Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We propose a turbulence-driven solar wind model for a fast solar wind flow in an open coronal hole where the solar wind flow and the magnetic field are highly aligned. We compare the numerical results of our model with Parker Solar Probe measurements of the fast solar wind flow and find good agreement between them. We find that (1) the majority quasi-2D turbulence is mainly responsible for coronal heating, raising the temperature to about <jats:inline-formula> <jats:tex-math> <?CDATA $\sim {10}^{6}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb132ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> K within a few solar radii, which leads in turn to the acceleration of the solar wind; (2) the heating rate due to quasi-2D turbulence near the coronal base is larger than that due to nearly incompressible/slab turbulence; (3) the quasi-2D energy in forward-propagating modes decreases with increasing distance, while the nearly incompressible/slab energy in forward-propagating modes increases, reaching a peak value at ∼11.7 <jats:inline-formula> <jats:tex-math> <?CDATA ${R}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb132ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> before decreasing with increasing heliocentric distance; (4) the correlation length increases with increasing distance from the coronal base; and (5) the variance of the density fluctuations decreases as a function of heliocentric distance.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Results of a search for ultra-high-energy neutrinos with the Pierre Auger Observatory from the direction of the blazar TXS 0506+056 are presented. They were obtained as part of the follow-up that stemmed from the detection of high-energy neutrinos and gamma rays with IceCube, Fermi-LAT, MAGIC, and other detectors of electromagnetic radiation in several bands. The Pierre Auger Observatory is sensitive to neutrinos in the energy range from 100 PeV to 100 EeV and in the zenith-angle range from <jats:italic>θ</jats:italic> = 60° to <jats:italic>θ</jats:italic> = 95°, where the zenith angle is measured from the vertical direction. No neutrinos from the direction of TXS 0506+056 have been found. The results were analyzed in three periods: one of 6 months around the detection of IceCube-170922 A, coinciding with a flare period of TXS 0506+056, a second one of 110 days during which the IceCube collaboration found an excess of 13 neutrinos from a direction compatible with TXS 0506+056, and a third one from 2004 January 1 up to 2018 August 31, over which the Pierre Auger Observatory has been taking data. The sensitivity of the Observatory is addressed for different spectral indices by considering the fluxes that would induce a single expected event during the observation period. For indices compatible with those measured by the IceCube collaboration the expected number of neutrinos at the Observatory is well below one. Spectral indices as hard as 1.5 would have to apply in this energy range to expect a single event to have been detected.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>High-precision measurement of the isotropic diffuse <jats:italic>γ</jats:italic>-ray background (IGRB) has been extrapolated to the TeV energy region using the Fermi-LAT experiment. Various kinds of astrophysical sources are candidates for its origin. However, a consensus on the dominant source has been difficult to reach. Recent observations of the <jats:italic>γ-</jats:italic>ray emission of <jats:italic>γ-</jats:italic>ray bursts (GRBs), denoted as the synchrotron self-Compton (SSC) component in the afterglow phase, in the sub-TeV energy region by MAGIC and HESS experiments shed new light on this topic. In this work, we revisit the contribution from the SSC component of GRBs to the IGRB. First, a sample set of GRB events is obtained and examined using observations from Fermi-LAT. Second, the SSC component, described by the energy ratio <jats:italic>R</jats:italic> <jats:sub>ext</jats:sub> and spectral index <jats:italic>β</jats:italic> <jats:sub>ext</jats:sub>, is assigned to every GRB event. We can obtain the total spectrum contribution based on this GRB sample. We find that when <jats:italic>R</jats:italic> <jats:sub>ext</jats:sub> and <jats:italic>β</jats:italic> <jats:sub>ext</jats:sub> reach ∼20% and −1.6, respectively, the contribution from GRB emission dominates in the energy region of hundreds of GeV. We hope that the LHAASO and CTA experiments under construction can observe a large number of GRBs to fix those parameters in coming years. A surviving tail is expected, which can serve to check our calculations based on future satellite experiments such as HERD and GAMMA400.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Electric field spectra measured on the Parker Solar Probe typically contain upwards of 1000 large-amplitude (∼15 mV m<jats:sup>−1</jats:sup>), wideband (∼100–15,000 Hz), few-second-duration, electric field waveforms per day. The satellite also collected about 85 three-second bursts of electric field waveforms per day at a data rate of ∼150,000 samples per second. Eight such bursts caught these waves, all of which were located in switchbacks of the magnetic field. A wave burst on 2019 September 7, when the spacecraft was at an altitude of 55 solar radii, is described. It contained Doppler-shifted ion acoustic waves that propagated in the direction opposite to the local magnetic field at all rest-frame frequencies from 60 Hz to nearly the proton plasma frequency of 2200 Hz, while no other wave modes were present. The eight bursts all contained ion acoustic waves whose individual net potentials were ≤1 V. A second burst, analyzed in conjunction with ion plasma measurements, showed that the ion acoustic waves were associated with broadened, plateaued, ion spectra containing unheated ions. Because the ion acoustic waves had phase velocities that varied from 140 to 90 km s<jats:sup>−1</jats:sup>, ions interacting with these waves via the Landau resonance had a chance to diffuse in parallel velocity space from 90 to 140 km s<jats:sup>−1</jats:sup> in the plasma rest frame. The most likely generation mechanism of the ion acoustic waves is the ion–ion acoustic instability, while the electron–ion instability is a less likely candidate.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present higher-order multiplicity results for 60 solar-type spectroscopic binaries based on 0.75 <jats:italic>μ</jats:italic>m imaging data taken by the robotic adaptive optics (Robo-AO) system at the Kitt Peak 2.1 m telescope. Our contrast curves show sensitivity up to ∼5 mag at ∼1″ separation; at very small separations, we identify candidate companions from image deviations relative to the point spread function. We find candidate tertiary companions for 62% of our binaries overall, but we find that this fraction is a strong function of the inner binary orbital period; it ranges from ∼47% for <jats:italic>P</jats:italic> <jats:sub>bin</jats:sub> &gt; 30 days to as high as ∼90% for <jats:italic>P</jats:italic> <jats:sub>bin</jats:sub> ≲ 5 days. We similarly find an increasing tertiary companion frequency for shorter-period binaries in a secondary sample of Kepler eclipsing binaries observed by Robo-AO. Using Gaia distances, we estimate an upper limit orbital period for each tertiary candidate and compare the tertiary-to-binary period ratios for systems in the field versus those in star-forming regions. Taken all together, these results provide further evidence for angular momentum transfer from three-body interactions, resulting in tight binaries with tertiaries that widen from pre-main-sequence to field ages.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Tidal disruption events (TDE) have been considered as cosmic-ray and neutrino sources for a decade. We suggest two classes of new scenarios for high-energy multi-messenger emission from TDEs that do not have to harbor powerful jets. First, we investigate high-energy neutrino and gamma-ray production in the core region of a supermassive black hole. In particular, we show that ∼1–100 TeV neutrinos and MeV gamma rays can efficiently be produced in hot coronae around an accretion disk. We also study the consequences of particle acceleration in radiatively inefficient accretion flows (RIAFs). Second, we consider possible cosmic-ray acceleration by sub-relativistic disk-driven winds or interactions between tidal streams, and show that subsequent hadronuclear and photohadronic interactions inside the TDE debris lead to GeV-PeV neutrinos and sub-GeV cascade gamma rays. We demonstrate that these models should be accompanied by soft gamma rays or hard X-rays as well as optical/UV emission, which can be used for future observational tests. Although this work aims to present models of non-jetted high-energy emission, we discuss the implications of the TDE AT2019dsg that might coincide with the high-energy neutrino IceCube-191001A, by considering the corona, RIAF, hidden sub-relativistic wind, and hidden jet models. It is not yet possible to be conclusive about their physical association and the expected number of neutrinos is typically much less than unity. We find that the most optimistic cases of the corona and hidden wind models could be consistent with the observation of IceCube-191001A, whereas jet models are unlikely to explain the multi-messenger observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We make use of sensitive (9.3 <jats:italic>μ</jats:italic>Jy beam<jats:sup>−1</jats:sup> rms) 1.2 mm continuum observations from the Atacama Large Millimeter/submillimeter Array (ALMA) Spectroscopic Survey in the Hubble Ultra-Deep Field (ASPECS) large program to probe dust-enshrouded star formation from 1362 Lyman-break galaxies spanning the redshift range <jats:italic>z</jats:italic> = 1.5–10 (to ∼7–28 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> at 4<jats:italic>σ</jats:italic> over the entire range). We find that the fraction of ALMA-detected galaxies in our <jats:italic>z</jats:italic> = 1.5–10 samples increases steeply with stellar mass, with the detection fraction rising from 0% at 10<jats:sup>9.0</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> to <jats:inline-formula> <jats:tex-math> <?CDATA ${85}_{-18}^{+9}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb830ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>% at &gt;10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. Moreover, on stacking all 1253 low-mass (&lt;10<jats:sup>9.25</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) galaxies over the ASPECS footprint, we find a mean continuum flux of −0.1 ± 0.4 <jats:italic>μ</jats:italic>Jy beam<jats:sup>−1</jats:sup>, implying a hard upper limit on the obscured star formation rate of &lt;0.6 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> (4<jats:italic>σ</jats:italic>) in a typical low-mass galaxy. The correlation between the infrared excess (IRX) of UV-selected galaxies (<jats:italic>L</jats:italic> <jats:sub>IR</jats:sub>/<jats:italic>L</jats:italic> <jats:sub>UV</jats:sub>) and the UV-continuum slope is also seen in our ASPECS data and shows consistency with a Calzetti-like relation at &gt;<jats:inline-formula> <jats:tex-math> <?CDATA ${10}^{9.5}\,{M}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb830ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> and an SMC-like relation at lower masses. Using stellar mass and <jats:italic>β</jats:italic> measurements for <jats:italic>z</jats:italic> ∼ 2 galaxies over the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, we derive a new empirical relation between <jats:italic>β</jats:italic> and stellar mass and then use this correlation to show that our IRX–<jats:italic>β</jats:italic> and IRX–stellar mass relations are consistent with each other. We then use these constraints to express the IRX as a bivariate function of <jats:italic>β</jats:italic> and stellar mass. Finally, we present updated estimates of star formation rate density determinations at <jats:italic>z</jats:italic> &gt; 3, leveraging present improvements in the measured IRX and recent probes of ultraluminous far-IR galaxies at <jats:italic>z</jats:italic> &gt; 2.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>If confirmed, a wide binary system consisting of a 70 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> black hole (BH) and an 8 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> main-sequence star (LB-1) is observed to reside in the Milky Way (MW). While we remain agnostic about the nature of LB-1, we show that long-term evolution of an 8 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> star around a BH with mass between 5 and 70 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> makes them visible as ultraluminous X-ray (ULX) sources in the sky. Given the expected ULX phase lifetime (≈0.1 Myr) and their lack of detection in the MW, we conclude that the frequency of an 8–20 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> star to be in binary around a stellar mass BH should be less (<jats:italic>f</jats:italic> &lt; 4 × 10<jats:sup>−3</jats:sup>). This is in tension with Liu et al., who claimed the detection frequency of an LB-1-like system to be around 8–20 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> stars (<jats:italic>f</jats:italic> ≈ 3 × 10<jats:sup>−2</jats:sup>). Moreover, the 8 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> star is likely to end as a neutron star (NS) born with a very small kick from an electron-capture supernova (ECSN), leaving behind a wide NS–BH binary. So far, less than 1% of all the detectable pulsars in the MW have been mapped and there has been no detection of any pulsars in binary systems around BHs, which sets an upper bound of about 100 possible pulsar–BH systems in the MW. We show whether the NS is born from ECSN, a frequency upper limit of (<jats:italic>f</jats:italic> ≈ 10<jats:sup>−3</jats:sup>) for stars with masses ≈8–20 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> in the MW to have a BH companion. The rate discrepancy will further increase as more pulsars are mapped in the MW, yet these searches would not be able to rule out the Liu et al. detection frequency if NSs are instead born in core collapse SNe with the commonly inferred high kick velocities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We examine the absorption-line spectra of a sample of 31 luminous (<jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{\mathrm{UV}}\simeq -23$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb597ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) Lyman break galaxies at redshift <jats:italic>z</jats:italic> ≃ 6 using data taken with the FOCAS and OSIRIS spectrographs on the Subaru and GTC telescopes. For two of these sources we present longer exposure data taken at higher spectral resolutions from ESO’s X-shooter spectrograph. Using these data, we demonstrate the practicality of stacking our lower-resolution data to measure the depth of various interstellar and stellar absorption lines to probe the covering fraction of low-ionization gas and the gas phase and stellar metallicities near the end of the era of cosmic reionization. From maximum absorption-line depths of Si <jats:sc>ii</jats:sc> <jats:italic>λ</jats:italic>1260 and C <jats:sc>ii</jats:sc> <jats:italic>λ</jats:italic>1334, we infer a mean covering fraction of ≥0.85 ± 0.16 for our sample. This is larger than that determined using similar methods for lower-luminosity galaxies at slightly lower redshifts, suggesting that the most luminous galaxies appear to have a lower escape fraction than fainter galaxies, and therefore may not play a prominent role in concluding reionization. Using various interstellar absorption lines we deduce gas-phase metallicities close to solar, indicative of substantial early enrichment. Using selected stellar absorption lines, we model our spectra with a range of metallicities using techniques successfully employed at lower redshift and deduce a stellar metallicity of <jats:inline-formula> <jats:tex-math> <?CDATA ${0.4}_{-0.1}^{+0.3}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb597ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> solar, consistent with the stellar mass—stellar metallicity relation recently found at <jats:italic>z</jats:italic> ∼ 3–5. We discuss the implications of these metallicity estimates for the typical ages of our luminous galaxies and conclude our results imply initial star formation at redshifts <jats:italic>z</jats:italic> ∼ 10, consistent with independent analyses of earlier objects.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>X-ray observations of the unique NLS1 galaxy Mrk 1239 spanning 18 yr are presented. Data from XMM-Newton, Suzaku, Swift, and NuSTAR are combined to obtain a broadband, multi-epoch view of the source. There is spectral variability in the 3–10 keV band over the 18 yr. An analysis of the NuSTAR and Suzaku lightcurves also suggests rapid variability in the 3–10  keV band, which is consistent with the NLS1 definition of the source. However, no variability is seen below 3 keV on any timescale. Two distinct physical models are adopted to describe the data above and below <jats:inline-formula> <jats:tex-math> <?CDATA $\sim 3\,\mathrm{keV}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb08aieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. The low energies are dominated by a hot, diffuse gas likely associated with a starburst component at large physical scales. The higher-energy spectrum is dominated by emission from the central region. Ionized partial covering and relativistic blurred reflection are considered for the central region emission. In both cases, the underlying power law has a photon index of Γ ∼ 2.3–2.4. A distant reflector, a neutral partial covering component with a covering fraction near ∼1, and contributions from starburst emission are always required. The blurred reflection model requires a reflection-dominated spectrum, which may be at odds with the low emissivity index and radio properties of the source. By contrast, the two absorption components required in the ionized partial covering model may correspond to the two distinct regions of polarization observed in the optical. Regardless of the physical model, spectral changes between epochs are driven by the absorption components—and on short timescales, by intrinsic active galactic nucleus variability.</jats:p>