Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Waves and oscillations are important solar phenomena, not only because they can propagate and dissipate energy in the chromosphere, but also because they carry information about the structure of the atmosphere in which they propagate. The nature of the 3 minute oscillations observed in the umbral region of sunspots is considered to be an effect of propagation of magnetohydrodynamic waves upward from below the photosphere. We present a study of sunspot oscillations and wave propagation in NOAA Active Region 12470 using an approximately 1 hr long data set acquired on 2015 December 17 by the Atacama Large Millimeter/submillimeter Array (ALMA), the Goode Solar Telescope (GST) operating at the Big Bear Solar Observatory, the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, and the Interface Region Imaging Spectrograph. The ALMA data are unique in providing a time series of direct temperature measurements in the sunspot chromosphere. The 2 s cadence of ALMA images allows us to well resolve the 3 minute periods typical of sunspot oscillations in the chromosphere. Fourier analysis is applied to ALMA Band 3 (∼100 GHz, ∼3 mm) and GST H<jats:italic>α</jats:italic> data sets to obtain power spectra as well as oscillation phase information. We analyzed properties of the wave propagation by combining multiple wavelengths that probe physical parameters of solar atmosphere at different heights. We find that the ALMA temperature fluctuations are consistent with that expected for a propagating acoustic wave, with a slight asymmetry indicating nonlinear steepening.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We introduce a semiparametric model for the primary mass distribution of binary black holes (BBHs) observed with gravitational waves (GWs) that applies a cubic-spline perturbation to a power law. We apply this model to the 46 BBHs included in the second gravitational-wave transient catalog (GWTC-2). The spline perturbation model recovers a consistent primary mass distribution with previous results, corroborating the existence of a peak at 35 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> (&gt;97% credibility) found with the P<jats:sc>owerlaw</jats:sc>+P<jats:sc>eak</jats:sc> model. The peak could be the result of pulsational pair-instability supernovae. The spline perturbation model finds potential signs of additional features in the primary mass distribution at lower masses similar to those previously reported by Tiwari and Fairhurst. However, with fluctuations due to small-number statistics, the simpler P<jats:sc>owerlaw</jats:sc>+P<jats:sc>eak</jats:sc> and B<jats:sc>roken</jats:sc>P<jats:sc>owerlaw</jats:sc> models are both still perfectly consistent with observations. Our semiparametric approach serves as a way to bridge the gap between parametric and nonparametric models to more accurately measure the BBH mass distribution. With larger catalogs we will be able to use this model to resolve possible additional features that could be used to perform cosmological measurements and will build on our understanding of BBH formation, stellar evolution, and nuclear astrophysics.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>NGC 1566 is a changing-look active galaxy that exhibited an outburst during 2017–2018 with a peak in 2018 June. We triggered AstroSat observations of NGC 1566 twice in 2018 August and October during its declining phase. Using the AstroSat observations, along with two XMM-Newton observations in 2015 (pre-outburst) and 2018 June (peak outburst), we found that the X-ray power law, the soft X-ray excess, and the disk components showed extreme variability during the outburst. Especially, the soft excess was negligible in 2015 before the outburst, increased to a maximum level by a factor of &gt;200 in 2018 June, and reduced dramatically by a factor of ∼7.4 in 2018 August and became undetectable in 2018 October. The Eddington fraction (<jats:italic>L</jats:italic>/<jats:italic>L</jats:italic> <jats:sub>Edd</jats:sub>) increased from ∼0.1% (2015) to ∼5% (2018 June) and then decreased to ∼1.5% (2018 August) and 0.3% (2018 October). Thus, NGC 1566 made a spectral transition from a high soft-excess state to a negligible soft-excess state at a few percent of the Eddington rate. The soft excess is consistent with warm Comptonization in the inner disk that appears to have developed during the outburst and disappeared toward the end of the outburst over a timescale comparable to the sound-crossing time. The multiwavelength spectral evolution of NGC 1566 during the outburst is most likely caused by the radiation pressure instability in the inner regions of the accretion disk in NGC 1566.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Eccentricity has emerged as a potentially useful tool for helping to identify the origin of black hole mergers. However, eccentric templates can be computationally very expensive owing to the large number of harmonics, making statistical analyses to distinguish formation channels very challenging. We outline a method for estimating the signal-to-noise ratio (S/N) for inspiraling binaries at lower frequencies such as those proposed for LISA and DECIGO. Our approximation can be useful more generally for any quasi-periodic sources. We argue that surprisingly, the S/N evaluated at or near the peak frequency (of the power) is well approximated by using a constant-noise curve, even if in reality the noise strain has power-law dependence. We furthermore improve this initial estimate over our previous calculation to allow for frequency dependence in the noise to expand the range of eccentricity and frequency over which our approximation applies. We show how to apply this method to get an answer accurate to within a factor of 2 over almost the entire projected observable frequency range. We emphasize this method is not a replacement for detailed signal processing. The utility lies chiefly in identifying theoretically useful discriminators among different populations and providing fairly accurate estimates for how well they should work. This approximation can furthermore be useful for narrowing down parameter ranges in a computationally economical way when events are observed. We furthermore show a distinctive way to identify events with extremely high eccentricity where the signal is enhanced relative to naive expectations on the high-frequency end.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present analytic integral solutions for the second-order induced gravitational waves (GWs). After presenting all the possible second-order source terms, we calculate explicitly the solutions for the GWs induced by the linear scalar and tensor perturbations during matter- and radiation-dominated epochs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the result of a search for neutrinos in coincidence with solar flares from the GOES flare database. The search was performed on a 10.8 kton-year exposure of KamLAND collected from 2002 to 2019. This large exposure allows us to explore previously unconstrained parameter space for solar flare neutrinos. We found no statistical excess of neutrinos and established 90% confidence level upper limits of 8.4 × 10<jats:sup>7</jats:sup> cm<jats:sup>−2</jats:sup> (3.0 × 10<jats:sup>9</jats:sup> cm<jats:sup>−2</jats:sup>) on the electron antineutrino (electron neutrino) fluence at 20 MeV normalized to the X12 flare, assuming that the neutrino fluence is proportional to the X-ray intensity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A multiwavelength observing campaign of the T Tauri star (TTS) GM Aur was undertaken in 2019 December. This campaign obtained Swift X-ray and NUV fluxes, HST NUV spectra, LCOGT <jats:inline-formula> <jats:tex-math> <?CDATA ${u}^{{\prime} }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mrow> <mml:mi>u</mml:mi> </mml:mrow> <mml:mrow> <mml:mo accent="true">′</mml:mo> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac365aieqn1.gif" xlink:type="simple" /> </jats:inline-formula> <jats:inline-formula> <jats:tex-math> <?CDATA ${g}^{{\prime} }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mrow> <mml:mi>g</mml:mi> </mml:mrow> <mml:mrow> <mml:mo accent="true">′</mml:mo> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac365aieqn2.gif" xlink:type="simple" /> </jats:inline-formula> <jats:inline-formula> <jats:tex-math> <?CDATA ${r}^{{\prime} }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> <mml:mrow> <mml:mo accent="true">′</mml:mo> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac365aieqn3.gif" xlink:type="simple" /> </jats:inline-formula> <jats:inline-formula> <jats:tex-math> <?CDATA ${i}^{{\prime} }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mrow> <mml:mi>i</mml:mi> </mml:mrow> <mml:mrow> <mml:mo accent="true">′</mml:mo> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac365aieqn4.gif" xlink:type="simple" /> </jats:inline-formula> and TESS photometry, CHIRON H<jats:italic>α</jats:italic> spectra, Atacama Large Millimeter/submillimeter Array (ALMA) <jats:sup>13</jats:sup>CO and C<jats:sup>18</jats:sup>O line fluxes, and Very Large Array (VLA) 3 cm continuum fluxes taken contemporaneously over one month. The X-ray to optical observations were presented previously. Here we present the ALMA and VLA data and make comparisons to GM Aur’s accretion and X-ray properties. We report no variability in the observed millimeter CO emission. Using disk chemistry models, we show that the magnitude of the changes seen in the FUV luminosity of GM Aur could lead to a variation of up to ∼6% in CO line emission and changes in the X-ray luminosity could lead to larger changes of ∼25%. However, the FUV and X-ray luminosity increases must last at least 100 years in order to induce changes, which seems implausible in the TTS stage; also, these changes would be too small to be detectable by ALMA. We report no variability in the 3 cm emission observed by the VLA, showing that changes of less than a factor of ∼3 in the accretion rates of TTSs do not lead to detectable changes in the mass-loss rate traced by the jet at centimeter wavelengths. We conclude that changes typically seen in the FUV and X-ray luminosities of TTSs do not lead to observable changes in millimeter CO line emission or jet centimeter continuum emission.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Neutral hydrogen has been shown to greatly impact the plasma flow in the heliosphere and the location of the heliospheric boundaries. We present the results of the Solar Wind with Hydrogen Ion Exchange and Large-scale Dynamics (SHIELD) model, a new, self-consistent, kinetic–MHD model of the outer heliosphere within the Space Weather Modeling Framework. The charge exchange mean free path is on the order of the size of the heliosphere; therefore, the neutral atoms cannot be described as a fluid. The numerical code SHIELD couples the MHD solution for a single plasma fluid to the kinetic solution for neutral hydrogen atoms streaming through the system. The kinetic code is based on the Adaptive Mesh Particle Simulator, a Monte Carlo method for solving the Boltzmann equation. The numerical code SHIELD accurately predicts the increased filtration of interstellar neutrals into the heliosphere. In order to verify the correct implementation within the model, we compare the results of the numerical code SHIELD to those of other, well-established kinetic–MHD models. The numerical code SHIELD matches the neutral hydrogen solution of these studies as well as the shift in all heliospheric boundaries closer to the Sun in comparison with the multi-fluid treatment of neutral hydrogen atoms. Overall the numerical code SHIELD shows excellent agreement with these models and is a significant improvement to the fluid treatment of interstellar hydrogen.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>High-resolution SUVI images reveal an interesting new picture of particle acceleration in powerful solar eruptions. Typically, powerful solar eruptions include a coronal wave component, as well the traditional CME and flare components. At low solar altitudes, coronal waves refract downward, toward the solar surface, because of the slower Alfvén speeds at the base of the corona. The refracted wave plus the shock wave ahead of an intense CME allow for a two-step shock acceleration process that can result in relativistic or GLE particles. This mechanism may be particularly applicable to the first-to-arrive, prompt relativistic particles measured by the Fort Smith neutron monitor during GLE # 72 on 2017 September 10.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This paper analyses images from 43 to 340 GHz to trace the structure of the Source I (SrcI) disk in Orion-KL with ∼12 au resolution. The data reveal an almost edge-on disk with an outside diameter ∼100 au, which is heated from the inside. The high opacity at 220–340 GHz hides the internal structure and presents a surface temperature ∼500 K. Images at 43, 86 and 99 GHz reveal structure within the disk. At 43 GHz there is bright compact emission with brightness temperature ∼1300 K. Another feature, most prominent at 99 GHz, is a warped ridge of emission. The data can be explained by a simple model with a hot inner structure, seen through cooler material. A wide-angle outflow mapped in SiO emission ablates material from the interior of the disk, and extends in a bipolar outflow over 1000 au along the rotation axis of the disk. SiO <jats:italic>v</jats:italic> = 0, <jats:italic>J</jats:italic> = 5–4 emission appears to have a localized footprint in the warped ridge. These observations suggest that the ridge is the working surface of the disk, and heated by accretion and the outflow. The disk structure may be evolving, with multiple accretion and outflow events. We discuss two sources of variability: (1) variable accretion onto the disk as SrcI travels through the filamentary debris from the Becklin–Neugebauer Object-SrcI encounter ∼550 yr ago; and (2) episodic accretion from the disk onto the protostar, which may trigger multiple outflows. The warped inner-disk structure is direct evidence that SrcI could be a binary experiencing episodic accretion.</jats:p>