Bulletin of the American Physical Society
2005 47th Annual Meeting of the Division of Plasma Physics
Monday–Friday, October 24–28, 2005; Denver, Colorado
Session FZ2: Mini-conference on Astrophysical Explosions: From Engines to Remnants II |
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Chair: Ben Chandran, University of New Hampshire Room: Adam's Mark Hotel Governor's Square 14 |
Tuesday, October 25, 2005 9:30AM - 10:00AM |
FZ2.00001: The Explosion of Cassiopeia A Una Hwang The 330 year old Galactic supernova remnant Cassiopeia A offers a uniquely detailed look at the supernova ejecta formed during its explosion through current X-ray and optical observations, including a deep 1Ms observation with the Chandra Observatory. The explosively synthesized ejecta are distributed in small-scale knots and filaments with an overall bipolar symmetry and X-ray spectra dominated by emission lines of Si, S, Ar, and Ca, with some Fe, except in Fe-rich regions of the remnant where the Fe lines are very strong. The displacement of the compact stellar remnant relative to the optically determined explosion center indicates that the birth kick of the neutron star had a component perpendicular to the polar axis of the ejecta. From modelling the X-ray spectra, we learn that the explosion energy was distributed aspherically, that the progenitor underwent substantial mass loss, and that the ejecta along the polar axes originated as ``jets'' during the explosion rather than being shaped by the progenitor's pre-supernova mass loss. The energetics of Cas A's explosion indicates that it was probably formed as a slightly energetic supernova. [Preview Abstract] |
Tuesday, October 25, 2005 10:00AM - 10:30AM |
FZ2.00002: Hydrodynamic instabilities in young supernova remnants Roger Chevalier The expansion of a supernova shock wave is subject to a variety of hydrodynamic instabilities as it moves through a massive star and into the surrounding medium. The same is true for the expansion of a relativistic wind nebula created by a central pulsar. In many cases, the results of the instabilities can be directly observed. [Preview Abstract] |
Tuesday, October 25, 2005 10:30AM - 11:00AM |
FZ2.00003: Collisionless Shocks in GRBs: from Speculations to Physics Mikhail Medvedev Many violent processes in astrophysics such as gamma-ray bursts, supernova explosions, jet outflows are accompanied by shocks. Most if not all our knowledge about the underlying phenomena comes from telescope observations of radiation emitted by these shocks at various photon energies, from gamma-rays through optical and radio waves. However, a fair question arises: Do we really understand what we are observing? It is an unacceptable fact that most data analyzes have been performed using a ``classical'' hydrodynamic shock model, whereas it is well known that all these astrophysical shocks are collisionless (meaning that the collisional thickness of the shock is many orders of magnitude larger then the size of an object itself). Until very recently our understanding of collisionless unmagnetized relativistic shocks was very limited. In this talk we will present important theoretical ideas in the field of strong collisionless shocks and link them to practical aspects --- observations and data analysis. In particular, we will discuss the internal structure of the shocks, the role of the Weibel instability, particle acceleration/heating, radiation processes and the physics jitter radiation, and the effects relativistic kinematics on the observed spectra. [Preview Abstract] |
Tuesday, October 25, 2005 11:00AM - 11:30AM |
FZ2.00004: Shock structure and particle acceleration in electron-position and electron-ion plasmas Anatoly Spitkovsky I discuss 3D simulations of relativistic collisionless shocks in electron-positron and electron-ion plasmas performed using the particle-in-cell (PIC) method. The shock structure is mainly controlled by the magnetization of the upstream flow (``sigma'' parameter). I will demonstrate how the structure of the shock varies as a function of sigma for both perpendicular and oblique shocks. At low magnetizations the shock is mediated mainly by the Weibel instability which generates transient magnetic fields that can exceed the initial field. At larger magnetizations the shock is dominated by magnetic reflections. I demonstrate where the transition occurs and argue that it is impossible to have very low magnetization collisionless shocks in nature (in more than one spatial dimension). I further discuss the acceleration properties of these shocks, and show that higher magnetization perpendicular shocks do not efficiently accelerate nonthermal particles in 3D. Among other astrophysical applications, this poses a restriction on the structure and composition of gamma-ray bursts and pulsar wind outflows. [Preview Abstract] |
Tuesday, October 25, 2005 11:30AM - 12:00PM |
FZ2.00005: Simulating Astrophysical Jets with Inertial Confinement Fusion Machines Brent Blue Large-scale directional outflows of supersonic plasma, also known as `jets', are ubiquitous phenomena in astrophysics. The traditional approach to understanding such phenomena is through theoretical analysis and numerical simulations. However, theoretical analysis might not capture all the relevant physics and numerical simulations have limited resolution and fail to scale correctly in Reynolds number and perhaps other key dimensionless parameters. Recent advances in high energy density physics using large inertial confinement fusion devices now allow controlled laboratory experiments on macroscopic volumes of plasma of direct relevance to astrophysics. This talk will present an overview of these facilities as well as results from current laboratory astrophysics experiments designed to study hydrodynamic jets and Rayleigh-Taylor mixing. This work is performed under the auspices of the U. S. DOE by Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48, Los Alamos National Laboratory under Contract No. W-7405-ENG-36, and the Laboratory for Laser Energetics under Contract No. DE-FC03-92SF19460. [Preview Abstract] |
Tuesday, October 25, 2005 12:00PM - 12:30PM |
FZ2.00006: Photon-Rich, Relativistic Magnetofluids and Gamma-Ray Bursts Christopher Thompson We describe how a relativistic magnetofluid containing a warm (1-10 keV) blackbody gas may be emitted from some peculiar types of core-collapse supernovae, examine the damping mechanism of the magnetohydrodynamic turbulence that is excited in the expanding fluid (and how this damping differs from what has been postulated for non-relativistic magnetofluids), explain how electron- positron pair creation in the surrounding medium controls the deceleration of the relativistically boosted fluid and regulates the optical depth to electron scattering through it, and summarize the implications of these various pieces of physics for the emission mechanism of gamma-ray bursts. [Preview Abstract] |
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