On the soft excess in the X-ray spectrum of Circinus X-1:: Revisitation of the distance to Circinus X-1

We report on a 300 ks BeppoSAX (0.12 - 200 keV) observation of Circinus X-1 (Cir X-1) at phases between 0.62 and 0.84 and on a 90 ks BeppoSAX observation of Cir X-1 at phases 0.11 - 0.16. Using the canonical model adopted until now to fit the energy spectrum of this source, large residuals appear below 1 keV. These are well fitted using an equivalent hydrogen column of 0.66 x 10(22) cm(-2), adding absorption edges of O VII, O VIII, and Ne IX in the spectra extracted from the observation at phases 0.62 - 0.84 and adding absorption edges of O VII, O VIII, Mg XI, and Mg XII and absorption lines of O VIII and Mg XII in the spectra extracted from the observation at phases 0.11 - 0.16. During the observation at phases 0.62 - 0.84 the electron density associated with the ionized matter is similar to 10(13) cm(-3), remaining quite constant going away from the compact object. During the observation at phases 0.11 - 0.16, the electron density profile varies along the distance going from similar to6 x 10(13) cm(-3) at similar to 10(11) cm to similar to9 x 10(10) cm(-3) at similar to 10(13) cm. The equivalent hydrogen column toward Cir X-1 is 3 times lower than the value obtained from previous models. This low value would imply that Cir X-1 is at a distance of 4.1 kpc.