2005A&A...439..575I

We report the results of a long, 350ks, BeppoSAX observation of the bright atoll source GX 9+1 in the 0.12-18keV energy range. During this observation GX 9+1 showed a large count rate variability in its lightcurve. From its color-color diagram we selected six zones and extracted the source energy spectrum from each zone. We find that the model, composed of a blackbody plus a Comptonized component absorbed by an equivalent hydrogen column of ∼1.4x10²²cm^–2, fits the spectra in the energy range 1-18keV well; however, below 1keV a soft excess is present. We find that the spectrum of GX 9+1, in the 0.12-18keV energy range, is well fitted by the model above, if we use an equivalent hydrogen column of ∼0.8x10²²cm^–2, together with several absorption edges from ionized matter (OVII, OVIII, NeIX, ArXVII, and CaXX) and an absorption line from SiXIV. From the study of these features we deduce that the electron density of the plasma and the equivalent hydrogen column density associated with the ionized matter is ∼10¹²cm^–3 and ∼10²³cm^–2, respectively, at a distance from the central object of r∼10¹¹cm, while at larger distances the equivalent hydrogen column density associated to the ionized matter decreases down to ∼10²²cm^–2. The value of the equivalent hydrogen column of ∼0.8x10²²cm^–2 associated to the interstellar matter implies that GX 9+1 is at a distance of 5kpc, and not 8.5-10kpc as usually assumed. This result implies that the atoll source GX 9+1 does not emit at the Eddington limit, as supposed until now, but has a luminosity of 6x10³⁷erg/s in the 0.1-18keV energy range, typical of LMXBs belonging to the bright atoll class.