New Ginga Observation and Model of NGC 6814 Periodicity

Summary

Abstract

Recent detailed data analysis of the last two Ginga observations of the Seyfert nucleus NGC6814 (Leighly et al. 1992, hereafter LKT92) has not only reconfirmed the periodicity of the fastest X-ray variability reported earlier for this source (Done et al. 1992, hereafter DMM92), but also has shown several very unique, definite characteristics which severely constrain any acceptable models. Consequently, various existing models have been ruled out (LKT92). Here we present, as a natural and self-consistent physical model which satisfies these detailed observational constraints, the occultation of the central X-ray source by matter overflowing the Roche lobe of a low mass star orbiting around a supermassive black hole. The importance of careful, detailed comparison of this type of model with further observations is emphasized, because the result may lead to strong circumstantial evidence for the presence of a supermassive black hole in the central engine of active galactic nuclei (AGN).

NGC6814 is among the most interesting Seyfert galaxies in the sense that its nuclear X-ray emission was found to be most rapidly variable, with the timescale of ∼ 300 seconds, and moreover the fastest variability exhibits periodicity of ∼ 12000 seconds (DMM92). The recent detailed data analyses of the last two Ginga observations, in April and October 1990, respectively, have shown several new detailed characteristics, such as the spectral variability and lags in flux between different energy bands (LKT92).