Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Multi-epoch narrowband Hubble Space Telescope images of the bipolar H <jats:sc>ii</jats:sc> region Sh2-106 reveal highly supersonic nebular proper motions that increase with projected distance from the massive young stellar object S106 IR, reaching over ∼30 mas yr<jats:sup>−1</jats:sup> (∼150 km s<jats:sup>−1</jats:sup> at D = 1.09 kpc) at a projected separation of ∼1.′4 (0.44 pc) from S106 IR. We propose that S106 IR experienced a ∼10<jats:sup>47</jats:sup> erg explosion ∼3500 yr ago. The explosion may be the result of a major accretion burst or a recent encounter with another star, or a consequence of the interaction of a companion with the bloated photosphere of S106 IR as it grew from ∼10 through ∼15 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> at a high accretion rate. Near-IR images reveal fingers of H<jats:sub>2</jats:sub> emission pointing away from S106 IR and an asymmetric photon-dominated region surrounding the ionized nebula. Radio continuum and Br<jats:italic>γ</jats:italic> emission reveal a C-shaped bend in the plasma, indicating either the motion of S106 IR toward the east, or the deflection of plasma toward the west by the surrounding cloud. The H <jats:sc>ii</jats:sc> region bends around a ∼1′ diameter dark bay west of S106 IR that may be shielded from direct illumination by a dense molecular clump. Herbig–Haro and Molecular Hydrogen Objects tracing outflows powered by stars in the Sh2-106 protocluster such as the Class 0 source S106 FIR are discussed.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Extremely variable quasars (EVQs) are a population of sources showing large optical photometric variability revealed by time-domain surveys. The physical origin of such extreme variability is yet unclear. In this first paper of a series, we construct the largest-ever sample of 14,012 EVQs using more than 15 yr of photometric data from Sloan Digital Sky Survey (SDSS) and Pan-STARRS1. We divide the EVQs into five subsamples according to the relative brightness of each EVQ during SDSS spectroscopic observation compared with the mean brightness from photometric observations. Corresponding control samples of normal quasars are built with matched redshift, bolometric luminosity, and supermassive black hole mass. We obtain the composite SDSS spectra of EVQs in various states and their corresponding control samples. We find EVQs exhibit clearly bluer SDSS spectra during bright states and clearly redder spectra during dim states, consistent with the “bluer-when-brighter” trend widely seen in normal quasars. We further find that the line equivalent widths (EWs) of broad Mg <jats:sc>II</jats:sc>, C <jats:sc>IV</jats:sc> and [O <jats:sc>III</jats:sc>] (but not broad H<jats:italic>β,</jats:italic> which is yet puzzling) gradually decreases from the dim state to the bright state, similar to the so-called intrinsic Baldwin effect commonly seen in normal active galactic nuclei. In addition, EVQs have consistently larger line EWs compared with the control samples. We also see that EVQs show slight excess in the very broad line component compared with control samples. Possible explanations for the discoveries are discussed. Our findings support the hypothesis that EVQs are in the tail of a broad distribution of quasar properties but are not a distinct population.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recently, the Hydrogen Epoch of Reionization Array (HERA) has produced the experiment’s first upper limits on the power spectrum of 21 cm fluctuations at <jats:italic>z</jats:italic> ∼ 8 and 10. Here, we use several independent theoretical models to infer constraints on the intergalactic medium (IGM) and galaxies during the epoch of reionization from these limits. We find that the IGM must have been heated above the adiabatic-cooling threshold by <jats:italic>z</jats:italic> ∼ 8, independent of uncertainties about IGM ionization and the radio background. Combining HERA limits with complementary observations constrains the spin temperature of the <jats:italic>z</jats:italic> ∼ 8 neutral IGM to 27 K <jats:inline-formula> <jats:tex-math> <?CDATA $\langle {\overline{T}}_{S}\rangle $?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〈</mml:mo> <mml:msub> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="true">¯</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mi>S</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">〉</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2ffcieqn1.gif" xlink:type="simple" /> </jats:inline-formula> 630 K (2.3 K <jats:inline-formula> <jats:tex-math> <?CDATA $\langle {\overline{T}}_{S}\rangle $?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〈</mml:mo> <mml:msub> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="true">¯</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mi>S</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">〉</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2ffcieqn2.gif" xlink:type="simple" /> </jats:inline-formula> 640 K) at 68% (95%) confidence. They therefore also place a lower bound on X-ray heating, a previously unconstrained aspects of early galaxies. For example, if the cosmic microwave background dominates the <jats:italic>z</jats:italic> ∼ 8 radio background, the new HERA limits imply that the first galaxies produced X-rays more efficiently than local ones. The <jats:italic>z</jats:italic> ∼ 10 limits require even earlier heating if dark-matter interactions cool the hydrogen gas. If an extra radio background is produced by galaxies, we rule out (at 95% confidence) the combination of high radio and low X-ray luminosities of <jats:italic>L</jats:italic> <jats:sub> <jats:italic>r</jats:italic>,<jats:italic>ν</jats:italic> </jats:sub>/SFR &gt; 4 × 10<jats:sup>24</jats:sup> W Hz<jats:sup>−1</jats:sup> <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{\odot }^{-1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2ffcieqn3.gif" xlink:type="simple" /> </jats:inline-formula> yr and <jats:italic>L</jats:italic> <jats:sub> <jats:italic>X</jats:italic> </jats:sub>/SFR &lt; 7.6 × 10<jats:sup>39</jats:sup> erg s<jats:sup>−1</jats:sup> <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{\odot }^{-1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2ffcieqn4.gif" xlink:type="simple" /> </jats:inline-formula> yr. The new HERA upper limits neither support nor disfavor a cosmological interpretation of the recent Experiment to Detect the Global EOR Signature (EDGES) measurement. The framework described here provides a foundation for the interpretation of future HERA results.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Relativistic reflection features in the X-ray spectra of black hole binaries and active galactic nuclei are thought to be produced through illumination of a cold accretion disk by a hot corona. In this work, we assume that the corona has the shape of an infinitesimally thin disk with its central axis the same as the rotational axis of the black hole. The corona can either be static or corotate with the accretion disk. We calculate the disk’s emissivity profiles and iron line shapes for a set of coronal radii and heights. We incorporate these emissivity profiles into <jats:monospace>relxill</jats:monospace>_<jats:monospace>nk</jats:monospace> and we simulate some observations of a black hole binary with the Nuclear Spectroscopic Telescope Array to study the impact of a disk-like coronal geometry on the measurement of the properties of the system, and in particular, on the possibility of testing the Kerr nature of the source. We find that, in general, the astrophysical properties of the accretion disk are recovered well even if we fit the data with a model employing a broken power law or a lamppost emissivity profile, while it is more challenging to constrain the geometric properties of the black hole spacetime.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using 2D particle-in-cell plasma simulations, we study electron acceleration by temperature anisotropy instabilities, assuming conditions typical of above-the-loop-top sources in solar flares. We focus on the long-term effect of <jats:italic>T</jats:italic> <jats:sub> <jats:italic>e</jats:italic>,⊥</jats:sub> &gt; <jats:italic>T</jats:italic> <jats:sub> <jats:italic>e</jats:italic>,∥</jats:sub> instabilities by driving the anisotropy growth during the entire simulation time through imposing a shearing or a compressing plasma velocity (<jats:italic>T</jats:italic> <jats:sub> <jats:italic>e</jats:italic>,⊥</jats:sub> and <jats:italic>T</jats:italic> <jats:sub> <jats:italic>e</jats:italic>,∥</jats:sub> are the temperatures perpendicular and parallel to the magnetic field). This magnetic growth makes <jats:italic>T</jats:italic> <jats:sub> <jats:italic>e</jats:italic>,⊥</jats:sub>/<jats:italic>T</jats:italic> <jats:sub> <jats:italic>e</jats:italic>,∥</jats:sub> grow due to electron magnetic moment conservation, and amplifies the ratio <jats:italic>ω</jats:italic> <jats:sub>ce</jats:sub>/<jats:italic>ω</jats:italic> <jats:sub>pe</jats:sub> from ∼0.53 to ∼2 (<jats:italic>ω</jats:italic> <jats:sub>ce</jats:sub> and <jats:italic>ω</jats:italic> <jats:sub>pe</jats:sub> are the electron cyclotron and plasma frequencies, respectively). In the regime <jats:italic>ω</jats:italic> <jats:sub>ce</jats:sub>/<jats:italic>ω</jats:italic> <jats:sub>pe</jats:sub> ≲ 1.2–1.7, the instability is dominated by oblique, quasi-electrostatic modes, and the acceleration is inefficient. When <jats:italic>ω</jats:italic> <jats:sub>ce</jats:sub>/<jats:italic>ω</jats:italic> <jats:sub>pe</jats:sub> has grown to <jats:italic>ω</jats:italic> <jats:sub>ce</jats:sub>/<jats:italic>ω</jats:italic> <jats:sub>pe</jats:sub> ≳ 1.2–1.7, electrons are efficiently accelerated by the inelastic scattering provided by unstable parallel, electromagnetic z modes. After <jats:italic>ω</jats:italic> <jats:sub>ce</jats:sub>/<jats:italic>ω</jats:italic> <jats:sub>pe</jats:sub> reaches ∼2, the electron energy spectra show nonthermal tails that differ between the shearing and compressing cases. In the shearing case, the tail resembles a power law of index <jats:italic>α</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub> ∼ 2.9 plus a high-energy bump reaching ∼300 keV. In the compressing runs, <jats:italic>α</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub> ∼ 3.7 with a spectral break above ∼500 keV. This difference can be explained by the different temperature evolutions in these two types of simulations, suggesting that a critical role is played by the type of anisotropy driving, <jats:italic>ω</jats:italic> <jats:sub>ce</jats:sub>/<jats:italic>ω</jats:italic> <jats:sub>pe</jats:sub>, and the electron temperature in the efficiency of the acceleration.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We carried out spectroscopic monitoring of 21 low-redshift Seyfert 1 galaxies using the Kast double spectrograph on the 3 m Shane telescope at Lick Observatory from 2016 April to 2017 May. Targeting active galactic nuclei (AGNs) with luminosities of <jats:italic>λ</jats:italic> <jats:italic>L</jats:italic> <jats:sub> <jats:italic>λ</jats:italic> </jats:sub>(5100 Å) ≈ 10<jats:sup>44</jats:sup> erg s<jats:sup>−1</jats:sup> and predicted H<jats:italic>β</jats:italic> lags of ∼20–30 days or black hole masses of 10<jats:sup>7</jats:sup>–10<jats:sup>8.5</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, our campaign probes luminosity-dependent trends in broad-line region (BLR) structure and dynamics as well as to improve calibrations for single-epoch estimates of quasar black hole masses. Here we present the first results from the campaign, including H<jats:italic>β</jats:italic> emission-line light curves, integrated H<jats:italic>β</jats:italic> lag times (8–30 days) measured against <jats:italic>V</jats:italic>-band continuum light curves, velocity-resolved reverberation lags, line widths of the broad H<jats:italic>β</jats:italic> components, and virial black hole mass estimates (10<jats:sup>7.1</jats:sup>–10<jats:sup>8.1</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>). Our results add significantly to the number of existing velocity-resolved lag measurements and reveal a diversity of BLR gas kinematics at moderately high AGN luminosities. AGN continuum luminosity appears not to be correlated with the type of kinematics that its BLR gas may exhibit. Follow-up direct modeling of this data set will elucidate the detailed kinematics and provide robust dynamical black hole masses for several objects in this sample.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>At scales much larger than the ion inertial scale and the gyroradius of thermal protons, the magnetohydrodynamic (MHD) theory is well equipped to describe the nature of solar wind turbulence. The turbulent spectrum itself is defined by a power law manifesting the energy cascading process. A break in the turbulence spectrum develops near-ion scales, signaling the onset of energy dissipation. The exact mechanism for the spectral break is still a matter of debate. In this work, we use the 20 Hz Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) magnetic field data during four planetary flybys at different heliocentric distances to examine the nature of the spectral break in the solar wind. We relate the spectral break frequencies of the solar wind MHD turbulence, found in the range of 0.3–0.7 Hz, with the well-known characteristic spectral bump at frequencies ∼1 Hz upstream of planetary bow shocks. Spectral breaks and spectral bumps during three planetary flybys are identified from the MESSENGER observations, with heliocentric distances in the range of 0.3–0.7 au. The MESSENGER observations are complemented by one Magnetospheric Multiscale observation made at 1 au. We find that the ratio of the spectral bump frequency to the spectral break frequency appears to be <jats:italic>r</jats:italic>- and <jats:italic>B</jats:italic>-independent. From this, we postulate that the wavenumber of the spectral break and the frequency of the spectral bump have the same dependence on the magnetic field strength ∣<jats:italic>B</jats:italic>∣. The implication of our work on the nature of the break scale is discussed.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The extremely high brightness temperature of fast radio bursts (FRBs) requires that their emission mechanism must be “coherent,” either through concerted particle emission by bunches or through the exponential growth of a plasma wave mode or radiation amplitude via certain maser mechanisms. The bunching mechanism has been mostly discussed within the context of curvature radiation or cyclotron/synchrotron radiation. Here we propose a family of models invoking the coherent inverse Compton scattering (ICS) of bunched particles that may operate within or just outside of the magnetosphere of a flaring magnetar. Crustal oscillations during the flaring event may excite low-frequency electromagnetic waves near the magnetar surface. The <jats:italic>X</jats:italic>-mode of these waves could penetrate through the magnetosphere. Bunched relativistic particles in the charge-starved region inside the magnetosphere or in the current sheet outside the magnetosphere would upscatter these low-frequency waves to produce gigahertz emission to power FRBs. The ICS mechanism has a much larger emission power for individual electrons than curvature radiation. This greatly reduces the required degree of coherence in bunches, alleviating several criticisms of the bunching mechanism raised in the context of curvature radiation. The emission is ∼100% linearly polarized (with the possibility of developing circular polarization) with a constant or varying polarization angle across each burst. The mechanism can account for a narrowband spectrum and a frequency downdrifting pattern, as commonly observed in repeating FRBs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Searches for electromagnetic counterparts of gravitational-wave signals have redoubled since the first detection in 2017 of a binary neutron star merger with a gamma-ray burst, optical/infrared kilonova, and panchromatic afterglow. Yet, one LIGO/Virgo observing run later, there has not yet been a second, secure identification of an electromagnetic counterpart. This is not surprising given that the localization uncertainties of events in LIGO and Virgo’s third observing run, O3, were much larger than predicted. We explain this by showing that improvements in data analysis that now allow LIGO/Virgo to detect weaker and hence more poorly localized events have increased the overall number of detections, of which well-localized, <jats:italic>gold-plated</jats:italic> events make up a smaller proportion overall. We present simulations of the next two LIGO/Virgo/KAGRA observing runs, O4 and O5, that are grounded in the statistics of O3 public alerts. To illustrate the significant impact that the updated predictions can have, we study the follow-up strategy for the Zwicky Transient Facility. Realistic and timely forecasting of gravitational-wave localization accuracy is paramount given the large commitments of telescope time and the need to prioritize which events are followed up. We include a data release of our simulated localizations as a public proposal planning resource for astronomers.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Long gamma-ray bursts (GRBs) are considered to originate from core collapse of massive stars. It is believed that the afterglow property is determined by the density of the material in the surrounding interstellar medium (ISM). Therefore, the circumburst density can be used to distinguish between an interstellar wind, <jats:italic>n</jats:italic>(<jats:italic>R</jats:italic>) ∝ <jats:italic>R</jats:italic> <jats:sup>−<jats:italic>k</jats:italic> </jats:sup>, and a constant-density medium (ISM), <jats:inline-formula> <jats:tex-math> <?CDATA $n(R)=\mathrm{const}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>n</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi>R</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:mi>const</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac3de4ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. Previous studies with different afterglow samples show that the circumburst medium of GRBs is neither simply supported by an interstellar wind nor completely favored by an ISM. In this work, our new sample consists of 39 GRBs with smoothly onset bump-like features in early X-ray afterglows, in which 20 GRBs have the redshift measurements. By using a smooth broken power-law function to fit the bumps of X-ray light curves, we derive the FWHM as the feature width (<jats:italic>ω</jats:italic>), as well as the rise and decay timescales of the bumps (<jats:italic>T</jats:italic> <jats:sub> <jats:italic>r</jats:italic> </jats:sub> and <jats:italic>T</jats:italic> <jats:sub> <jats:italic>d</jats:italic> </jats:sub>). The correlations between the timescales of X-ray bumps are similar to those found previously in the optical afterglows. Based on the fireball forward shock model of the thin shell case, we obtain the distribution of the electron spectral index <jats:italic>p</jats:italic> and further constrain the medium density distribution index <jats:italic>k</jats:italic>. The new inferred <jats:italic>k</jats:italic> is found to be concentrated at 1.0, with a range from 0.2 to 1.8. This finding is consistent with previous studies. The conclusion of our detailed investigation for X-ray afterglows suggests that the ambient medium of the selected GRBs is not homogeneous, i.e., neither ISM nor the typical interstellar wind.</jats:p>