The BeppoSAX broad-band spectrum and variability of the Seyfert 1 NGC 3783

Abstract

BeppoSAX observed the Seyfert 1 galaxy NGC 3783 for ∼5 days from 1998 June 6 to 1998 June 10. The average flux during the observation was F2-10 keV ∼ 6 × 10-11 erg cm-2 s-1. The long exposure provided a very high quality spectrum that exhibits all the typical features of Seyfert 1s. The high energy cut-off of the intrinsic continuum, at Ec = 340±107560 keV, was detected for the first time in this object. During the observation the source showed modest flux variations (∼20% in 2-10 keV) and spectral variability that can be completely explained by a change of the intrinsic slope ΔΓ ∼ 0.1. NGC 3783 is one of the few Seyfert 1s that exhibits a soft emission component in the BeppoSAX spectrum. This soft excess is well reproduced by a black body component with temperature kT ∼ 0.2 keV. A warm absorber is also required to fit the soft X-ray spectrum. Both reprocessing features, the Compton reflection hump and the Fe emission line, were detected in our observation. In addition to a narrow iron line (as observed by Chandra) a broad component with σ = 0.72±0.271.28 keV and EW = 115 ± 76 eV, is required to fit the line. The observed Compton hump and the Fe line are well reproduced with the ionized (log ζ = 2.73±0.050.04) disc reflection model of Ross & Fabian. in this case the soft excess observed below 2 kev can be accounted for by the disc emissivity and no additional soft X-rays component is required to fit the spectrum.