The evolution of fast, radiative shocks in a high-density medium is discussed. Approximate broad-band light curves of the shocked gas are calculated, and the emitted spectra are used as the input spectra for photoionization models. The results are in good agreement with parameters characteristic of Active Galactic Nuclei.

Introduction

Over a decade ago Chevalier & Imamura (1982) showed that radiative, steady shocks are subject to an oscillatory instability. This result was confirmed on the basis of non-linear hydrodynamical analysis for nonstationary shocks (Gaetz, Edgar & Chevalier 1988) as well as for steady radiative shocks (Innes, Giddings & Falle 1987). Both groups found unstable behavior of shocks faster than ∼ 130 km s−1.

In a series of papers Terlevich and collaborators (see e.g. Terlevich et al. 1992) developed the starburst model for Active Galactic Nuclei (AGNs). In this model AGNs are powered by compact, dense supernova remnants (cSNRs), and the bulk of the radiation is emitted by the supernova shock wave evolving in a dense medium (n = 107 cm−3). Terlevich et al. (1992) calculated 1-D and 2-D hydrodynamical models of cSNR evolution and demonstrated that it was possible to recover observed characteristics of the Broad Line Region of AGNs. Using very simple assumptions, Terlevich et al. (1994a) successfully explained observed differences between times of maximum continuum and line emission taking into account the dependence on the ionization parameter.