Astronomy & Astrophysics

Free access article

Issue		A&A Volume 366, Number 1, January IV 2001
Page(s)		138 - 145
Section		Formation, structure and evolution of stars
DOI		10.1051/0004-6361:20000028

A&A 366, 138-145 (2001)
DOI: 10.1051/0004-6361:20000028

Simultaneous BeppoSAX and RXTE observations of the X-ray burst sources GX 3+1 and Ser X-1

T. Oosterbroek¹, D. Barret², M. Guainazzi³ and E. C. Ford⁴

¹ Astrophysics Division, Space Science Department of ESA, ESTEC, Postbus 299, 2200 AG Noordwijk, The Netherlands
² Centre d'Étude Spatiale des Rayonnements, CNRS/UPS, 9 avenue du Colonel Roche, 31028 Toulouse Cedex 04, France
³ XMM-Newton SOC, VILSPA, ESA, Apartado 50727, 28080 Madrid, Spain
⁴ Astronomical Institute, "Anton Pannekoek,"University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands

(Received 25 July 2000 / Accepted 16 October 2000 )

Abstract
We have obtained spectral and timing data on GX 3+1 and Ser X-1. Both sources were observed simultaneously with BeppoSAX and RXTE. The RXTE data is used to provide power spectra and colour-colour diagrams in order to constrain the state (and thus track $\dot M$ ) the sources are in. The BeppoSAX data provide the broad-band spectra. The spectra of both sources are reasonably well-fit using a model consisting of a disk-blackbody, a comptonized component and a Fe line, absorbed by interstellar absorption. The electron temperature ( $kT_{\rm e}$ ) of the Comptonizing plasma is in both cases $\sim$ 2.5 keV. This implies that no strong high-energy tail from the Comptonized component is present in either of the sources. We discuss the similarities between these burst sources and the luminous X-ray sources located in globular clusters. We find that the spectral parameters of the comptonized component provide information about the mass-accretion rate, which agrees well with estimates from the timing and spectral variations.

Key words: accretion, accretion disks -- stars: GX 3+1, Ser X-1 -- stars: neutron -- X-rays: bursts -- X-rays: general

Offprint request: T. Oosterbroek, toosterb@astro.estec.esa.nl

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