AAS 205th Meeting, 9-13 January 2005
Session 106 SNRs and Loops
Poster, Wednesday, January 12, 2005, 9:20am-6:30pm, Exhibit Hall

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[106.09] Modeling Dynamic Wisps in the Crab Nebula as a Synchrotron Cooling Instability

J. P. Foy, J. J. Hester (Arizona State University)

Hubble Space Telescope and Chandra X-Ray observations of the Crab Synchrotron Nebula confirm that the ring-like features called "wisps" - first observed by Lampland in 1921, then later by Scargle in 1969 - are dynamic structures that move outward at relativistic speeds. The wisps form, sharpen and disperse on a time scale of weeks to months, decelerating as they propagate (Hester, J.J. 1998, Mem. Soc. Astron. Italiana, 69, 883, and Hester et al. 2002, ApJ, 557, L49). These authors have suggested that the wisps are the result of a classic synchrotron cooling instability. Particles in a magnetized electron-positron plasma are assumed to flow outward from the pulsar, and their outflow momenta is randomized at a shock. These particles lose energy as they emit synchrotron radiation at nearly constant pressure, causing a compression of magnetic field lines and a resulting enhancement in emission from the wisp structures. This mechanism requires that the post-shock pressure is carried by the most energetic particles with short synchrotron lifetimes. We present the results of a preliminary model of this process by including synchrotron losses in the calculation of the post-shocked flow in the pulsar wind.

J.P.F. acknowledges support from the Arizona State University NASA Space Grant Program.

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