Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Spiky whistlers are short duration chirps of electric field that have fine structures in both frequency and time. They are observed on the Parker Solar Probe for the first time. From the limited available data, they appear to be accompanied by low-frequency ion waves and to occur relatively frequently. The origin of these wave pairs and their correlations are not understood.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the two-dimensional (2D) line-of-sight velocity (<jats:italic>V</jats:italic> <jats:sub>los</jats:sub>) field of the low-inclination, late-type galaxy VV304a. The resulting 2D kinematic map reveals a global, coherent, and extended perturbation that is likely associated with a recent interaction with the massive companion VV304b. We use multiband imaging and a suite of test-particle simulations to quantify the plausible strength of in-plane flows due to nonaxisymmetric perturbations and show that the observed velocity flows are much too large to be driven either by a spiral structure or by a bar. We use fully cosmological hydrodynamical simulations to characterize the contribution from in- and off-plane velocity flows to the <jats:italic>V</jats:italic> <jats:sub>los</jats:sub> field of recently interacting galaxy pairs like the VV304 system. We show that, for recently perturbed low-inclination galactic disks, the structure of the residual velocity field, after subtraction of an axisymmetric rotation model, can be dominated by vertical flows. Our results indicate that the <jats:italic>V</jats:italic> <jats:sub>los</jats:sub> perturbations in VV304a are consistent with a corrugation pattern. Its <jats:italic>V</jats:italic> <jats:sub>los</jats:sub> map suggests the presence of a structure similar to the Monoceros ring seen in the Milky Way. Our study highlights the possibility of addressing important questions regarding the nature and origin of vertical perturbations by measuring the line-of-sight velocities in low-inclination nearby galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Coronal holes (CHs) are darker than the quiet Sun (QS) when observed in coronal channels. This study aims to understand the similarities and differences between CHs and QS in the transition region using the Si <jats:sc>iv</jats:sc> 1394 Å line, recorded by the Interface Region Imaging Spectrograph, by considering the distribution of magnetic field measured by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. We find that Si <jats:sc>iv</jats:sc> intensities obtained in CHs are lower than those obtained in QS for regions with identical magnetic flux densities. Moreover, the difference in intensities between CHs and QS increases with increasing magnetic flux. For the regions with equal magnetic flux density, QS line profiles are more redshifted than those measured in CHs. Moreover, the blueshifts measured in CHs show an increase with increasing magnetic flux density unlike in the QS. The non-thermal velocities in QS, as well as in CHs, show an increase with increasing magnetic flux. However, no significant difference was observed in QS and CHs, albeit a small deviation at small flux densities. Using these results, we propose a unified model for the heating of the corona in the QS and in CHs and the formation of solar wind.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Solar flares are explosive releases of magnetic energy. Hard X-ray (HXR) flare emission originates from both hot (millions of Kelvin) plasma and nonthermal accelerated particles, giving insight into flare energy release. The Nuclear Spectroscopic Telescope ARray (NuSTAR) utilizes direct-focusing optics to attain much higher sensitivity in the HXR range than that of previous indirect imagers. This paper presents 11 NuSTAR microflares from two active regions (AR 12671 on 2017 August 21 and AR 12712 on 2018 May 29). The temporal, spatial, and energetic properties of each are discussed in context with previously published HXR brightenings. They are seen to display several “large flare” properties, such as impulsive time profiles and earlier peak times in higher-energy HXRs. For two events where the active region background could be removed, microflare emission did not display spatial complexity; differing NuSTAR energy ranges had equivalent emission centroids. Finally, spectral fitting showed a high-energy excess over a single thermal model in all events. This excess was consistent with additional higher-temperature plasma volumes in 10/11 microflares and  only with an accelerated particle distribution in the last. Previous NuSTAR studies focused on one or a few microflares at a time, making this the first to collectively examine a sizable number of events. Additionally, this paper introduces an observed variation in the NuSTAR gain unique to the extremely low livetime (&lt;1%) regime and establishes a correction method to be used in future NuSTAR solar spectral analysis.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We examine Lyman continuum (LyC) leakage through H <jats:sc>ii</jats:sc> regions regulated by turbulence and radiative feedback in a giant molecular cloud in the context of fully coupled radiation hydrodynamics (RHD). The physical relations of the LyC escape with H <jats:sc>i</jats:sc> covering fraction, kinematics, ionizing photon production efficiency, and emergent Ly<jats:italic>α</jats:italic> line profiles are studied using a series of RHD turbulence simulations performed with <jats:sc>ramses-rt</jats:sc>. The turbulence-regulated mechanism allows ionizing photons to leak out at early times before the onset of supernova feedback. The LyC photons escape through turbulence-generated low column density channels that are evacuated efficiently by radiative feedback via photoheating-induced shocks across the D-type ionization fronts. The Ly<jats:italic>α</jats:italic> photons funnel through the photoionized channels along the paths of LyC escape, resulting in a diverse Ly<jats:italic>α</jats:italic> spectral morphology including narrow double-peaked profiles. The Ly<jats:italic>α</jats:italic> peak separation is controlled by the residual H <jats:sc>i</jats:sc> column density of the channels, and the line asymmetry correlates with the porosity and multiphase structure of the H <jats:sc>ii</jats:sc> region. This mechanism through the turbulent H <jats:sc>ii</jats:sc> regions can naturally reproduce the observed Ly<jats:italic>α</jats:italic> spectral characteristics of some of the LyC-leaking galaxies. This RHD turbulence origin provides an appealing hypothesis to explain high LyC leakage from very young (∼3 Myr) star-forming galaxies found in the local universe without need of extreme galactic outflows or supernova feedback. We discuss the implications of the turbulent H <jats:sc>ii</jats:sc> regions on other nebular emission lines and a possible observational test with the Magellanic System and local blue compact dwarf galaxies as analogs of reionization-era systems.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent observations have shown a remarkable diversity of observational behaviors and explosion mechanisms in thermonuclear supernovae (SNe). An emerging class of peculiar thermonuclear SNe, called Type Iax, show photometric and spectroscopic behaviors distinct from normal Type Ia. Their origin remains highly controversial, but pure turbulent deflagration of white dwarfs (WDs) has been regarded as the leading formation theory. The large population of Type Iax indicates the existence of unidentified Galactic Type Iax supernova remnants (SNRs). We report evidence that SNR Sgr A East in the Galactic center resulted from a pure turbulent deflagration of a Chandrasekhar-mass carbon–oxygen WD, an explosion mechanism used for Type Iax SNe. Our X-ray spectroscopic study of Sgr A East using 3 Ms of Chandra data shows a low ratio of intermediate-mass elements to Fe and large Mn/Fe and Ni/Fe ratios. This abundance pattern does not accord with the core-collapse or normal Type Ia models. Sgr A East is thus the first Galactic SNR for which a likely Type Iax origin has been proposed and is the nearest target for studying this peculiar class. We compared Sgr A East with the Fe-rich SNRs 3C 397 and W49B, which also have high Mn and Cr abundances and were claimed to result from deflagration-to-detonation explosions of Chandrasekhar-mass WDs (although with disputes). Our study shows that they have distinct abundance patterns. The X-ray spectroscopic studies of thermonuclear SNRs provide observational evidence for the theories that there are diverse explosion channels and various metal outputs for Chandrasekhar-mass WDs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Weak gravitational lensing measurements based on photometry are limited by shape noise: the variance in the unknown unlensed orientations of the source galaxies. If the source is a disk galaxy with a well-ordered velocity field, however, velocity field data can support simultaneous inference of the shear, inclination, and position angle, virtually eliminating shape noise. We use the Fisher information matrix formalism to forecast the precision of this method in the idealized case of a perfectly ordered velocity field defined on an infinitesimally thin disk. For nearly face-on targets, one shear component, <jats:italic>γ</jats:italic> <jats:sub>×</jats:sub>, can be constrained to <jats:inline-formula> <jats:tex-math> <?CDATA $0.003\tfrac{90}{{I}_{0}}\tfrac{25}{{n}_{\mathrm{pix}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd548ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, where <jats:italic>I</jats:italic> <jats:sub>0</jats:sub> is the signal-to-noise ratio of the central intensity pixel and <jats:italic>n</jats:italic> <jats:sub>pix</jats:sub> is the number of pixels across a diameter enclosing 80% of the light. This precision degrades with inclination angle by a factor of 3 by <jats:italic>i</jats:italic> = 50°. The uncertainty on the other shear component, <jats:italic>γ</jats:italic> <jats:sub>+</jats:sub>, is about 1.5 (7) times larger than the <jats:italic>γ</jats:italic> <jats:sub>×</jats:sub> uncertainty for targets at <jats:italic>i</jats:italic> = 10° (50°). For an arbitrary galaxy position angle on the sky, these forecasts apply not to <jats:italic>γ</jats:italic> <jats:sub>+</jats:sub> and <jats:italic>γ</jats:italic> <jats:sub>×</jats:sub> as defined on the sky but to two eigenvectors in (<jats:italic>γ</jats:italic> <jats:sub>+</jats:sub>, <jats:italic>γ</jats:italic> <jats:sub>×</jats:sub>, <jats:italic>μ</jats:italic>) space, where <jats:italic>μ</jats:italic> is the magnification. We also forecast the potential of less expensive partial observations of the velocity field, such as slit spectroscopy. We conclude by outlining some ways in which real galaxies depart from our idealized model and thus create random or systematic uncertainties not captured here. In particular, our forecast <jats:italic>γ</jats:italic> <jats:sub>×</jats:sub> precision is currently limited only by the data quality rather than scatter in galaxy properties because the relevant type of scatter has yet to be measured.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Our understanding of the background of the EPIC/pn camera on board XMM-Newton is incomplete. This affects the study of extended sources and can influence the predictions of the expected background of future X-ray missions, such as the Advanced Telescope for High Energy Astrophysics (ATHENA). Here we provide new results based on the analysis of the largest data set ever used. We focus on the unconcentrated component of the EPIC/pn background, supposedly related to cosmic rays interacting with detector and telescope structures. We show that the so-called out field-of-view region of the pn detector is actually exposed to the sky. After carefully cleaning from the sky contamination, the unconcentrated background measured in the out field-of-view region does not show significant spatial variations, and its time behavior is anticorrelated with the solar cycle. We find a very tight linear correlation between unconcentrated backgrounds detected in the EPIC/pn and EPIC/MOS2 cameras. This relationship permits the correct evaluation of the pn unconcentrated background of each exposure on the basis of MOS2 data, avoiding the use of the contaminated out field-of-view region of the pn, as done in standard techniques. We find a tight linear correlation between the pn unconcentrated background and the proton flux in the 630–970 MeV energy band, as measured by the EPHIN instrument on board SOHO. Through this relationship, we quantify the contribution of cosmic-ray interaction to the pn unconcentrated background. This reveals a second source that contributes to the pn unconcentrated background for a significant fraction (30%–70%). This agent does not depend on the solar cycle or vary with time and is roughly isotropic. After having ruled out several candidates, we find that the hard X-ray photons of the cosmic X-ray background satisfy all known properties of the constant component. Our findings provide an important observational confirmation of simulation results on ATHENA and suggest that a high-energy particle monitor could contribute decisively to the reproducibility of the background for both experiments on ATHENA.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The transition from prompt to afterglow emission is one of the most exciting and least understood phases in gamma-ray bursts (GRBs). Correlations among optical, X-ray, and gamma-ray emission in GRBs have been explored, to attempt to answer whether the earliest optical emission comes from internal and/or external shocks. We present optical photometric observations of GRB 180325A collected with the TAROT and RATIR ground-based telescopes. These observations show two strong optical flashes with separate peaks at ∼50 and ∼120 s, followed by a temporally extended optical emission. We also present X-rays and gamma-ray observations of GRB 180325A, detected by the Burst Alert Telescope and X-ray Telescope, on the Neil Gehrels Swift observatory, which both observed a narrow flash at ∼80 s. We show that the prompt gamma-ray and X-ray early emission shares similar temporal and spectral features consistent with internal dissipation within the relativistic outflow (e.g., by internal shocks or magnetic reconnection), while the early optical flashes are likely generated by the reverse shock that decelerates the ejecta as it sweeps up the external medium.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Shock parameters at Earth’s bow shock in rare instances can approach the Mach numbers predicted at supernova remnants. We present our analysis of a high Alfvén Mach number (<jats:italic>M</jats:italic> <jats:sub>A</jats:sub> = 27) shock utilizing multipoint measurements from the Magnetospheric Multiscale spacecraft during a crossing of Earth’s quasi-perpendicular bow shock. We find that the shock dynamics are mostly driven by reflected ions, perturbations that they generate, and nonlinear amplification of the perturbations. Our analyses show that reflected ions create modest magnetic enhancements upstream of the shock, which evolve in a nonlinear manner as they traverse the shock foot. They can transform into proto-shocks that propagate at small angles to the magnetic field and toward the bow shock. The nonstationary bow shock shows signatures of both reformation and surface ripples. Our observations indicate that although shock reformation occurs, the main shock layer never disappears. These observations are at high plasma <jats:italic>β</jats:italic>, a parameter regime that has not been well explored by numerical models.</jats:p>