A variable ultraluminous X-ray source in a globular cluster in NGC 4649

Abstract

We report the discovery of a new ultraluminous X-ray source (ULX) 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, but in subsequent observations 7 and 11 years later it had brightened substantially to 2 - 3 x 10^39 erg/s. 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

7 pages, 4 figures, accepted for publication in ApJ

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Cited by in corpus (19)

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• MOCCA-SURVEY Database I: Galactic Globular Clusters Harbouring a Black Hole Subsystem
• X-Ray Spectral Variability of Ultraluminous X-Ray Sources in Extragalactic Globular Clusters
• CG X-1: an eclipsing Wolf-Rayet ULX in the Circinus galaxy
• Deep Chandra Monitoring Observations of NGC 4649: I. Catalog of Source Properties
• The radial distribution of X-ray Binaries and Globular Clusters in NGC 4649 and their relation with the local stellar mass density
• Dynamically formed black hole+millisecond pulsar binaries in globular clusters
• X-Ray Spectroscopy of Newly Identified ULXs Associated With M87's Globular Cluster Population
• Three Ultraluminous X-ray Sources Hosted by Globular Clusters in NGC 1316
• X-ray Variability from the Ultraluminous Black Hole Candidate X-ray Binary in the Globular Cluster RZ 2109
• Variability in Ultra-luminous X-ray Sources
• The fading of two transient ULXs to below the stellar mass Eddington limit
• Slow Decline and Rise of the Broad [OIII] Emission Line in Globular Cluster Black Hole Candidate RZ2109
• Gravitational Brownian motion as inhomogeneous diffusion: black hole populations in globular clusters
• MOCCA-Survey Database: Extra Galactic Globular Clusters. III. The population of black holes in Milky Way and Andromeda-like galaxies
• Ultraluminous X-ray sources in Globular Clusters
• Optical and X-ray Follow-Up to a Globular Cluster Ultraluminous X-ray Source in NGC 4472
• The X-ray Point Source Population Hosted by Globular Clusters in the Elliptical Galaxy NGC 4261