XMM-Newton X-ray and optical observations of the globular clusters M 55 and NGC 3201

Astronomy and Astrophysics (Impact Factor: 4.38). 09/2005; 445(1). DOI: 10.1051/0004-6361:20053010
Source: arXiv


We have observed two low concentration Galactic globular clusters with the X-ray observatory XMM-Newton. We detect 47 faint X-ray sources in the direction of M 55 and 62 in the field of view of NGC 3201. Using the statistical Log N-Log S relationship of extragalactic sources derived from XMM-Newton Lockman Hole observations, to estimate the background source population, we estimate that very few of the sources (1.5+/-1.0) in the field of view of M 55 actually belong to the cluster. These sources are located in the centre of the cluster as we expect if the cluster has undergone mass segregation. NGC 3201 has approximately 15 related sources, which are centrally located but are not constrained to lie within the half mass radius. The sources belonging to this cluster can lie up to 5 core radii from the centre of the cluster which could imply that this cluster has been perturbed. Using X-ray (and optical, in the case of M 55) colours, spectral and timing analysis (where possible) and comparing these observations to previous X-ray observations, we find evidence for sources in each cluster that could be cataclysmic variables, active binaries, millisecond pulsars and possible evidence for a quiescent low mass X-ray binary with a neutron star primary, even though we do not expect any such objects in either of the clusters, due to their low central concentrations. The majority of the other sources are background sources, such as AGN. Comment: 12 pages, 7 figures, accepted to be published in A&A

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    ABSTRACT: Using the new generation of X-ray observatories, we are now beginning to identify populations of close binaries in globular clusters, previously elusive in the optical domain because of the high stellar density. These binaries are thought to be, at least in part, responsible for delaying the inevitable core collapse of globular clusters and their identification is therefore essential in understanding the evolution of globular clusters, as well as being valuable in the study of the binaries themselves. Here, we present observations made with XMM-Newton of six globular clusters, in which we have identified neutron star low mass X-ray binaries and their descendants (millisecond pulsars), cataclysmic variables and other types of binaries. We discuss not only the characteristics of these binaries, but also their formation and evolution in globular clusters and their use in tracing the dynamical history of these clusters.
    Advances in Space Research 01/2006; 38(12-38):2930-2933. DOI:10.1016/j.asr.2006.02.066 · 1.36 Impact Factor
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    ABSTRACT: Globular clusters have long been known to contain large excesses of a variety of objects formed through dynamical processes. The past few years have seen a dramatic increase in our knowledge about these systems. Comment: 20 pages, review article accepted for October edition of Astronomy & Geophysics. A more colorful version of this paper with a few extra figures will appear in A&G. The scientific content is the same in both versions
    Astronomy & Geophysics 09/2007; DOI:10.1111/j.1468-4004.2007.48512.x · 0.32 Impact Factor
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    ABSTRACT: Low-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. Comment: 10 pages, 7 figures, to appear in IAUS 246, Dynamical evolution of dense stellar systems, ed. E. Vesperini
    Proceedings of the International Astronomical Union 10/2007; 3(S246). DOI:10.1017/S1743921308015822
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