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 GZ2: Mini-conference on Astrophysical Explosions: From Engines to Remnants III |
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Chair: Hui Li, Los Alamos National Laboratory Room: Adam's Mark Hotel Governor's Square 14 |
Tuesday, October 25, 2005 2:00PM - 2:30PM |
GZ2.00001: Optical Observations of Core-Collapse Supernovae Alex Filippenko I present an overview of optical observations of Type II, IIb, Ib, and Ic supernovae (SNe), all of which are thought to arise from core collapse in massive progenitors that have previously experienced different amounts of mass loss. SNe Ic appear to have been stripped the most, followed by SNe Ib and SNe IIb. In the case of SNe IIn, part of the hydrogen envelope remains, yet the ejecta interact with unusually dense circumstellar gas, probably a wind from the progenitor star. Some SNe IIn, however, might not be genuine supernovae, but rather ``super-outbursts" of luminous variable stars. Spectropolarimetry of core-collapse SNe reveals that asphericity tends to increase toward the core. It has recently been shown that several long-duration gamma-ray bursts were undeniably associated with peculiar SNe Ic having exceptionally high ejecta velocities. [Preview Abstract] |
Tuesday, October 25, 2005 2:30PM - 3:00PM |
GZ2.00002: Spectropolarimetric diagnostics of thermonuclear supernova Lifan Wang Even at extragalactic distances, the shape of Supernova (SN) ejecta can be effectively diagnosed by spectropolarimetry. We present here results for 12 Type Ia supernovae (SNe) obtained during the past years through our program of SN polarimetry, using primarily the Very Large Telescopes (VLT) of European Southern Observatory (ESO). These observations show that SN Ia ejecta typically consist of a smooth, central iron rich core and an outer layer with significant asymmetries and chemical inhomogeneities. The degree of this peripheral asphericity is anti-correlated with the intrinsic luminosity of Type Ia supernovae. [Preview Abstract] |
Tuesday, October 25, 2005 3:00PM - 3:30PM |
GZ2.00003: Exploding Stars with Magnetic Towers Dmitri Uzdensky, Andrew MacFadyen We consider the formation and propagation of a magnetically dominated outflow, similar to Lynden-Bell's ``magnetic tower,'' inside a collapsing star. We calculate the structure of this flow as it burrows through the stellar envelope. The passage of the tower through the star drives a strong bow shock behind which an over-pressured cocoon forms. In turn, the cocoon collimates the tower forming a narrow jet-like structure. The channel cleared by the expanding tower is plausibly free of baryons and allows the escape of magnetic energy from the central engine through the star. Applications include asymmetric supernova explosions, collapsars and GRBs. [Preview Abstract] |
Tuesday, October 25, 2005 3:30PM - 4:00PM |
GZ2.00004: Dynamics and dissipation in magnetically-dominated astrophysical outflows Maxim Lyutikov Magnetic fields play crucial role in launching and collimation of relativistic outflows. Far away from the central source the fate of magnetic field remains unclear: they may either transfer their energy to matter or may remain dominant until very large distances. These two possibilities lead to different paradigms for particle acceleration: shocks in matter-dominated jets and magnetic dissipation in Poynting flux-dominated jets. I will discuss plasma physics issues specific to dynamics and dissipation in magnetically-dominated astrophysical plasma. I will then compare observational consequences of the two paradigms and discuss how they fare against phenomenology of Gamma Ray Bursts. [Preview Abstract] |
Tuesday, October 25, 2005 4:00PM - 4:30PM |
GZ2.00005: Sustained Particle Acceleration by Poynting Flux Edison Liang, Koichi Noguchi, Scott Wilks We review particle acceleration by electromagnetic (EM)-dominated outflows (Poynting flux) and potential applications to astrophysical explosions. Of particular interest is the sustained comoving acceleration of electron-positron (e+e-) pairs by intense EM pulses in overdense plasmas. Such acceleration may be relevant to GRBs and pulsar winds. We will present 2-and-3D PIC simulation results that include radiative effects, hybrid e+e- and e-ion plasmas, interaction with ambient plasmas, and highlight the key differences between Poynting flux acceleration and shock acceleration. Connections with laboratory experiments using ultra-intense lasers will also be discussed. [Preview Abstract] |
Tuesday, October 25, 2005 4:30PM - 5:00PM |
GZ2.00006: Probing the Magnetic Field Structure in Gamma-Ray Bursts through Polarization Measurements Jonathan Granot Linear polarization at the level of a few percent has been measured in several gamma-ray burst (GRB) optical afterglows, hours to days after the burst. This supports synchrotron emission as the dominant radiation mechanism, while the evolution of the degree of polarization and its position angle probe the magnetic field structure in the shocked external medium as well as the structure and dynamics of GRB jets. The magnetic field structure in the GRB ejecta could potentially be tested by the polarization properties of the prompt gamma-ray emission. However, reliable polarization measurements in gamma-rays are extremely difficult. Therefore, it is much more promising to probe the magnetic field structure in the GRB ejecta through polarization measurements of the optical or radio emission from the reverse shock that propagates into the ejecta as it is decelerated by the external medium. Such optical emission that is attributed to the reverse shock has been observed in a few GRBs from tens of seconds to about ten minutes after the burst, while the radio emission from the reverse shock has been detected in a few cases after about a day. Upper limits of the linear and circular polarization from this radio emission for three GRBs already provide interesting constraints on the magnetic field structure in the GRB ejecta, while polarization measurements of the optical emission from the reverse shock may become available soon by robotic telescopes following rapid localizations by the recently launched Swift satellite. [Preview Abstract] |
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