Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Using measurements from the PAMELA and ARINA spectrometers on board the Resurs-DK1 satellite, we have examined the 27 day intensity variations in galactic cosmic ray (GCR) proton fluxes in 2007–2008. The PAMELA and ARINA data allow for the first time a study of time profiles and the rigidity dependence of the 27 day variations observed directly in space in a wide rigidity range from ∼300 MV to several gigavolts. We find that the rigidity dependence of the amplitude of the 27 day GCR variations cannot be described by the same power law at both low and high energies. A flat interval occurs at rigidity <jats:inline-formula> <jats:tex-math> <?CDATA $R=\langle 0.6\mbox{--}1.0\rangle $?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbdacieqn1.gif" xlink:type="simple" /> </jats:inline-formula> GV with a power-law index <jats:italic>γ</jats:italic> = −0.13 ± 0.44 for PAMELA, whereas for <jats:italic>R</jats:italic> ≥ 1 GV, the power-law dependence is evident with index <jats:italic>γ</jats:italic>  = −0.51 ± 0.11. We describe the rigidity dependence of the 27 day GCR variations for PAMELA and ARINA data in the framework of the modulation potential concept using the force-field approximation for GCR transport. For a physical interpretation, we have considered the relationship between the 27 day GCR variations and solar wind plasma and other heliospheric parameters. Moreover, we have discussed possible implications of MHD modeling of the solar wind plasma together with a stochastic GCR transport model concerning the effects of corotating interaction regions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Shock interaction has been argued to play a role in powering a range of optical transients, including supernovae, classical novae, stellar mergers, tidal disruption events, and fast blue optical transients. These same shocks can accelerate relativistic ions, generating high-energy neutrino and gamma-ray emission via hadronic pion production. The recent discovery of time-correlated optical and gamma-ray emission in classical novae has revealed the important role of radiative shocks in powering these events, enabling an unprecedented view of the properties of ion acceleration, including its efficiency and energy spectrum, under similar physical conditions to shocks in extragalactic transients. Here we introduce a model for connecting the radiated optical fluence of nonrelativistic transients to their maximal neutrino and gamma-ray fluence. We apply this technique to a wide range of extragalactic transient classes in order to place limits on their contributions to the cosmological high-energy gamma-ray and neutrino backgrounds. Based on a simple model for diffusive shock acceleration at radiative shocks, calibrated to novae, we demonstrate that several of the most luminous transients can accelerate protons up to 10<jats:sup>16</jats:sup> eV, sufficient to contribute to the IceCube astrophysical background. Furthermore, several of the considered sources—particularly hydrogen-poor supernovae—may serve as “gamma-ray-hidden” neutrino sources owing to the high gamma-ray opacity of their ejecta, evading constraints imposed by the nonblazar Fermi Large Area Telescope background. However, adopting an ion acceleration efficiency of ∼0.3%–1% motivated by nova observations, we find that currently known classes of nonrelativistic, potentially shock-powered transients contribute at most a few percent of the total IceCube background.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>LIGO’s third observing run (O3) has reported several neutron star–black hole (NSBH) merger candidates. From a theoretical point of view, NSBH mergers have received less attention in the community than either binary black holes, or binary neutron stars. Here we examine single–single (sin–sin) gravitational wave (GW) captures in different types of star clusters—galactic nuclei, globular clusters, and young stellar clusters—and compare the merger rates from this channel to other proposed merger channels in the literature. There are currently large uncertainties associated with every merger channel, making a definitive conclusion about the origin of NSBH mergers impossible. However, keeping these uncertainties in mind, we find that sin–sin GW capture is unlikely to significantly contribute to the overall NSBH merger rate. In general, it appears that isolated binary evolution in the field or in clusters, and dynamically interacting binaries in triple configurations, may result in a higher merger rate.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>GRB 190114C is an unusual gamma-ray burst (GRB) due to its detection at sub-TeV energies by MAGIC, seen at redshift <jats:italic>z</jats:italic> = 0.42. This burst is one of the brightest GRB detected by Fermi. A joint GBM-LAT analysis of the prompt emission reveals the presence of sub-GeV spectral cutoff when the LAT low-energy event (LLE) data is also examined. A similar high-energy cutoff was likewise reported in GRB 160509A and GRB 100724B earlier, as well as a handful of other sources. The cutoff can be explained by the intrinsic opacity due to pair production within the emitting region. GRB 190114C shows a transition from nonthermal to a quasi-thermal-like spectrum and a radiation component that can be attributed to afterglow. Based on spectral analysis, we constrain the site of the prompt emission and Lorentz factor. Knowing that sub-TeV photons are detected in MAGIC, we perceive that the observed spectrum is indeed an overlap from two emission sites, where the emission observed in Fermi is more consistent with prompt emission produced via photospheric dissipation along with a concurrent component from the external shock.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We studied the magnetic field structures and dynamics of magnetized multiphase gas on parsec scales around supermassive black holes by using global 3D magnetohydrodynamics (MHD) simulations. We considered the effect of radiative cooling and X-ray heating due to active galactic nuclei (AGNs). The gas disk consists of a multiphase gas with (1) cold (≤10<jats:sup>3</jats:sup> K) and thin, and (2) warm (∼10<jats:sup>4</jats:sup> K) and thick components with a wide range of number densities. The turbulent magnetic energy at maximum is comparable to the thermal and turbulent kinetic energies in the turbulent motion. We confirmed that the turbulent velocity of the warm gas in the ambient cold gas is caused by magnetoconvective instability. The turbulent magnetic field due to magnetorotational instability (MRI) is developed in the disk, but the mean toroidal magnetic field dominates and supports in a quasi-steady state, where the plasma-<jats:italic>β</jats:italic>, the ratio between gas pressure and magnetic pressure, is low (<jats:italic>β</jats:italic> &lt; 1). As often seen in adiabatic MHD simulations of rotating disks, the direction of the mean toroidal field periodically reverses with time even in multiphase gas structures. The direction reversal is caused by magnetic flux vertically escaping from the disk and by the combination of the MRI and the Parker instability.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The search for life in the universe mainly uses modern Earth as a template. However, we know that Earth’s atmospheric composition changed significantly through its geological evolution. Recent discoveries show that transiting, potentially Earthlike, exoplanets orbit a wide range of host stars, which strongly influence their atmospheric composition and remotely detectable spectra. Thus, a database for transiting terrestrial exoplanets around different host stars at different geological times is a crucial missing ingredient to support observational searches for signs of life in exoplanet atmospheres. Here, we present the first high-resolution transmission spectra database for Earthlike planets, orbiting a wide range of host stars, throughout four representative stages of Earth’s history. These correspond to a prebiotic high-CO<jats:sub>2</jats:sub> world—about 3.9 billion years ago in Earth’s history—and three epochs through the increase in oxygen from 0.2% to modern atmospheric levels of 21%. We demonstrate that the spectral biosignature pairs O<jats:sub>2</jats:sub>+CH<jats:sub>4</jats:sub> and O<jats:sub>3</jats:sub>+CH<jats:sub>4</jats:sub> in the atmosphere of a transiting Earthlike planet would show a remote observer that a biosphere exists for oxygen concentrations of about 1% of modern Earth’s—corresponding to about 1–2 billion years ago in Earth’s history—for all host stars. The full model and high-resolution transmission spectra database, covering 0.4–20 <jats:italic>μ</jats:italic>m, for transiting exoplanets—from young prebiotic worlds to modern Earth analogs orbiting a wide range of host stars—is available online. It is a tool to plan and optimize our observation strategy, train retrieval methods, and interpret upcoming observations with ground- and space-based telescopes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Rotational modulations of emission spectra in brown dwarf and exoplanet atmospheres show that clouds are often distributed non-uniformly in these ultracool atmospheres. The spatial heterogeneity in cloud distribution demonstrates the impact of atmospheric dynamics on cloud formation and evolution. In this study, we update the Hubble Space Telescope (HST) time-series data analysis of the previously reported rotational modulations of WISEP J004701+680352—an unusually red late-L brown dwarf with a spectrum similar to that of the directly imaged planet HR 8799e. We construct a self-consistent spatially heterogeneous cloud model to explain the HST and the Spitzer time-series observations, as well as the time-averaged spectra of WISE 0047. In the heterogeneous cloud model, a cloud thickness variation of around one pressure scale height explains the wavelength dependence in the HST near-IR spectral variability. By including disequilibrium CO/CH<jats:sub>4</jats:sub> chemistry, our models also reproduce the redder <jats:inline-formula> <jats:tex-math> <?CDATA $J-{K}_{{\rm{s}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb81dieqn1.gif" xlink:type="simple" /> </jats:inline-formula> color of WISE 0047 compared to that of field brown dwarfs. We discuss the impact of vertical cloud structure on atmospheric profile and estimate the minimum eddy diffusivity coefficient for other objects with redder colors. Our data analysis and forward modeling results demonstrate that time-series spectrophotometry with a broad wavelength coverage is a powerful tool for constraining heterogeneous atmospheric structure.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The black hole of an active galactic nucleus is encircled by an accretion disk. The surface density of the disk is always too low to affect the tidal disruption of a star, but it can be high enough that a vigorous interaction results when the debris stream returns to pericenter and punches through the disk. Shocks excited in the disk dissipate the kinetic energy of the disk interior to the impact point and expedite inflow toward the black hole. Radiatively efficient disks with luminosity <jats:inline-formula> <jats:tex-math> <?CDATA $\gtrsim {10}^{-3}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabb776ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> Eddington have a high enough surface density that the initial stream–disk interaction leads to energy dissipation at a super-Eddington rate. Because of the rapid inflow, only part of this dissipated energy emerges as radiation, while the rest is advected into the black hole. Dissipation, inflow, and cooling balance to keep the bolometric luminosity at an Eddington-level plateau whose duration is tens of days, with an almost linear dependence on stellar mass. After the plateau, the luminosity decreases in proportion to the disk surface density, with a power-law index between −3 and −2 at earlier times, and possibly a steeper index at later times.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Gamma-ray Bursts (GRBs) are the most explosive phenomena in the universe after the big bang. A large fraction of GRB lightcurves (LCs) shows X-ray plateaus. We perform the most comprehensive analysis of all GRBs (with known and unknown redshifts) with plateau emission observed by The Neil Gehrels Swift Observatory from its launch until 2019 August. We fit 455 LCs showing a plateau and explore whether these LCs follow closure relations, relations between the temporal and spectral indices of the afterglow, corresponding to two distinct astrophysical environments and cooling regimes within the external forward shock (ES) model, and find that the ES model works for the majority of cases. The most favored environments are a constant-density interstellar or wind medium with slow cooling. We also confirm the existence of the fundamental plane relation between the rest-frame time and luminosity at the end of the plateau emission and the peak prompt luminosity for this enlarged sample, and test this relation on groups corresponding to the astrophysical environments of our known redshift sample. The plane becomes a crucial discriminant corresponding to these environments in terms of the best-fitting parameters and dispersions. Most GRBs for which the closure relations are fulfilled with respect to astrophysical environments have an intrinsic scatter <jats:italic>σ</jats:italic> compatible within 1<jats:italic>σ</jats:italic> of that of the “Gold” GRBs, a subset of long GRBs with relatively flat plateaus. We also find that GRBs satisfying closure relations indicating a fast cooling regime have a lower <jats:italic>σ</jats:italic> than ever previously found in literature.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Because the 157.74 <jats:italic>μ</jats:italic>m [C <jats:sc>ii</jats:sc>] line is the dominant coolant of star-forming regions, it is often used to infer the global star formation rates of galaxies. By characterizing the [C <jats:sc>ii</jats:sc>] and far-infrared emission from nearby Galactic star-forming molecular clumps, it is possible to determine whether extragalactic [C <jats:sc>ii</jats:sc>] emission arises from a large ensemble of such clumps, and whether [C <jats:sc>ii</jats:sc>] is indeed a robust indicator of global star formation. We describe [C <jats:sc>ii</jats:sc>] and far-infrared observations using the FIFI-LS instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA) airborne observatory toward four dense, high-mass, Milky Way clumps. Despite similar far-infrared luminosities, the [C <jats:sc>ii</jats:sc>] to far-infrared luminosity ratio, <jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{[{\rm{C}}{\rm\small{II}}]}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabba2eieqn1.gif" xlink:type="simple" /> </jats:inline-formula>/<jats:italic>L</jats:italic> <jats:sub>FIR</jats:sub>, varies by a factor of at least 140 among these four clumps. In particular, for AGAL313.576+0.324, no [C <jats:sc>ii</jats:sc>] line emission is detected despite a FIR luminosity of 24,000 <jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabba2eieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. AGAL313.576+0.324 lies a factor of more than 100 below the empirical correlation curve between <jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{[{\rm{C}}{\rm\small{II}}]}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabba2eieqn3.gif" xlink:type="simple" /> </jats:inline-formula>/<jats:italic>L</jats:italic> <jats:sub>FIR</jats:sub> and <jats:inline-formula> <jats:tex-math> <?CDATA ${S}_{\nu }(63\,\mu {\rm{m}})/{S}_{\nu }(158\,\mu {\rm{m}})$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabba2eieqn4.gif" xlink:type="simple" /> </jats:inline-formula> found for galaxies. AGAL313.576+0.324 may be in an early evolutionary “protostellar” phase with insufficient ultraviolet flux to ionize carbon, or in a deeply embedded “‘hypercompact” <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{H}}\,{\rm\small{II}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabba2eieqn5.gif" xlink:type="simple" /> </jats:inline-formula> region phase where dust attenuation of UV flux limits the region of ionized carbon to undetectably small volumes. Alternatively, its apparent lack of [C <jats:sc>ii</jats:sc>] emission may arise from deep absorption of the [C <jats:sc>ii</jats:sc>] line against the 158 <jats:italic>μ</jats:italic>m continuum, or self-absorption of brighter line emission by foreground material, which might cancel or diminish any emission within the FIFI-LS instrument’s broad spectral resolution element (<jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{\Delta }}V\sim 250$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabba2eieqn6.gif" xlink:type="simple" /> </jats:inline-formula> km s<jats:sup>−1</jats:sup>).</jats:p>