XMM-Newton broad-band observations of NGC 7582: N variations and fading out of the active nucleus

¹ Osservatorio Astronomico di Roma (INAF), via Frascati 33, 00040 Monteporzio Catone, Italy e-mail: piconcelli@oa-roma.inaf.it
² European Space Astronomy Center of ESA, Apartado 50727, 28080 Madrid, Spain
³ Dipartimento di Fisica, Università degli Studi Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy
⁴ Space Telescope Science Institute, 3700 San Martin Drive, MD 21218, USA

Received: 25 September 2006
Accepted: 7 February 2007

Abstract

We present results from two XMM–Newton observations of the bright classical Seyfert 2 galaxy NGC 7582 taken four years apart (2001 May and 2005 April). We present the analysis of the high-resolution (0.3-1 keV) RGS and low-resolution (0.3-10 keV) EPIC spectroscopic data.
A comparison with a 1998 BeppoSAX observation suggests that XMM–Newton caught the source in a “reflection-dominated” phase, measuring the lowest continuum flux level ever (F_2-10 = 2.3 10^-12 erg cm^-2 s^-1) in 2005. NGC 7582 therefore experienced a dramatic spectral transition most likely due to the partial switching-off of the nuclear activity. The XMM–Newton spectrum of the continuum emission is very complex. It can be well described by a model consisting of a combination of a heavily absorbed (N_H ~ 10²⁴ cm^-2) power law and a pure reflection component both obscured by a column density of ~ cm^-2. Notably, we detect a significant increase by a factor of ~2 in the column density of the inner, thicker absorber covering the primary X-ray source between 2001 and 2005. The 2005 XMM–Newton spectrum shows the strongest Fe Kα emission line ever measured in this source. This is consistent with the line delayed time response to the decrease of the nuclear activity. Our analysis also reveals that the soft X-ray spectrum is dominated by emission lines from highly ionized metals. The detection of a narrow OVIII radiative recombination continuum suggests an origin in a photoionized plasma.