Accretion of material onto a supermassive black hole has long been believed
to be the fundamental power source of active galactic nuclei (AGN; e.g. see
Rees 1984 for a review). However, the physical processes by which the
gravitational potential energy of the accretion flow energizes the observed
spectrum are still far from certain. Recent spectroscopic studies in the
X-ray waveband have shown that, in the innermost regions (i.e. 
; where 
is the Schwarzschild
radius of the central black hole) of at least some AGN, there is a
geometrically-thin, radiatively-efficient accretion disk (Tanaka et
al. 1995; Fabian et al. 1995). A significant fraction of the accretion
energy appears to be liberated in a hot, optically-thin, disk-corona which
is a prolific radiator of X-rays and 
-rays (probably via the
Comptonization of optical/UV photons from the cold accretion disk: Haardt
& Maraschi 1991; Field & Rogers 1993; Zdziarski et al. 1994). Although
most of the primary radiation is produced in the inner regions of the
accretion flow, a significant fraction of this radiation is reprocessed at
greater distances from the black hole into UV, optical and IR wavelengths.
Studying these reprocessing mechanisms allows the structures surrounding
the accreting black hole to be probed and are necessary if we are to
disentangle the primary emission from the reprocessed emission.
In recent years, much has been learnt about the various reprocessing mechanisms. It has been realized that approximately half of the X-ray photons emitted from the corona will strike the cold accretion disk, thereby producing `reflection' features in the X-ray spectrum (Guilbert & Rees 1988; Lightman & White 1988; Pounds et al. 1990). The emission that emerges from these central regions can also be intercepted by more distant structures: these include the broad-line region (BLR), the putative molecular torus of the unified Seyfert schemes and the warm absorber. The scattering of primary radiation into our line-of-sight is also known to be important in at least some AGN. Multi-waveband studies of nearby, bright AGN are invaluable in studying such complex systems.
Many such multi-wavelength studies of AGN have been performed. For example, Alloin et al. (1995) utilized many ground-based and space observatories to obtain a snapshot (i.e. all data taken almost simultaneously) of the Seyfert 1 galaxy NGC 3783. After careful consideration of possible contaminating sources, these authors fit thermal accretion disk models to the classical big blue bump displayed by this object and hence constrain the black hole mass and accretion rate. They also find an infrared bump which they interpret as thermal emission from hot and warm dust. Many other studies focus on multi-wavelength monitoring in an attempt to map the central engine. For example, extensive monitoring campaigns have been performed on NGC 4151 (Edelson et al. 1996) and NGC 5548 (Korista et al. 1995).
In this paper we perform a multiwaveband study of the nearby Seyfert 1 galaxy MCG-6-30-15 (z=0.008; Pineda et al. 1978; Pineda et al. 1980). Snapshot optical imaging with the Hubble Space Telescope (HST) clearly shows this object to be a S0-type galaxy with a bright, nuclear point source. This X-ray bright AGN has recently been the subject of intense spectroscopic study in the X-ray band and so is a good candidate for a multiwavelength study. We present new optical data from the Anglo-Australian Telescope (AAT) and new ultraviolet data from the International Ultraviolet Explorer satellite (IUE). Together with archival infrared and X-ray data, this represents the most detailed multiwaveband study of this nearby AGN to date. In particular, we review and reinforce evidence that there is a significant column of dusty ionized material along our line of sight to the central continuum source and BLR, the so-called dusty warm absorber. This material is shown to have a major effect on the observed spectrum of this source.
In Section 2, the data are presented and the basic characteristics at each waveband are discussed. Section 3 examines various estimates for the amount of extinction and absorption towards the central source. A discrepancy between the optical/UV extinction and the X-ray absorption leads us to discuss the possibility of dusty warm absorbers in Section 4. Section 5 probes the connection between the warm absorber and coronal line emission. We discuss our results and their implications for the energetics of the system in Section 6. Section 7 presents our conclusions.