EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 401/ 2 Article

Free access article

Issue A&A
Volume 401, Number 2, April II 2003
Page(s) 499 - 504
Section Galactic structure and dynamics
DOI http://dx.doi.org/10.1051/0004-6361:20030162



A&A 401, 499-504 (2003)
DOI: 10.1051/0004-6361:20030162

Does circular polarisation reveal the rotation of quasar engines?

T. A. Enßlin

Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, Postfach 1317, 85741 Garching, Germany
(Received 6 November 2002 / Accepted 30 January 2003)

Abstract
Many radio sources like quasars, blazars, radio galaxies, and micro-quasars exhibit circular polarisation (CP) with surprising temporal persistent handedness. As a possible explanation we propose that the CP is due to Faraday conversion (FC) of linear polarisation (LP) synchrotron light which propagates along a line-of-sight (LOS) through twisted magnetic fields. The rotational nature of accretion flows onto black holes naturally generates the required magnetic twist in the emission region, independent of whether it is a jet or an advection dominated accretion flow (ADAF). The expected twist in both types of flows is of the order of what is required for optimal CP generation. This scenario requires that Faraday rotation (FR) is insignificant in the emission region. Although this is an assumption, it relaxes constraints on the plasma parameters, that were given in scenarios which rely on FR, since there the strength of FR can not be too far from the optimum. The proposed mechanism works in electron-positron ( ${\rm e}^\pm$) as well as electron-proton ( ${\rm e}/{\rm p}$) plasma. In the latter case, the emission region should consist of individual flux tubes with independent polarities in order to suppress too strong FR. The predominant CP is expected to mostly counter-rotate (rotation is measured here in sky-projection) with respect to the central engine in all cases (jet or ADAF, ${\rm e}^\pm$ or ${\rm e}/{\rm p}$ plasma). If the proposed mechanism is indeed operating, it will allow to measure the sense of rotation of quasar engines. The engine of SgrA * is then expected to rotate clockwise and therefore counter-Galactic, as do the young hot stars in its vicinity, which are thought to feed SgrA * by their winds. Similarly, we expect the microquasars SS 443 and GRS 1915+105 to rotate clockwise. Generally, sources with Stokes- V<0 ( V>0) are expected to rotate clockwise (counter-clockwise) in this scenario.


Key words: radiation mechanisms: non-thermal -- radio continuum: general -- polarization -- galaxies: active -- galaxies: jets -- galaxies: magnetic fields

SIMBAD Objects



© ESO 2003

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.