A broad-band X-ray view of the Warm Absorber in radio-quiet quasar MR2251-178

Abstract

We present the analysis of a new broad-band X-ray spectrum (0.6-180.0 keV) of the radio-quiet quasar MR 2251-178 which uses data obtained with both Suzaku and the Swift/BAT. In accordance with previous observations, we find that the general continuum can be well described by a power-law with {\Gamma}=1.6 and an apparent soft-excess below 1 keV. Warm absorption is clearly present and absorption lines due to the Fe UTA, Fe L (Fe XXIII-XXIV), S XV and S XVI are detected below 3 keV. At higher energies, Fe K absorption from Fe XXV-XXVI is detected and a relatively weak (EW=25[+12,-8] eV) narrow Fe K{\alpha} emission line is observed at E=6.44\pm0.04 keV. The Fe K{\alpha} emission is well modelled by the presence of a mildly ionised ({\xi}\leq30) reflection component with a low reflection fraction (R<0.2). At least 5 ionised absorption components with 10^{20} \leq N_H \leq 10^{23} cm^{-2} and 0 \leq log({\xi})/erg cm s^{-1} \leq 4 are required to achieve an adequate spectral fit. Alternatively, we show that the continuum can also be fit if a {\Gamma}~2.0 power-law is absorbed by a column of N_H~10^{23} cm^{-2} which covers ~30% of the source flux. Independent of which continuum model is adopted, the Fe L and Fe XXV He{\alpha} lines are described by a single absorber outflowing with v_out~0.14 c. Such an outflow/disk wind is likely to be substantially clumped (b~10^{-3}) in order to not vastly exceed the likely accretion rate of the source.