Physics – Nuclear Physics
Scientific paper
Jan 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999nuphs..69..509m&link_type=abstract
Nuclear Physics B Proceedings Supplements, Volume 69, Issue 1-3, p. 509-514.
Physics
Nuclear Physics
8
Scientific paper
We present RXTE PCA observations of temporal and spectral variability of the four X-ray bright Seyfert galaxies NGC051, NGC506, NGC548 and MGC-6-30-15 covering a period of 18 months from February 1996. We find evidence of a knee in the long timescale power spectrum of NGC051 at a frequency of 5x10-5Hz. There is possible evidence of a knee at a slightly lower frequency in the higher luminosity source MCG-6-30-15 but no knees have been found in the still higher luminosity sources NGC506 and NGC548. If the knee frequency scales inversely with the central black hole mass then, by companson with galactic black hole X-ray binaries, we deduce a mass of approximately 105Msolar in NGC051. Strong continuum reflection components and iron fluorescent lines are seen in all four galaxies and we find evidence of strong X-ray spectral variability in all four galaxies. Here we discuss the spectra of NGC506 and MCG-6-30-15 as NGC051 is discussed elsewhere in these proceedings [1] and a possibly confusing BL Lac lies within the PCA field of view of NGC548. In both NGC506 and MCG-6-30-15 we find strong evidence for a steeping of the continuum spectral slope as the intensity increases. In MCG-6-30-15 the iron line flux increases only weakly as the continuum flux rises and, indeed, the iron line flux is consistent with being constant. In NGC506, however, there is an approximately linear relationship between the iron line flux and continuum flux with only weak evidence for an additional steady component. One explanation, although by no means confirmed, of the spectral index variability and relative quiescence of the iron line flux is that, in addition to rapidly varying steep spectrum continuum emission, there is also a harder reflected component from the surrounding torus. The torus component would not vary on the timescales of our observations and would dominates at very low flux levels. The difference between the variability of NGC506 and MCG-6-30-15 may be a lesser contribution from the torus in NGC506.
McHardy Ian M.
Papadakis Iossif E.
Uttley Phil
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