Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Despite the uncovered association of a high-energy neutrino with the apparent flaring state of blazar TXS 0506+056 in 2017, the mechanisms leading to astrophysical particle acceleration and neutrino production are still uncertain. Recent studies found that when transparent to <jats:italic>γ</jats:italic>-rays, <jats:italic>γ</jats:italic>-flaring blazars do not have the opacity for protons to produce neutrinos. Here we present observational evidence for an alternative explanation, in which <jats:italic>γ</jats:italic>-ray emission is suppressed during efficient neutrino production. A large proton and target photon density helps produce neutrinos while temporarily suppressing the observable <jats:italic>γ</jats:italic>-emission due to a large <jats:italic>γ</jats:italic> <jats:italic>γ</jats:italic> opacity. We show that the Fermi-LAT <jats:italic>γ</jats:italic>-flux of blazar PKS 1502+106 was at a local minimum when IceCube recorded the coincident high-energy neutrino IC-190730A. Using data from the OVRO 40 m Telescope, we find that radio emission from PKS 1502+106 at the time period of the coincident neutrino IC-190730A was in a high state, in contrast to earlier time periods when radio and <jats:italic>γ</jats:italic> fluxes are correlated for both low and high states. This points to an active outflow that is <jats:italic>γ</jats:italic>-suppressed at the time of neutrino production. We find similar local <jats:italic>γ</jats:italic>-suppression in other blazars, including in MAGIC’s TeV flux of TXS 0506+056 and Fermi-LAT’s flux of blazar PKS B1424-418 at the time of coincident IceCube neutrino detections. Using temporary <jats:italic>γ</jats:italic>-suppression, neutrino–blazar coincidence searches could be substantially more sensitive than previously assumed, enabling the identification of the origin of IceCube’s diffuse neutrino flux possibly with already existing data.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Both long-duration gamma-ray bursts (LGRBs) from the core collapse of massive stars and short-duration GRBs (SGRBs) from mergers of a binary neutron star or a neutron star–black hole are expected to occur in the accretion disk of active galactic nuclei (AGNs). We show that GRB jets embedded in the migration traps of AGN disks are promised to be choked by the dense disk material. Efficient shock acceleration of cosmic rays at the reverse shock is expected, and high-energy neutrinos would be produced. We find that these sources can effectively produce detectable TeV–PeV neutrinos through <jats:italic>pγ</jats:italic> interactions. From a choked LGRB jet with isotropic equivalent energy of 10<jats:sup>53</jats:sup> erg at 100 Mpc, one expects ∼2(7) neutrino events detectable by IceCube (IceCube-Gen2). The contribution from choked LGRBs to the observed diffuse neutrino background depends on the unknown local event rate density of these GRBs in AGN disks. For example, if the local event rate density of choked LGRBs in an AGN disk is ∼5% that of low-luminosity GRBs (∼10 Gpc<jats:sup>−3</jats:sup> yr<jats:sup>−1</jats:sup>), the neutrinos from these events would contribute to ∼10% of the observed diffuse neutrino background. Choked SGRBs in AGN disks are potential sources for future joint electromagnetic, neutrino, and gravitational wave multimessenger observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We independently determine the zero-point offset of the Gaia early Data Release-3 (EDR3) parallaxes based on ∼110,000 W Ursae Majoris (EW)-type eclipsing binary systems. EWs cover almost the entire sky and are characterized by a relatively complete coverage in magnitude and color. They are an excellent proxy for Galactic main-sequence stars. We derive a W1-band period–luminosity relation with a distance accuracy of 7.4%, which we use to anchor the Gaia parallax zero-point. The final, global parallax offsets are −28.6 ± 0.6 <jats:italic>μ</jats:italic>as and −25.4 ± 4.0 <jats:italic>μ</jats:italic>as (before correction) and 4.2 ± 0.5 <jats:italic>μ</jats:italic>as and 4.6 ± 3.7 <jats:italic>μ</jats:italic>as (after correction) for the five- and six-parameter solutions, respectively. The total systematic uncertainty is 1.8 <jats:italic>μ</jats:italic>as. The spatial distribution of the parallax offsets shows that the bias in the corrected Gaia EDR3 parallaxes is less than 10 <jats:italic>μ</jats:italic>as across 40% of the sky. Only 15% of the sky is characterized by a parallax offset greater than 30 <jats:italic>μ</jats:italic>as. Thus, we have provided independent evidence that the parallax zero-point correction provided by the Gaia team significantly reduces the prevailing bias. Combined with literature data, we find that the overall Gaia EDR3 parallax offsets for Galactic stars are [−20, −30] <jats:italic>μ</jats:italic>as and 4–10 <jats:italic>μ</jats:italic>as, respectively, before and after correction. For specific regions, an additional deviation of about 10 <jats:italic>μ</jats:italic>as is found.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present evidence that multiple accretion events are required to explain the origin of the Gaia-Sausage and Enceladus (GSE) structures, based on an analysis of dynamical properties of main-sequence stars from the Sloan Digital Sky Survey Data Release 12 and Gaia Data Release 2. GSE members are selected to have eccentricity (<jats:italic>e</jats:italic>) &gt; 0.7 and [Fe/H] &lt; −1.0, and separated into low and high orbital-inclination (LOI/HOI) groups. We find that the LOI stars mainly have <jats:italic>e</jats:italic> &lt; 0.9 and are clearly separable into two groups with prograde and retrograde motions. The LOI stars exhibit prograde motions in the inner-halo region and strong retrograde motions in the outer-halo region (OHR). We interpret the LOI stars in these regions to be stars accreted from two massive dwarf galaxies with low-inclination prograde and retrograde orbits, affected to different extents by dynamical friction due to their different orbital directions. In contrast, the majority of the HOI stars have <jats:italic>e</jats:italic> &gt; 0.9, and exhibit a globally symmetric distribution of rotational velocities (<jats:italic>V</jats:italic> <jats:sub> <jats:italic>ϕ</jats:italic> </jats:sub>) near zero, although there is evidence for a small retrograde motion for these stars (<jats:italic>V</jats:italic> <jats:sub> <jats:italic>ϕ</jats:italic> </jats:sub> ∼ −15 km s<jats:sup>−1</jats:sup>) in the OHR. We consider these stars to be stripped from a massive dwarf galaxy on a high-inclination orbit. We also find that the LOI and HOI stars on highly eccentric and tangential orbits with clear retrograde motions exhibit different metallicity peaks at [Fe/H] = −1.7 and −1.9, respectively, and argue that they are associated with two low-mass dwarf galaxies accreted in the OHR of the Galaxy.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Long secondary periods (LSPs), observed in a third of pulsating red giant stars, are the only unexplained type of large-amplitude stellar variability known at this time. Here we show that this phenomenon is a manifestation of a substellar or stellar companion orbiting the red giant star. Our investigation is based on a sample of about 16,000 well-defined LSP variables detected in the long-term OGLE photometric database of the Milky Way and Magellanic Clouds, combined with the mid-infrared data extracted from the NEOWISE-R archive. From this collection, we selected about 700 objects with stable, large-amplitude, well-sampled infrared light curves and found that about half of them exhibit secondary eclipses, thus presenting an important piece of evidence that the physical mechanism responsible for LSPs is binarity. Namely, the LSP light changes are due to the presence of a dusty cloud orbiting the red giant together with the companion and obscuring the star once per orbit. The secondary eclipses, visible only in the infrared wavelength, occur when the cloud is hidden behind the giant. In this scenario, the low-mass companion is a former planet that has accreted a significant amount of mass from the envelope of its host star and grown into a brown dwarf.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a low-metallicity map of the Milky Way consisting of ∼110,000 metal-poor giants with −3.5 &lt; [Fe/H] &lt; −0.75, based on public photometry from the second data release of the SkyMapper survey. These stars extend out to ∼7 kpc from the solar neighborhood and cover the main Galactic stellar populations, including the thick disk and the inner halo. Notably, this map can reliably differentiate metallicities down to [Fe/H] ∼ −3.0, and thus provides an unprecedented view into the ancient, metal-poor Milky Way. Among the more metal-rich stars in our sample ([Fe/H] &gt; −2.0), we recover a clear spatial dependence of decreasing mean metallicity as a function of scale height that maps onto the thick disk component of the Milky Way. When only considering the very metal-poor stars in our sample ([Fe/H] &lt; −2), we recover no such spatial dependence in their mean metallicity out to a scale height of ∣<jats:italic>Z</jats:italic>∣ ∼ 7 kpc. We find that the metallicity distribution function (MDF) of the most metal-poor stars in our sample (−3.0 &lt; [Fe/H] &lt; −2.3) is well fit with an exponential profile with a slope of and <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{\Delta }}\mathrm{log}(N)/{\rm{\Delta }}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabd629ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>[Fe/H] = 1.52 ± 0.05, and slightly shifts to <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{\Delta }}\mathrm{log}(N)/{\rm{\Delta }}[\mathrm{Fe}/{\rm{H}}]=1.53\pm 0.10$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabd629ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> after accounting for target selection effects. For [Fe/H] &lt; −2.3, the MDF is largely insensitive to scale height ∣<jats:italic>Z</jats:italic>∣ out to ∼5 kpc, showing that very and extremely metal-poor stars are in every galactic component.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The asteroid exploration project “Hayabusa2” has successfully returned samples from the asteroid (162173) Ryugu. In this study, we measured the linear polarization degrees of Ryugu using four ground-based telescopes from 2020 September 27 to December 25, covering a wide-phase angle (Sun-target-observer’s angle) range from 28° to 104°. We found that the polarization degree of Ryugu reached 53% around a phase angle of 100°, the highest value among all asteroids and comets thus far reported. The high polarization degree of Ryugu can be attributed to the scattering properties of its surface layers, in particular the relatively small contribution of multiply scattered light. Our polarimetric results indicate that Ryugu’s surface is covered with large grains. On the basis of a comparison with polarimetric measurements of pulverized meteorites, we can infer the presence of submillimeter-sized grains on the surface layer of Ryugu. We also conjecture that this size boundary represents the grains that compose the aggregate. It is likely that a very brittle structure has been lost in the recovered samples, although they may hold a record of its evolution. Our data will be invaluable for future experiments aimed at reproducing the surface structure of Ryugu.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the discovery of an extreme flaring event from Proxima Cen by the Australian Square Kilometre Array Pathfinder (ASKAP), Atacama Large Millimeter/submillimeter Array (ALMA), Hubble Space Telescope (HST), Transiting Exoplanet Survey Satellite (TESS), and the du Pont Telescope that occurred on 2019 May 1. In the millimeter and FUV, this flare is the brightest ever detected, brightening by a factor of &gt;1000 and &gt;14,000 as seen by ALMA and HST, respectively. The millimeter and FUV continuum emission trace each other closely during the flare, suggesting that millimeter emission could serve as a proxy for FUV emission from stellar flares and become a powerful new tool to constrain the high-energy radiation environment of exoplanets. Surprisingly, optical emission associated with the event peaks at a much lower level with a time delay. The initial burst has an extremely short duration, lasting for &lt;10 s. Taken together with the growing sample of millimeter M dwarf flares, this event suggests that millimeter emission is actually common during stellar flares and often originates from short burst-like events.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the discovery of the first new pulsar with the Murchison Widefield Array (MWA), PSR J0036−1033, a long-period (0.9 s) nonrecycled pulsar with a dispersion measure (DM) of 23.1 pc cm<jats:sup>−3</jats:sup>. It was found after processing only a small fraction (∼1%) of data from an ongoing all-sky pulsar survey. Follow-up observations have been made with the MWA, the upgraded Giant Metrewave Radio Telescope (uGMRT), and the Parkes 64 m telescopes, spanning a frequency range from ∼150 MHz to 4 GHz. The pulsar is faint, with an estimated flux density (<jats:italic>S</jats:italic>) of ∼1 mJy at 400 MHz and a spectrum <jats:inline-formula> <jats:tex-math> <?CDATA $S(\nu )\propto \,{\nu }^{-2.0\pm 0.2}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabec7bieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, where <jats:italic>ν</jats:italic> is frequency. The DM-derived distance implies that it is also a low-luminosity source (∼0.1 mJy kpc<jats:sup>2</jats:sup> at 1400 MHz). The analysis of archival MWA observations reveals that the pulsar’s mean flux density varies by up to a factor of ∼5–6 on timescales of several weeks to months. By combining MWA and uGMRT data, the pulsar position was determined to arcsecond precision. We also report on polarization properties detected in the MWA and Parkes bands. The pulsar’s nondetection in previous pulsar and continuum imaging surveys, the observed high variability, and its detection in a small fraction of the survey data searched to date, all hint at a larger population of pulsars that await discovery in the southern hemisphere, with the MWA and the future low-frequency Square Kilometre Array.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The highest-energy known gamma-ray sources are all located within 0.°5 of extremely powerful pulsars. This raises the question of whether ultra-high-energy (UHE; &gt;56 TeV) gamma-ray emission is a universal feature expected near pulsars with a high spin-down power. Using four years of data from the High Altitude Water Cherenkov Gamma-Ray Observatory, we present a joint-likelihood analysis of 10 extremely powerful pulsars to search for subthreshold UHE gamma-ray emission correlated with these locations. We report a significant detection (&gt;3<jats:italic>σ</jats:italic>), indicating that UHE gamma-ray emission is a generic feature of powerful pulsars. We discuss the emission mechanisms of the gamma rays and the implications of this result. The individual environment, such as the magnetic field and particle density in the surrounding area, appears to play a role in the amount of emission.</jats:p>