Observational Evidence for the Origin of X-ray Sources in Globular Clusters

AbstractLow-mass X-ray binaries, recycled pulsars, cataclysmic variables and magnetically active binaries are observed as X-ray sources in globular clusters. We discuss the classification of these systems, and find that some presumed active binaries are brighter than expected. We discuss a new statistical method to determine from observations how the formation of X-ray sources depends on the number of stellar encounters and/or on the cluster mass. We show that cluster mass is not a proxy for the encounter number, and that optical identifications are essential in proving the presence of primordial binaries among the low-luminosity X-ray sources.

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X-ray sources in Galactic globular clusters and old open clusters

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319007981 ◽

2019 ◽

Vol 14 (S351) ◽

pp. 367-376

Author(s):

Maureen van den Berg

Keyword(s):

Globular Clusters ◽

Cataclysmic Variables ◽

Star Clusters ◽

Open Clusters ◽

Encounter Rate ◽

X Ray ◽

Low Mass ◽

New Perspective ◽

X Ray Binaries ◽

Cluster Age

AbstractThe features and make up of the population of X-ray sources in Galactic star clusters reflect the properties of the underlying stellar environment. Cluster age, mass, stellar encounter rate, binary frequency, metallicity, and maybe other properties as well, determine to what extent we can expect a contribution to the cluster X-ray emission from low-mass X-ray binaries, millisecond pulsars, cataclysmic variables, and magnetically active binaries. Sensitive X-ray observations withXMM-Newton and certainlyChandra have yielded new insights into the nature of individual sources and the effects of dynamical encounters. They have also provided a new perspective on the collective X-ray properties of clusters, in which the X-ray emissivities of globular clusters and old open clusters can be compared to each other and to those of other environments. I will review our current understanding of cluster X-ray sources, focusing on star clusters older than about 1 Gyr, illustrated with recent results.

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Observational evidence for origin of stellar exotica in globular clusters

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307011271 ◽

2006 ◽

Vol 2 (14) ◽

pp. 440-441

Author(s):

Franciscus W.M. Verbunt

Keyword(s):

Neutron Star ◽

Globular Clusters ◽

Cataclysmic Variables ◽

Observational Evidence ◽

Encounter Rate ◽

X Ray ◽

Blue Stragglers ◽

Direct Collision ◽

Orbital Periods ◽

X Ray Binaries

AbstractThe formation of special binaries in a globular cluster is regulated by the total encounter rate γ in the cluster, but their life expectancy by the number of encounters γ that one system experiences. The orbital periods indicate whether a neutron star or white dwarf entered a binary via direct collision, via tidal capture, or via exchange encounter. The numbers of X-ray binaries with a neutron star scales with γ. Magnetically active binaries (including blue stragglers) are formed via evolution of primordial binaries, and their numbers scale with the cluster mass. Cataclysmic variables are formed by stellar encounters or via evolution of a primordial binary in clusters with high and low central density, respectively.

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THE X-RAY LUMINOSITY FUNCTION OF LOW MASS X-RAY BINARIES IN EARLY-TYPE GALAXIES, THEIR METAL-RICH, AND METAL-POOR GLOBULAR CLUSTERS

The Astrophysical Journal ◽

10.3847/0004-637x/818/1/33 ◽

2016 ◽

Vol 818 (1) ◽

pp. 33 ◽

Cited By ~ 14

Author(s):

Mark B. Peacock ◽

Stephen E. Zepf

Keyword(s):

Globular Clusters ◽

Luminosity Function ◽

Early Type ◽

X Ray ◽

Low Mass ◽

X Ray Binaries

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Common Envelope Evolution and Formation of Cataclysmic Variables and Low-Mass X-ray Binaries

X-Ray Binaries and Recycled Pulsars ◽

10.1007/978-94-011-2704-2_26 ◽

1992 ◽

pp. 269-280 ◽

Cited By ~ 26

Author(s):

R. F. Webbink

Keyword(s):

Cataclysmic Variables ◽

X Ray ◽

Common Envelope ◽

Low Mass ◽

X Ray Binaries

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Theory of Accretion Disk Coronae

International Astronomical Union Colloquium ◽

10.1017/s025292110001232x ◽

1990 ◽

Vol 115 ◽

pp. 187-196

Author(s):

T. R. Kallman

Keyword(s):

Active Galactic Nuclei ◽

Accretion Disk ◽

Cataclysmic Variables ◽

Galactic Nuclei ◽

X Ray ◽

Spectral Signatures ◽

Low Mass ◽

X Ray Absorption ◽

X Ray Binaries ◽

Theoretical Issues

AbstractAccretion disk coronae are likely to be the dominant site for X-ray absorption and reprocessed emission in low mass X-ray binaries, and may be present in other classes of compact X-ray sources such as active galactic nuclei and cataclysmic variables. In spite of this fact, and in spite of the observational evidence for their existence, there remain many uncertainties about the structure of accretion disk coronae. This paper will discuss the coronal structure and dynamics, their X-ray spectral signatures including coupling to the variability behavior of compact X-ray sources, and the major unsolved theoretical issues surrounding them.

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Using X-Rays to Probe the Compact Binary Content of Globular Clusters

International Astronomical Union Colloquium ◽

10.1017/s0252921100151978 ◽

2004 ◽

Vol 194 ◽

pp. 75-76

Author(s):

N. A. Webb ◽

B. Gendre ◽

D. Barret

Keyword(s):

Globular Clusters ◽

Cataclysmic Variables ◽

Close Binaries ◽

X Rays ◽

X Ray ◽

Compact Binaries ◽

Compact Binary ◽

Low Mass ◽

Evolutionary Paths ◽

New Generation

AbstractGlobular clusters (GCs) harbour a large number of close binaries which are hard to identify optically due to high stellar densities. Observing these GCs in X-rays, in which the compact binaries are bright, diminishes the over-crowding problem. Using the new generation of X-ray observatories, it is possible to identify populations of neutron star low mass X-ray binaries, cataclysmic variables and millisecond pulsars as well as other types of binaries. We present the spectra of a variety of binaries that we have identified in four GCs observed by XMM-Newton. We show that through population studies we can begin to understand the formation of individual classes of binaries in GCs and hence start to unfold the complex evolutionary paths of these systems.

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The Globular Cluster Population of X-ray Binaries

Symposium - International Astronomical Union ◽

10.1017/s0074180900160711 ◽

1987 ◽

Vol 125 ◽

pp. 187-197 ◽

Cited By ~ 5

Author(s):

Frank Verbunt ◽

Piet Hut

Keyword(s):

Globular Cluster ◽

Globular Clusters ◽

Mass Function ◽

Initial Mass Function ◽

Encounter Rate ◽

Formation Mechanisms ◽

Main Sequence Stars ◽

X Ray ◽

Low Mass ◽

X Ray Binaries

We discuss formation mechanisms for low-mass X-ray binaries in globular clusters. We apply the most efficient mechanism, tidal capture in close two-body encounters between neutron and main-sequence stars, to the clusters of our galaxy. The observed number of X-ray sources in these can be explained if the birth velocities of neutron stars are higher than estimated from velocity measurements of radiopulsars, or if the initial mass function steepens at high masses. We perform a statistical test on the distribution of X-ray sources with respect to the number of close encounters in globular clusters, and find satisfactory agreement between the tidal capture theory and observation, apart from the presence of low-mass X-ray binaries in four clusters with a very low encounter rate: Ter 1, Ter 2, Gr 1 and NGC 6712.EXOSAT observations indicate that some dim globular cluster sources may be less luminous than hitherto assumed, and support the view that the brighter dim sources may be soft X-ray transients in quiescence.

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