X-ray Variability in Supermassive and Stellar-mass Black Holes

Rick Edelson

Recent observations of our Galaxy and other nearby galaxies yields strong evidence that supermassive (>~10^6 solar masses) black holes lie at their centers. I will discuss recent X-ray and ultraviolet variability studies that indicate that supermassive black holes are also responsible for the extraordinary luminosities of active galactic nuclei (AGN), regions that are smaller than our Solar system but can outshine the combined output of the rest of the host galaxy. Specifically, we have gathered and combined data from three X-ray telescopes to measure X-ray fluctuation Power Spectral Density functions (PSDs) for six AGN. Although the PSDs are noisy, they show a broken power-law shape that is reminiscent of PSDs of Galactic X-Ray Binaries (XRBs), sources that are thought to be powered by stellar-mass black holes. Furthermore, we find an apparent linear scaling between the PSD break time scale and the putative black hole mass. Remarkably, the linear scaling measured for supermassive (AGN) black holes appears to extrapolate almost perfectly down to stellar-mass (XRB) black holes. This could indicate that the same processes power black hole emission over a range of >10^8 in mass. I will conclude with a discussion of how current and future missions can further improve our understanding of Seyfert 1 emission processes.