Rapid variability of the iron fluorescence line from the Seyfert 1 galaxy NGC6814

Abstract

LUMINOUS broad-band emission from active galactic nuclei (AGN) is thought to be due to accretion onto a massive black hole. Because X-ray emission shows variability on a faster time-scale than any other wavelength band that has been observed it is assumed to be produced very close to the central energy source. Observations of AGN with the 4,000-cm2 Large Area Counters (LACs) aboard the Ginga satellite have obtained the highest quality data on X-ray variability to date, allowing examination of detailed spectra up to 20 keV in energy on relatively short time-scales1. We have observed NGC6814, one of the faster2 X-ray-variable AGN (δt < 200 s), with Ginga to obtain data on the variability of the iron fluorescence line, and thus to constrain the distribution of cold gas from which the line originates. A positive correlation measured between the variability of the iron-line flux and the continuum emission suggests an upper limit of 1013 cm for the size of the iron reprocessing region.