X-ray and optical variability of the seyfert galaxy NGC 7469

Based on our UBV RI observations and X-ray data from the RXTE satellite, we have investigated the variability of the galaxy NGC 7469 over the period 1995-2009. In 1995-2000, the optical brightness of the galactic nucleus changed almost by 1 (m) in the U band. In 2000-2009, the amplitude of the optical variations was considerably lower. Regular X-ray observations began only in 2003. The X-ray fractional variability amplitude is higher than the optical one. The optical variability amplitude decreases with increasing wavelength. The full width at half maximum of the X-ray and B-band autocorrelation functions is about 8 and 62 days, respectively. The structure functions (SF) in the X-ray range on time scales up to 7 days and in the optical range on time scales up to 100 days have the form of a power law SF(tau) similar to tau (b) , where tau is the time shift. On time scales of more than a day, where both structure functions have been determined rather reliably, their slopes differ markedly: b = 1.34 +/- 0.06 and b = 0.25 +/- 0.05 for the optical and X-ray ranges, respectively. The X-ray and B-band structure functions begin to flatten, respectively, near 6-8 days and on time scales of about 90 days. The observed structure functions can be described by the model of a superposition of independent Gaussian flares whose number changes with duration omega as n(omega) similar to omega (alpha) and whose amplitudes depend on duration as A(omega) similar to omega (beta). The flux distribution and the flux-amplitude relation are consistent with the model of a light curve in the form of a superposition of random flares. Once the fast intensity variations have been filtered out on long time scales, the X-ray light curve correlates well with the optical one. No lag of the X-ray variations relative to those in the B band is detected. The light variations in the R and I bands lag behind those in the B band calculated from the centroid of the cross-correlation function by 2.6 and 3.5 days, respectively, at a 3 sigma confidence level.