Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Collapsar disks have been proposed to be rich factories of heavy elements, but the major question of whether their outflows are neutron rich and could therefore represent significant sites of the rapid neutron-capture (<jats:italic>r</jats:italic>-) process or dominated by iron-group elements remains unresolved. We present the first global models of collapsars that start from a stellar progenitor and self-consistently describe the evolution of the disk, its composition, and its outflows in response to the imploding stellar mantle, using energy-dependent M1 neutrino transport and an <jats:italic>α</jats:italic>-viscosity to approximate turbulent angular-momentum transport. We find that a neutron-rich, neutrino-dominated accretion flow (NDAF) is established only marginally—either for short times or relatively low viscosities—because the disk tends to disintegrate into an advective disk already at relatively high mass-accretion rates, launching powerful outflows but preventing it from developing a hot, dense, and therefore neutron-rich core. Viscous outflows disrupt the star within ∼100 s with explosion energies close to that of hypernovae. If viscosity is ignored, a stable NDAF with disk mass of about 1 <jats:italic>M</jats:italic> <jats:sub>☉</jats:sub> is formed but is unable to release neutron-rich ejecta, while it produces a relatively mild explosion powered by a neutrino-driven wind blown off its surface. With ejecta electron fractions close to 0.5, all models presumably produce large amounts of <jats:sup>56</jats:sup>Ni. Our results suggest that collapsar models based on the <jats:italic>α</jats:italic>-viscosity are inefficient <jats:italic>r</jats:italic>-process sites and that genuinely magnetohydrodynamic effects may be required to generate neutron-rich outflows. A relatively weak effective viscosity generated by magnetohydrodynamic turbulence would improve the prospects for obtaining neutron-rich ejecta.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The majority of Type II-plateau supernovae (SNe IIP) have light curves that are not compatible with the explosions of stars in a vacuum; instead, the light curves require the progenitors to be embedded in circumstellar matter (CSM). We report on the successful fitting of the well-observed SN IIP 2021yja as a core-collapse explosion of a massive star with an initial mass of ∼15 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and a pre-explosion radius of 631 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub>. To explain the early-time behavior of the broadband light curves, the presence of 0.55 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> CSM within ∼2 × 10<jats:sup>14</jats:sup> cm is needed. Like many other SNe IIP, SN 2021yja exhibits an early-time flux excess including ultraviolet wavelengths. This, together with the short rise time (&lt;2 days) in the <jats:italic>gri</jats:italic> bands, indicates the presence of a compact component in the CSM, essentially adjacent to the progenitor. We discuss the origin of the preexisting CSM, which is most likely a common property of highly convective red supergiant envelopes. We argue that the difficulty in fitting the entire light curve with one spherical distribution indicates that the CSM around the SN 2021yja progenitor was asymmetric.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Observing habitable exoplanets that may resemble Earth is a key priority in astronomy that is dependent on not only detecting such worlds but also ascertaining that apparent signatures of habitability are not due to other sources. Space telescopes designed to observe such worlds, such as that recommended by NASA’s 2020 Astrophysics Decadal Survey, have a diffraction-limited resolution that effectively spreads light from a source in a region around the source point. In this Letter, we show that the diffraction limit of a 6 m space telescope results in a point-spread function of an Earth-like planet that may contain additional unanticipated bodies for systems at distances relevant to the proposed searches. These unexpected additional objects, such as other planets and moons, can influence obtained spectra for a putative habitable planet by producing spurious features and adding additional uncertainty to the spectra. A model of Earth observed by a 6 m space telescope as though it was an exoplanet shows that the light from the Earth would be blended with the Moon, Mercury, Venus, and Mars in various combinations and at different times for numerous combinations of distance to the system and wavelength. Given the importance of extricating the true spectra of a potentially habitable planet in order to search for biosignatures, we highlight the need to account for this effect during the development of relevant telescopes and suggest some potential means of accounting for this photobombing effect.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The rapid increase of the horizontal magnetic field (<jats:italic>B</jats:italic> <jats:sub> <jats:italic>h</jats:italic> </jats:sub>) around the flaring polarity inversion line is the most prominent photospheric field change during flares. It is considered to be caused by the contraction of flare loops, the details behind which is still not fully understood. Here we investigate the <jats:italic>B</jats:italic> <jats:sub> <jats:italic>h</jats:italic> </jats:sub> increase in 35 major flares using HMI high-cadence vector magnetograms. We find that the <jats:italic>B</jats:italic> <jats:sub> <jats:italic>h</jats:italic> </jats:sub> increase is always accompanied by the increase of field inclination. It usually initiates near the flare ribbons, showing a step-like change in between the ribbons. In particular, its evolution in the early flare phase shows a close spatiotemporal correlation to flare ribbons. We further find that the <jats:italic>B</jats:italic> <jats:sub> <jats:italic>h</jats:italic> </jats:sub> increase tends to have similar intensity in confined and eruptive flares but a larger spatial extent in eruptive flares in a statistical sense. Its intensity and timescale have inverse and positive correlations to the initial ribbon separations, respectively. The results altogether are well consistent with a recent proposed scenario that suggests that the reconnection-driven contraction of flare loops enhances the photospheric <jats:italic>B</jats:italic> <jats:sub> <jats:italic>h</jats:italic> </jats:sub> according to the ideal induction equation, providing statistical evidence of the reconnection-driven origin for the<jats:italic> B</jats:italic> <jats:sub> <jats:italic>h</jats:italic> </jats:sub> increase for the first time.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Optically quiescent quasars (OQQs) represent a recently systematized class of infrared-luminous active galactic nuclei (AGNs) that have galaxy-like optical continua. They may represent an interesting, brief phase in the AGN life cycle, e.g., either cocooned within high-covering-factor media or indicative of recent triggering, though their nature remains unclear. Here, we present the first targeted simultaneous X-ray observations of an OQQ, our previously identified prototype, SDSS J075139.06+402811.2 at <jats:italic>z</jats:italic> = 0.587. The source is significantly detected over 0.5–16 keV with XMM-Newton and NuSTAR, unambiguously confirming the presence of current accretion activity. Spectral modeling yields an intrinsic luminosity <jats:italic>L</jats:italic> <jats:sub>2–10 keV</jats:sub> ≈ 4.4 × 10<jats:sup>43</jats:sup> erg s<jats:sup>−1</jats:sup>, well within the AGN regime, but underluminous relative to its infrared power. It is lightly obscured, with log <jats:italic>N</jats:italic> <jats:sub>H</jats:sub> [cm<jats:sup>−2</jats:sup>] ≈ 22.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Low-mass compact stellar systems (CSSs; <jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub> &lt; 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) are thought to be a mixed bag of objects with various formation mechanisms. Previous surveys of CSSs were biased to relatively high-density environments and cannot provide a complete view of the environmental dependence of the formation of CSSs. We conduct the first-ever unbiased flux-limited census of nearby quiescent CSSs over a total sky area of ∼200 deg<jats:sup>2</jats:sup> observed by the GAMA spectroscopic survey. The complete sample includes 82 quiescent CSSs, of which 85% fall within the stellar mass range of classical compact ellipticals (cEs). By quantifying the local environment with the normalized projected distance <jats:italic>D/R</jats:italic> <jats:sub>vir</jats:sub> to the nearest luminous neighboring galaxy, we find that these CSSs have a bimodal <jats:italic>D/R</jats:italic> <jats:sub>vir</jats:sub> distribution, with one group peaking near ∼0.1 × <jats:italic>R</jats:italic> <jats:sub>vir</jats:sub> (satellite) and the other peaking near ∼10 × <jats:italic>R</jats:italic> <jats:sub>vir</jats:sub> (field). In contrast to the CSSs, ordinary quiescent galaxies of similar masses have a unimodal <jats:italic>D/R</jats:italic> <jats:sub>vir</jats:sub> distribution. Satellite CSSs are older and more metal-rich than field CSSs on average. The bimodal <jats:italic>D/R</jats:italic> <jats:sub>vir</jats:sub> distribution of quiescent CSSs reinforces the existence of two distinct formation channels (tidal stripping and born-to-be) for cEs and may be understood in two mutually inclusive perspectives, i.e., substantial tidal stripping happens only when satellite galaxies travel sufficiently close to their massive hosts, and there exists an excess of high-density cE-bearing subhalos close to massive halos.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>During its 10th orbit around the Sun, the Parker Solar Probe sampled two intervals where the local Alfvén speed exceeded the solar wind speed, lasting more than 10 hours in total. In this paper, we analyze the turbulence and wave properties during these periods. The turbulence is observed to be Alfvénic and unbalanced, dominated by outward-propagating modes. The power spectrum of the outward-propagating Elsässer <jats:italic>z</jats:italic> <jats:sup>+</jats:sup> mode steepens at high frequencies while that of the inward-propagating <jats:italic>z</jats:italic> <jats:sup>−</jats:sup> mode flattens. The observed Elsässer spectra can be explained by the nearly incompressible (NI) MHD turbulence model with both 2D and Alfvénic components. The modeling results show that the <jats:italic>z</jats:italic> <jats:sup>+</jats:sup> spectra are dominated by the NI/slab component, and the 2D component mainly affects the <jats:italic>z</jats:italic> <jats:sup>−</jats:sup> spectra at low frequencies. An MHD wave decomposition based on an isothermal closure suggests that outward-propagating Alfvén and fast magnetosonic wave modes are prevalent in the two sub-Alfvénic intervals, while the slow magnetosonic modes dominate the super-Alfvénic interval in between. The slow modes occur where the wavevector is nearly perpendicular to the local mean magnetic field, corresponding to nonpropagating pressure-balanced structures. The alternating forward and backward slow modes may also be features of magnetic reconnection in the near-Sun heliospheric current sheet.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In order to constrain the size of the optical continuum emission region in the dwarf Seyfert 1 galaxy NGC 4395 through reverberation mapping, we carried out high-cadence photometric monitoring in the <jats:italic>griz</jats:italic> filter bands on two consecutive nights in 2022 April using the four-channel MuSCAT3 camera on the Faulkes Telescope North at Haleakalā Observatory. Correlated variability across the <jats:italic>griz</jats:italic> bands is clearly detected, and the <jats:italic>r</jats:italic>-, <jats:italic>i</jats:italic>-, and <jats:italic>z</jats:italic>-band light curves show lags of <jats:inline-formula> <jats:tex-math> <?CDATA ${7.72}_{-1.09}^{+1.01}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>7.72</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.09</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.01</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac7e54ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, <jats:inline-formula> <jats:tex-math> <?CDATA ${14.16}_{-1.25}^{+1.22}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>14.16</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.25</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.22</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac7e54ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, and <jats:inline-formula> <jats:tex-math> <?CDATA ${20.78}_{-2.09}^{+1.99}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>20.78</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2.09</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.99</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac7e54ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> minutes with respect to the <jats:italic>g</jats:italic> band when measured using the full-duration light curves. When lags are measured for each night separately, the Night 2 data exhibit lower cross-correlation amplitudes and shorter lags than the Night 1 light curves. Using the full-duration lags, we find that the lag–wavelength relationship is consistent with the <jats:italic>τ</jats:italic> ∝ <jats:italic>λ</jats:italic> <jats:sup>4/3</jats:sup> dependence found for more luminous active galactic nuclei. Combining our results with continuum lags measured for other objects, the lag between <jats:italic>g</jats:italic> and <jats:italic>z</jats:italic> band scales with optical continuum luminosity as <jats:italic>τ</jats:italic> <jats:sub>gz</jats:sub> ∝ <jats:italic>L</jats:italic> <jats:sup>0.56±0.05</jats:sup>, similar to the scaling of broad-line region size with luminosity, reinforcing recent evidence that diffuse continuum emission from the broad-line region may contribute substantially to optical continuum variability and reverberation lags.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Multiwavelength observations suggest that the accretion disk in the hard and intermediate states of X-ray binaries (XRBs) and active galactic nucleus transitions from a cold, thin disk at large distances into a hot, thick flow close to the black hole (BH). However, the formation, structure, and dynamics of such truncated disks are poorly constrained due to the complexity of the thermodynamic, magnetic, and radiative processes involved. We present the first radiation-transport two-temperature general relativistic magnetohydrodynamic (GRMHD) simulations of truncated disks radiating at ∼35% of the Eddington luminosity with and without large-scale poloidal magnetic flux. We demonstrate that when a geometrically thin accretion disk is threaded by large-scale net poloidal magnetic flux, it self-consistently transitions at small radii into a two-phase medium of cold gas clumps floating through a hot, magnetically dominated corona. This transition occurs at a well-defined truncation radius determined by the distance out to which the disk is saturated with magnetic flux. The average ion and electron temperatures in the semiopaque corona reach, respectively, <jats:italic>T</jats:italic> <jats:sub> <jats:italic>i</jats:italic> </jats:sub> ≳ 10<jats:sup>10</jats:sup> K and <jats:italic>T</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub> ≳ 5 × 10<jats:sup>8</jats:sup> K. The system produces radiation, powerful collimated jets, and broader winds at the total energy efficiency exceeding 90%, the highest ever energy extraction efficiency from a spinning BH by a radiatively efficient flow in a GRMHD simulation. This is consistent with jetted ejections observed during XRB outbursts. The two-phase medium may naturally lead to broadened iron line emission observed in the hard state.</jats:p>