Session 4: Our Galaxy and other galaxies

Title: Optical and X-ray monitoring of the NLS1 Galaxy Ark 564
Author(s): E. Detsis, I. E. Papadakis, J. Papamastorakis  (Poster)
Contact: E. Detsis, University of Crete, Greece

The Narrow-line Seyfert galaxy Ark564 was monitored between June 04, 2000 and June 24, 2000 from Skinakas Observatory. The light curves obtained in B, V, R and I bands show night-to-night variations of Dm~0.1$ mag. Comparison with X-ray data from a simultaneous ASCA long-look observation shows that the variations in X-rays are much more pronounced than in the optical band. A cross correlation analysis yields a time lag of ~0.8 days between X-rays and optical light (with the X-rays leading the optical), however with low statistical significance. We discuss possible implications of our results for physical models involving the reprocessing of the primary X-rays by the accretion disc.