A possible jet precession in the periodic quasar B0605–085

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: nkudryav@mpifr-bonn.mpg.de
² Physics Department, University College Cork, Cork, Ireland
³ Astronomical Institute of St. Petersburg State University, Universitetskiy Prospekt 28, Petrodvorets 198504, St. Petersburg, Russia
⁴ Departament d’Astronomia i Astrofìsica, Universitat de València, 46100 Burjassot, València, Spain
⁵ Astronomy Department, University of Michigan, Ann Arbor, MI 48109, USA
⁶ Metsähovi Radio Observatory, TKK, Helsinki University of Technology, Metsähovintie 114, 02540 Kylmälä, Finland
⁷ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany

Received: 10 May 2010
Accepted: 6 July 2010

Abstract

Context. The quasar B0605−085 (OH 010) shows a hint for probable periodical variability in the radio total flux-density light curves.

Aims. We study the possible periodicity of B0605−085 in the total flux-density, spectra, and opacity changes in order to compare it with jet kinematics on parsec scales.

Methods. We have analyzed archival total flux-density variabilities at ten frequencies (408 MHz, 4.8 GHz, 6.7 GHz, 8 GHz, 10.7 GHz, 14.5 GHz, 22 GHz, 37 GHz, 90 GHz, and 230 GHz) together with the archival high-resolution very long baseline interferometry data at 15 GHz from the MOJAVE monitoring campaign. Using the Fourier transform and discrete autocorrelation methods we have searched for periods in the total flux-density light curves. In addition, spectral evolution and changes of the opacity have been analyzed.

Results. We found a period in multi-frequency total flux-density light curves of 7.9 ± 0.5 yrs. Moreover, a quasi-stationary jet component C1 follows a prominent helical path on a similar timescale of eight years. We have also found that the average instantaneous speeds of the jet components show a clear helical pattern along the jet with a characteristic scale of 3 mas. Taking into account average speeds of jet components, this scale corresponds to a timescale of about 7.7 years. Jet precession can explain the helical path of the quasi-stationary jet component C1 and the periodical modulation of the total flux-density light curves. We have fitted a precession model to the trajectory of the jet component C1, with a viewing angle φ₀ = 2.6° ± 2.2°, aperture angle of the precession cone Ω = 23.9° ± 1.9° and fixed precession period (in the observers frame) P = 7.9 yrs.