Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>For single-point measurements of quasi-perpendicular shocks, analytical measurements of the foot width are often used to evaluate the velocity of the shock relative to the satellite. This velocity is of crucial importance for in situ observations because it enables the identification of the spatial scale of other regions of the shock front such as a magnetic ramp for which the comprehensive understanding of their formation is not yet achieved. Knowledge of the spatial scale is one of the key parameters for the validation of theoretical models that are developed to explain the formation of these regions. Previously available estimates of the foot width for a quasi-perpendicular shock are based on several simplifications such as zero upstream ion temperature and specular ion reflection by the cross-shock electrostatic potential. The occurrence of specular reflection implies high values of the cross-shock electrostatic potential that significantly exceed the values obtained from in situ measurements. In this paper the effects of nonzero ion temperature and nonspecular ion reflection on the foot width are investigated. It is shown that in the case of nonspecular reflection the foot width can be as small as half of the size of the standard widely used estimate. Results presented here enable more reliable identification of the shock velocity from single-point observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on gamma-ray orbital modulation of the transitioning MSP binary XSS J12270–4859 detected in the Fermi Large Area Telescope (LAT) data. We use long-term optical data taken with the XMM-Newton OM and the Swift UltraViolet Optical Telescope to inspect radio timing solutions that are limited to relatively short time intervals and find that extrapolation of the solutions aligns well with the phasing of the optical data over 15 yr. The Fermi-LAT data folded on the timing solutions exhibit significant modulation (<jats:italic>p</jats:italic> = 5 × 10<jats:sup>−6</jats:sup>) with a gamma-ray minimum at the inferior conjunction of the pulsar. Intriguingly, the source seems to show similar modulation in both the low-mass X-ray binary and the MSP states, implying that mechanisms for gamma-ray emission in the two states are similar. We discuss these findings and their implications using an intrabinary shock scenario.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Mergers between galaxy clusters often drive shocks into the intracluster medium, the effects of which are sometimes visible via temperature and density jumps in the X-ray and via radio emission from relativistic particles energized by the shock’s passage. A2108 was selected as a likely merger system through comparing the X-ray luminosity to the Planck Sunyaev–Zeldovich signal, where this cluster appeared highly X-ray underluminous. Follow-up observations confirmed it to be a merging low-mass cluster featuring two distinct subclusters, both with a highly disturbed X-ray morphology. Giant Metrewave Radio Telescope (GMRT) data in bands 2, 3, &amp; 4 (covering 120–750 MHz) show an extended radio feature resembling a radio relic near the location of a temperature discontinuity in the X-rays. We measure a Mach number from the X-ray temperature jump (<jats:inline-formula> <jats:tex-math> <?CDATA ${{ \mathcal M }}_{{\rm{X}}}=1.6\pm 0.2$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="italic"></mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">X</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>1.6</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.2</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac3b5aieqn1.gif" xlink:type="simple" /> </jats:inline-formula>). Several characteristics of radio relics (location and morphology of extended radio emission) are found in A2108, making this cluster one of the few low-mass mergers (<jats:italic>M</jats:italic> <jats:sub>L−M</jats:sub> = 1.8 ± 0.4 × 10<jats:sup>14</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) likely hosting a radio relic. The radio spectrum is exceptionally steep (<jats:italic>α</jats:italic> = −2 at the lowest frequencies), and the radio power is very weak (<jats:italic>P</jats:italic> <jats:sub>1.4 GHz</jats:sub> = 1 × 10<jats:sup>22</jats:sup> W Hz<jats:sup>−1</jats:sup>). To account for the shock/relic offset, we propose a scenario in which the shock created the relic by re-accelerating a cloud of pre-existing relativistic electrons and then moved away, leaving behind a <jats:italic>fading</jats:italic> relic. The electron-aging timescale derived from the high-frequency steepening in the relic spectrum is consistent with the shock travel time to the observed X-ray discontinuity. However, the lower flux in GMRT band 4 data causing the steepening could be due to instrumental limitations and deeper radio data are needed to constrain the spectral slope of the relic at high frequencies. A background cluster, 4′ from the merger, may have contributed to the ROSAT and Planck signals, but SZ modeling shows that the merger system is still X-ray underluminous, supporting the use of this approach to identifying merger-disrupted clusters.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Based on the Parker Solar Probe mission, this paper presents the observations of two correlations in solar wind turbulence near the Sun for the first time, demonstrating the clear existence of the following two correlations. One is positive correlation between the proton temperature and turbulent magnetic energy density. The other is negative correlation between the spectral index and magnetic helicity. It is found that the former correlation has a maximum correlation coefficient (CC) at the wavenumber <jats:italic>k</jats:italic> <jats:italic>ρ</jats:italic> <jats:sub> <jats:italic>p</jats:italic> </jats:sub> ≃ 0.5 (<jats:italic>ρ</jats:italic> <jats:sub> <jats:italic>p</jats:italic> </jats:sub> being the proton thermal gyroradius), and the latter correlation has a maximum absolute value of CC at <jats:italic>k</jats:italic> <jats:italic>ρ</jats:italic> <jats:sub> <jats:italic>p</jats:italic> </jats:sub> ≃ 1.8. In addition, investigations based on 11 yr of Wind observations reveal that the dimensionless wavenumbers (<jats:italic>k</jats:italic> <jats:italic>ρ</jats:italic> <jats:sub> <jats:italic>p</jats:italic> </jats:sub>) corresponding to the maximum (absolute) values of CC remain nearly the same for different data sets. These results tend to suggest that the two correlations enhanced near the proton gyroradius scale would be a common feature of solar wind turbulence.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent observational evidence has demonstrated that white dwarf (WD) mergers are a highly efficient mechanism for mass accretion onto WDs in the galaxy. In this paper, we show that WD mergers naturally produce highly magnetized, uniformly rotating WDs, including a substantial population within a narrow mass range close to the Chandrasekhar mass (<jats:italic>M</jats:italic> <jats:sub>Ch</jats:sub>). These near-<jats:italic>M</jats:italic> <jats:sub>Ch</jats:sub> WD mergers subsequently undergo rapid spin up and compression on a ∼ 10<jats:sup>2</jats:sup> yr timescale, either leading to central ignition and a normal SN Ia via the DDT mechanism, or alternatively to a failed detonation and SN Iax through pure deflagration. The resulting SNe Ia and SNe Iax will have spectra, light curves, polarimetry, and nucleosynthetic yields similar to those predicted to arise through the canonical near-<jats:italic>M</jats:italic> <jats:sub>Ch</jats:sub> single degenerate (SD) channel, but with a <jats:italic>t</jats:italic> <jats:sup>−1</jats:sup> delay time distribution characteristic of the double-degenerate channel. Furthermore, in contrast to the SD channel, WD merger near-<jats:italic>M</jats:italic> <jats:sub>Ch</jats:sub> SNe Ia and SNe Iax will not produce observable companion signatures. We discuss a range of implications of these findings, from SNe Ia explosion mechanisms, to galactic nucleosynthesis of iron peak elements including manganese.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The nanohertz gravitational wave background (GWB) is believed to be dominated by GW emission from supermassive black hole binaries (SMBHBs). Observations of several dual-active galactic nuclei (AGN) strongly suggest a link between AGN and SMBHBs, given that these dual-AGN systems will eventually form bound binary pairs. Here we develop an exploratory SMBHB population model based on empirically constrained quasar populations, allowing us to decompose the GWB amplitude into an underlying distribution of SMBH masses, SMBHB number density, and volume enclosing the GWB. Our approach also allows us to self-consistently predict the number of local SMBHB systems from the GWB amplitude. Interestingly, we find the local number density of SMBHBs implied by the common-process signal in the NANOGrav 12.5-yr data set to be roughly five times larger than previously predicted by other models. We also find that at most ∼25% of SMBHBs can be associated with quasars. Furthermore, our quasar-based approach predicts ≳95% of the GWB signal comes from <jats:italic>z</jats:italic> ≲ 2.5, and that SMBHBs contributing to the GWB have masses ≳10<jats:sup>8</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. We also explore how different empirical galaxy–black hole scaling relations affect the local number density of GW sources, and find that relations predicting more massive black holes decrease the local number density of SMBHBs. Overall, our results point to the important role that a measurement of the GWB will play in directly constraining the cosmic population of SMBHBs, as well as their connections to quasars and galaxy mergers.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present velocity-resolved Stratospheric Observatory for Infrared Astronomy (SOFIA)/upgrade German REceiver for Astronomy at Terahertz Frequencies observations of [O <jats:sc>i</jats:sc>] and [C <jats:sc>ii</jats:sc>] lines toward a Class I protostar, L1551 IRS 5, and its outflows. The SOFIA observations detect [O <jats:sc>i</jats:sc>] emission toward only the protostar and [C <jats:sc>ii</jats:sc>] emission toward the protostar and the redshifted outflow. The [O <jats:sc>i</jats:sc>] emission has a width of ∼100 km s<jats:sup>−1</jats:sup> only in the blueshifted velocity, suggesting an origin in shocked gas. The [C <jats:sc>ii</jats:sc>] lines are narrow, consistent with an origin in a photodissociation region. Differential dust extinction from the envelope due to the inclination of the outflows is the most likely cause of the missing redshifted [O <jats:sc>i</jats:sc>] emission. Fitting the [O <jats:sc>i</jats:sc>] line profile with two Gaussian components, we find one component at the source velocity with a width of ∼20 km s<jats:sup>−1</jats:sup> and another extremely broad component at −30 km s<jats:sup>−1</jats:sup> with a width of 87.5 km s<jats:sup>−1</jats:sup>, the latter of which has not been seen in L1551 IRS 5. The kinematics of these two components resemble cavity shocks in molecular outflows and spot shocks in jets. Radiative transfer calculations of the [O <jats:sc>i</jats:sc>], high-<jats:italic>J</jats:italic> CO, and H<jats:sub>2</jats:sub>O lines in the cavity shocks indicate that [O <jats:sc>i</jats:sc>] dominates the oxygen budget, making up more than 70% of the total gaseous oxygen abundance and suggesting [O]/[H] of ∼1.5 × 10<jats:sup>−4</jats:sup>. Attributing the extremely broad [O <jats:sc>i</jats:sc>] component to atomic winds, we estimate an intrinsic mass-loss rate of (1.3 ± 0.8) × 10<jats:sup>−6</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>. The intrinsic mass-loss rates derived from low-<jats:italic>J</jats:italic> CO, [O <jats:sc>i</jats:sc>], and H <jats:sc>i</jats:sc> are similar, supporting the model of momentum-conserving outflows, where the atomic wind carries most momentum and drives the molecular outflows.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A significant fraction of observed galaxies in the Rubin Observatory Legacy Survey of Space and Time (LSST) will overlap at least one other galaxy along the same line of sight, in a so-called “blend.” The current standard method of assessing blend likelihood in LSST images relies on counting up the number of intensity peaks in the smoothed image of a blend candidate, but the reliability of this procedure has not yet been comprehensively studied. Here we construct a realistic distribution of blended and unblended galaxies through high-fidelity simulations of LSST-like images, and from this we examine the blend classification accuracy of the standard peak-finding method. Furthermore, we develop a novel Gaussian process blend classifier model, and show that this classifier is competitive with both the peak finding method as well as with a convolutional neural network model. Finally, whereas the peak-finding method does not naturally assign probabilities to its classification estimates, the Gaussian process model does, and we show that the Gaussian process classification probabilities are generally reliable.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Great Red Spot (GRS) at about latitude 22° S of Jupiter has been observed for hundreds of years, yet the driving mechanism of the formation of this giant anticyclone still remains unclear. Two scenarios were proposed to explain its formation. One is a shallow model suggesting that it might be a weather feature formed through a merging process of small shallow storms generated by moist convection, while the other is a deep model suggesting that it might be a deeply rooted anticyclone powered by the internal heat of Jupiter. In this work, we present numerical simulations showing that the GRS could be naturally generated in a deep rotating turbulent flow and can survive for a long time, when the convective Rossby number is smaller than a certain critical value. From this critical value, we predict that the Great Red Spot extends to at least about 500 km deep into the Jovian atmosphere. Our results demonstrate that the Great Red Spot is likely to be a feature deep-seated in the Jovian atmosphere.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Flat-spectrum radio quasars (FSRQs) are the most luminous blazars at GeV energies but only rarely emit detectable fluxes of TeV gamma rays, typically during bright GeV flares. We explore the gamma-ray variability and spectral characteristics of three FSRQs that have been observed at GeV and TeV energies by Fermi-LAT and VERITAS, making use of almost 100 hr of VERITAS observations spread over 10 yr: 3C 279, PKS 1222+216, and Ton 599. We explain the GeV flux distributions of the sources in terms of a model derived from a stochastic differential equation describing fluctuations in the magnetic field in the accretion disk and estimate the timescales of magnetic flux accumulation and stochastic instabilities in their accretion disks. We identify distinct flares using a procedure based on Bayesian blocks and analyze their daily and subdaily variability and gamma-ray energy spectra. Using observations from VERITAS, as well as Fermi, Swift, and the Steward Observatory, we model the broadband spectral energy distributions of PKS 1222+216 and Ton 599 during very high energy (VHE)–detected flares in 2014 and 2017, respectively, strongly constraining the jet Doppler factors and gamma-ray emission region locations during these events. Finally, we place theoretical constraints on the potential production of PeV-scale neutrinos during these VHE flares.</jats:p>