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Long-time-scale X-ray and optical variability is a key characteristic of AGN. Here, we summarise our current understanding of the X-ray and optical continuum variability of radio-quiet AGN and the relation between the two bands. We demonstrate the strong connection between the X-ray variability properties of AGN and the variability of stellar-mass black hole candidates on much shorter time-scales, and discuss the implications of this result for the origins of the variability. The relationship between optical and X-ray variability is complex, with some AGN showing strong X-ray/optical correlations while others show no obvious correlation. We suggest a possible explanation for this variety of behaviour.
A large number of AGN have been monitored for nearly 30 years at 22, 37 and 87 GHz in Metsahovi Radio Observatory. These data were combined with lower frequency 4.8, 8.0 and 14.5 GHz data from the University of Michigan Radio Astronomy Observatory, h
We present the results from the spectral analysis of more than 7,500 RXTE spectra of 10 AGN, which have been observed by RXTE regularly over a long period of time ~ 7-11 years. These observations most probably sample most of the flux and spectral var
Long time scale radio-X-ray correlations in black holes during the hard state have been found in many sources and there seems to emerge a universal underlying relationship which quantitatively describes this behavior. Although it would appear only na
We have conducted a 3-month program of simultaneous optical, soft and hard X-ray monitoring of the LMXB 4U1636-536/V801 Ara using the SMARTS 1.3m telescope and archival RXTE/ASM and Swift/XRT data. 4U1636-536 has been exhibiting a large amplitude, qu
Variability at all observed wavelengths is a distinctive property of AGN. Hard X-rays provide us with a view of the innermost regions of AGN, mostly unbiased by absorption along the line of sight. Swift/BAT offers the unique opportunity to follow, on