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Durham University

Department of Physics

Staff profile

Publication details for Prof Tim Roberts

Middleton, M.J., Walton, D.J., Roberts, T.P. & Heil, L. (2014). Broad absorption features in wind-dominated ultraluminous X-ray sources? Monthly Notices of the Royal Astronomical Society 438(1): L51-L55.

Author(s) from Durham

Abstract

The luminosities of ultraluminous X-ray sources (ULXs) require an exotic solution with either supercritical accretion modes on to stellar-mass black holes or subcritical accretion on to intermediate-mass black holes (IMBHs) being invoked. Discriminating between the two is non-trivial due to the present lack of a direct mass measurement. A key expectation of the supercritical mode of accretion is the presence of powerful radiatively driven winds. Here we analyse XMM–Newton data from NGC 5408 X-1 and NGC 6946 X-1 and find that strong soft residuals present in the X-ray spectra can be reconciled with broadened, blueshifted absorption by a partially ionized, optically thin phase of this wind. We derive initial values for the physical parameters of the wind; we also discuss other possible origins for the observed features.