Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>On 2019 August 14 at 21:10:39 UTC, the LIGO/Virgo Collaboration (LVC) detected a possible neutron star–black hole merger (NSBH), the first ever identified. An extensive search for an optical counterpart of this event, designated GW190814, was undertaken using the Dark Energy Camera on the 4 m Victor M. Blanco Telescope at the Cerro Tololo Inter-American Observatory. Target of Opportunity interrupts were issued on eight separate nights to observe 11 candidates using the 4.1 m Southern Astrophysical Research (SOAR) telescope’s Goodman High Throughput Spectrograph in order to assess whether any of these transients was likely to be an optical counterpart of the possible NSBH merger. Here, we describe the process of observing with SOAR, the analysis of our spectra, our spectroscopic typing methodology, and our resultant conclusion that none of the candidates corresponded to the gravitational wave merger event but were all instead other transients. Finally, we describe the lessons learned from this effort. Application of these lessons will be critical for a successful community spectroscopic follow-up program for LVC observing run 4 (O4) and beyond.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>By using self-consistent 2.5-dimensional particle-in-cell simulations, we study the excitation efficiency of electromagnetic waves by power-law energetic electrons with an anisotropic pitch-angle velocity distribution, which can simultaneously trigger the Langmuir and electron cyclotron maser instabilities, in differently magnetized coronal plasmas. It is found that the (transverse) electromagnetic waves can be excited much more efficiently in the case of strongly magnetized plasmas with <jats:italic>ω</jats:italic> <jats:sub>ce</jats:sub> &gt; <jats:italic>ω</jats:italic> <jats:sub>pe</jats:sub> than that of weakly magnetized plasmas with <jats:italic>ω</jats:italic> <jats:sub>ce</jats:sub> &lt; <jats:italic>ω</jats:italic> <jats:sub>pe</jats:sub>, where <jats:italic>ω</jats:italic> <jats:sub>ce</jats:sub> and <jats:italic>ω</jats:italic> <jats:sub>pe</jats:sub> are the electron cyclotron frequency and the electron plasma frequency, respectively. In particular, in a weakly magnetized plasma the electromagnetic wave is hardly excited effectively via the nonlinear coupling of Langmuir waves; although the Langmuir waves can be generated by the power-law energetic electrons, implying that the so-called plasma emission does not effectively work. These results can be helpful for us to better understand the physical mechanism of solar radio bursts.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We determine three independent Population II distance moduli to the Fornax dwarf spheroidal (dSph) galaxy, using wide-field, ground-based <jats:italic>VI</jats:italic> imaging acquired with the Magellan-Baade telescope at Las Campanas Observatory. After subtracting foreground stars using Gaia EDR3 proper motions, we measure an <jats:italic>I</jats:italic>-band tip of the red giant branch (TRGB) magnitude of <jats:inline-formula> <jats:tex-math> <?CDATA ${I}_{0}^{\mathrm{TRGB}}=16.753\pm {0.03}_{\mathrm{stat}}\pm {0.037}_{\mathrm{sys}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>I</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>TRGB</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mn>16.753</mml:mn> <mml:mo>±</mml:mo> <mml:msub> <mml:mrow> <mml:mn>0.03</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>stat</mml:mi> </mml:mrow> </mml:msub> <mml:mo>±</mml:mo> <mml:msub> <mml:mrow> <mml:mn>0.037</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>sys</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5b07ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> mag, with a calibration based in the LMC giving a distance modulus of <jats:inline-formula> <jats:tex-math> <?CDATA ${\mu }_{0}^{\mathrm{TRGB}}=20.80\pm {0.037}_{\mathrm{stat}}\pm {0.057}_{\mathrm{sys}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>TRGB</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mn>20.80</mml:mn> <mml:mo>±</mml:mo> <mml:msub> <mml:mrow> <mml:mn>0.037</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>stat</mml:mi> </mml:mrow> </mml:msub> <mml:mo>±</mml:mo> <mml:msub> <mml:mrow> <mml:mn>0.057</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>sys</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5b07ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> mag. We determine an RR Lyrae (RRL) distance from template mean magnitudes, with periods adopted from the literature. Adopting a Gaia DR2 calibration of first overtone RRL period–luminosity and period–Wesenheit relations, we find <jats:inline-formula> <jats:tex-math> <?CDATA ${\mu }_{0}^{\mathrm{PLZ}}=20.74\pm {0.01}_{\mathrm{stat}}\pm {0.12}_{\mathrm{sys}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>PLZ</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mn>20.74</mml:mn> <mml:mo>±</mml:mo> <mml:msub> <mml:mrow> <mml:mn>0.01</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>stat</mml:mi> </mml:mrow> </mml:msub> <mml:mo>±</mml:mo> <mml:msub> <mml:mrow> <mml:mn>0.12</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>sys</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5b07ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> mag and <jats:inline-formula> <jats:tex-math> <?CDATA ${\mu }_{0}^{\mathrm{PWZ}}=20.68\pm {0.02}_{\mathrm{stat}}\pm {0.07}_{\mathrm{sys}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>PWZ</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mn>20.68</mml:mn> <mml:mo>±</mml:mo> <mml:msub> <mml:mrow> <mml:mn>0.02</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>stat</mml:mi> </mml:mrow> </mml:msub> <mml:mo>±</mml:mo> <mml:msub> <mml:mrow> <mml:mn>0.07</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>sys</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5b07ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> mag. Finally, we determine a distance from Fornax’s horizontal branch (HB) and two galactic globular cluster calibrators, giving <jats:inline-formula> <jats:tex-math> <?CDATA ${\mu }_{0}^{\mathrm{HB}}=20.83\pm {0.03}_{\mathrm{stat}}\pm {0.09}_{\mathrm{sys}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>HB</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mn>20.83</mml:mn> <mml:mo>±</mml:mo> <mml:msub> <mml:mrow> <mml:mn>0.03</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>stat</mml:mi> </mml:mrow> </mml:msub> <mml:mo>±</mml:mo> <mml:msub> <mml:mrow> <mml:mn>0.09</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>sys</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5b07ieqn5.gif" xlink:type="simple" /> </jats:inline-formula> mag. These distances are each derived from homogeneous IMACS photometry, are anchored to independent geometric zero-points, and utilize different classes of stars. We therefore average over independent uncertainties and report the combined distance modulus 〈<jats:italic>μ</jats:italic> <jats:sub>0</jats:sub>〉 =20.770 ± 0.042<jats:sub>stat</jats:sub> ± 0.024<jats:sub>sys</jats:sub> mag (corresponding to a distance of 143 ± 3 kpc).</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report TeV gamma-ray observations of the ultra-high-energy source MGRO J1908+06 using data from the High Altitude Water Cherenkov Observatory. This source is one of the highest-energy known gamma-ray sources, with emission extending past 200 TeV. Modeling suggests that the bulk of the TeV gamma-ray emission is leptonic in nature, driven by the energetic radio-faint pulsar PSR J1907+0602. Depending on what assumptions are included in the model, a hadronic component may also be allowed. Using the results of the modeling, we discuss implications for detection prospects by multi-messenger campaigns.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present novel effects of uniform rapid stellar rotation on the minimum mass of stable hydrogen burning in very low mass stars, using an analytic model and relaxing the assumption of spherical symmetry. We obtain an analytic formula for the minimum mass of hydrogen burning as a function of the angular speed of stellar rotation. Further, we show the existence of a maximum mass of stable hydrogen burning in such stars, which is purely an artifact of rapid rotation. The existence of this extremum in mass results in a minimum admissible value of the stellar rotation period of ∼22 minutes, below which a very low mass object does not reach the main sequence, within the ambit of our model. For a given angular speed, we predict a mass range beyond which such an object will not evolve into a main-sequence star.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study a large sample of dwarf galaxies using archival Chandra X-ray observations, with the aim of detecting accreting intermediate-mass black holes (IMBHs). IMBHs are expected to inhabit dwarf galaxies and to produce specific signatures in terms of luminosity and X-ray spectra. We report the discovery of an X-ray source associated with an A85 dwarf galaxy that fits the IMBH description. The stellar mass of the host galaxy is estimated to be 2 × 10<jats:sup>8 </jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, which makes it one of the least massive galaxies to potentially host an accreting black hole. The source is detected in the soft band, under 1 keV, and is undetected at higher energies. The X-ray luminosity is ≈10<jats:sup>41</jats:sup> erg s<jats:sup>−1</jats:sup>, making it almost three orders of magnitude more luminous than the most luminous stellar-mass supersoft emitters. From the galaxy stellar mass versus black hole mass relation, we estimate the mass to be within the intermediate regime. Another method that resulted in an intermediate mass relies on the fact that supersoft emission is expected to be associated with high accretion rates, approaching the Eddington limit. We suggest that the observed offset of the X-ray source from the galactic center (≈1.8 kpc) is due to galaxy interactions, and we present evidence from the literature that supports the relation between black hole activity and galaxy interactions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a spatially resolved H <jats:sc>ii</jats:sc> region study of the gas-phase metallicity, ionization parameter, and interstellar medium (ISM) pressure maps of six local star-forming and face-on spiral galaxies from the TYPHOON program. Self-consistent metallicity, ionization parameter, and pressure maps are calculated simultaneously through an iterative process to provide useful measures of the local chemical abundance and its relation to localized ISM properties. We constrain the presence of azimuthal variations in metallicity by measuring the residual metallicity offset Δ(O/H) after subtracting the linear fits to the radial metallicity profiles. We, however, find weak evidence of azimuthal variations in most of the galaxies, with small (mean 0.03 dex) scatter. The galaxies instead reveal that H <jats:sc>ii</jats:sc> regions with enhanced and reduced abundances are found distributed throughout the disk. While the spiral pattern plays a role in organizing the ISM, it alone does not establish the relatively uniform azimuthal variations we observe. Differences in the metal abundances are more likely driven by the strong correlations with the local physical conditions. We find a strong and positive correlation between the ionization parameter and the local abundances as measured by the relative metallicity offset Δ(O/H), indicating a tight relationship between local physical conditions and their localized enrichment of the ISM. Additionally, we demonstrate the impact of unresolved observations on the measured ISM properties by rebinning the data cubes to simulate low-resolution (1 kpc) observations, typical of large IFU surveys. We find that the ionization parameter and ISM pressure diagnostics are impacted by the loss of resolution such that their measured values are larger relative to the measured values on sub-H <jats:sc>ii</jats:sc> region scales.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Accretion disk turbulence along with its effect on large-scale magnetic fields plays an important role in understanding disk evolution in general, and the launching of astrophysical jets in particular. Motivated by enabling a comprehensive subgrid description for global long-term simulations of accretions disks, we aim to further characterize the transport coefficients emerging in local simulations of magnetorotational disk turbulence. For the current investigation, we leverage a time-dependent version of the test-field method, which is sensitive to the turbulent electromotive force (EMF) generated as a response to a set of pulsating background fields. We obtain Fourier spectra of the transport coefficients as a function of oscillation frequency. These are well approximated by a simple response function, describing a finite-time buildup of the EMF as a result of a time-variable mean magnetic field. For intermediate timescales (i.e., slightly above the orbital frequency), we observe a significant phase lag of the EMF compared to the causing field. Augmented with our previous result on a nonlocal closure relation in space, and incorporated into a suitable mean-field description that we briefly sketch out here, the new framework will allow us to drop the restrictive assumption of scale separation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The lack of observations of abundance patterns originating in pair-instability supernovae has been a long-standing problem in relation to the first stars. This class of supernovae is expected to have an abundance pattern with a strong odd–even effect, making it substantially different from present-day supernovae. In this study, we use a cosmological radiation hydrodynamics simulation to model such supernovae and the subsequent formation of the second generation of stars. We incorporate streaming velocities for the first time. There are 14 star-forming minihalos in our 1 cMpc <jats:italic>h</jats:italic> <jats:sup>−1</jats:sup> box, leading to 14 supernovae occurring before redshift <jats:italic>z</jats:italic> = 19.5, where we start reducing the complexity of the simulation. Following the explosions, extremely metal-poor stars form in 10 halos via internal and external enrichment, which makes it the most common outcome. Only one halo does not recollapse during the simulations. This result is at variance with the current (lack of) observations of metal-poor stars with pair-instability supernova abundance patterns, suggesting that these very massive stars might be rare even in the early universe. The results from this simulation also give us insights into what drives different modes of recollapse and what determines the mixing behavior of metals after very energetic supernovae.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Compton Spectrometer and Imager (COSI) is a balloon-borne compact Compton telescope designed to survey the 0.2–5 MeV sky. COSI’s energy resolution of ∼0.2% at 1.8 MeV, single-photon reconstruction, and wide field of view make it capable of studying astrophysical nuclear lines, particularly the 1809 keV <jats:italic>γ</jats:italic>-ray line from decaying Galactic <jats:sup>26</jats:sup>Al. Most <jats:sup>26</jats:sup>Al originates in massive stars and core-collapse supernova nucleosynthesis, but the path from stellar evolution models to Galaxy-wide emission remains unconstrained. In 2016, COSI had a successful 46 day flight on a NASA superpressure balloon. Here, we detail the first search for the 1809 keV <jats:sup>26</jats:sup>Al line in the COSI 2016 balloon flight using a maximum-likelihood analysis. We find a Galactic <jats:sup>26</jats:sup>Al flux of (8.6 ± 2.5) × 10<jats:sup>−4</jats:sup> ph cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> within the Inner Galaxy (∣<jats:italic>ℓ</jats:italic>∣ ≤ 30°, ∣<jats:italic>b</jats:italic>∣ ≤ 10°) with 3.7<jats:italic>σ</jats:italic> significance above background. Within uncertainties, this flux is consistent with expectations from previous measurements by SPectrometer on INTEGRAL (SPI) and the Compton Telescope on the Compton Gamma-Ray Observatory (COMPTEL). This analysis demonstrates COSI’s powerful capabilities for studies of <jats:italic>γ</jats:italic>-ray lines and underscores the scientific potential of future compact Compton telescopes. In particular, the next iteration of COSI as a NASA Small Explorer satellite has recently been approved for launch in 2025.</jats:p>