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Authors: Roberts, T. P.
Fabbiano, G.
Luo, B.
Kim, D.-W.
Strader, J.
Middleton, M. J.
Brodie, J. P.
Fragos, T.
Gallagher, J. S.
Kalogera, V.
King, A. R.
Zezas, A.
First Published: 1-Dec-2012
Publisher: IOP Publishing
Citation: Astrophysical Journal, 2012, 760:135
Abstract: We report the discovery of a new ultraluminous X-ray source associated with a globular cluster in the elliptical galaxy NGC 4649. The X-ray source was initially detected with a luminosity below 5 × 1038 erg s–1, but in subsequent observations 7 and 11 years later it had brightened substantially to 2-3 × 1039 erg s–1. Over the course of six separate observations it displayed significant spectral variability, in both continuum slope and absorption column. Short-term variability in the X-ray flux was also present in at least one observation. The properties of this object appear consistent with a stellar-mass black hole accreting at super-Eddington rates (i.e., in the ultraluminous accretion state), although a highly super-Eddington neutron star cannot be excluded. The coincidence of an increase in absorption column with a possible enhancement in short-term variability in at least one observation is suggestive of a clumpy, radiatively driven wind crossing our line of sight to the object.
DOI Link: 10.1088/0004-637X/760/2/135
ISSN: 0004-637X
eISSN: 1538-4357
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2012, IOP Publishing. This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License ( ), which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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