Broad band variability of SS433: accretion disk at work?

¹ Max-Planck-Institute für Astrophysik, Karl-Schwarzschild-Str. 1, 85740 Garching bei München, Germany e-mail: mikej@mpa-garching.mpg.de
² Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32, 117810 Moscow, Russia
³ Special Astrophysical Observatory, Nizhnij Arkhyz, Karachaevo-Cherkesiya 369167, Russia
⁴ Sternberg Astronomical Institute, 119992 Moscow, Russia
⁵ University of Oulu, Finland
⁶ Kazan State University, Kremlevskaya Str. 18, 420008 Kazan, Russia
⁷ Academy of Sciences of Tatarstan, Bauman Str. 20, 420111 Kazan, Russia
⁸ TUBITAK National Observatory, Akdeniz Universitesi Yerleskesi, 07058 Antalya, Turkey

Received: 24 January 2005
Accepted: 8 September 2005

Abstract

We present broad band power spectra of variations of SS433 in radio, optical and X-ray spectral bands. We show that at frequencies lower than 10^-5 Hz the source demonstrates the same variability pattern in all these bands. The broad band power spectrum can be fitted by one power law down to frequencies ~ 10^-7 Hz with flattening afterwards. Such a flattening means that on time scales longer than ~ 10⁷ s the source variability becomes uncorrelated. This naturally leads to the appearance of quasi-poissonian flares in the source light curve, which have been regularly observed in radio and optical spectral bands. The radio flux power spectrum appears to have a second break at Fourier frequencies ∼10^-5 Hz which can be caused by the smearing of the intrinsic radio variability on timescale of the light-crossing time of the radio emitting region. We find a correlation of the radio and optical fluxes of SS433 and the radio flux is delayed by about ∼2 days with respect to the optical one. Power spectra of optical and X-ray variabilities continue with the same power law from 10^-7 Hz up to ~ Hz. The broad band power spectrum of SS433 can be interpreted in terms of self-similar accretion rate modulations in the accretion disk proposed by Lyubarskii (1997, MNRAS, 292, 679) and elaborated by Churazov et al. (2001, MNRAS, 321, 759). We discuss a viscous time-scale in the accretion disk of SS433 with reference to the observed broad band power spectrum.