Regresar

Chandra LETGS spectroscopy of ionized absorbers: The quasar mr 2251-178

Abstract:

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 × 1021 cm-2, an ionization parameter log(ε) ≈ 0.6, and a global best-fit outflow velocity of ≈ -1100 kms-1. We find in the spectrum evidence of narrow absorption lines. The Kα, and Kβ transitions of C VI and N VI ions display an outflow with (at least three) components traveling at ≈ -600, -2000 and -3000 kms -1. We measure a (0.1 - 2) keV flux of 2.58 -0.04+0.03 × 10-11 ergscm-2 s-1, and a (2 - 10) keV flux of 1.64 -0.05+0.05× 10 -11 erg s cm-2 s-1. This flux implies that the nuclear source of MR 2251-178 is in a relatively low state. We did not find 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 NcI ≈2 × 1019 cm-2 and NoI ≈9× 1019 cm-2, respectively. ©2008: Instituto de Astronomía.