The nature of the absorbing torus in compact radio galaxies

¹ INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
³ Observatoire de Haute-Provence, CNRS, 04870 Saint-Michel l'Observatoire, France

Corresponding author: G. Risaliti, risaliti@arcetri.astro.it

Received: 7 October 2002
Accepted: 21 January 2003

Abstract

We present BeppoSAX observations of the two radio galaxies PKS 1934-63 and S5 1946+708. Strong Iron Kα lines are detected in both objects indicating that the two sources are absorbed by column densities higher than 10²⁴ cm^-2. 
Combining radio continuum, HI absorption and X-ray data we can constrain the physical state and the dimensions of the absorber. We find that the putative obscuring torus is molecular and located at a distance higher than 20 pc from the center in S5 1946+70. In PKS 1934-63 no radio nucleus has been observed. If this is due to free-free absorption a radius of only a few pc is inferred. Since the Kα lines have been detected only at 90% confidence, we also discuss the implications if they would be not as strong as found from our data. From our results it appears that the combination of hard X-ray data and spatially resolved HI absorption measurements provides a powerful diagnostic for conditions in the absorbing “torus”.