A swan song: The disappearance of the nucleus of NGC 4051 and the echo of its past glory

Abstract

On 1998 May 9-11, BeppoSAX observed the low-luminosity Seyfer I-galaxy NGC 4051 in an ultra-dim X-ray state. The 2-10 keV flux (1.26 × 10-12 erg cm-2 s-1) was about 20 times fainter than its historical average value, and remained steady along the whole observation (∼2.3 d). The observed flat spectrum (Γ ≃ 0.8) and intense iron line (EW ≃600 eV) are best explained by assuming that the active nucleus has switched off, leaving only a residual reflection component visible.