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Institut für Astronomie und Astrophysik

Abteilung Astronomie

Sand 1, D-72076 Tübingen, Germany

Preprint 12/96

The Seyfert Galaxy NGC 6814 - a highly variable X-ray source

Michael König(1), Susanne Friedrich(1), Rüdiger Staubert(1), and Jens Timmer(2,3)

(1)Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen
(2)Fakultät für Physik, Albert-Ludwigs-Universität, Hermann-Herder Str. 3,D-79104 Freiburg
(3)Freiburger Zentrum für Datenanalyse und Modellbildung, Eckerstr. 1, D-79104 Freiburg

accepted by Astronomy & Astrophysics

Abstract. The Seyfert galaxy NGC 6814 is a highly variable X-ray source despite the fact that it has recently been shown not to be the source of periodic variability. The 1.5 year monitoring by ROSAT has revealed a long term downward trend of the X-ray flux and an episode of high and rapidly varying flux (e.g. by a factor of about 3 in 8 hours) during the October 1992 PSPC observation. Temporal analysis of this data using both Fourier and autoregressive techniques have shown that the variability timescales are larger than a few hundred seconds. The behavior at higher frequencies can be described by white noise.

Key words: X-rays: galaxies - Galaxies: active - Galaxies: Seyfert - methods: statistical - objects: NGC 6814

Paper (102k gzip'ed Postscript including figures)

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Jürgen Barnstedt (barnstedt AT astro.uni-tuebingen.de)
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