Bulletin of the American Physical Society
APS April Meeting 2015
Volume 60, Number 4
Saturday–Tuesday, April 11–14, 2015; Baltimore, Maryland
Session E14: Tidal Disruption Events and Compact Object Binaries |
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Sponsoring Units: DAP Chair: Brad Cenko, NASA Room: Key 10 |
Saturday, April 11, 2015 3:30PM - 3:42PM |
E14.00001: Tidal Disruptions Events with Prompt Hyperaccretion Christopher Evans, Pablo Laguna A bright flare from a galactic nucleus followed at late times by a $t^{-5/3}$ decay in luminosity is often considered to be the signature of a tidal disruption of a star by a massive black hole. The flare and afterglow are produced when the stream of stellar debris released by the disruption returns to the vicinity of the black hole, self-intersects, and eventually forms an accretion disk or torus. In the canonical scenario of a solar-type star disrupted by a $10^{6}\; M_\odot$ black hole, the time between the disruption of the star and the formation of the accretion torus could be years. We present fully general relativistic simulations of a new class of tidal disruption events involving ultra-close encounters of solar-type stars with intermediate mass black holes. In these encounters, a thick disk forms promptly after disruption, on timescales of hours. After a brief initial flare, the accretion rate remains steady and highly super-Eddington for a few days at $\sim 10^2\,M_\odot\,{\rm yr}^{-1}$. [Preview Abstract] |
Saturday, April 11, 2015 3:42PM - 3:54PM |
E14.00002: Relativistic simulations of black hole-neutron star coalescence: the jet emerges I Vasileios Paschalidis, Milton Ruiz, Stuart Shapiro The merger of binary black hole--neutron stars (BHNS) can form accretion disks, which are thought to support relativistic jets, thus providing the engine for a short-hard gamma-ray burst (sGRB). Until recently there existed no self-consistent calculation in full GR that starts from the late BHNS inspiral and demonstrates that jets can be launched after NS tidal disruption. This step is crucial to establishing BHNS systems as viable central engines for sGRBs and solidifying their role as multimessenger systems. In this talk I will provide the motivation for and review the fully relativistic simulations we have performed which, for the first time, show that BHNS mergers naturally give rise to jets. [Preview Abstract] |
Saturday, April 11, 2015 3:54PM - 4:06PM |
E14.00003: Relativistic simulations of black hole-neutron star coalescence: the jet emerges II Milton Ruiz, Vasileios Paschalidis, Stuart Shapiro Black hole-Neutron star (BHNS) systems have been suggested as viable central engines that power short-hard gamma ray bursts. We will present ideal magnetohydrodynamic simulations of BHNS systems in full general relativity that for the first time demonstrate that jets can be launched after NS tidal disruption if the NS is endowed with a dipolar B-field extending into the exterior. The exterior is initially characterized by a low density atmosphere with constant plasma parameter $\beta\equiv P_{\mathrm{gas}}/P_{\mathrm{mag}}$. Varying $\beta$ in the exterior from 0.1 to 0.01, we find that at $\sim 100 (M_{\mathrm {NS}}/1.4M_\odot)$ms following the onset of accretion of tidally disrupted debris, magnetic field winding above the remnant black hole poles builds up the magnetic field sufficiently to launch a mildly relativistic, collimated outflow - an incipient jet. The duration of the accretion and the lifetime of the jet is $\Delta t \sim 0.5(M_{\mathrm{NS}}/1.4M_\odot$)s. [Preview Abstract] |
Saturday, April 11, 2015 4:06PM - 4:18PM |
E14.00004: Short gamma-ray bursts in the ``time-reversal" scenario Riccardo Ciolfi, Daniel Siegel Leading models relate short gamma-ray bursts (SGRBs) to a relativistic jet launched by the black hole (BH)-accretion torus system that can be formed in a binary neutron star (BNS) or a NS-BH binary merger. However, recent observations by \textit{Swift} have revealed a large fraction of SGRB events accompanied by X-ray afterglows with durations $\sim\!10^2-10^5~\mathrm{s}$, suggesting continuous energy injection from a long-lived central engine, which is incompatible with the short ($\sim\!1~\mathrm{s}$) accretion timescale of a BH-torus system. The formation of a supramassive NS (SMNS), resisting the collapse on much longer spin-down timescales, can explain these afterglow durations, but leaves serious doubts on whether a relativistic jet can be launched at merger. Here we present a novel scenario that can solve this dichotomy, in which the SGRB is produced \textit{after} the eventual collapse of the SMNS, but observed \textit{before} (part of) its long-lasting spin-down emission. The ``time-reversal" in the observation of the two signals is caused by the substantial delay affecting the spin-down emission, due to the optically thick environment surrounding the system generated by the early differential rotation and the subsequent spin-down emission itself. [Preview Abstract] |
Saturday, April 11, 2015 4:18PM - 4:30PM |
E14.00005: Electromagnetic transients and r-process nucleosynthesis from the disk wind outflows of neutron star merger remnants Rodrigo Fernandez, Daniel Kasen, Eliot Quataert, Brian Metzger, Josiah Schwab, Stephan Rosswog The remnant accretion disk formed in binaries that involve neutron stars and/or black holes is a source of non-relativistic ejecta. The outflow is launched on a viscous and/or thermal timescale, and can provide an amount of material comparable to that in the dynamical ejecta. I will present work aimed at characterizing the properties of these winds through two-dimensional, time-dependent hydrodynamic simulations that include the relevant physics needed to follow the ejecta composition. In particular, I will focus on the effect of the spin of a promptly-formed black hole remnant on the wind, and on the interaction of the disk wind with the dynamical ejecta. I will discuss the implications of these results for the optical/IR signal from these events and for the origin of r-process elements in the Galaxy. [Preview Abstract] |
Saturday, April 11, 2015 4:30PM - 4:42PM |
E14.00006: Light curves from binary neutron star coalescence Nestor Ortiz, Stephen Green, Luis Lehner, Marcelo Ponce Evolution of binary neutron stars, and the extraction of associated gravitational waveforms, have acquired certain maturity using numerical simulations. In this work we look to augment the observational predictions by extracting electromagnetic counterparts. That is, given results from a merger simulation, we produce a photon emission sky map. Our ray-tracing algorithm employ the two-pole caustic model of gamma-ray emission from the binary system's magnetosphere. The combined measurement of both gravitational and electromagnetic wave signals provides additional information to characterize the merger. [Preview Abstract] |
Saturday, April 11, 2015 4:42PM - 4:54PM |
E14.00007: Modelling precession effects with a single effective precession parameter Patricia Schmidt, Frank Ohme, Mark Hannam Gravitational waves (GWs) from generic black-hole binaries show a rich structure that directly reflects the complex dynamics of the precessing orbital plane. Recent progress in modelling these signals relies on an approximate decoupling between the non-precessing secular inspiral and a precession-induced rotation. The latter depends in general on all physical parameters of the binary which significantly complicates modelling efforts. We show that the dominant precession effects can be captured by a single effective precession spin parameter, $\chi_p$, which is defined from the spin components that lie in the instantaneous orbital plane at some time during the inspiral. We show that for an overwhelming majority of random precessing configurations, the precession dynamics during the inspiral is well approximated by corresponding configurations defined from a subset of physical parameters. Our results suggest that in that in the comparable-mass regime waveform models with only three spin parameters faithfully represent generic waveforms, which has practical implications for the prospects of GW searches, parameter estimation and the numerical exploration of the precessing-binary parameter space. [Preview Abstract] |
Saturday, April 11, 2015 4:54PM - 5:06PM |
E14.00008: Distinguishing black-hole spin-orbit resonances via gravitational waves II: Full parameter estimation Daniele Trifir\`o, Richard O'Shaughnessy, Davide Gerosa, Emanuele Berti, Michael Kesden, Tyson Littenberg, Ulrich Sperhake Gravitational waves can constrain the magnitude and orientation of binary black holes' spins, providing a powerful diagnostic of compact binary formation mechanisms. Post-Newtonian spin evolution has three solutions: librating around two fixed point families (``resonances'') or circulating; as binaries inspiral, they become preferentially trapped near the two resonant families. In this work, we infer the properties of a two-parameter family of exactly resonant binaries from their gravitational wave signal by performing full parameter estimation. We show that these measurements reproducibly and correctly identify the neighborhood associated to each resonance, except for highly symmetric configurations, and that resonances can be distinguished for a wide range of binaries. Our results confirm and significantly extend previous results which had assumed almost all source parameters were known, corroborating the hypothesis by Gerosa et al (2013, 2014) that morphologies can be identified from the gravitational wave signal. Finally, motivated by new insight into double spin evolution (Kesden et al, 2014), we present results in coordinates that respect the separation of timescales of the problem. [Preview Abstract] |
Saturday, April 11, 2015 5:06PM - 5:18PM |
E14.00009: Theoretical Study of White Dwarf Double Stars Ajit Hira, Ted Koetter, Ruben Rivera, Juan Diaz We continue our interest in the computational simulation of the astrophysical phenomena with a study of gravitationally-bound binary stars, composed of at least one white dwarf star. Of particular interest to astrophysicists are the conditions inside a white dwarf star in the time frame leading up to its explosive end as a Type Ia supernova, for an understanding of the massive stellar explosions. In addition, the studies of the evolution of white dwarfs could serve as promising probes of theories of gravitation. We developed FORTRAN computer programs to implement our models for white dwarfs and other stars. These codes allow for different sizes and masses of stars. Simulations were done in the mass interval from 0.1 to 2.0 solar masses. Our goal was to obtain both atmospheric and orbital parameters. The computational results thus obtained are compared with relevant observational data. The data are further analyzed to identify trends in terms of sizes and masses of stars. We hope to extend our computational studies to blue giant stars in the future. [Preview Abstract] |
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