1 Introduction

Dedicated monitoring programs with the BeppoSAX Wide Field Cameras (WFCs; e.g. In 't Zand 2001) and the RXTE Proportional Counter Array (PCA; Swank & Markwardt 2001) have revealed in recent years tens of faint X-ray binary transients in a $\sim$ $20^{\rm o}$ field around the galactic center. About three quarters of these exhibit type-I X-ray bursts, diagnosing the compact component as a neutron star. Others involve optically confirmed black hole systems (e.g., SAX J1819.3-2525=XTE J1819-253, Orosz et al. 2001) and microquasar-type suspected black hole systems (e.g. XTE J1748-288, Naik et al. 2000; Revnivtsev et al. 2000).

A recent addition to the group of faint transients is SAX J1711.6-3808 which was discovered in an observation with the BeppoSAX Wide Field Cameras during Feb. 8.8-11.5, 2001 when the average flux was 55 mCrab in the 2 to 9 keV bandpass (In 't Zand et al. 2001). Its galactic coordinates are $l^{\rm II}=348\fdg4, b^{\rm II}=+0\fdg8$. This source was followed up with sensitive X-ray devices on BeppoSAX, RXTE, and XMM-Newton. Wijnands & Miller (2002) reported on an analysis carried out on part of the RXTE-PCA data and found that the soft/hard state behavior is decoupled from the X-ray luminosity and possibly the mass accretion rate. They find that these data, including a detected quasi-periodic oscillation, are inconclusive as to the nature of the compact object.

In the present paper we discuss all the X-ray data obtained with BeppoSAX and RXTE, and the position as determined with XMM-Newton. We start in Sect. 2 with an overview of all observations and the technical details of the analysis. This is necessarily a long overview because most observations are complicated due to source confusion. We continue with discussions of the 1-200 keV spectrum (Sect. 3), the 3-20 keV spectral variability (Sect. 4), the light curve (Sect. 5), the 3-20 keV rapid variability (Sect. 6), and the archival search for an optical counterpart (Sect. 7). In Sect. 8 we discuss the implications of the measurements for our understanding of this object. Finally, we summarize our conclusions in Sect. 9.

 

 

Table 1: Log of X-ray observations on SAX J1711.6-3808.

Day in 2001$^\dag$ (UT)	Instrument$^\ddag$	ObsID
36.557- 39.658	WFC	OP10695,10696,10697
39.685- 42.000	WFC	OP10703,10704
45.634- 47.518	WFC	OP10733,10734
45.704- 45.713	PCA (3)	50138-01-01
47.68 - 48.57	NFI	21286001
47.729- 47.769	PCA (3)	50138-01-02
50.845- 50.884	PCA (2)	50138-01-03
56.836- 56.856	PCA (4)	50138-01-04
61.93 - 62.09	XMM$^\P$	0135520401
62.460- 62.497	PCA (3)	50138-01-05
68.836- 68.862	PCA (3)	50138-01-06
75.759- 76.637	WFC	OP10898
77.247- 77.264	PCA (4)	60407-01-01
80.196- 80.876	WFC	OP10927
86.007- 86.023	PCA (2)	60407-01-02
92.770- 92.798	PCA (2)	60407-01-03
93.482- 94.438	WFC	OP11033
99.651- 99.719	PCA (3 and 2)	60407-01-04
107.673-107.712	PCA (3)	60407-01-05
112.797-113.586	WFC$^\ast$	OP11170
114.049-114.079	PCA (3)	60407-01-06
121.745-121.770	PCA (2)	60407-01-07
126.974-127.002	PCA (2)	60407-01-08
133.923-133.950	PCA (2)	60407-01-09
149.635-149.665	PCA (3)	60407-01-10
168.441-168.482	PCA (2)$^\ast$	60407-01-11
184.759-184.773	PCA (3)$^\ast$	60407-01-12
313.573-313.592	PCA (2)$^\ast$	60407-01-13

$^\dag$ Jan. 1, 2001, is MJD 51910.
$^\ddag$ For the PCA, the number of active PCUs outside PCU0 is given between parentheses (for day 99 this number changed within the observation).
$^\P$ The spectral XMM-Newton data will be dealt with in a separate paper, the XMM-determined position is discussed in Sect. 7.
$^\ast$ SAX J1711.6-3808 was not detected in this observation.