An x-ray timing analysis of NGC 6814

Abstract

We perform an X-ray timing analysis of the type 1.5 Seyfert galaxy NGC 6814 to characterise its variability as a means of understanding the structure and properties of its active galactic nucleus (AGN). Using data from five observations by the XMMNewton and NuSTAR observatories, we employ a number of X-ray timing analysis techniques to investigate the relationships between the different components of the AGN. We find that variability in NGC 6814 during the 2016 eclipse was dominated by changes in the absorption, and that at all other epochs behaviour was similar to that of normal AGN. Our analysis of hardness ratio against flux confirms that NGC 6814 follows the “softer when brighter” trend observed in other AGN, and, from the fractional variabilities, the amplitude of these variations is found to decrease with increasing energy. No significant frequency or energy dependent lags are detected in any of the observations, indicating that the inner-disc blurred reflection component is quite weak in this source. We discuss the implications of these findings and how they support previous works that suggest a compact source of high-energy X-rays and the possibility of a non-standard accretion disc.