Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The nature of the rare “Changing-look” (CL) phenomenon in active galactic nuclei (AGNs) is still under debate. We present Swift/XRT and UVOT follow-up observations of UGC 3223, a newly discovered repeat CL-AGN with type transitions of S1.5 → S2 → S1.8 occurring in a period of about 30 yr. By comparing the values previously reported in the ROSAT All-sky Survey and in the second Swift-XRT Point Source catalog, we clearly find that the X-ray flux tightly follows the optical spectral transition, in which a spectral type closer to a Seyfert 1 type is associated with a higher X-ray flux. An invariable X-ray spectral shape is, however, found in the CL phenomenon of the object. An extremely low Eddington ratio of ∼2 × 10<jats:sup>−4</jats:sup> can be obtained from the X-ray luminosity for its Seyfert 2 state, which suggests the disk-wind broad-line region model best explains the CL phenomenon. A variation of the total UV emission is not revealed when compared to the previous Galaxy Evolution Explorer NUV observation, since the UVOT images indicate that ∼90% UV emission comes from intensive star formation in the host galaxy.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Utilizing the latest and the most sensitive radio and optical catalogs, we completed a new blazar candidate catalog, Blazar Radio and Optical Survey (BROS), which includes 88,211 sources located at decl. <jats:italic>δ</jats:italic> &gt; −40° and outside the galactic plane (<jats:inline-formula> <jats:tex-math> <?CDATA $| b| \gt 10^\circ $?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabab07ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>). We list compact flat-spectrum radio sources of <jats:italic>α</jats:italic> &gt; −0.6 (<jats:italic>α</jats:italic> is defined as <jats:italic>F</jats:italic> <jats:sub> <jats:italic>ν</jats:italic> </jats:sub> ∝ <jats:italic>ν</jats:italic> <jats:sup> <jats:italic>α</jats:italic> </jats:sup>) from 0.15 GHz TGSS to 1.4 GHz NVSS catalogs. We further identify optical counterparts of the selected sources by cross-matching with Pan-STARRS1 photometric data. Color–color and color–magnitude plots for the selected BROS sources clearly show two distinct populations, a “quasar-like” population consisting of both flat-spectrum radio quasars and BL Lac type objects. On the other hand, an “elliptical-like” population of mostly BL Lac type objects is buried in the elliptical galaxy. The latter population is also reported in previous catalogs, but the BROS catalog provided a new larger sample of this population, due to the lower radio flux threshold of our selection. Model calculations show that the “elliptical-like” population consists of elliptical galaxies located at redshift <jats:italic>z</jats:italic> ≲ 0.5, which is also supported by the logN-logS distribution of the power-law index of 1.49 ± 0.05. This BROS catalog is useful for identifying the electromagnetic counterparts of ultra-high-energy cosmic rays and PeV neutrinos recently detected by IceCube, as well as nearby BL Lac objects detectable by future high-sensitivity TeV telescopes, such as the Cherenkov Telescope Array.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>White dwarfs (WDs) comprise 95% of all stellar remnants, and are thus an excellent tracer of old stellar populations in the Milky Way. Current and planned telescopes are not able to directly probe the WD population in its entirety due to its inherently low luminosity. However, the Galactic population of double white dwarf binaries (DWDs) gives rise to a millihertz gravitational-wave foreground detectable by the Laser Interferometer Space Antenna (LISA). Here we show how characterizing the angular power of the WD foreground will enable probes of the Galactic structure in a novel way to determine whether the Galactic WD population traces the spatial distribution of young, bright stars, or traces a vertically heated spatial distribution associated with the Galaxy’s oldest stellar populations. We do this using a binary population synthesis study that incorporates different Galactic spatial distributions for the DWD population. We find that the level of anisotropy in the WD foreground’s angular power spectrum is dependent on the vertical scale height of the population, but show that multipole coefficients from the spherical harmonic decomposition must be considered individually because of LISA’s angular resolution. Finally, we show that LISA can probe the vertical scale height of the Galactic WD population with an accuracy of 300 pc, using the hexadecapole moment of the WD foreground.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>What is the expected infrared output of elliptical galaxies? We report the latest findings obtained in this high time resolution (∼10 yr) and high spatial resolution (2.5 pc at center) study. We add a set of grain physics to the Massive active galactic nucleus (AGN) Controlled Ellipticals Resolved code, including (a) dust grains made in passive stellar evolution; (b) dust grain growth due to collision and sticking; (c) grain destruction due to thermal sputtering; (d) dust cooling of hot gas via inelastic collisions; and (e) radiation pressure on dust grains. The code improvements enable us to analyze metal depletion and AGN obscuration due to dust, and to assess its infrared output. We simulate a representative massive elliptical galaxy of a central stellar velocity dispersion ∼260 km s<jats:sup>−1</jats:sup> and modest rotation. We find that: (1) the circumnuclear disk (∼1 kpc in diameter) is dusty in its outer region where most of the metals are contained in dust grains, while in the inner disk, dust grains are mostly destroyed by the AGN irradiation; (2) the dusty disk is optically thick to both the starlight within the disk and the radiation from the central AGN; thus the AGN is obscured behind the disk, and the covering factor is ∼0.2; and (3) the duty cycles of the AGN activities, star formation, and the dust infrared luminosity roughly match observations; e.g., in most of its lifetime, the simulated galaxy is a stereotypical “quiescent” elliptical galaxy with <jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{\mathrm{IR}}\sim {10}^{11}{L}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabacc0ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, but it can reach ≳10<jats:sup>46</jats:sup> erg s<jats:sup>−1</jats:sup> during outbursts with a star formation rate <jats:inline-formula> <jats:tex-math> <?CDATA $\gtrsim 250\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabacc0ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The High-energy Particle Detector (HEPD) on board the China Seismo-Electromagnetic Satellite (CSES-01)—launched on 2018 February 2—is a light and compact payload suitable for measuring electrons (3–100 MeV), protons (30–250 MeV), and light nuclei (up to a few hundreds of MeV). The Sun-synchronous orbit and large acceptance allow HEPD to measure cosmic-ray particles near the ±65° latitude limit for a fair amount of time per day. In this work, three semiannual galactic hydrogen energy spectra between ∼40 and 250 MeV are presented, including a comparison with theoretical spectra from HelMod, a 2D Monte Carlo model developed to simulate the solar modulation of cosmic rays throughout the heliosphere. To our knowledge, these are the first hydrogen energy spectra below 250 MeV measured at 1 au between 2018 and 2020.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Multiple-ribbon flares are usually complex in their magnetic topologies and eruption mechanisms. In this paper, we investigate an X2.1 flare (SOL2015-03-11T16:22) that occurred in active region 12297 near the center of the solar disk by both potential and nonlinear force-free field models extrapolated with the data observed by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. We calculate the three-dimensional squashing degree distribution. The results reveal that there are two flux ropes in this active region covered by a large-scale hyperbolic flux tube (HFT), which is the intersection of quasi-separatrix layers with a null point embedded in it. When the background magnetic field diminishes due to the separation of the northwest dipole and the flux cancellation, the central flux rope rises up, forming the two brightest central ribbons. It then squeezes the overlying HFT structure to generate further brightenings. This very energetic flare with a complex shape is accompanied by a coronal mass ejection (CME). We adopt the simplified line-tied force-balance equation of the current ring model and assign the observed value of the decay index to the equation to simulate the acceleration profile of the CME in the early stage. It is found that the path with an inclination of 45° from radial best fits the profile of the actual acceleration.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Wind-driven outflows are observed around a broad range of accreting objects throughout the universe, ranging from forming low-mass stars to supermassive black holes. We study the interaction between a central isotropic wind and an infalling, rotating envelope, which determines the steady-state cavity shape formed at their interface under the assumption of weak mixing. The shape of the resulting wind-blown cavity is elongated and self-similar, with a physical size determined by the ratio between wind ram pressure and envelope thermal pressure. We compute the growth of a warm turbulent mixing layer between the shocked wind and the deflected envelope, and calculate the resultant broad-line profile, under the assumption of a linear (Couette-type) velocity profile across the layer. We then test our model against the warm broad velocity component observed in CO <jats:italic>J</jats:italic> = 16–15 by Herschel/HIFI in the protostar Serpens-Main SMM1. Given independent observational constraints on the temperature and density of the dust envelope around SMM1, we find an excellent match to all its observed properties (line profile, momentum, temperature) and to the SMM1 outflow cavity width for a physically reasonable set of parameters: a ratio of wind to infall mass flux of ≃4%, a wind speed of <jats:italic>v</jats:italic> <jats:sub>w</jats:sub> ≃ 30 km s<jats:sup>−1</jats:sup>, an interstellar abundance of CO and H<jats:sub>2</jats:sub>, and a turbulent entrainment efficiency consistent with laboratory experiments. The inferred ratio of ejection to disk accretion rate, ≃6%–20%, is in agreement with current disk wind theories. Thus, the model provides a new framework to reconcile the modest outflow cavity widths in protostars with large observed flow velocities. Being self-similar, it is applicable over a broader range of astrophysical contexts as well.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>KIC 10685175 (TIC 264509538) was discovered to be a rapidly oscillating Ap star from Kepler long-cadence data using super-Nyquist frequency analysis. It was reobserved by the Transiting Exoplanet Survey Satellite (TESS) with 2 minute cadence data in Sectors 14 and 15. We analyzed the TESS light curves, finding that the previously determined frequency is a Nyquist alias. The revised pulsation frequency is 191.5151 ± 0.0005 day<jats:sup>−1</jats:sup> (<jats:italic>P</jats:italic> = 7.52 minutes) and the rotation frequency is 0.32229 ± 0.00005 day<jats:sup>−1</jats:sup> (<jats:italic>P</jats:italic> <jats:sub>rot</jats:sub> = 3.1028 days). The star is an oblique pulsator with a pulsation amplitude modulated by the rotation, reaching a maximum pulsation amplitude at the time of the rotational light minimum. The oblique pulsation generates a frequency quintuplet split by exactly the rotation frequency. The phases of sidelobes, the pulsation phase modulation, and a spherical harmonic decomposition all show this star to be pulsating in a distorted quadrupole mode. Following the oblique pulsator model, we calculated the rotation inclination <jats:italic>i</jats:italic> and magnetic oblique <jats:italic>β</jats:italic> of this star, which provide detailed information of pulsation geometry. The <jats:italic>i</jats:italic> and <jats:italic>β</jats:italic> derived by the best fit of pulsation amplitude and phase modulation through a theoretical model differ from those calculated for a pure quadrupole, indicating the existence of strong magnetic distortion. The model also predicts the polar magnetic field strength is as high as about 6 kG which is predicted to be observed in a high-resolution spectrum of this star.</jats:p>