Research Papers in Physics and Astronomy



O. Shemmer, Tel Aviv University
P. Romano, Ohio State University
R. Bertram, Ohio State University
W. Brinkmann, Max-Planck-Institut für extraterrestrische Physik
S. Collier, Ohio State University
K. A. Crowley, University of Nebraska-Lincoln
E. Detsis, University of Crete
A. V. Filippenko, University of California, BerkeleyFollow
C. Martin Gaskell, University of Nebraska-LincolnFollow
T. A. George, University of Nebraska-Lincoln
M. Gliozzi, Max-Planck-Institut für extraterrestrische Physik
M. E. Hiller, University of Nebraska-Lincoln
T. L. Jewell, University of Nebraska-Lincoln
Shai Kaspi, Tel Aviv UniversityFollow
Elizabeth S. Klimek, University of Nebraska-LincolnFollow
M. H. Lannon, Ohio State University
W D. Li
P. Martini, Carnegie Observatories, Pasadena, CA
Smita Mathur, Ohio State UniversityFollow
H. Negoro, Cosmic Radiation Laboratory, Japan
Hagai Netzer, Tel Aviv UniversityFollow
Iossif Papadakis, University of CreteFollow
Ioannis Papamastorakis, University of CreteFollow
Bradley M. Peterson, Ohio State UniversityFollow
Bradley W. Peterson, University of Nebraska-LincolnFollow
Richard William Pogge, Ohio State UniversityFollow
V. I. Pronik, Crimean Astrophysical Observatory
Kenneth S. Rumstay, Valdosta State UniversityFollow
S. G. Sergeev, Crimean Astrophysical Observatory
G. M. Stirpe, Osservatorio Astronomico di Bologna, Italy
C. J. Taylor, The Lawrenceville School, Lawrenceville, NJ
R. R. Treffers, University of California, Berkeley
T. J. Turner, Laboratory for High Energy Astrophysics, NASA/Goddard Space Flight Center, Greenbelt, MD
P. Uttley, University of SouthamptonFollow
Marianne Vestergaard, Ohio State UniversityFollow
Kaspar von Braun, University of MichiganFollow
R. M. Wagner, Ohio State University
Z. Zheng, Ohio State University

Date of this Version



Published in Astrophysical Journal 561, 162-170 (2001). Copyright 2001 American Astronomical Society & University of Chicago Press. Used by permission. Available online at


We present the results of a 2 yr long optical monitoring program of the narrow-line Seyfert 1 galaxy Ark 564. The majority of this monitoring project was also covered by X-ray observations (RXT E), and for a period of ~50 days, we observed the galaxy in UV (HST) and X-rays (RXTE and ASCA) simultaneously with the ground-based observations. Rapid and large-amplitude variations seen in the X-ray band, on a daily and hourly timescale, were not detected at optical and UV wavelengths, which in turn exhibited much lower variability either on short (1 day) or long (several months) timescales. The only significant optical variations can be described as two 2È4 day events with ~10% flux variations. We detect no significant optical line variations and thus cannot infer a reverberation size for the broad-line region. Similarly, the large X-ray variations seem to vanish when the light curve is smoothed over a period of 30 days. The UV continuum follows the X-rays with a lag of ~0.4 days, and the optical band lags the UV band by ~2 days. No signiÐcant correlation was found between the entire X-ray data set and the optical band. Focusing on a 20 day interval around the strongest optical event we detect a significant X-ray--optical correlation with similar events seen in the UV and X-rays. Our data are consistent with reprocessing models on the grounds of the energy emitted in this single event. However, several large X-ray flares produced no corresponding optical emission.

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