Searching For Breaks In The Hard X-ray Power Spectral Density Functions Of AGN

Scientific/Technical/Management

Introduction

The physics of accretion disks in active galactic nuclei (AGN) have been the subject of intensive recent work. While their huge energy output over a broad range of wavelengths (i.e. radio to X-ray) allows for detailed spectral characterization, their extremely small sizes are not resolved by even the best observatories. The Event Horizon Telescope is the current best hope for directly imaging the accretion disk of black holes however it will only be able to observe the two nearest black holes Sgr A\(^{*}\) and M87. A large resolved survey of extragalactic AGN is not possible currently or even in the near future. Time variability analysis in different spectral bands is one of the best ways to study the structure of accretion disks as well as the mechanisms controlling the mass accretion rate crucial to understanding the physics of AGN.

We propose to combine short timescale NuSTAR observations with the latest Swift/Burst Alert Telescope (BAT) long timescale light curves (Shimizu et al., 2013) to study the time variability of a sample of AGN designed to span a wide range of black hole mass, AGN luminosity and Eddington ratio in the previously unexplored hard X-ray band. We will use a new maximum likelihood technique (Zoghbi et al., 2013) to construct the power spectral density functions (PSD) over a large range of timescales (years to hundreds of seconds) as well as measure the important break frequency in the PSD for the first time at high energies. The PSDs will allow us to test relationships between the observed properties of the AGN (e.g. \(M_{BH}\) and \(L/L_{Edd}\)) and time variability (Kelly et al., 2013) and to provide important constraints on models of accretion.