Journal Article

A broad-band X-ray view of the warm absorber in radio-quiet quasar MR 2251−178

J. Gofford, J. N. Reeves, T. J. Turner, F. Tombesi, V. Braito, D. Porquet, L. Miller, S. B. Kraemer and Y. Fukazawa

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 414, issue 4, pages 3307-3321
Published in print July 2011 | ISSN: 0035-8711
Published online July 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.18634.x
A broad-band X-ray view of the warm absorber in radio-quiet quasar MR 2251−178

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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 both Suzaku and Swift/Burst Alert Telescope data. In accordance with previous observations, we find that the general continuum can be well described by a power law with Γ= 1.6 and an apparent soft excess below 1 keV. Warm absorption is clearly present, and absorption lines due to the Fe unresolved transition array, 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 Kα emission line is observed (E= 6.44 ± 0.04 keV) which is well modelled by the presence of a mildly ionized (ξ≲ 30) reflection component with a low reflection fraction (R < 0.2). At least five ionized absorption components with 1020NH≲ 1023 cm−2 and 0 ≲ log ξ/erg cm s−1≲ 4 are required to achieve an adequate spectral fit. Alternatively, we show that the continuum can also be fit if a Γ∼ 2.0 power law is absorbed by a column of NH∼ 1023 cm−2 which covers ∼30 per cent of the source flux. Independent of which continuum model is adopted, the Fe L and Fe xxv Heα lines are well fit by a single absorber outflowing with vout∼ 0.14c. Such an outflow/disc-wind is likely to be substantially clumped (b∼ 10−3) in order to not vastly exceed the likely accretion rate of the source.

Keywords: galaxies: active; galaxies: individual: MR 2251−178; X-rays: galaxies

Journal Article.  11290 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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