The nature of the X-ray transient SAX J1711.6-3808

¹ Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands
² SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
³ Dept. of Astronomy, University of Maryland, College Park, MD 20742, USA
⁴ NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771, USA
⁵ Istituto di Astrofisica Spaziale (CNR), Area Ricerca Roma Tor Vergata, Via del Fosso del Cavaliere, 00133 Roma, Italy
⁶ XMM-Newton Science Operations Center, Vilspa Satellite Tracking Station, Apartado 50727, 28080 Madrid, Spain

Corresponding author: J. J. M. in 't Zand, jeanz@sron.nl

Received: 1 March 2002
Accepted: 15 May 2002

Abstract

SAX J1711.6-3808 is an X-ray transient in the Galactic bulge that was active from January through May of 2001 and whose maximum 1–200 keV luminosity was measured to be  erg cm^-2 s^-1 which is less than ~25% of the Eddington limit, if placed at a distance equal to that of the galactic center. We study the X-ray data that were taken of this moderately bright transient with instruments on BeppoSAX and RXTE. The spectrum shows two interesting features on top of a Comptonized continuum commonly observed in low-state X-ray binaries: a broad emission feature peaking at 7 keV and extending from 4 to 9 keV, and a soft excess with a color temperature below 1 keV which reveals itself only during one week of data. High time-resolution analysis of 412 ksec worth of data fails to show bursts, coherent or high-frequency quasi-periodic oscillations. Given the dynamic range of the flux measurements, this would be unusual if a neutron star were present. SAX J1711.6-3808 appears likely to contain a black hole. No quiescent optical counterpart could be identified in archival data within the 5´´-radius XMM error circle, but the limits are not very constraining because of heavy extinction ().