A search for changing-look AGN in the Grossan catalog

¹ XMM-Newton Science Operations Center, European Space Astronomy Center, ESA, Apartado 50727, 28080 Madrid, Spain e-mail: Stefano.Bianchi@sciops.esa.int
² Dipartimento di Fisica, Università degli Studi Roma Tre, Via della Vasca Navale 84, 00146, Roma, Italy
³ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁴ INAF – Istituto di Radioastronomia, Via P. Gobetti 101, 40129 Bologna, Italy
⁵ Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, UK
⁶ INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monteporzio, Italy
⁷ INAF – Osservatorio Astrofisico di Arcetri, Largo Fermi 5, 50125 Firenze, Italy

Received: 9 May 2005
Accepted: 13 July 2005

Abstract

We observed with XMM-Newton 4 objects selected from the Grossan (1992, Ph.D. Thesis) catalog, with the aim to search for new “changing-look” AGN. The sample includes all the sources which showed in subsequent observations a flux much lower than the one measured with HEAO A-1: NGC 7674, NGC 4968, IRAS 13218+0552 and NGC 1667. None of the sources was caught in a high flux state during the XMM-Newton observations, whose analysis reveal they are all likely Compton-thick objects. We suggest that, for all the sources, potential problems with the HEAO A-1 source identification and flux measurement prevent us from being certain that the HEAO A-1 data represent a putative “high” state for these objects. Nonetheless, based on the high flux state and Compton-thin spectrum of its GINGA observation, NGC 7674 represents probably the sixth known case of a “changing-look” Seyfert 2 galaxy. From the X-ray variability pattern, we can estimate a likely lower limit of a few parsec to the distance of the inner walls of the torus in this object. Remarkably, IRAS 13218+0552 was not detected by XMM-Newton, despite being currently classified as a Seyfert 1 with a large [OIII] flux. However, the original classification was likely to be affected by an extreme velocity outflow component in the emission lines. The object likely harbors an highly obscured AGN and should be re-classified as a type 2 source.