Faraday Signature Of Magnetic Helicity From Reduced Depolarization

AXEL BRANDENBURG AND RODION STEPANOV FARADAY SIGNATURE OF MAGNETIC HELICITY FROM REDUCED DEPOLARIZATION (PREPRINT)

Abstract:

Using one-dimensional models, we show that a helical magnet ic field with an appropriate sign of a helicity can compensate the Faraday depolarization resulting from the superposition of Faraday-rotated polarization planes from a spatially extended source. For radio emission from a helical magnetic field, the polarization as a function of the square of the wavelength becomes asymmetric with respect to zero. Mathematically speaking, the resulting emission occurs then either at observable or at unobservable (imaginary) wavelengths. We demonstrate that rotation measure (RM) synthesis allows the reconstruction of the underlying Faraday dispersion function in the former case, but not in the latter. The presence of positive magnetic helicity can thus be detected by observing positive RM in highly polarized regions in the sky and negative RM in weakly polarized regions. Conversely, negative magnetic helicity can be detected by observing negative RM in highly polarized
regions and positive RM in weakly polarized regions. The simultaneous presence of two magnetic constituents with opposite signs of helicity is shown to possess signatures that can be quantified through polarization peaks at specific wavelengths and the gradient of the phase of the Faraday dispersion function. We discuss the possibility of detecting magnetic fields with such properties in external galaxies using the Square Kilometre Array.
Subject headings:polarization – methods: data analysis – galaxies: magnetic fields

Download (PDF, Неизвестный)

Written by

Suspendisse sodales elit quis diam varius sit amet condimentum odio fringilla. Nunc pellentesque est velit. Suspendisse ut dapibus erat. Vivamus pharetra arcu vitae libero luctus commodo. Vestibulum sapien magna, blandit sed elementum eget, faucibus sit amet risus. Proin dapibus velit posuere ligula accumsan in sollicitudin tellus euismod. Nam quis turpis augue, at scelerisque magna. Integer eu enim arcu. Aenean pretium pretium nibh id porttitor.

Комментариев нет.

Оставить комментарий

Сообщение