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

¹ Istituto di Astrofisica Spaziale, C.N.R.,Via Fosso del Cavaliere, Roma, Italy
² Osservatorio Astronomico di Roma, Monteporzio Catone, Italy
³ Osservatorio Astronomico di Brera, Milano, Italy
⁴ Dipartimento di Fisica, Università degli Studi “Roma Tre”, Via della Vasca Navale 84, 00146 Roma, Italy
⁵ Harvard-Smithsonian Center of Astrophysics, Cambridge, MA 02138 USA
⁶ Laboratoire d'Astrophysique, Grenoble, France

Corresponding author: A. De Rosa, derosa@ias.rm.cnr.it

Received: 16 November 2001
Accepted: 20 March 2002

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 . 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 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 . 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 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 keV and  eV, is required to fit the line. The observed Compton hump and the Fe line are well reproduced with the ionized () 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.