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Astron. Astrophys. 341, 789-794 (1999)

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An ASCA X-ray observation of 1E 1724-3045 in the globular cluster Terzan 2

D. Barret 1, J.E. Grindlay 2, I.M. Harrus 2 and J.F. Olive 1

1 Centre d'Etude Spatiale des Rayonnements, CNRS/UPS, 9 Avenue du Colonel Roche, F-31028 Toulouse Cedex 04, France
(e-mail: Didier.Barret@cesr.fr)
2 Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

Received 11 September 1998 / Accepted 27 October 1998

Abstract

The bright persistent X-ray source and type I X-ray burster 1E 1724-3045 located in the globular cluster Terzan 2 was observed by ASCA for about 10 ksec on September 24-25th, 1995 while it was in its hard state, with a luminosity of [FORMULA] ergs s-1 in the 0.5-10 keV band (d=7.7 kpc). The ASCA spectrum is hard, and reveals the presence of a soft component below 2-3 keV. When combined with non simultaneous RXTE/HEXTE data, we show that the ASCA spectrum can be adequately fitted by a Comptonization model for which the electron temperature is [FORMULA] keV, the optical depth is [FORMULA] for a spherical scattering cloud. The soft component carries off about 13%, and 35% of the 0.1-200 keV luminosity for a blackbody and disk blackbody fit respectively. It is more likely to arise from the accretion disk, whereas the hard Comptonized component is generated in a hot boundary layer interior to the disk. The column density measured towards the source ([FORMULA] [FORMULA] cm-2) is consistent with the value expected from the optical reddening of the cluster. No emission lines were detected, and an upper limit of 30 eV for the equivalent width of a 6.4 keV line ([FORMULA] keV) has been derived.

Key words: stars: individual: 1E 1724-3045 – galaxy: globular clusters: individual: Terzan 2 – X-rays: stars

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© European Southern Observatory (ESO) 1999

Online publication: December 16, 1998
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