CHANDRA LETGS SPECTROSCOPY OF IONIZED ABSORBERS: THE

We analyze the Chandra Low Energy Transmission Grating Spectrometer (LETGS) observation of the quasar MR 2251 178. The warm absorber of MR 2251 178 is well described by a hydrogen column density of 2 10 21 cm 2 , an ionization parameter log( ) 0:6, and a global best-t outo w velocity of 1100 km s 1 . We nd in the spectrum evidence of narrow absorption lines. The K and K transitions of C vi and N vi ions display an outo w with (at least three) components traveling at 600, 2000 and 3000 km s 1 . We measure a (0:1 2) keV ux of 2.58 +0:03 0:04 10 11 erg s cm 2 s 1 , and a (2 10) keV ux of 1.64 +0:05 0:05 10 11 erg s cm 2 s 1 . This ux implies that the nuclear source of MR 2251 178 is in a relatively low state. We did not nd evidence for an extra cold material in the line of sight, that would be associated to the giant [O iii] emission region surrounding the nucleus of MR 2251 178. If present, we can set an upper limit of 1:2 10 20 cm 2 . The X-ray spectrum does not appear to show evidence for dusty material, though an upper limit in the neutral carbon and oxygen column densities can only be set to NC I 2 10 19 cm 2 and NO I 9 10 19 cm 2 , respectively.