Free access article

A&A 388, 787-792 (2002)
DOI: 10.1051/0004-6361:20020471

The Phoenix galaxy: UGC 4203 re-birth from its ashes?

M. Guainazzi¹, G. Matt², F. Fiore³ and G. C. Perola<sup>2

1</sup>  XMM-Newton Science Operation Center, VILSPA, ESA, Apartado 50727, 28080 Madrid, Spain
²  Dipartimento di Fisica, Università degli Studi Roma Tre Via della Vasca Navale 84, 00146 Roma, Italy
³  Osservatorio Astronomico di Roma, Via dell'Osservatorio, 00144 Monteporzio Catone, Italy

(Received 3 September 2001 / Accepted 26 March 2002 )

Abstract
We report on a dramatic transition between a Compton-thick, reflection-dominated state and a Compton-thin state in the Seyfert 2 galaxy UGC 4203, discovered by comparing a recent (May 2001) XMM-Newton observation with ASCA observations performed about six years earlier. This transition can be explained either as a change in the column density of the absorber, maybe due to moving clouds in a clumpy torus, or as the revival of a transient active nucleus, which was in a phase of very low activity when observed by ASCA. If the latter explanation is correct, spectral transitions of this kind provide observational support to the idea that Compton-thick and Compton-thin regions coexist in the same source, the former likely to be identified with the "torus", the latter with dust lanes on much larger scales.

Key words: X-rays: galaxies -- galaxies: active -- galaxies: Seyfert -- galaxies: individual: UGC 4203 -- galaxies: nuclei

Offprint request: M. Guainazzi, mguainaz@xmm.vilspa.esa.es

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