Optical Variability of the Narrow-Line Seyfert 1 Galaxy Akn 564 on Timescales from Hours to Years.

We present the results of V-band monitoring of the Narrow-Line Seyfert 1 (NLS1) galaxy Akn 564 on timescales ranging from less than an hour to over 14 years. During some of this period Akn 564 was also monitored by ASCA and RXTE. We detect variations on all timescales. We find evidence for low-amplitude (0.05 magnitude) variability on a timescale of hours. This timescale is comparable to that of the X-ray variability of Akn 564, and the variations are similar to, although not as extreme as, the rapid optical variability Miller et al. (2000) discovered in the NLS1 IRAS 13224-3809. Akn 564 shows significant optical variability from day to day (confirmed by photometry from different observatories). One of the optical ``drop outs'' follows a strong X-ray drop out observed by ASCA (Turner et al. 2001) by about 12 hours. Akn 564 also shows smooth quasi-sinusoidal long-term variations on timescales comparable to the sampling window (14 years). Although the variations of Akn 564 on both long and short timescales are of small amplitude, the amplitude of variations of NLS1s in general does not seem to be significantly less than for non-NLS1s.