Abstract
We observed the Seyfert 1 galaxy Mrk 509 for ∼59 ks with the Chandra high-energy transmission gratings, simultaneously with HST/STIS and RXTE. Here we present a detailed analysis of the soft X-ray spectrum observed with Chandra. We measure strong absorption lines from He-like Ne and Mg and from H-like N, O, and Ne. Weaker absorption lines may also be present. The lines are unresolved except for Ne x Lyα (λ12.134) and Ne IX 1s2-1s2p (λ13.447), which appear to be marginally resolved. The profiles are blueshifted with respect to the systemic velocity of Mrk 509, indicating an outflow of ∼-200 km s-1. There is also a hint that the profiles may have a velocity component near systemic. The soft X-ray spectrum can be described in remarkable detail with a simple, single-zone photoionized absorber having an equivalent neutral hydrogen column density of 2.06 +0.45 +0.39 × 1021 cm-2 and an ionization parameter of log U = 1.76-0.14 +0.13 (or log U = 0.27). Although the photoionized gas almost certainly is comprised of matter in more than one ionization state and may consist of several kinematic components, data with better spectral resolution and signal-to-noise ratio would be required to justify a more complex model. The UV data, on the other hand, have a velocity resolution of ∼10 km s-1 and can easily detect eight kinematic components, covering roughly the same velocities as the X-ray absorption profiles. Even though the X-ray and UV absorbers share the same velocity space, the UV absorbers have a much smaller column density and ionization state. We show that models of the X-ray data do not predict significant UV absorption and are therefore consistent with the UV data. Finally, we do not detect any soft X-ray emission lines.