Suzaku Observations of the Hard X-Ray Variability of MCG −6–30–15: the Effects of Strong Gravity around a Kerr Black Hole

Abstract Suzaku has, for the first time, enabled the hard X-ray variability of the Seyfert 1 galaxy MCG $-$6–30–15 to be measured. The variability in the 14–45 keV band, which is dominated by a strong reflection hump, is quenched relative to that at a few keV. This directly demonstrates that the whole reflection spectrum is much less variable than the power-law continuum. The broadband spectral variability can be decomposed into two components—a highly variable power-law and constant reflection—as previously inferred from other observations in the 2–10 keV band. The strong reflection and high iron abundance give rise to a strong broad iron line, which requires the inner disc radius to be at about 2 gravitational radii. Our results are consistent with the predictions of the light bending model which invokes the very strong gravitational effects expected very close to a rapidly spinning black hole.