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Folded Fields as the Source of Extreme Radio-Wave Scattering in the Galactic Center

Goldreich, Peter and Sridhar, S. (2006) Folded Fields as the Source of Extreme Radio-Wave Scattering in the Galactic Center. Astrophysical Journal Letters, 640 (2). L159-L162. ISSN 2041-8205. doi:10.1086/503668.

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A strong case has been made that radio waves from sources within about half a degree of the Galactic center undergo extreme diffractive scattering. However, problems arise when standard ("Kolmogorov") models of electron density fluctuations are employed to interpret the observations of scattering in conjunction with those of free-free radio emission. Specifically, the outer scale of a Kolmogorov spectrum of electron density fluctuations is constrained to be so small that it is difficult to identify an appropriate astronomical setting. Moreover, an unacceptably high turbulent heating rate results if the outer scale of the velocity field coincides with that of the density fluctuations. We propose an alternative model based on folded magnetic field structures that have been reported in numerical simulations of small-scale dynamos. Nearly isothermal density variations across thin current sheets suffice to account for the scattering. There is no problem of excess turbulent heating, because the outer scale for the velocity fluctuations is much larger than the widths of the current sheets. We speculate that interstellar magnetic fields could possess geometries that reflect their origins: fields maintained by the Galactic dynamo could have large correlation lengths, whereas those stirred by local energetic events might exhibit folded structures.

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Additional Information:© 2006 The American Astronomical Society. Received 2005 October 28; accepted 2006 February 24; published 2006 March 13.
Subject Keywords:Galaxy: center—ISM: general—radio continuum: ISM—scattering
Issue or Number:2
Record Number:CaltechAUTHORS:20130228-103838219
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Official Citation:Folded Fields as the Source of Extreme Radio-Wave Scattering in the Galactic Center Peter Goldreich and S. Sridhar 2006 ApJ 640 L159
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37202
Deposited By: Tony Diaz
Deposited On:28 Feb 2013 19:59
Last Modified:09 Nov 2021 23:27

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