Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We report the discovery of seven new Galactic pulsars with the Canadian Hydrogen Intensity Mapping Experiment’s Fast Radio Burst (CHIME/FRB) backend. These sources were first identified via single pulses in CHIME/FRB, then followed up with CHIME/Pulsar. Four sources appear to be rotating radio transients, pulsar-like sources with occasional single-pulse emission with an underlying periodicity. Of those four sources, three have detected periods ranging from 220 ms to 2.726 s. Three sources have more persistent but still intermittent emission and are likely intermittent or nulling pulsars. We have determined phase-coherent timing solutions for the latter two. These seven sources are the first discovery of previously unknown Galactic sources with CHIME/FRB and highlight the potential of fast radio burst detection instruments to search for intermittent Galactic radio sources.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Compared to the diversity seen in exoplanets, Venus is a veritable astrophysical twin of the Earth; however, its global cloud layer truncates features in transmission spectroscopy, masking its non-Earth-like nature. Observational indicators that can distinguish an exo-Venus from an exo-Earth must therefore survive above the cloud layer. The above-cloud atmosphere is dominated by photochemistry, which depends on the spectrum of the host star and therefore changes between stellar systems. We explore the systematic changes in photochemistry above the clouds of Venus-like exoplanets orbiting K-dwarf or M-dwarf host stars, using a recently validated model of the full Venus atmosphere (0–115 km) and stellar spectra from the Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems (MUSCLES) Treasury survey. SO<jats:sub>2</jats:sub>, OCS, and H<jats:sub>2</jats:sub>S are key gas species in Venus-like planets that are not present in Earth-like planets, and could therefore act as observational discriminants if their atmospheric abundances are high enough to be detected. We find that SO<jats:sub>2</jats:sub>, OCS, and H<jats:sub>2</jats:sub>S all survive above the cloud layer when irradiated by the coolest K dwarf and all seven M dwarfs, whereas these species are heavily photochemically depleted above the clouds of Venus. The production of sulfuric acid molecules that form the cloud layer decreases for decreasing stellar effective temperature. Less steady-state photochemical oxygen and ozone forms with decreasing stellar effective temperature, and the effect of chlorine-catalyzed reaction cycles diminish in favor of HO<jats:sub> <jats:italic>x</jats:italic> </jats:sub> and SO<jats:sub> <jats:italic>x</jats:italic> </jats:sub> catalyzed cycles. We conclude that trace sulfur gases will be prime observational indicators of Venus-like exoplanets around M-dwarf host stars, potentially capable of distinguishing an exo-Venus from an exo-Earth.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Particles may be accelerated in magnetized coronae via magnetic reconnections and/or plasma turbulence, leading to high-energy neutrinos and soft <jats:italic>γ</jats:italic>-rays. We evaluate the detectability of neutrinos from nearby bright Seyfert galaxies identified by X-ray measurements. In the disk-corona model, we find that NGC 1068 is the most promising Seyfert galaxy in the Northern sky, where IceCube is the most sensitive, and show prospects for the identification of aggregated neutrino signals from Seyfert galaxies bright in X-rays. Moreover, we demonstrate that nearby Seyfert galaxies are promising targets for the next generation of neutrino telescopes such as KM3NeT and IceCube-Gen2. For KM3NeT, Cen A can be the most promising source in the Southern sky if a significant fraction of the observed X-rays come from the corona, and it could be identified in few years of KM3NeT operation. Our results reinforce the idea that hidden cores of supermassive black holes are the dominant sources of the high-energy neutrino emission and underlines the necessity of better sensitivity to medium-energy ranges in future neutrino detectors for identifying the origin of high-energy cosmic neutrinos.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We explore the fundamental physics of narrow toroidal rings during their nonlinear magnetohydrodynamic evolution at tachocline depths. Using a shallow-water model, we simulate the nonlinear evolution of spot-producing toroidal rings of 6° latitudinal width and a peak field of 15 kG. We find that the rings split; the split time depends on the latitude of each ring. Ring splitting occurs fastest, within a few weeks, at latitudes 20°–25°. Rossby waves work as perturbations to drive the instability of spot-producing toroidal rings; the ring split is caused by the “mixed stress” or cross-correlations of perturbation velocities and magnetic fields, which carry magnetic energy and flux from the ring peak to its shoulders, leading to the ring split. The two split rings migrate away from each other, the high-latitude counterpart slipping poleward faster due to migrating mixed stress and magnetic curvature stress. Broader toroidal bands do not split. Much stronger rings, despite being narrow, do not split due to rigidity from stronger magnetic fields within the ring. Magnetogram analysis indicates the emergence of active regions sometimes at the same longitudes but separated in latitude by 20° or more, which could be evidence of active regions emerging from split rings, which consistently contribute to observed high-latitude excursions of butterfly wings during the ascending, peak, and descending phases of a solar cycle. Observational studies in the future can determine how often new spots are found at higher latitudes than their lower-latitude counterparts and how the combinations influence solar eruptions and space weather events.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Extinction curves observed toward individual Active Galactic Nuclei (AGN) usually show a steep rise toward far-ultraviolet (FUV) wavelengths and can be described by the Small Magellanic Cloud (SMC)-like dust model. This feature suggests the dominance of small dust grains of size <jats:italic>a</jats:italic> ≤ 0.1 <jats:italic>μ</jats:italic>m in the local environment of AGN, but the origin of such small grains is unclear. In this paper, we aim to explain this observed feature by applying the RAdiative Torque Disruption (RATD) to model the extinction of AGN radiation from FUV to mid-infrared (MIR) wavelengths. We find that in the intense radiation field of AGN, large composite grains of size <jats:italic>a</jats:italic> ≥ 0.1 <jats:italic>μ</jats:italic>m are significantly disrupted to smaller sizes by RATD up to <jats:italic>d</jats:italic> <jats:sub>RATD</jats:sub> &gt; 100 pc in the polar direction and <jats:italic>d</jats:italic> <jats:sub>RATD</jats:sub> ∼ 10 pc in the torus region. Consequently, optical–MIR extinction decreases, whereas FUV-near-ultraviolet extinction increases, producing a steep far-UV rise extinction curve. The resulting total-to-selective visual extinction ratio thus significantly drops to <jats:italic>R</jats:italic> <jats:sub>V</jats:sub> &lt; 3.1 with decreasing distances to AGN center due to the enhancement of small grains. The dependence of <jats:italic>R</jats:italic> <jats:sub>V</jats:sub> with the efficiency of RATD will help us to study the dust properties in the AGN environment via photometric observations. In addition, we suggest that the combination of the strength between RATD and other dust destruction mechanisms that are responsible for destroying very small grains of <jats:italic>a</jats:italic> ≤ 0.05 <jats:italic>μ</jats:italic>m is the key for explaining the dichotomy observed “SMC” and “gray” extinction curve toward many AGN.</jats:p>