0120121

The physical connection between active galactic nuclei (AGN) and black hole X-ray binaries (BHXRBs) implied by their similar X-ray spectra is further confirmed by variability studies of AGN using the power spectrum. AGN power spectra appear to be identical in shape and RMS amplitude to BHXRB power spectra except scaled down in frequency by the black hole mass. It has been previously assumed that AGN are comparable to BHXRBs in the low accretion state. However our power-spectral study of the Seyfert galaxy NGC5506 using more than 4 years of RXTE monitoring data suggests that this is a high state source. The energy spectra of low state BHXRBs have spectral cut-offs from 100-300 keV but no spectral cut-off in the high state (suggesting a significant population of non-thermal electrons in the Comptonising medium). We propose to exploit the difference in hard X-ray spectral shape in the low and high states to probe the BHXRB-AGN connection at high energies and test the hypothesis that the power spectrum of AGN is a good predictor of the energy spectrum. We will search for and constrain the presence of high energy cut-offs in the hard X-ray spectra of NGC5506 and the Seyfert galaxy NGC3516 which has a low state power spectrum. If the electron temperature distribution in AGN and BHXRBs is the same in both low and high states we will be able to measure a high energy cut-off in NGC3516 and set a stringent lower limit of 700 keV on any cut-off in NGC5506. [truncated! Please see actual data for full text]