SIMBAD references

We present XMM-Newton observations of the Seyfert 1 active galactic nucleus (AGN) H0557-385. We have conducted a study into the warm absorber present in this source, and using high-resolution Reflection Grating Spectrometer (RGS) data we find that the absorption can be characterized by two phases: a phase with log ionization parameter ξ of 0.50 (where ξ is in units of erg.cm/s) and a column of 0.2x10²¹/cm2, and a phase with log ξ of 1.62 and a column of 1.3x10²²/cm2. An iron Kα line is detected. Neutral absorption is also present in the source, and we discuss possible origins for this. On the assumption that the ionized absorbers originate as an outflow from the inner edge of the torus, we use a new method for finding the volume filling factor. Both phases of H0557-385 have small volume filling factors (≤1 per cent). We also derive the volume filling factors for a sample of 23 AGN using this assumption and for the absorbers with logξ > 0.7, we find reasonable agreement with the filling factors obtained through the alternative method of equating the momentum flow of the absorbers to the momentum loss of the radiation field. By comparing the filling factors obtained by the two methods, we infer that some absorbers with logξ < 0.7 occur at significantly larger distances from the nucleus than the inner edge of the torus.