Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989apj...347..171f&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 347, Dec. 1, 1989, p. 171-178. Research supported by CNR, and MPI.
Astronomy and Astrophysics
Astronomy
21
Coherent Electromagnetic Radiation, Light Curve, Seyfert Galaxies, X Ray Astronomy, X Ray Sources, Background Radiation, Exosat Satellite, Harmonic Analysis, Power Spectra, Schwarzschild Metric
Scientific paper
The results of the temporal analysis performed on four EXOSAT medium-energy observations of the Seyfert galaxy NGC 4151, selected for their long duration and background stability, are presented. The light curves can be adequately described in terms of regular trends (representing variations on time scales of not less than one day) to which small-amplitude fluctuations are superposed. The harmonic analysis, applied separately to each one of the observations, provides evidence that a substantial fraction of the power in these fluctuations is contained in coherent signals occurring at either one or both of the frequencies 0.000079 and 0.00017 Hz, which, within the frequency resolution achieved, are in a ratio compatible with 2 and can be therefore assumed to be harmonically related. The amplitude (peak-to-peak) of these signals varies from one observation to the other and reaches at most 7 percent. If the period corresponding to the lower frequency is interpreted as the signature of the orbital time of matter near the innermost stable orbit around a collapsed object, its mass can be estimated to be close to 2.5 x 10 to the 7th solar masses for the Schwarzschild metric.
Fiore Fabrizio
Massaro Enrico
Perola Giuseppe Cesare
Piro Luigi
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