X-ray observations of NGC 1851 and the globular cluster LMXBs

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Abstract
We present new Ginga observations of the globular cluster X-ray source 4U 0513-40 in NGC 1851. Despite the 2-d time-base of the observations, no eclipsing or dipping modulation was found. The spectrum can be well modelled by a power law of index 2.1 to energies of at least 10 keV. We find from archive EXOSAT data that an additional blackbody contribution is required at lower energies. We reanalyse the EXOSAT spectra of the other cluster sources, and find that in the majority of cases the addition of a blackbody significantly improves the fit: blackbody radii of ∼a few km are found. We discuss the implications of these findings for our models of the cluster sources.

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