Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Ultralight bosons are a proposed solution to outstanding problems in cosmology and particle physics: they provide a dark-matter candidate while potentially explaining the strong charge-parity problem. If they exist, ultralight bosons can interact with black holes through the superradiant instability. In this work we explore the consequences of this instability on the evolution of hierarchical black holes within dense stellar clusters. By reducing the spin of individual black holes, superradiance reduces the recoil velocity of merging binary black holes, which, in turn, increases the retention fraction of hierarchical merger remnants. We show that the existence of ultralight bosons with mass 2 × 10<jats:sup>−14</jats:sup> ≲ <jats:italic>μ</jats:italic>/eV ≲ 2 × 10<jats:sup>−13</jats:sup> would lead to an increased rate of hierarchical black hole mergers in nuclear star clusters. An ultralight boson in this energy range would result in up to ≈60% more present-day nuclear star clusters supporting hierarchical growth. The presence of an ultralight boson can also double the rate of intermediate-mass black hole mergers to ≈0.08 Gpc<jats:sup>−3</jats:sup> yr<jats:sup>−1</jats:sup> in the local universe. These results imply that a select range of ultralight boson masses can have far-reaching consequences for the population of black holes in dense stellar environments. Future studies into black hole cluster populations and the spin distribution of hierarchically formed black holes will test this scenario.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The joint detection of gravitational waves and the gamma-ray counterpart of a binary neutron star merger event, GW170817, unambiguously validates the connection between short gamma-ray bursts and compact binary object (CBO) mergers. We focus on a special scenario where short gamma-ray bursts produced by CBO mergers are embedded in disks of active galactic nuclei (AGNs), and we investigate the <jats:italic>γ</jats:italic>-ray emission produced in the internal dissipation region via synchrotron, synchrotron self-Compton, and external inverse Compton (EIC) processes. In this scenario, isotropic thermal photons from the AGN disks contribute to the EIC component. We show that a low-density cavity can be formed in the migration traps, leading to the embedded mergers producing successful GRB jets. We find that the EIC component would dominate the GeV emission for typical CBO mergers with an isotropic-equivalent luminosity of <jats:italic>L</jats:italic> <jats:sub> <jats:italic>j</jats:italic>,iso</jats:sub> = 10<jats:sup>48.5</jats:sup> erg s<jats:sup>−1</jats:sup> that are located close to the central supermassive black hole. Considering a long-lasting jet of duration <jats:italic>T</jats:italic> <jats:sub>dur</jats:sub> ∼ 10<jats:sup>2</jats:sup>–10<jats:sup>3</jats:sup> s, we find that the future Cherenkov Telescope Array (CTA) will be able to detect its 25–100 GeV emission out to a redshift <jats:italic>z</jats:italic> = 1.0. In the optimistic case, it is possible to detect the on-axis extended emission simultaneously with GWs within one decade using MAGIC, H.E.S.S., VERITAS, CTA, and LHAASO-WCDA. Early diagnosis of prompt emissions with Fermi-GBM and HAWC can provide valuable directional information for the follow-up observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Dust-induced polarization in the interstellar medium (ISM) is due to asymmetric grains aligned with an external reference direction, usually the magnetic field. For both the leading alignment theories, the alignment of the grain’s angular momentum with one of its principal axes and the coupling with the magnetic field requires the grain to be paramagnetic. Of the two main components of interstellar dust, silicates are paramagnetic, while carbon dust is diamagnetic. Hence, carbon grains are not expected to align in the ISM. To probe the physics of carbon grain alignment, we have acquired Stratospheric Observatory for Infrared Astronomy/Higch-resolution Airborne Wideband Camera-plus far-infrared photometry and polarimetry of the carbon-rich circumstellar envelope (CSE) of the asymptotic giant branch star IRC+10° 216. The dust in such CSEs are fully carbonaceous and thus provide unique laboratories for probing carbon grain alignment. We find a centrosymmetric, radial, polarization pattern, where the polarization fraction is well correlated with the dust temperature. Together with estimates of a low fractional polarization from optical polarization of background stars, we interpret these results to be due to a second-order, direct radiative external alignment of grains without internal alignment. Our results indicate that (pure) carbon dust does not contribute significantly to the observed ISM polarization, consistent with the nondetection of polarization in the 3.4 <jats:italic>μ</jats:italic>m feature due to aliphatic CH bonds on the grain surface.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The search for extraterrestrial intelligence at radio frequencies has largely been focused on continuous-wave narrowband signals. We demonstrate that broadband pulsed beacons are energetically efficient compared to narrowband beacons over longer operational timescales. Here, we report the first extensive survey searching for such broadband pulsed beacons toward 1883 stars as a part of the Breakthrough Listen’s search for advanced intelligent life. We conducted 233 hr of deep observations across 4–8 GHz using the Robert C. Byrd Green Bank Telescope and searched for three different classes of signals with artificial (or negative) dispersion. We report a detailed search—leveraging a convolutional neural network classifier on high-performance GPUs—deployed for the very first time in a large-scale search for signals from extraterrestrial intelligence. Due to the absence of any signal-of-interest from our survey, we place a constraint on the existence of broadband pulsed beacons in our solar neighborhood: ≲1 in 1000 stars have transmitter power densities ≳10<jats:sup>5</jats:sup> W Hz<jats:sup>−1</jats:sup> repeating ≤500 s at these frequencies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We assemble a large comprehensive sample of 2534 <jats:italic>z</jats:italic> ∼ 2, 3, 4, 5, 6, 7, 8, and 9 galaxies lensed by the six clusters from the Hubble Frontier Fields (HFF) program. Making use of the availability of multiple independent magnification models for each of the HFF clusters and alternatively treating one of the models as the “truth,” we show that the median magnification factors from the v4 parametric models are typically reliable to values of 30–50, and in one case to 100. Using the median magnification factor from the latest v4 models, we estimate the UV luminosities of the 2534 lensed <jats:italic>z</jats:italic> ∼ 2–9 galaxies, finding sources as faint as −12.4 mag at <jats:italic>z</jats:italic> ∼ 3 and −12.9 mag at <jats:italic>z</jats:italic> ∼ 7. We explicitly demonstrate the power of the surface density–magnification relations Σ(<jats:italic>z</jats:italic>) versus <jats:italic>μ</jats:italic> in the HFF clusters to constrain both distant galaxy properties and cluster lensing properties. Based on the Σ(<jats:italic>z</jats:italic>) versus <jats:italic>μ</jats:italic> relations, we show that the median magnification estimates from existing public models must be reliable predictors of the true magnification <jats:italic>μ</jats:italic> to <jats:italic>μ</jats:italic> &lt; 15 (95% confidence). We also use the observed Σ(<jats:italic>z</jats:italic>) versus <jats:italic>μ</jats:italic> relations to derive constraints on the evolution of the luminosity function faint-end slope from <jats:italic>z</jats:italic> ∼ 7 to <jats:italic>z</jats:italic> ∼ 2, showing that faint-end slope results can be consistent with blank-field studies if, and only if, the selection efficiency shows no strong dependence on the magnification factor <jats:italic>μ</jats:italic>. This can only be the case if very low-luminosity galaxies are very small, being unresolved in deep lensing probes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Rocky bodies of the inner solar system display a systematic depletion of “moderately volatile elements” (MVEs) that correlates with the expected condensation temperature of their likely host materials under protoplanetary nebula conditions. In this paper, we present and test a new hypothesis in which open-system loss processes irreversibly remove vaporized MVEs from high nebula altitudes, leaving behind the more refractory solids residing much closer to the midplane. The MVEs irreversibly lost from the nebula through these open-system loss processes are then simply unavailable for condensation onto planetesimals forming even much later, after the nebula has cooled, overcoming a critical difficulty encountered by previous models of this type. We model open-system loss processes operating at high nebula altitudes, such as resulting from disk winds flowing out of the system entirely, or layered accretion directly onto the young Sun. We find that mass-loss rates higher than those found in typical T-Tauri disk winds, lasting short periods of time, are most satisfactory, pointing to multiple intense early outburst stages. Using our global nebula model, incorporating realistic particle growth and inward drift for solids, we constrain how much the MVE-depletion signature in the inner region is diluted by the drift of undepleted material from the outer nebula. We also find that a significant irreversible loss of the common rock-forming elements (Fe, Mg, Si) can occur, leading to a new explanation of another long-standing puzzle of the apparent “enhancement” in the relative abundance of highly refractory elements in chondrites.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Active galactic nuclei (AGNs) are promising environments for the assembly of merging binary black hole (BBH) systems. Interest in AGNs as nurseries for merging BBHs is rising, following the detection of gravitational waves from a BBH system from the purported pair-instability mass gap, most notably GW190521. AGNs have also been invoked to explain the formation of the high-mass-ratio system GW190814. We draw on simulations of BBH systems in AGNs to propose a phenomenological model for the distribution of black hole spins of merging binaries in AGN disks. The model incorporates distinct features that make the AGN channel potentially distinguishable from other channels, such as assembly in the field and in globular clusters. The model parameters can be mapped heuristically to the age and density of the AGN disks. We estimate the extent to which different populations of mergers in AGNs can be distinguished. If the majority of merging black holes are assembled in AGNs, future gravitational-wave observations may provide insights into the dynamics of AGN disks.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on the study of six Chandra observations (four epochs) of the Central Compact Object (CCO) in the Cassiopeia A supernova remnant with the ACIS instrument in the subarray mode. This mode minimizes spectrum-distorting instrumental effects such as pileup. The data were taken over a time span of ∼14 yr. If a non-magnetic carbon atmosphere is assumed for this youngest known CCO, then the temperature change is constrained to be <jats:inline-formula> <jats:tex-math> <?CDATA $\dot{T}=-2900\pm 600$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:mn>2900</mml:mn> <mml:mo>±</mml:mo> <mml:mn>600</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6dcaieqn1.gif" xlink:type="simple" /> </jats:inline-formula> K yr<jats:sup>−1</jats:sup> or <jats:inline-formula> <jats:tex-math> <?CDATA $\dot{T}=-4500\pm 800$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:mn>4500</mml:mn> <mml:mo>±</mml:mo> <mml:mn>800</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6dcaieqn2.gif" xlink:type="simple" /> </jats:inline-formula> K yr<jats:sup>−1</jats:sup> (1<jats:italic>σ</jats:italic> uncertainties) for constant or varying absorbing hydrogen column density. These values correspond to cooling rates of −1.5% ± 0.3% per 10 yr and −2.3% ± 0.4% per 10 yr, respectively. We discuss an apparent increase in the cooling rate in the last five years and the variations of the inferred absorbing hydrogen column densities between epochs. Considered together, these changes could indicate systematic effects such as caused by, e.g., an imperfect calibration of the increasing contamination of the ACIS filter.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The variability of blazars in the X-ray and optical regions both informs the physics of their emitting region and places demands on the observer if a program requires that the object be bright or faint. The extensive simultaneous X-ray and optical observation by the Neil Gehrels Swift Observatory (Swift) provides the best insight into the variable nature of these objects. This program uses Swift data for 19 X-ray-bright blazars, generally at <jats:italic>z</jats:italic> &gt; 0.1, to determine their variability properties. The analysis is based on structure functions and provides insight into the nature of the variability and how it depends on time, luminosity, and redshift. We also consider strategies for observing blazars at or above average brightness, given a time delay between planning an observation and obtaining the data. This is critical to observations with orbiting X-ray telescopes, current or future. The variability in the soft X-ray band is typically three to eight times larger than at UV–optical wavelengths, at fixed time differences (i.e., 30 or 100 days). There is almost no difference in the amplitude of variation (X-ray or UV–optical) as a function of redshift (time delay of 30 days) and a modest positive correlation with luminosity. In the X-ray band, blazars that become brighter than normal typically remain bright for at least 2–3 months, although with significant flickering. One can avoid observing objects that are significantly below the average X-ray flux by scheduling the observation when <jats:italic>F</jats:italic> <jats:sub>X</jats:sub> &gt; 0.9<jats:italic>F</jats:italic> <jats:sub>X,avg</jats:sub>, which requires monitoring observations near the time of the scheduling activity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Progenitor models for the “luminous” subclass of Fast Blue Optical Transients (LFBOTs; prototype: AT2018cow) are challenged to simultaneously explain all of their observed properties: fast optical rise times of days or less; peak luminosities ≳10<jats:sup>44</jats:sup> erg s<jats:sup>−1</jats:sup>; low yields ≲0.1<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> of <jats:sup>56</jats:sup>Ni; aspherical ejecta with a wide velocity range (≲3000 km s<jats:sup>−1</jats:sup> to ≳0.1–0.5<jats:italic>c</jats:italic> with increasing polar latitude); presence of hydrogen-depleted-but-not-free dense circumstellar material (CSM) on radial scales from ∼10<jats:sup>14</jats:sup> cm to ∼3 × 10<jats:sup>16</jats:sup> cm; embedded variable source of non-thermal X-ray/<jats:italic>γ</jats:italic>-rays, suggestive of a compact object. We show that all of these properties are consistent with the tidal disruption and hyper-accretion of a Wolf-Rayet (WR) star by a black hole or neutron star binary companion. In contrast with related previous models, the merger occurs with a long delay (≳100 yr) following the common envelope (CE) event responsible for birthing the binary, as a result of gradual angular momentum loss to a relic circumbinary disk. Disk-wind outflows from the merger-generated accretion flow generate the <jats:sup>56</jats:sup>Ni-poor aspherical ejecta with the requisite velocity range. The optical light curve is powered primarily by reprocessing X-rays from the inner accretion flow/jet, though CSM shock interaction also contributes. Primary CSM sources include WR mass loss from the earliest stages of the merger (≲10<jats:sup>14</jats:sup> cm) and the relic CE disk and its photoevaporation-driven wind (≳10<jats:sup>16</jats:sup> cm). Longer delayed mergers may instead give rise to supernovae Type Ibn/Icn (depending on the WR evolutionary state), connecting these transient classes with LFBOTs.</jats:p>