INTEGRAL long-term monitoring of the supergiant fast X-ray transient XTE J1739-302

¹ Institut de Ciència dels Materials, Universitat de València, PO Box 22085, 46071 Valencia, Spain e-mail: pere.blay@uv.es
² Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain e-mail: ignacio@dfists.ua.es
³ CRESST & Department of Physics, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA
⁴ NASA Goddard Space Flight Center, Astrophysics Science Division, Code 661, Greenbelt, MD 20771, USA
⁵ Department of Physics and Santa Cruz Institute for Particle Physics, University of California, Santa Cruz, Santa Cruz, CA 95064, USA
⁶ Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, Cambridge MA 02139, USA
⁷ IESL, Foundation for Research and Technology, 711 10 Heraklion, Crete, Greece
⁸ Physics Department, University of Crete, PO Box 2208, 710 03 Heraklion, Crete, Greece
⁹ ESA, ESAC, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
¹⁰ Institut für Astronomie und Astrophysik, Abteilung Astronomie, Sand 1, 72076 Tübingen, Germany
¹¹ INTEGRAL Science Data Centre, 16 Ch. d'Ecogia, 1290 Versoix, Switzerland

Received: 10 January 2008
Accepted: 19 June 2008

Abstract

Context. In the past few years, a new class of high mass X-ray binaries (HMXRB) has been claimed to exist, the supergiant fast X-ray transients (SFXT). These are X-ray binary systems with a compact companion orbiting a supergiant star which show very short and bright outbursts in a series of activity periods overimposed on longer quiescent periods. Only very recently the first attempts to model the behaviour of these sources have been published, some of them within the framework of accretion from clumpy stellar winds.

Aims. Our goal is to analyze the properties of XTE J1739-302/IGR J17391-3021 within the context of the clumpy structure of the supergiant wind.

Methods. We have used INTEGRAL and RXTE/PCA observations to obtain broad band (1–200 keV) spectra and light curves of XTE J1739-302 and investigate its X-ray spectrum and temporal variability.

Results. We have found that XTE J1739-302 follows a much more complex behaviour than expected. Far from presenting a regular variability pattern, XTE J1739-302 shows periods of high, intermediate, and low flaring activity.