Chandra LETGS spectroscopy of the Quasar MR2251-178 and its warm absorber

TL;DR

This paper analyzes Chandra LETGS observations of quasar MR2251-178, revealing a warm absorber with ionized outflow features, spectral variability, and low cold absorption, contributing new insights into the quasar's ionization state and outflow dynamics.

Contribution

First detailed X-ray spectral analysis of MR2251-178's warm absorber using Chandra LETGS data, identifying ionization parameters, outflow signatures, and spectral variability.

Findings

Warm absorber characterized by N_H~2x10^21 cm^-2 and log(xi)~0.6.

Detected weak narrow absorption lines indicating outflow.

No significant cold or dusty material along the line of sight.

Abstract

We present an analysis of our Chandra Low Energy Transmission Grating Spectrometer (LETGS) observation of the quasar MR2251-178. The warm absorber of MR2251-178 is well described by a hydrogen column density, N_H~2x10^21 cm^-2, and an ionization parameter log(xi)~0.6. We find in the spectrum weak evidence for narrow absorption lines from Carbon and Nitrogen which indicate that the ionized material is in outflow. We note changes (in time) of the absorption structure in the band (0.6-1) keV (around the UTAs plus the OVII and OVIII K-edges) at different periods of the observation. We measure a (0.1-2) keV flux of 2.58x10^-11 ergs cm^-2 s^-1. This flux implies that the nuclear source of MR2251-178 is in a relatively low state. No significant variability is seen in the light curve. We do not find evidence for an extra cold material in the line of sight, and set an upper limit of N_H~1.2x10^20 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 N_CI~2x10^19 cm^-2 and N_OI~9x10^19 cm^-2, respectively.