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 Seyfert 1 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 (G 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.