Journal Article

X-ray polarization in relativistic jets

Aimee L. McNamara, Zdenka Kuncic and Kinwah Wu

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 395, issue 3, pages 1507-1514
Published in print May 2009 | ISSN: 0035-8711
Published online May 2009 | e-ISSN: 1365-2966 | DOI:
X-ray polarization in relativistic jets

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We investigate the polarization properties of Comptonized X-rays from relativistic jets in active galactic nuclei (AGN) using Monte Carlo simulations. We consider three scenarios commonly proposed for the observed X-ray emission in AGN: Compton scattering of blackbody photons emitted from an accretion disc; scattering of cosmic microwave background (CMB) photons and self-Comptonization of intrinsically polarized synchrotron photons emitted by jet electrons. Our simulations show that for Comptonization of disc and CMB photons, the degree of polarization of the scattered photons increases with the viewing inclination angle with respect to the jet axis. In both cases, the maximum linear polarization is ≈20 per cent. In the case of synchrotron self-Comptonization (SSC), we find that the resulting X-ray polarization depends strongly on the seed synchrotron photon injection site, with typical fractional polarizations P≈ 10–20 per cent when synchrotron emission is localized near the jet base, while P≈ 20–70 per cent for the case of uniform emission throughout the jet. These results indicate that X-ray polarimetry may be capable of providing unique clues to identify the location of particle acceleration sites in relativistic jets. In particular, if synchrotron photons are emitted quasi-uniformly throughout a jet, then the observed degree of X-ray polarization may be sufficiently different for each of the competing X-ray emission mechanisms (synchrotron, SSC or external Comptonization) to determine which is the dominant process. However, X-ray polarimetry alone is unlikely to be able to distinguish between disc and CMB Comptonization.

Keywords: polarization; scattering; galaxies: jets; X-rays: general

Journal Article.  5443 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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