Broad band variability of SS433: accretion disk at work?

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 ∼10 7 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 ∼0.01-0.05 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.