Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The Canadian Hydrogen Intensity Mapping Experiment (CHIME) has become a leading facility for detecting fast radio bursts (FRBs) through the CHIME/FRB backend. CHIME/FRB searches for fast transients in polarization-summed intensity data streams that have 24 kHz spectral and 1 ms temporal resolution. The intensity beams are pointed to predetermined locations in the sky. A triggered baseband system records the coherent electric field measured by each antenna in the CHIME array at the time of FRB detections. Here we describe the analysis techniques and automated pipeline developed to process these full-array baseband data recordings. Whereas the real-time FRB detection pipeline has a localization limit of several arcminutes, offline analysis of baseband data yields source localizations with subarcminute precision, as characterized by using a sample of pulsars and one repeating FRB with known positions. The baseband pipeline also enables resolving temporal substructure on a microsecond scale and the study of polarization including detections of Faraday rotation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>UV/optical variation, likely driven by accretion disk turbulence, is a defining characteristic of type 1 active galactic nuclei and quasars. In this work we investigate an interesting consequence of such turbulence using quasars in Sloan Digital Sky Survey Stripe 82 for which the measurements of the UV/optical variability amplitude are available from ∼10 yr long light curves. We discover positive correlations between the UV/optical variability amplitude <jats:italic>σ</jats:italic> <jats:sub>rms</jats:sub> and equivalent widths of C <jats:sc>iv</jats:sc>, Mg <jats:sc>ii</jats:sc>, and [O <jats:sc>iii</jats:sc>]5007 emission lines. Such correlations remain statistically robust through partial correlation analyses, i.e., after controlling the effects of other variables including bolometric luminosity, central supermassive black hole mass, Eddington ratio, and redshift. This, for the first time, indicates a causal link between disk turbulence and emission line production. We propose two potential underlying mechanisms, both of which may be involved: (1) quasars with stronger disk turbulence have on average a bluer/harder broadband spectral energy distribution, an expected effect of the disk thermal fluctuation model; (2) stronger disk turbulence could lead to the launch of emission line regions with larger covering factors.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using the Atacama Large Millimeter/submillimeter Array (ALMA), we investigated the peculiar millimeter source MMS 3 located in the Orion Molecular Cloud 3 (OMC-3) region in the 1.3 mm continuum, CO (<jats:italic>J</jats:italic> = 2–1), SiO (<jats:italic>J</jats:italic> = 5–4), C<jats:sup>18</jats:sup>O (<jats:italic>J</jats:italic> = 2–1), N<jats:sub>2</jats:sub>D<jats:sup>+</jats:sup> (<jats:italic>J</jats:italic> = 3–2), and DCN (<jats:italic>J</jats:italic> = 3–2) emissions. With the ALMA high angular resolution (∼0.″2), we detected a very compact and highly centrally condensed continuum emission with a size of 0.″45 × 0.″32 (P.A. = 0.°22). The peak position coincides with the locations of previously reported Spitzer/IRAC and X-ray sources within their positional uncertainties. We also detected an envelope with a diameter of ∼6800 au (P.A. = 75°) in the C<jats:sup>18</jats:sup>O (<jats:italic>J</jats:italic> = 2–1) emission. Moreover, a bipolar outflow was detected in the CO (<jats:italic>J</jats:italic> = 2–1) emission for the first time. The outflow is elongated roughly perpendicular to the long axis of the envelope detected in the C<jats:sup>18</jats:sup>O (<jats:italic>J</jats:italic> = 2–1) emission. Compact high-velocity CO gas in the (redshifted) velocity range of 22–30 km s<jats:sup>−1</jats:sup>, presumably tracing a jet, was detected near the 1.3 mm continuum peak. A compact and faint redshifted SiO emission was marginally detected in the CO outflow lobe. The physical quantities of the outflow in MMS 3 are somewhat smaller than those in other sources in the OMC-3 region. The centrally condensed object associated with the near-infrared and X-ray sources, the flattened envelope, and the faint outflow indicate that MMS 3 harbors a low-mass protostar with an age of ∼10<jats:sup>3</jats:sup> yr.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the first spectroscopic measurements of the ATLAS and Aliqa Uma streams from the Southern Stellar Stream Spectroscopic Survey (<jats:italic>S</jats:italic> <jats:sup>5</jats:sup>), in combination with the photometric data from the Dark Energy Survey and astrometric data from Gaia. From the coherence of spectroscopic members in radial velocity and proper motion, we find that these two systems are extremely likely to be one stream with discontinuity in morphology and density on the sky (the “kink” feature). We refer to this entire stream as the ATLAS-Aliqa Uma stream, or the AAU stream. We perform a comprehensive exploration of the effect of baryonic substructures and find that only an encounter with the Sagittarius dwarf ∼0.5 Gyr ago can create a feature similar to the observed “kink.” In addition, we also identify two gaps in the ATLAS component associated with the broadening in the stream width (the “broadening” feature). These gaps have likely been created by small mass perturbers, such as dark matter halos, as the AAU stream is the most distant cold stream known with severe variations in both the stream surface density and the stream track on the sky. With the stream track, stream distance, and kinematic information, we determine the orbit of the AAU stream and find that it has been affected by the Large Magellanic Cloud, resulting in a misalignment between the proper motion and stream track. Together with the Orphan-Chenab Stream, AAU is the second stream pair that has been found to be a single stream separated into two segments by external perturbation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The formation mechanism of the W50/SS 433 complex has long been a mystery. We propose a new scenario in which the SS 433 jets themselves form the W50/SS 433 system. We carry out magnetohydrodynamics simulations of the propagation of two side jets using the public code CANS+. As found in previous jet studies, when the propagating jet is lighter than the surrounding medium, the shocked plasma flows back from the jet tip to the core. We find that the morphology of light jets is spheroidal at early times; afterward, the shell and wings are developed by the broadening spherical cocoon. The morphology depends strongly on the density ratio of the injected jet to the surrounding medium. Meanwhile, the ratio of the lengths of the two side jets depends only on the density profile of the surrounding medium. We also find that most of the jet kinetic energy is dissipated at the oblique shock formed by the interaction between the backflow and beam flow, rather than at the jet terminal shock. The position of the oblique shock is spatially consistent with the X-ray and TeV gamma-ray hotspots of W50.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>M-stars are the most common hosts of planetary systems in the Galaxy. Protoplanetary disks around M-stars thus offer a prime opportunity to study the chemistry of planet-forming environments. We present an Atacama Large Millimeter/submillimeter Array survey of molecular line emission toward a sample of five protoplanetary disks around M4–M5 stars (FP Tau, J0432+1827, J1100-7619, J1545-3417, and Sz 69). These observations can resolve chemical structures down to tens of astronomical units. Molecular lines of <jats:sup>12</jats:sup>CO, <jats:sup>13</jats:sup>CO, C<jats:sup>18</jats:sup>O, C<jats:sub>2</jats:sub>H, and HCN are detected toward all five disks. Lines of H<jats:sub>2</jats:sub>CO and DCN are detected toward 2/5 and 1/5 disks, respectively. For disks with resolved C<jats:sup>18</jats:sup>O, C<jats:sub>2</jats:sub>H, HCN, and H<jats:sub>2</jats:sub>CO emission, we observe substructures similar to those previously found in disks around solar-type stars (e.g., rings, holes, and plateaus). C<jats:sub>2</jats:sub>H and HCN excitation conditions estimated interior to the pebble disk edge for the bright disk J1100-7619 are consistent with previous measurements around solar-type stars. The correlation previously found between C<jats:sub>2</jats:sub>H and HCN fluxes for solar-type disks extends to our M4–M5 disk sample, but the typical C<jats:sub>2</jats:sub>H/HCN ratio is higher for the M4–M5 disk sample. This latter finding is reminiscent of the hydrocarbon enhancements found by previous observational infrared surveys in the innermost (&lt;10 au) regions of M-star disks, which is intriguing since our disk-averaged fluxes are heavily influenced by flux levels in the outermost disk, exterior to the pebble disk edge. Overall, most of the observable chemistry at 10–100 au appears similar for solar-type and M4–M5 disks, but hydrocarbons may be more abundant around the cooler stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The dark matter halos that surround Milky Way–like galaxies in cosmological simulations are, to first order, triaxial. Nearly 30 yr ago it was predicted that such triaxial dark matter halos should exhibit steady figure rotation or tumbling motions for durations of several gigayears. The angular frequency of figure rotation predicted by cosmological simulations is described by a log-normal distribution of pattern speed Ω<jats:sub> <jats:italic>p</jats:italic> </jats:sub> with a median value 0.15 <jats:italic>h</jats:italic> km s<jats:sup>−1</jats:sup> kpc<jats:sup>−1</jats:sup> (∼0.15 <jats:italic>h</jats:italic> rad Gyr<jats:sup>−1</jats:sup> ∼ 9° <jats:italic>h</jats:italic> Gyr<jats:sup>−1</jats:sup>) and a width of 0.83<jats:italic>h</jats:italic> km s<jats:sup>−1</jats:sup> kpc<jats:sup>−1</jats:sup>. These pattern speeds are so small that they have generally been considered both unimportant and undetectable. In this work we show that even extremely slow figure rotation can significantly alter the structure of extended stellar streams produced by the tidal disruption of satellites in the Milky Way halo. We simulate the behavior of a Sagittarius-like polar tidal stream in triaxial dark matter halos with different shapes, when the halos are rotated about the three principal axes. For pattern speeds typical of cosmological halos, we demonstrate, for the first time, that a Sagittarius-like tidal stream would be altered to a degree that is detectable even with current observations. This discovery will potentially allow for a future measurement of figure rotation of the Milky Way’s dark matter halo, perhaps enabling the first evidence of this relatively unexplored prediction of cold dark matter.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A recently observed bump in the cosmic-ray (CR) spectrum from 0.3 to 30 TV is likely caused by a stellar bow shock that reaccelerates preexisting CRs, which further propagate to the Sun along the magnetic field lines. Along their way, these particles generate an Iroshnikov–Kraichnan (I-K) turbulence that controls their propagation and sustains the bump. Ad hoc fitting of the bump shape requires six adjustable parameters. Our model requires none, merely depending on three physical unknowns that we constrain using the fit<jats:italic>.</jats:italic> These are the shock Mach number, <jats:italic>M</jats:italic>, its size, <jats:italic>l</jats:italic> <jats:sub>⊥</jats:sub>, and the distance to it, <jats:italic>ζ</jats:italic> <jats:sub>obs</jats:sub>. Altogether, they define the bump rigidity <jats:italic>R</jats:italic> <jats:sub>0</jats:sub>. With <jats:italic>M</jats:italic> ≈ 1.5–1.6 and <jats:italic>R</jats:italic> <jats:sub>0</jats:sub> ≈ 4.4 TV, the model fits the data with ≈0.08% accuracy. The fit critically requires the I-K spectrum predicted by the model and rules out the alternatives. These attributes of the fit make an accidental agreement highly unlikely. In turn, the <jats:italic>R</jats:italic> <jats:sub>0</jats:sub> and <jats:italic>M</jats:italic> derived from the fit impose the distance−size relation on the shock: <jats:italic>ζ</jats:italic> <jats:sub>obs</jats:sub>(pc) ∼ <jats:inline-formula> <jats:tex-math> <?CDATA ${10}^{2}\sqrt{{l}_{\perp }(\mathrm{pc})}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabe855ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. For sufficiently large bow shocks, <jats:italic>l</jats:italic> <jats:sub>⊥</jats:sub> = 10<jats:sup>−3</jats:sup>−10<jats:sup>−2</jats:sup> pc, we find the distance of <jats:italic>ζ</jats:italic> <jats:sub>obs</jats:sub> = 3–10 pc. Three promising stars in this range are the Scholz’s Star at 6.8 pc, Epsilon Indi at 3.6 pc, and Epsilon Eridani at 3.2 pc. Based on their current positions and velocities, we propose that Epsilon Indi and Epsilon Eridani can produce the observed spectral bump. Moreover, Epsilon Eridani’s position is only ∼67 off of the magnetic field direction in the solar neighborhood, which also changes the CR arrival direction distribution. Given the proximity of these stars, the bump appearance may change in a relatively short time.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the early discovery and multicolor (<jats:italic>BVI</jats:italic>) high-cadence light-curve analyses of the rapidly declining sub-Chandrasekhar Type Ia supernova KSP-OT-201509b (= AT 2015cx) from the KMTNet Supernova Program. The Phillips and color stretch parameters of KSP-OT-201509b are Δ<jats:italic>M</jats:italic> <jats:sub> <jats:italic>B</jats:italic>,15</jats:sub> ≃ 1.62 mag and <jats:italic>s</jats:italic> <jats:sub> <jats:italic>BV</jats:italic> </jats:sub> ≃ 0.54, respectively, at an inferred redshift of 0.072. These, together with other measured parameters (such as the strength of the secondary <jats:italic>I</jats:italic>-band peak, colors, and luminosity), identify the source to be a rapidly declining Type Ia of a transitional nature that is closer to Branch-normal than 91bg-like. Its early light-curve evolution and bolometric luminosity are consistent with those of homologously expanding ejecta powered by radioactive decay and a Type Ia SN explosion with 0.32 ± 0.01 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> of synthesized <jats:sup>56</jats:sup>Ni mass, 0.84 ± 0.12 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> of ejecta mass, and (0.61 ± 0.14) × 10<jats:sup>51</jats:sup> erg of ejecta kinetic energy. While its <jats:italic>B</jats:italic> − <jats:italic>V</jats:italic> and <jats:italic>V</jats:italic> − <jats:italic>I</jats:italic> colors evolve largely synchronously with the changes in the <jats:italic>I</jats:italic>-band light curve, as found in other supernovae, we also find the presence of an early redward evolution in <jats:italic>V</jats:italic> − <jats:italic>I</jats:italic> prior to −10 days since peak. The bolometric light curve of the source is compatible with a stratified <jats:sup>56</jats:sup>Ni distribution extended to shallow layers of the exploding progenitor. Comparisons between the observed light curves and those predicted from ejecta–companion interactions clearly disfavor Roche lobe–filling companion stars at large separation distances, thus supporting a double-degenerate scenario for its origin. The lack of any apparent host galaxy in our deep stack images reaching a sensitivity limit of ∼28 mag arcsec<jats:sup>−2</jats:sup> makes KSP-OT-201509b a hostless Type Ia supernova and offers new insights into supernova host galaxy environments.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We have developed a collective plasma radio emission model for the radio pulsars based on the implications of the tangent model. The secondary pair (electron–positron) plasma particles get arranged into a phased array like an antenna due to plasma waves and radiate in phase. We have reproduced the polarization profiles by considering different viewing conditions in the pulsars having an oblique dipolar magnetic field. We find that when there is a resonance between the radio and the plasma waves, the flux of emitted radio waves gets enhanced. We numerically estimated the collective radio emission due to relativistic plasma. The model predicts the correlation between the sign reversal circular polarization and the polarization angle swing and the brightness temperature in the range ∼10<jats:sup>31</jats:sup>–10<jats:sup>33</jats:sup> K.</jats:p>