A Chandra X-ray observation of the globular cluster Terzan 1 |
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| Authors: | E M Cackett R Wijnands C O Heinke † D Pooley ‡ W H G Lewin J E Grindlay P D Edmonds P G Jonker J M Miller |
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| Institution: | School of Physics and Astronomy, University of St. Andrews, KY16 9SS;Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Kruislaan 403, 1098 SJ, Amsterdam, the Netherlands;Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA;Astronomy Department, UC Berkeley, 601 Campbell Hall, Berkeley, CA 94720-3411, USA;Center for Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA;Harvard–Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA;SRON, National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, the Netherlands;University of Michigan, Department of Astronomy, 500 Church Street, Dennison 814, Ann Arbor, MI 48105, USA |
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| Abstract: | We present a ～19-ks Chandra Advanced CCD Imaging Spectrometer (ACIS)-S observation of the globular cluster Terzan 1. 14 sources are detected within 1.4 arcmin of the cluster centre with two of these sources predicted to be not associated with the cluster (background active galactic nuclei or foreground objects). The neutron star X-ray transient, X1732?304, has previously been observed in outburst within this globular cluster with the outburst seen to last for at least 12 yr. Here, we find four sources that are consistent with the ROSAT position for this transient, but none of the sources are fully consistent with the position of a radio source detected with the Very Large Array that is likely associated with the transient. The most likely candidate for the quiescent counterpart of the transient has a relatively soft spectrum and an unabsorbed 0.5–10 keV luminosity of 2.6 × 1032 erg s?1 , quite typical of other quiescent neutron stars. Assuming standard core cooling, from the quiescent flux of this source we predict long (>400 yr) quiescent episodes to allow the neutron star to cool. Alternatively, enhanced core cooling processes are needed to cool down the core. However, if we do not detect the quiescent counterpart of the transient this gives an unabsorbed 0.5–10 keV luminosity upper limit of 8 × 1031 erg s?1 . We also discuss other X-ray sources within the globular cluster. From the estimated stellar encounter rate of this cluster we find that the number of sources we detect is significantly higher than expected by the relationship of Pooley et al. |
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| Keywords: | stars: individual: X 1732?304 stars: neutron globular clusters: individual: Terzan 1 X-rays: binaries |
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