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Title: A bright ultraluminous X-ray source in NGC 5907
Authors: Sutton, A. D.
Roberts, T. P.
Gladstone, J. C.
Farrell, Sean A.
Reilly, Emma
Goad, Michael R.
Gehrels, N.
First Published: 15-Jul-2013
Publisher: Oxford University Press (OUP), Royal Astronomical Society
Citation: Monthly Notices of the Royal Astronomical Society, 2013, 434 (2), pp. 1702-1712 (11)
Abstract: We present a multimission X-ray analysis of a bright (peak observed 0.3–10 keV luminosity of ∼6 × 1040 erg s−1), but relatively highly absorbed ultraluminous X-ray source (ULX) in the edge-on spiral galaxy NGC 5907. The ULX is spectrally hard in X-rays (Γ ∼ 1.2–1.7, when fitted with an absorbed power law), and has a previously reported hard spectral break consistent with it being in the ultraluminous accretion state. It is also relatively highly absorbed for a ULX, with a column of ∼0.4–0.9 × 1022 atom cm−2 in addition to the line-of-sight column in our Galaxy. Although its X-ray spectra are well represented by accretion disc models, its variability characteristics argue against this interpretation. The ULX spectra instead appear dominated by a cool, optically thick Comptonizing corona. We discuss how the measured 9 per cent rms variability and a hardening of the spectrum as its flux diminishes might be reconciled with the effects of a very massive, radiatively driven wind and subtle changes in the corona, respectively. We speculate that the cool disc-like spectral component thought to be produced by the wind in other ULXs may be missing from the observed spectrum due to a combination of a low temperature (∼0.1 keV), and the high column to the ULX. We find no evidence, other than its extreme X-ray luminosity, for the presence of an intermediate mass black hole (MsBHs, ∼ 102−104 M⊙) in this object. Rather, the observations can be consistently explained by a massive (≳ 20 M⊙) stellar remnant black hole in a super-Eddington accretion state.
DOI Link: 10.1093/mnras/stt1133
ISSN: 0035-8711
eISSN: 1365-2966
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Archived with reference to SHERPA/RoMEO and publisher website.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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