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

¹ 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

Corresponding author: M. Guainazzi, mguainaz@xmm.vilspa.esa.es

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.