OPTICAL VARIABILITY OF THE SEYFERT NUCLEUS NGC-7469 IN TIMESCALES FROM DAYS TO MINUTES

We report optical photometric observations of the Seyfert nucleus NGC 7469. During the first observing run in 1989, night-to-night measurements were done during 13 photometric nights spanning November 3-30. The largest variation, DELTA-m = 0.403m, within a 20 arcsec diaphragm, occurred in eleven days and a decrease in brightness of DELTA-m = 0.337m (approximately 70% of the luminosity of the unresolved nuclear component) occurred in only five days. During the second run in August 1990, all-night monitoring was done during five photometric nights (approximately 29 hr) using differential photometry techniques. After a very thorough discrimination of errors and their analysis, we conclude that random variability was present during the first four nights with average amplitude approximately 0.040m (at a sigma greater-than-or-equal-to 4.5 level) on average timescales of approximately 13 min. During the fifth night the variability nearly disappeared. A maximum DELTA-m approximately 0.081m (9.3-sigma) was observed in DELTA-t = 2.35 hr. The average fluctuations imply an 8 % variation in the luminosity of the unresolved nucleus and a rate of change of DELTA-L(var)/DELTA-t approximately 6 X 10(37) erg S-2. We argue that our observations favor the black hole model and that random variability (flickering or "microvariability") may be explained by the development of local instabilities in the accretion disk. There is also strong evidence for tidal interaction of this galaxy with its companion, IC 5283, and for the existence of a circumnuclear starburst, making NGC 7469 a most suitable galaxy to study the relation of all these phenomena.