Variability of the Seyfert galaxy MKN 766 in the ROSAT all sky survey

Details Variability of the Seyfert galaxy MKN 766 in the ROSAT all sky survey Variability of the Seyfert galaxy MKN 766 in the ROSAT all sky survey

Oct 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992stin...9417591m&link_type=abstract

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Astronomy and Astrophysics

Astronomy

Light Curve, Rosat Mission, Seyfert Galaxies, Stellar Mass Accretion, Variability, X Ray Spectra, Algorithms, Astronomical Models, Spectral Emission, Spectral Signatures, Spectrum Analysis, X Ray Astronomy

Scientific paper

Results from the Rosat All Sky Survey (RASS) observation of the Seyfert galaxy MKN 766 are presented. Using a technique developed for the analysis of point sources in the RASS it is shown that MKN 766 is highly variable. Comparison of the soft X-ray spectrum with Exosat medium energy archive data shows that the spectrum of MKN 766 is characterized by a strong soft excess. The low energy resolution of the Position Sensitive Proportional Counter (PSPC) instrument on board the Rosat spacecraft does not allow discrimination between different spectral models for the soft access. Both a power law or a thermal component yield an acceptable fit. Of the two thermal models only the first can be accepted since the best fitting parameters derived for the latter are not consistent with bremsstrahlung emission. A comparison with theoretical models for the soft excess is presented. The lack of a strong bump rules out models in which soft X-ray are produced by Comptonizing ultraviolet photons. The soft excess in the spectrum of MKN 766 can be fitted with the emission spectrum from an accretion disk. The accretion disk parameters derived from the fit, the mass, and the accretion rate are consistent with those found by comparing the two variability timescales observed in the lightcurve to two fundamental timescales operating in the disk.

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