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Astron. Astrophys. 322, 747-750 (1997)
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, Germany
2 Fakultät für Physik,
Albert-Ludwigs-Universität, Hermann-Herder Str. 3, D-79104
Freiburg, Germany
3 Freiburger Zentrum für Datenanalyse und
Modellbildung, Albert Str. 26-28, D-79104 Freiburg, Germany
Received 7 October 1996 / Accepted 6 December 1996
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:
Seyfert
methods:
statistical
galaxies: NGC 6814
Contents
- 1. Introduction
- 2. ROSAT observations
- 3. Flux and spectral variability
- 4. Short term variability
- 5. Discussion
- References
© European Southern Observatory (ESO) 1997
Online publication: June 5, 1998
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