Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992a%26a...261..405f&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 261, no. 2, p. 405-414.
Astronomy and Astrophysics
Astronomy
15
Exosat Satellite, Seyfert Galaxies, Spaceborne Astronomy, X Ray Astronomy, Astronomical Models, Light Curve, Power Spectra, Time Series Analysis
Scientific paper
We present the results of an accurate temporal analysis of five EXOSAT observations of the Seyfert 1 galaxy NGC 6814 covering about 2 yr. As firstly reported by Mittaz & Branduardi-Raymont (1989), the power spectrum of the longest (about 1 d) observation is characterized by two major components: a low frequency noise which can be described, in the 6 x 10 exp -5 to 10 exp -2 Hz frequency interval, by a power law with exponent about -1.0, and a series of four outstanding peaks at frequencies harmonic of the fundamental at f(a) = 8.2 x 10 exp -5 Hz, which can be considered as the signature of a periodic signal. The analysis of the other shorter (about 1/4 d each) observations shows that a peak is present in their composite power spectrum at 4 x 10 exp -4 Hz, a frequency which is compatible with the fourth harmonics of f(a) within the uncertainties due to the coarser frequency resolution, at the confidence level of about 4 sigma.
Barone Paolo
Fiore Fabrizio
Massaro Enrico
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