Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Magnetospheric clouds have been proposed as explanations for depth-varying dips in the phased light curves of young, magnetically active stars such as <jats:italic>σ</jats:italic> Ori E and RIK-210. However, the stellar theory that first predicted magnetospheric clouds also anticipated an associated mass-balancing mechanism known as centrifugal breakout for which there has been limited empirical evidence. In this paper, we present data from the Transiting Exoplanet Survey Satellite, Las Cumbres Observatory, All-Sky Automated Survey for Supernovae, and Veloce on the 45 Myr M3.5 star <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="object" xlink:href="TIC 234284556" xlink:type="simple">TIC 234284556</jats:named-content>, and propose that it is a candidate for the direct detection of centrifugal breakout. In assessing this hypothesis, we examine the sudden (∼1 day timescale) disappearance of a previously stable (∼1 month timescale) transit-like event. We also interpret the presence of an anomalous brightening event that precedes the disappearance of the signal, analyze rotational amplitudes and optical flaring as a proxy for magnetic activity, and estimate the mass of gas and dust present immediately prior to the potential breakout event. After demonstrating that our spectral and photometric data support a magnetospheric cloud and centrifugal breakout model and disfavor alternate scenarios, we discuss the possibility of a coronal mass ejection or stellar wind origin of the corotating material and we introduce a reionization mechanism as a potential explanation for more gradual variations in eclipse parameters. Finally, after comparing TIC 234284556 with previously identified “flux-dip” stars, we argue that TIC 234284556 may be an archetypal representative of a whole class of young, magnetically active stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Radio free–free emission is considered to be one of the most reliable tracers of star formation in galaxies. However, as it constitutes the faintest part of the radio spectrum—being roughly an order of magnitude less luminous than radio synchrotron emission at the GHz frequencies typically targeted in radio surveys—the usage of free–free emission as a star formation rate tracer has mostly remained limited to the local universe. Here, we perform a multifrequency radio stacking analysis using deep Karl G. Jansky Very Large Array observations at 1.4, 3, 5, 10, and 34 GHz in the COSMOS and GOODS-North fields to probe free–free emission in typical galaxies at the peak of cosmic star formation. We find that <jats:italic>z</jats:italic> ∼ 0.5–3 star-forming galaxies exhibit radio emission at rest-frame frequencies of ∼65–90 GHz that is ∼1.5–2 times fainter than would be expected from a simple combination of free–free and synchrotron emission, as in the prototypical starburst galaxy M82. We interpret this as a deficit in high-frequency synchrotron emission, while the level of free–free emission is as expected from M82. We additionally provide the first constraints on the cosmic star formation history using free–free emission at 0.5 ≲ <jats:italic>z</jats:italic> ≲ 3, which are in good agreement with more established tracers at high redshift. In the future, deep multifrequency radio surveys will be crucial in order to accurately determine the shape of the radio spectrum of faint star-forming galaxies, and to further establish radio free–free emission as a tracer of high-redshift star formation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Morphological and chemical structures of M33 are investigated with the LAMOST DR7 survey. Physical parameters; extinction; chemical composition of He, N, O, Ne, S, Cl, and Ar (where available); and radial velocities were determined for 110 nebulae (95 H <jats:sc>ii</jats:sc> regions and 15 planetary nebulae) in M33. Among them, 8 planetary nebulae and 55 H <jats:sc>ii</jats:sc> regions in M33 are newly discovered. We obtained the following O abundance gradients: −<jats:inline-formula> <jats:tex-math> <?CDATA ${0.199}_{-0.030}^{+0.030}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>0.199</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.030</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.030</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac38abieqn1.gif" xlink:type="simple" /> </jats:inline-formula> dex <jats:inline-formula> <jats:tex-math> <?CDATA ${R}_{25}^{-1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>25</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac38abieqn2.gif" xlink:type="simple" /> </jats:inline-formula> (based on 95 H <jats:sc>ii</jats:sc> regions), −<jats:inline-formula> <jats:tex-math> <?CDATA ${0.124}_{-0.036}^{+0.036}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>0.124</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.036</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.036</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac38abieqn3.gif" xlink:type="simple" /> </jats:inline-formula> dex <jats:inline-formula> <jats:tex-math> <?CDATA ${R}_{25}^{-1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>25</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac38abieqn4.gif" xlink:type="simple" /> </jats:inline-formula> (based on 93 H <jats:sc>ii</jats:sc> regions), and −<jats:inline-formula> <jats:tex-math> <?CDATA ${0.207}_{-0.174}^{+0.160}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>0.207</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.174</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.160</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac38abieqn5.gif" xlink:type="simple" /> </jats:inline-formula> dex <jats:inline-formula> <jats:tex-math> <?CDATA ${R}_{25}^{-1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>25</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac38abieqn6.gif" xlink:type="simple" /> </jats:inline-formula> (based on 21 H <jats:sc>ii</jats:sc> regions), utilizing abundances from N2 at O3N2 diagnostics and the <jats:italic>T</jats:italic> <jats:italic> <jats:sub>e</jats:sub> </jats:italic>-sensitive method, respectively. The He, N, Ne, S, and Ar gradients resulted in slopes of −<jats:inline-formula> <jats:tex-math> <?CDATA ${0.179}_{-0.146}^{+0.145}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>0.179</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.146</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.145</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac38abieqn7.gif" xlink:type="simple" /> </jats:inline-formula>, −<jats:inline-formula> <jats:tex-math> <?CDATA ${0.431}_{-0.281}^{+0.282}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>0.431</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.281</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.282</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac38abieqn8.gif" xlink:type="simple" /> </jats:inline-formula>, −<jats:inline-formula> <jats:tex-math> <?CDATA ${0.171}_{-0.239}^{+0.234}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>0.171</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.239</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.234</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac38abieqn9.gif" xlink:type="simple" /> </jats:inline-formula>, −<jats:inline-formula> <jats:tex-math> <?CDATA ${0.417}_{-0.182}^{+0.174}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>0.417</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.182</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.174</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac38abieqn10.gif" xlink:type="simple" /> </jats:inline-formula>, and −<jats:inline-formula> <jats:tex-math> <?CDATA ${0.340}_{-0.157}^{+0.156}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>0.340</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.157</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.156</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac38abieqn11.gif" xlink:type="simple" /> </jats:inline-formula>, respectively, utilizing abundances from the <jats:italic>T</jats:italic> <jats:italic> <jats:sub>e</jats:sub> </jats:italic>-sensitive method. Our results confirm the existence of the negative axisymmetric global metallicity distribution that is assumed in the literature. We noticed one new WC star candidate and one transition W-R WN/C candidate. The grand-design pattern of the spiral structure of M33 is presented.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A cosmological zoom-in simulation that develops into a Milky Way-like halo begins at redshift 7. The initial dark matter distribution is seeded with dense star clusters of median mass 5 × 10<jats:sup>5</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, placed in the largest subhalos present, which have a median peak circular velocity of 25 km s<jats:sup>−1</jats:sup>. Three simulations are initialized using the same dark matter distribution with the star clusters starting on approximately circular orbits having initial median radii 6.8, 0.14 kpc, and, at the exact center of the subhalos. The simulations are evolved to the current epoch at which time the median galactic orbital radii of the three sets of clusters are 30, 5, and 16 kpc, with the clusters losing about 2%, 50%, and 15% of their mass, respectively. Clusters beginning at small orbital radii have so much tidal forcing that they are often not in equilibrium. Clusters that start at larger subhalo radii have a velocity dispersion that declines smoothly to ≃20% of the central value at ≃20 half-mass radii. The clusters that begin in the subhalo centers can show a rise in velocity dispersion beyond 3–5 half-mass radii. That is, the clusters that form without local dark matter always have stellar-mass-dominated kinematics at all radii, whereas about 25% of the clusters that begin in subhalo centers have remnant local dark matter.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>While the Milky Way nuclear star cluster (MW NSC) has been studied extensively, how it formed is uncertain. Studies have shown it contains a solar and supersolar metallicity population that may have formed in situ, along with a subsolar-metallicity population that may have formed via mergers of globular clusters and dwarf galaxies. Stellar abundance measurements are critical to differentiate between formation scenarios. We present new measurements of [M/H] and <jats:italic>α</jats:italic>-element abundances [<jats:italic>α</jats:italic>/Fe] of two subsolar-metallicity stars in the Galactic center. These observations were taken with the adaptive-optics-assisted high-resolution (<jats:italic>R</jats:italic> = 24,000) spectrograph NIRSPEC in the <jats:italic>K </jats:italic>band (1.8–2.6 micron). These are the first <jats:italic>α</jats:italic>-element abundance measurements of subsolar-metallicity stars in the MW NSC. We measure [M/H] = − 0.59 ± 0.11, [<jats:italic>α</jats:italic>/Fe] = 0.05 ± 0.15 and [M/H] = − 0.81 ± 0.12, [<jats:italic>α</jats:italic>/Fe] = 0.15 ± 0.16 for the two stars at the Galactic center; the uncertainties are dominated by systematic uncertainties in the spectral templates. The stars have an [<jats:italic>α</jats:italic>/Fe] in between the [<jats:italic>α</jats:italic>/Fe] of globular clusters and dwarf galaxies at similar [M/H] values. Their abundances are very different than the bulk of the stars in the nuclear star cluster. These results indicate that the subsolar-metallicity population in the MW NSC likely originated from infalling dwarf galaxies or globular clusters and are unlikely to have formed in situ.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The search for signs of extraterrestrial technology, or technosignatures, includes the search for objects which collect starlight for some technological use, such as those composing a Dyson sphere. These searches typically account for a star’s light and some blackbody temperature for the surrounding structure. However, such a structure inevitably returns some light back to the surface of its star, either from direct reflection or thermal reemission. In this work, we explore how this feedback may affect the structure and evolution of stars, and when such feedback may affect observations. We find that in general this returned light can cause stars to expand and cool. Our <jats:monospace>MESA</jats:monospace> models show that this energy is only transported toward a star’s core effectively by convection, so low-mass stars are strongly affected, while higher-mass stars with radiative exteriors are not. Ultimately, the effect only has significant observational consequences for spheres with very high temperatures (much higher than the often assumed ∼300 K) and/or high specular reflectivity. Lastly, we produce color–magnitude diagrams of combined star–Dyson sphere systems for a wide array of possible configurations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the origin of the observed scaling <jats:italic>j</jats:italic> ∼ <jats:italic>R</jats:italic> <jats:sup>3/2</jats:sup> between the specific angular momentum <jats:italic>j</jats:italic> and the radius <jats:italic>R</jats:italic> of molecular clouds (MCs) and their their substructures, and of the observed near independence of <jats:italic>β</jats:italic>, the ratio of rotational to gravitational energy, from <jats:italic>R</jats:italic>. To this end, we measure the angular momentum (AM) of “Lagrangian” particle sets in a smoothed particle hydrodynamics (SPH) simulation of the formation, collapse, and fragmentation of giant MCs. The Lagrangian sets are initially defined as connected particle sets above a certain density threshold at a certain time <jats:italic>t</jats:italic> <jats:sub>def</jats:sub>, and then the same set of SPH particles is followed either forward or backward in time. We find the following. (i) The Lagrangian particle sets evolve along the observed <jats:italic>j</jats:italic>–<jats:italic>R</jats:italic> relation when the volume containing them also contains a large number of other “intruder” particles. Otherwise, they evolve with <jats:italic>j</jats:italic> ∼ cst. (ii) Tracking Lagrangian sets to the future, we find that a subset of the SPH particles participates in the collapse, while the rest disperses away. (iii) These results suggest that the Lagrangian sets of fluid particles exchange their AM with other neighboring fluid particles via turbulent viscosity. (iv) We conclude that the <jats:italic>j</jats:italic>–<jats:italic>R</jats:italic> relation arises from a global tendency toward gravitational contraction, mediated by AM loss via turbulent viscosity, which induces fragmentation into dense, low-AM clumps, and diffuse, high-AM envelopes, which disperse away, limiting the mass efficiency of the fragmentation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this paper we present an extensive analysis of the GW190521 gravitational wave event with the current (fourth) generation of phenomenological waveform models for binary black hole coalescences. GW190521 stands out from other events since only a few wave cycles are observable. This leads to a number of challenges, one being that such short signals are prone to not resolving approximate waveform degeneracies, which may result in multimodal posterior distributions. The family of waveform models we use includes a new fast time-domain model (IMRP<jats:sc>henomTPHM</jats:sc>), which allows us to extensively test different priors and robustness with respect to variations in the waveform model, including the content of spherical harmonic modes. We clarify some issues raised in a recent paper, Nitz &amp; Capano, associated with possible support for a high-mass-ratio source, but confirm their finding of a multimodal posterior distribution, albeit with important differences in the statistical significance of the peaks. In particular, we find that the support for both masses being outside the pair instability supernova mass gap, and the support for an intermediate-mass-ratio binary are drastically reduced with respect to what Nitz &amp; Capano found. We also provide updated probabilities for associating GW190521 to the potential electromagnetic counterpart from the Zwicky Transient Facility (ZTF) Graham et al.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In order to explore how the ubiquitous short-term stochastic variability in the photometric observations of Wolf–Rayet (WR) stars is related to various stellar characteristics, we examined a sample of 50 Galactic WR stars using 122 lightcurves obtained by the BRIght Target Explorer-Constellation, Transiting Exoplanet Survey Satellite and Microvariability and Oscillations of Stars satellites. We found that the periodograms resulting from a discrete Fourier transform of all our detrended lightcurves are characterized by a forest of random peaks showing an increase in power starting from ∼0.5 day<jats:sup>−1</jats:sup> down to ∼0.1 day<jats:sup>−1</jats:sup>. After fitting the periodograms with a semi-Lorentzian function representing a combination of white and red noise, we investigated possible correlations between the fitted parameters and various stellar and wind characteristics. Seven correlations were observed, the strongest and only significant one being between the amplitude of variability, <jats:italic>α</jats:italic> <jats:sub>0</jats:sub>, observed for hydrogen-free WR stars, while WNh stars exhibit correlations between <jats:italic>α</jats:italic> <jats:sub>0</jats:sub> and the stellar temperature, <jats:italic>T</jats:italic> <jats:sub>*</jats:sub>, and also between the characteristic frequency of the variations, <jats:italic>ν</jats:italic> <jats:sub>char</jats:sub>, and both <jats:italic>T</jats:italic> <jats:sub>*</jats:sub> and <jats:italic>v</jats:italic> <jats:sub>∞</jats:sub>. We report that stars observed more than once show significantly different variability parameters, indicating an epoch-dependent measurement. We also find that the observed characteristic frequencies for the variations generally lie between <jats:inline-formula> <jats:tex-math> <?CDATA $-0.5\lt {\mathrm{log}}_{10}{\nu }_{\mathrm{char}}\lt 0.5$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>−</mml:mo> <mml:mn>0.5</mml:mn> <mml:mo>&lt;</mml:mo> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>char</mml:mi> </mml:mrow> </mml:msub> <mml:mo>&lt;</mml:mo> <mml:mn>0.5</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac397dieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, and that the values of the steepness of the amplitude spectrum are typically found in the range <jats:inline-formula> <jats:tex-math> <?CDATA $-0.1\lt {\mathrm{log}}_{10}\gamma \lt 0.5$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>−</mml:mo> <mml:mn>0.1</mml:mn> <mml:mo>&lt;</mml:mo> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mi>γ</mml:mi> <mml:mo>&lt;</mml:mo> <mml:mn>0.5</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac397dieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. We discuss various physical processes that can lead to this correlation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a comprehensive review of AGILE follow-up observations of the Gravitational Wave (GW) events and the unconfirmed marginal triggers reported in the first LIGO-Virgo (LV) Gravitational Wave Transient Catalog (GWTC-1). For seven GW events and 13 LV triggers, the associated 90% credible region was partially or fully accessible to the AGILE satellite at the <jats:italic>T</jats:italic> <jats:sub>0</jats:sub>; for the remaining events, the localization region was not accessible to AGILE due to passages into the South Atlantic Anomaly, or complete Earth occultations (as in the case of GW170817). A systematic search for associated transients, performed on different timescales and on different time intervals about each event, led to the detection of no gamma-ray counterparts. We report AGILE MCAL upper limit fluences in the 400 keV–100 MeV energy range, evaluated in a time window of <jats:italic>T</jats:italic> <jats:sub>0</jats:sub> ± 50 s around each event, as well as AGILE GRID upper limit (UL) fluxes in the 30 MeV–50 GeV energy range, evaluated in a time frame of <jats:italic>T</jats:italic> <jats:sub>0</jats:sub> ± 950 s around each event. All ULs are estimated at different integration times and are evaluated within the portions of GW credible region accessible to AGILE at the different times under consideration. We also discuss the possibility of AGILE MCAL to trigger and detect a weak soft-spectrum burst such as GRB 170817A.</jats:p>