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  1. Free, publicly-accessible full text available October 1, 2022
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    Free, publicly-accessible full text available September 29, 2022
  3. Free, publicly-accessible full text available August 1, 2022
  4. Long gamma-ray bursts are associated with the core-collapse of massive, rapidly spinning stars. However, the believed efficient angular momentum transport in stellar interiors leads to predominantly slowly-spinning stellar cores. Here, we report on binary stellar evolution and population synthesis calculations, showing that tidal interactions in close binaries not only can explain the observed sub-population of spinning, merging binary black holes, but also lead to long gamma-ray bursts at the time of black-hole formation, with rates matching the empirical ones. We find that ≈10% of the GWTC-2 reported binary black holes had a long gamma-ray burst associated with their formation, withmore »GW190517 and GW190719 having a probability of ≈85% and ≈60%, respectively, being among them.« less
  5. Our understanding of the formation and evolution of binary black holes (BBHs) is significantly impacted by the recent discoveries made by the LIGO/Virgo collaboration. Of utmost importance is the detection of the most massive BBH system, GW190521. Here we investigate what it takes for field massive stellar binaries to account for the formation of such massive BBHs. Whether the high mass end of the BH mass function is populated by remnants of massive stars that either formed at extremely low metallicities and avoid the pair-instability mass gap or increase their birth mass beyond the pair-instability mass gap through the accretionmore »of gas from the surrounding medium. We show that assuming that massive stars at very low metallicities can form massive BHs by avoiding pair-instability supernova, coupled with a correspondingly high formation efficiency for BBHs, can explain the observed BH mass function. To this end, one requires a relation between the initial and final mass of the progenitor stars at low metallicities that is shallower than what is expected from wind mass loss alone. On the other hand, assuming pair-instability operates at all metallicities, one can account for the observed BH mass function if at least about 10% of the BHs born at very low metallicities double their mass before they merge because of accretion of ambient gas. Such BBHs will have to spend about a Gyr within a parsec length-scale of their parent atomic cooling halos or a shorter timescale if they reside in the inner sub-parsecs of their host dark matter halos. Future stellar evolution calculations of massive stars at very low metallicity and hydrodynamical simulations of gas accretion onto BBHs born in atomic cooling halos can shed light on this debate.« less
  6. ABSTRACT The discovery of GRB 170817A, the first unambiguous off-axis short gamma-ray burst (sGRB) arising from a neutron star merger, has challenged our understanding of the angular structure of relativistic jets. Studies of the jet propagation usually assume that the jet is ejected from the central engine with a top-hat structure and its final structure, which determines the observed light curve and spectra, is primarily regulated by the interaction with the nearby environment. However, jets are expected to be produced with a structure that is more complex than a simple top-hat, as shown by global accretion simulations. We present numericalmore »simulations of sGRBs launched with a wide range of initial structures, durations, and luminosities. We follow the jet interaction with the merger remnant wind and compute its final structure at distances ≳1011 cm from the central engine. We show that the final jet structure, as well as the resulting afterglow emission, depends strongly on the initial structure of the jet, its luminosity, and duration. While the initial structure of the jet is preserved for long-lasting sGRBs, it is strongly modified for jets barely making their way through the wind. This illustrates the importance of combining the results of global simulations with propagation studies in order to better predict the expected afterglow signatures from neutron star mergers. Structured jets provide a reasonable description of the GRB 170817A afterglow emission with an off-axis angle θobs ≈ 22.5°.« less
  7. Stellar-mass black holes can become embedded within the gaseous disks of active galactic nuclei (AGNs). Afterwards, their interactions are mediated by their gaseous surroundings. In this work, we study the evolution of stellar-mass binary black holes (BBHs) embedded within AGN disks using a combination of three-dimensional hydrodynamic simulations and analytic methods, focusing on environments in which the AGN disk scale height H is ≳ the BBH sphere of influence. We model the local surroundings of the embedded BBHs using a wind tunnel formalism and characterize different accretion regimes based on the local properties of the disk, which range from wind-dominatedmore »to quasi-spherical. We use our simulations to develop prescriptions for mass accretion and drag for embedded BBHs. We use these prescriptions, along with AGN disk models that can represent the Toomre-unstable outer regions of AGN disks, to study the long-term evolution of the BBHs as they migrate through the disk. We find that BBHs typically merge within ≲5−30Myr , increasing their mass significantly in the process, allowing BBHs to enter (or cross) the pair-instability supernova mass gap. The rate at which gas is supplied to these BBHs often exceeds the Eddington limit, sometimes by several orders of magnitude. We conclude that most embedded BBHs will merge before migrating significantly in the disk. Depending on the conditions of the ambient gas and the distance to the system, LISA can detect the transition between the gas-dominated and gravitational wave dominated regime for inspiraling BBHs that are formed sufficiently close to the AGN ( ≲ 0.1 pc). We also discuss possible electromagnetic signatures during and following the inspiral, finding that it is generally unlikely but not inconceivable for the bolometric luminosity of the BBH to exceed that of the host AGN.« less
  8. ABSTRACT The detection of the optical transient AT2017gfo proved that binary neutron star mergers are progenitors of kilonovae (KNe). Using a combination of numerical-relativity and radiative-transfer simulations, the community has developed sophisticated models for these transients for a wide portion of the expected parameter space. Using these simulations and surrogate models made from them, it has been possible to perform Bayesian inference of the observed signals to infer properties of the ejected matter. It has been pointed out that combining inclination constraints derived from the KN with gravitational-wave measurements increases the accuracy with which binary parameters can be estimated, inmore »particular breaking the distance-inclination degeneracy from gravitational wave inference. To avoid bias from the unknown ejecta geometry, constraints on the inclination angle for AT2017gfo should be insensitive to the employed models. In this work, we compare different assumptions about the ejecta and radiative reprocesses used by the community and we investigate their impact on the parameter inference. While most inferred parameters agree, we find disagreement between posteriors for the inclination angle for different geometries that have been used in the current literature. According to our study, the inclusion of reprocessing of the photons between different ejecta types improves the modeling fits to AT2017gfo and, in some cases, affects the inferred constraints. Our study motivates the inclusion of large ∼ 1-mag uncertainties in the KN models employed for Bayesian analysis to capture yet unknown systematics, especially when inferring inclination angles, although smaller uncertainties seem appropriate to capture model systematics for other intrinsic parameters. We can use this method to impose soft constraints on the ejecta geometry of the KN AT2017gfo.« less