Journal
ASTROPHYSICAL JOURNAL
Volume 760, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/760/2/135
Keywords
globular clusters: general; X-rays: binaries; X-rays: galaxies
Categories
Funding
- Royal Society
- NASA [GO-12369.01-A HST, GO1-12110X Chandra]
- CXC behalf NASA [NAS8-03060]
- Science and Technology Facilities Council [ST/H002235/1, ST/G001588/1] Funding Source: researchfish
- STFC [ST/H002235/1, ST/G001588/1] Funding Source: UKRI
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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 x 10(38) erg s(-1), but in subsequent observations 7 and 11 years later it had brightened substantially to 2-3 x 10(39) 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.
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