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

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

Sep 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010astl...36..611d&link_type=abstract

Astronomy Letters, Volume 36, Issue 9, pp.611-633

Astronomy and Astrophysics

Astronomy

Active Galactic Nuclei, Seyfert Galaxies, Photometry, Ngc 7469

Scientific paper

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( τ) ˜ τ b , where τ 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 ω as n( ω) ˜ ω α and whose amplitudes depend on duration as A( ω) ˜ ω β. 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 σ confidence level.

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