Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Plasma Physics
Volume 65, Number 11
Monday–Friday, November 9–13, 2020; Remote; Time Zone: Central Standard Time, USA
Session PP11: Poster Session: Astrophysics (2:00pm - 5:00pm)On Demand
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PP11.00001: Heating and acceleration processes in galaxy cluster plasmas Francisco Ley, Ellen Zweibel, Mario Riquelme, Lorenzo Sironi Galaxy clusters are the most massive gravitationally bound structures in the Universe. Space among galaxies is filled with hot ($\beta\gg1$), weakly collisional plasma, the Intracluster Medium (ICM). The nature of kinetic processes in these plasmas, such as particle energization and heating mechanisms and transport, and the interplay between them and the large-scale dynamics of galaxy clusters are not well understood. We perform Particle in Cell (PIC) simulations of a plasma with an oscillating magnetic field $B$ that is periodically amplified and decreased in magnitude to study the heating and acceleration of particles. Both the amplification and dwindle of $B$ can generate a pressure anisotropy $\Delta=p_{\perp}-p_{\parallel}$ that heats the plasma by gyroviscosity and is self-regulated by triggering kinetic microinstabilities. When $\beta=10$ initially, both mirror ($\Delta>1$) and firehose ($\Delta<1$) instabilities arise, limiting $\Delta$ and creating a nonthermal tail. This acceleration mechanism is mediated by the instabilities, but ultimately it acts by extracting energy from the thermal pool and giving it to the nonthermal population of particles. These results are compared with a similar study of a steadily growing magnetic field at lower $\beta$ (Ley at al. 2019) [Preview Abstract] |
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PP11.00002: Spectral analysis of PIC simulations of the filamentation instability Michael Sitarz, Mikhail Medvedev, Alexander Philippov The Weibel or, in general, the filamentation instability is ubiquitous of plasmas with high-energy-density content. It is present in laser-produced plasmas and astrophysical sources, such as in collisionless shocks of cosmic blasts (gamma-ray bursts and supernovae), possibly in outskirts of galaxy clusters and others. The is generated in unmagnetized and weakly-magnetized plasmas by anisotropy of the particle distribution function, e.g. by anisotropic temperature or multi-stream configurations. The generated electromagnetic fields reside on the plasma skin-depth scale which is smaller than the effective larmor scale. Radiation from such sub-Larmor-scale fields is known as the jitter radiation; it markedly differs from the cyclotron or synchrotron radiation. Its spectrum carries wealth of information about the magnetic field properties. Here we present the spectral analysis of state-of-the-art PIC simulations of the Weibel instability. It demonstrates the generation of high-frequency electromagnetic fluctuations. We discuss the spectrum, the temporal and angular distribution of the emitted power. The origin and nature of these waves is discussed. [Preview Abstract] |
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PP11.00003: Interplay of ionized gas dynamics and dark matter physics in galaxy formation Keita Todoroki, Mikhail Medvedev, Mark Vogelsberger The problem of galaxy formation remains an outstanding problem in cosmology. Conventional paradigm assumes that dark matter is passive: it forms large halos which gravitationally pull gas into them. The rich physics of star formation, ISM physics, cosmic ray production and other baryonic effects and feedback are regulated by MHD or plasma kinetics. Such a paradigm seems to face some problems at galactic and sub-galactic, scales known as the missing satellite, core-cusp, and too-big-to-fail problems. We propose a model in which dark matter may experience inelastic interactions in the dark sector. The simplest two-component dark matter model has recently been shown to robustly resolve the small-scale problems in N-body dark-matter-only simulations [1,2]. Here we present simulations of an isolated galaxy using the full, state-of-the-art baryonic feedback machinery used in IllustrisTNG simulations. Our results indicate that the novel dark matter effects lead to `effective' heating of the central parts of the galaxy akin to that due to the stellar and supernova outflow feedback. We discuss some observational predictions following from our study. [1,2] K. Todoroki, M.V. Medvedev, MNRAS, 483, 3983 (2019); MNRAS, 483, 4004 (2019) [Preview Abstract] |
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PP11.00004: Time-Dependent Grid for Fluid MHD Simulations in Athena++ Roark Habegger, Fabian Heitsch Many phenomena in astrophysics (collapse, blast waves, jets, etc.) involve drastically changing spatial scales. This poses a challenge for models and numerical simulations. I address this issue by implementing an expanding grid formalism in the magnetohydrodynamics code Athena++. This gives every cell a generic time dependence. It can be used to define a comoving grid, an expanding grid, or a shrinking grid in any coordinate frame offered by the code. Instead of requiring unique simulations for each spatial scale involved, the expanding grid allows for a single simulation to contain the entire time evolution of the fluid. [Preview Abstract] |
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PP11.00005: Particle-in-cell simulations of neutron star magnetospheres including general relativity effects Rui Torres, Fabio Cruz, Thomas Grismayer, Luis Silva The magnetospheres of compact objects such as neutron stars and black holes, commonly connected to some of the most violent events in the Universe, are complex systems that comprise quantum electrodynamic (QED) processes, kinetic-scale pair plasma physics and general relativity (GR). To study such intricate and exotic systems, advanced simulation techniques are required. In this work, we present a GR module recently developed for the particle-in-cell code OSIRIS, including a field solver and a new particle pusher for arbitrary curvilinear coordinate systems. We present two-dimensional simulations performed with this GR-PIC module of neutron star magnetospheres, and discuss the differences in the plasma current distribution in the vicinity of the star when compared to classical simulations of these systems for different ratios between the Schwarzschild and the stellar radii. We also discuss preliminary steps to extend this code to simulate black hole magnetospheres. [Preview Abstract] |
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PP11.00006: On FRBs from a magnetar Mikhail Medvedev Fast radio bursts (FRBs) remains an enigmatic phenomenon for over a decade. FRBs are short radio pulses of tens of milliseconds duration (de-dispersed) in the frequency range around a Gigaherz. Their very large dispersion measure indicate their extragalactic origin and thus their exceptional brightness. Some FRB sources were found to be repeaters. Recently, a connection of a galactic underluminous FRB to a magnetar has been firmly established. Conventionally, FRBs are attributed to the cyclotron/synchrotron maser instability operating at a shock outside the magnetosphere driven by a magnetar flare. Such a maser would exciting an X-mode observed as an FRB. Such a model seems problematic at explaining the observed periodicities of FRB repeaters. Here we will critically address viability of the shock scenario. We propose a scenario in which an FRBs can originate from within magnetar's magnetosphere. [Preview Abstract] |
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PP11.00007: Electron acceleration in Compton driven plasma wakes Fabrizio Del Gaudio, Thomas Grismayer, Luis Silva Several astrophysical emitters like active galactic nuclei, supernovae remnants, and gamma-ray bursts are sources of energetic photons which can propagate across tenuous plasmas. Its has been shown that the effect of Compton scattering of the photons onto the electron of the plasmas can excite plasma wakes [1]. We investigate the possible acceleration of electrons in these plasma wakes. Leveraging the scaling laws already derived for wake amplitude, phase velocity, the predict maximum energy gain in the linear and nonlinear regimes. We also analyse the limiting factors which restrain the acceleration process such as the electron dephasing, the driver divergence and depletion. Our results are confirmed by self-consistent particle-in-cell simulations performed with the PIC code OSIRIS where a Compton scattering module has been implemented [2]. Our findings suggest that ultra relativistic acceleration of electrons can occur via Compton driven wakes in extreme astrophysical environments. [1] F. Del Gaudio et al. submitted arXiv:2003.04249 [2] F. Del Gaudio et al. submitted arXiv:2004.11404 [Preview Abstract] |
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