AND ASTROPHYSICS The Seyfert galaxy NGC 6814 – a highly variable X-ray source

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 Xray 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 1.