A Multicloud Warm‐Absorber Model for NGC 4051

Abstract

A multicloud model is presented which explains the soft X-ray excess in NGC 4051 and, consistently, the optical line spectrum and the spectral energy distribution (SED) of the continuum. The clouds are heated and ionized by the photoionizing flux from the active center and by shocks. Diffuse radiation, partly absorbed throughout the clouds, nicely fits the bump in the soft X-ray domain, while bremsstrahlung radiation from the gaseous clouds contributes to the fit of the continuum SED. Debris from high-density fragmented clouds are necessary to explain the absorption oxygen throats observed at 0.87 and 0.74 keV. The debris are heated by shocks of about 200-300 km s-1. Low-velocity (≤100 km s-1), low-density (100 cm-3) clouds contribute to the line and continuum spectra, as well as high-velocity (1000 km s-1), high-density (8000 cm-3) clouds that are revealed by the FWHM of the line profiles. The SED in the IR is explained by reradiation of dust; however, the dust-to-gas ratio is not particularly high (≤ 3 × 10-15). Radio emission is well fitted by synchrotron radiation created at the shock front by a Fermi mechanism.