QLF that is fully defined after the specification of a free parameter, the internal duty cycle, <jats:italic>ε</jats:italic> <jats:sub>DC</jats:sub>, along with minimal other assumptions. All remaining model parameters are fixed upon calibration against the QLF at two redshifts, <jats:italic>z</jats:italic> = 4 and <jats:italic>z</jats:italic> = 5. Our modeling shows that the evolution at the bright end results from the stochasticity in the median quasar luminosity versus halo mass relation, while the faint end shape is determined by the evolution of the halo mass function (HMF) with redshift. Additionally, our model suggests the overall quasar density is determined by the evolution of the HMF, irrespective of the value of <jats:italic>ε</jats:italic> <jats:sub>DC</jats:sub>. The <jats:italic>z</jats:italic> ≥ 4 QLFs from our model are in excellent agreement with current observations for all <jats:italic>ε</jats:italic> <jats:sub>DC</jats:sub>, with model predictions suggesting that observations at <jats:italic>z</jats:italic> ≳ 7.5 are needed to discriminate between different <jats:italic>ε</jats:italic> <jats:sub>DC</jats:sub>. We further extend the model at <jats:italic>z</jats:italic> ≤ 4, successfully describing the QLF between 1 ≤ <jats:italic>z</jats:italic> ≤ 4, albeit with additional assumptions on Σ and <jats:italic>ε</jats:italic> <jats:sub>DC</jats:sub>. We use the existing measurements of quasar duty cycle from clustering to constrain <jats:italic>ε</jats:italic> <jats:sub>DC</jats:sub>, finding <jats:italic>ε</jats:italic> <jats:sub>DC</jats:sub> ∼ 0.01 or <jats:italic>ε</jats:italic> <jats:sub>DC</jats:sub> ≳ 0.1 dependent on observational data sets used for reference. Finally, we present forecasts for future wide-area surveys with promising expectations for the Nancy Grace Roman Telescope to discover <jats:italic>N</jats:italic> ≳ 10, bright, <jats:italic>m</jats:italic> <jats:sub>UV</jats:sub> &lt; 26.5 quasars at <jats:italic>z</jats:italic> ∼ 8.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Rapid binary population synthesis codes are often used to investigate the evolution of compact-object binaries. They typically rely on analytical fits of single-star evolutionary tracks and parameterized models for interactive phases of evolution (e.g., mass transfer on a thermal timescale, determination of dynamical instability, and common envelope) that are crucial to predict the fate of binaries. These processes can be more carefully implemented in stellar structure and evolution codes such as <jats:monospace>MESA</jats:monospace>. To assess the impact of such improvements, we compare binary black hole mergers as predicted in models with the rapid binary population synthesis code <jats:monospace>COSMIC</jats:monospace> to models ran with <jats:monospace>MESA</jats:monospace> simulations through mass transfer and common-envelope treatment. We find that results significantly differ in terms of formation paths, the orbital periods and mass ratios of merging binary black holes, and consequently merger rates. While common-envelope evolution is the dominant formation channel in <jats:monospace>COSMIC</jats:monospace>, stable mass transfer dominates in our <jats:monospace>MESA</jats:monospace> models. Depending upon the black hole donor mass, and mass-transfer and common-envelope physics, at subsolar metallicity, <jats:monospace>COSMIC</jats:monospace> overproduces the number of binary black hole mergers by factors of 2–35 with a significant fraction of them having merger times orders of magnitude shorter than the binary black holes formed when using detailed <jats:monospace>MESA</jats:monospace> models. Therefore we find that some binary black hole merger rate predictions from rapid population syntheses of isolated binaries may be overestimated by factors of ∼ 5–500. We conclude that the interpretation of gravitational-wave observations requires the use of detailed treatment of these interactive binary phases.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present three new Chandra X-ray epochs along with new ground-based optical–UV observations as the third installment in a time-series analysis of four high-redshift (<jats:italic>z</jats:italic> ≈ 4.1–4.4) radio-quiet quasars. In total, we present nine epochs for these sources with rest-frame temporal baselines of ∼1300–2000 days. We utilize the X-ray data to determine basic variability properties, as well as produce mean spectra and stacked images based on effective exposure times of ∼40–70 ks per source. We perform time-series analyses in the soft and hard bands, separately, and compare variability properties to those of sources at lower redshifts and luminosities. The magnitude of X-ray variability of our sources remains consistent with or lower than that of similar sources at lower redshifts, in agreement with the variability–luminosity anticorrelation. The mean power-law photon indices in the stacked Chandra spectra of our sources are consistent with the values measured from their archival XMM-Newton spectra separated by about 3 yr in the rest frame. Along with the X-ray observations, we provide near-simultaneous optical monitoring of the sources in the optical–UV regime. The overall variability in the optical-to-X-ray spectral slope is consistent with sources at lower redshifts, and the optical–UV observations display mild variability on monthly timescales.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The microquasar V404 Cygni (also known as GS 2023+338) was previously reported to have weak GeV <jats:italic>γ</jats:italic>-ray emission in subday time periods during its 2015 outburst. In order to provide more detailed information at the high energy range for this black hole binary system, we conduct analysis on the data obtained with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (Fermi). Both the LAT database and source catalog used are the latest versions. In addition to the previously reported detection at the peak of the 2015 outburst, we find a possible detection (∼4<jats:italic>σ</jats:italic>) of the source during the 3 day time period of 2015 August 17–19 (at the end of the 2015 outburst) and one convincing detection (≃7<jats:italic>σ</jats:italic>) in 2016 August 23–25. The latter high-significance detection shows that the <jats:italic>γ</jats:italic>-ray emission of the source is soft with photon index Γ ∼ 2.9. As <jats:italic>γ</jats:italic>-ray emission from microquasars is considered to be associated with their jet activity, we discuss the results by comparing with those well-studied cases, namely, Cyg X-3 and Cyg X-1. The detection helps identify V404 Cygni as a microquasar with detectable <jats:italic>γ</jats:italic>-ray emission in its quiescent state, and adds interesting features to the microquasar group, or in a more general context to X-ray binaries with jets.</jats:p>