Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Magnetic reconnection is a complex mechanism that converts magnetic energy into particle kinetic energy and plasma thermal energy in space and astrophysical plasmas. In addition, magnetic reconnection and turbulence appear to be intimately related in plasmas. We analyze the magnetic-field turbulence at the exhaust of four reconnection events detected in the solar wind using the Jensen–Shannon complexity-entropy index. The interplanetary magnetic field is decomposed into the LMN coordinates using the hybrid minimum variance technique. The first event is characterized by an extended exhaust period that allows us to obtain the scaling exponents of higher-order structure functions of magnetic-field fluctuations. By computing the complexity-entropy index we demonstrate that a higher degree of intermittency is related to lower entropy and higher complexity in the inertial subrange. We also compute the complexity-entropy index of three other reconnection exhaust events. For all four events, the <jats:italic>B</jats:italic> <jats:sub> <jats:italic>L</jats:italic> </jats:sub> component of the magnetic field displays a lower degree of entropy and higher degree of complexity than the <jats:italic>B</jats:italic> <jats:sub> <jats:italic>M</jats:italic> </jats:sub> and <jats:italic>B</jats:italic> <jats:sub> <jats:italic>N</jats:italic> </jats:sub> components. Our results show that coherent structures can be responsible for decreasing entropy and increasing complexity within reconnection exhausts in magnetic-field turbulence.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the XFaster analysis package, a fast, iterative angular power spectrum estimator based on a diagonal approximation to the quadratic Fisher matrix estimator. It uses Monte Carlo simulations to compute noise biases and filter transfer functions and is thus a hybrid of both Monte Carlo and quadratic estimator methods. In contrast to conventional pseudo-<jats:italic>C</jats:italic> <jats:sub> <jats:italic>ℓ</jats:italic> </jats:sub>–based methods, the algorithm described here requires a minimal number of simulations and does not require them to be precisely representative of the data to estimate accurate covariance matrices for the bandpowers. The formalism works with polarization-sensitive observations and also data sets with identical, partially overlapping, or independent survey regions. The method was first implemented for the analysis of BOOMERanG data and also used as part of the <jats:italic>Planck</jats:italic> analysis. Here we describe the full, publicly available analysis package, written in Python, as developed for the analysis of data from the 2015 flight of the <jats:sc>Spider</jats:sc> instrument. The package includes extensions for self-consistently estimating null spectra and estimating fits for Galactic foreground contributions. We show results from the extensive validation of XFaster using simulations and its application to the <jats:sc>Spider</jats:sc> data set.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Granules observed in the solar photosphere are believed to be convective and turbulent, but the physical picture of the granular dynamical process remains unclear. Here we performed an investigation of granular dynamical motions of full length scales based on data obtained by the 1 m New Vacuum Solar Telescope and the 1.6 m Goode Solar Telescope. We developed a new granule segmenting method, which can detect both small faint and large bright granules. A large number of granules were detected, and two critical sizes, 265 and 1420 km, were found to separate the granules into three length ranges. The granules with sizes above 1420 km follow Gaussian distribution, and demonstrate <jats:italic>flat</jats:italic> in flatness function, which shows that they are non-intermittent and thus are dominated by convective motions. Small granules with sizes between 265 and 1420 km are fitted by a combination of power-law function and Gauss function, and exhibit nonlinearity in flatness function, which reveals that they are in the mixing motions of convection and turbulence. Mini granules with sizes below 265 km follow the power-law distribution and demonstrate linearity in flatness function, indicating that they are intermittent and strongly turbulent. These results suggest that a cascade process occurs: large granules break down due to convective instability, which transports energy into small ones; then turbulence is induced and grows, which competes with convection and further causes the small granules to continuously split. Eventually, the motions in even smaller scales enter in a turbulence-dominated regime.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The coagulation of micrometer-sized particles marks the beginning of planet formation. For silicates a comprehensive picture already exists, which describes under which conditions growth can take place and which barriers must be overcome. With increasing distance to the central star volatiles freeze out and the collision dynamics is governed by the properties of the frozen volatiles. We present a novel experiment facility to analyze collisions of CO<jats:sub>2</jats:sub> agglomerates consisting of micrometer-sized particles with agglomerate sizes up to 100 <jats:italic>μ</jats:italic>m. Experiments are conducted at temperatures around 100 K with collision velocities up to 3.4 m s<jats:sup>−1</jats:sup>. Below impact velocities of around 0.1 m s<jats:sup>−1</jats:sup> sticking is observed and at collision velocities of 1 m s<jats:sup>−1</jats:sup> fragmentation also starts to occur. The experiments show that agglomerates of CO<jats:sub>2</jats:sub> ice behave like silicate agglomerates with a comparable grain size distribution. Models developed to describe the collision dynamics of silicate dust can be applied to CO<jats:sub>2</jats:sub> ice. This holds for the coefficient of restitution as well as for the threshold conditions for the transitions between sticking, bouncing, or fragmentation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Even small solar flares can display a surprising level of complexity regarding their morphology and temporal evolution. Many of their properties, such as energy release and electron acceleration can be studied using highly complementary observations at X-ray and radio wavelengths. We present X-ray observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager and radio observations from the Karl G. Jansky Very Large Array (VLA) of a series of GOES A3.4–B1.6 class flares observed on 2013 April 23. The flares, as seen in X-ray and extreme ultraviolet, originated from multiple locations within active region NOAA 11726. A veritable zoo of different radio emissions between 1 GHz and 2 GHz was observed cotemporally with the X-ray flares. In addition to broadband continuum emission, broadband short-lived bursts and narrowband spikes, indicative of accelerated electrons, were observed. However, these sources were located up to 150″ away from the flaring X-ray sources but only some of these emissions could be explained as signatures of electrons that were accelerated near the main flare site. For other sources, no obvious magnetic connection to the main flare site could be found. These emissions likely originate from secondary acceleration sites triggered by the flare, but may be due to reconnection and acceleration completely unrelated to the cotemporally observed flare. Thanks to the extremely high sensitivity of the VLA, not achieved with current X-ray instrumentation, it is shown that particle acceleration happens frequently and at multiple locations within a flaring active region.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The afterglow of GRB 190114C has been observed at 60–1200 s after the burst in the sub-TeV range by the MAGIC Cerenkov telescope. The simultaneous observations in the X-ray range, which is presumed to be of synchrotron origin, and in the sub-TeV range, where the emission is presumed to be inverse Compton, provide new stringent constraints on the conditions within the emitting regions and their evolution in time. While the additional data contain a lot of new information, it turns out that fitting both the X-ray and the TeV emission is much more complicated than what was originally anticipated. We find that optical flux measurements provide important complementary information that, in combination with TeV measurements, breaks degeneracy in the parameter space. We present here a numerical fit to the multiwavelength observed spectrum using a new code that calculates the single-zone synchrotron including self-Compton emission, taking into account the exact Klein–Nishina cross sections, as well as pair production via absorption of the high-energy photons inside the emitting zone and the emission from the resulting secondary pairs. We also present a revised set of single-zone parameters and a method for fitting the data to the observations. Our model for GRB 190114C that fits all the observations, from the optical data point to the sub-TeV range, suggests that it is in the fast-cooling regime. The inferred parameters for observations at two separate moments of time show significant deviations from some of the common expectations in afterglow modeling but are all consistent with the predictions of the pair-balance model.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on the extinction properties in the fields around the clusters NGC 1854, NGC 1856, and NGC 1858 in the bar of the Large Magellanic Cloud. The color–magnitude diagrams of the stars in all these regions show an elongated red giant clump that reveals a variable amount of extinction across these fields, ranging from <jats:italic>A</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> ≃ 0.2 to <jats:italic>A</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> ≃ 1.9, including Galactic foreground extinction. The extinction properties nonetheless are remarkably uniform. The slope of the reddening vectors measured in the (<jats:italic>V</jats:italic> − <jats:italic>I</jats:italic>, <jats:italic>V</jats:italic>) and (<jats:italic>B</jats:italic> − <jats:italic>I</jats:italic>, <jats:italic>B</jats:italic>) color–magnitude planes is fully in line with the <jats:italic>A</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub>/<jats:italic>E</jats:italic>(<jats:italic>B</jats:italic> − <jats:italic>V</jats:italic>) ≃ 5.5 value found in the outskirts of 30 Dor. This indicates the presence of an additional gray extinction component in the optical requiring big grains to be about twice as abundant as in the diffuse Galactic interstellar medium (ISM). Areas of higher extinction appear to be systematically associated with regions of more intense star formation, as measured by the larger number of stars more massive than 8 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, thus making injection of big grains into the ISM by a SNII explosion the likely mechanism at the origin of the observed gray extinction component.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use magnetic field measurements by the Juno spacecraft to catalog and investigate interplanetary coronal mass ejections (ICMEs) beyond 1 au. During its cruise phase, Juno spent about 5 yr in the solar wind between 2011 September and 2016 June, providing measurements of the interplanetary magnetic field (IMF) between 1 and 5.4 au. Juno therefore presents the most recent opportunity for a statistical analysis of ICME properties beyond 1 au since the Ulysses mission (1990–2009). Our catalog includes 80 such ICME events, 32 of which contain associated flux-rope-like structures. We find that the dependency of the mean magnetic field strength of the magnetic flux ropes decreases with heliocentric distance as <jats:italic>r</jats:italic> <jats:sup>−1.24±0.43</jats:sup> between 1 and 5.4 au, in good agreement with previous relationships calculated using ICME catalogs at Ulysses. We combine the Juno catalog with the HELCATS catalog to create a data set of ICMEs covering 0.3–5.4 au. Using a linear regression model to fit the combined data set on a double-logarithmic plot, we find that there is a clear difference between global expansion rates for ICMEs observed at shorter heliocentric distances and those observed farther out beyond 1 au. The cataloged ICMEs at Juno present a good basis for future multispacecraft studies of ICME evolution between the inner heliosphere, 1 au, and beyond.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Sunyaev–Zel’dovich (SZ) effect introduces a specific distortion of the blackbody spectrum of the cosmic microwave background (CMB) radiation when it scatters off hot gas in clusters of galaxies. The frequency dependence of the distortion is only independent of the cluster redshift when the evolution of the CMB radiation is adiabatic. Using 370 clusters within the redshift range 0.07 ≲ <jats:italic>z</jats:italic> ≲ 1.4 from the largest SZ-selected cluster sample to date from the Atacama Cosmology Telescope, we provide new constraints on the deviation of CMB temperature evolution from the standard model <jats:inline-formula> <jats:tex-math> <?CDATA $\alpha ={0.017}_{-0.032}^{+0.029}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>α</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>0.017</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.032</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.029</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac26b6ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, where <jats:inline-formula> <jats:tex-math> <?CDATA $T(z)={T}_{0}{\left(1+z\right)}^{1-\alpha }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>T</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi>z</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> <mml:msup> <mml:mrow> <mml:mfenced close=")" open="("> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>+</mml:mo> <mml:mi>z</mml:mi> </mml:mrow> </mml:mfenced> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>−</mml:mo> <mml:mi>α</mml:mi> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac26b6ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. This result is consistent with no deviation from the standard adiabatic model. Combining it with previous, independent data sets we obtain a joint constraint of <jats:italic>α</jats:italic> = −0.001 ± 0.012. Attributing deviation from adiabaticity to the decay of dark energy, this result constrains its effective equation of state <jats:inline-formula> <jats:tex-math> <?CDATA ${w}_{\mathrm{eff}}=-{0.998}_{-0.010}^{+0.008}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>w</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>eff</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>0.998</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.010</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.008</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac26b6ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The high incidence rate of the O <jats:sc>vi</jats:sc> <jats:italic> λλ</jats:italic>1032, 1038 absorption around low-redshift, ∼<jats:italic>L</jats:italic> <jats:sup>*</jats:sup> star-forming galaxies has generated interest in studies of the circumgalactic medium. We use the high-resolution <jats:monospace>EAGLE</jats:monospace> cosmological simulation to analyze the circumgalactic O <jats:sc>vi</jats:sc> gas around <jats:italic>z</jats:italic> ≈ 0.3 star-forming galaxies. Motivated by the limitation that observations do not reveal where the gas lies along the line of sight, we compare the O <jats:sc>vi</jats:sc> measurements produced by gas within fixed distances around galaxies and by gas selected using line-of-sight velocity cuts commonly adopted by observers. We show that gas selected by a velocity cut of ±300 km s<jats:sup>−1</jats:sup> or ±500 km s<jats:sup>−1</jats:sup> produces a higher O <jats:sc>vi</jats:sc> column density, a flatter column density profile, and a higher covering fraction compared to gas within 1, 2, or 3 times the virial radius (<jats:italic>r</jats:italic> <jats:sub>vir</jats:sub>) of galaxies. The discrepancy increases with impact parameter and worsens for lower-mass galaxies. For example, compared to the gas within 2<jats:italic> r</jats:italic> <jats:sub>vir</jats:sub>, identifying the gas using velocity cuts of 200–500 km s<jats:sup>−1</jats:sup> increases the O <jats:sc>vi</jats:sc> column density by 0.2 dex (0.1 dex) at 1 <jats:italic>r</jats:italic> <jats:sub>vir</jats:sub> to over 0.75 dex (0.7 dex) at ≈ 2<jats:italic> r</jats:italic> <jats:sub>vir</jats:sub> for galaxies with stellar masses of 10<jats:sup>9</jats:sup>–10<jats:sup>9.5</jats:sup> <jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub> (10<jats:sup>10</jats:sup>–10<jats:sup>10.5</jats:sup> <jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub>). We furthermore estimate that excluding O <jats:sc>vi</jats:sc> outside <jats:italic>r</jats:italic> <jats:sub>vir</jats:sub> decreases the circumgalactic oxygen mass measured by Tumlinson et al. (2011) by over 50%. Our results demonstrate that gas at large line-of-sight separations but selected by conventional velocity windows has significant effects on the O <jats:sc>vi</jats:sc> measurements and may not be observationally distinguishable from gas near the galaxies.</jats:p>