Chandra observations of the bursting X-ray transient SAX J1747.0-2853 during low-level accretion activity

Abstract

We present Chandra/ACIS observations of the bursting X-ray transient SAX J1747.0-2853 performed on 18 July 2001. We detected a bright source at the position of R.A = 17^h 47^m 02.60^s and Dec. = -28 52' 58.9'' (J2000.0; with a 1 sigma error of ~0.7 arcseconds), consistent with the BeppoSAX and ASCA positions of SAX J1747.0-2853 and with the Ariel V position of the transient GX +0.2,-0.2, which was active during the 1970's. The 0.5-10 keV luminosity of the source during our observations was ~3 x 10^{35} erg/s (assuming a distance of 9 kpc) demonstrating that the source was in a low-level accretion state. We also report on the long-term light curve of the source as observed with the all sky monitor aboard the Rossi X-ray Timing Explorer. After the initial 1998 outburst, two more outbursts (in 2000 and 2001) were detected with peak luminosities about two orders of magnitude larger than our Chandra luminosity. Our Chandra observation falls in-between those two outbursts, making the outburst history for SAX J1747.0-2853 complex. Those bright 2000 and 2001 outbursts combined with the likely extended period of low level activity in-between those outbursts strongly suggest that the classification of SAX J1747.0-2853 as a faint X-ray transient was premature. It might be possible that the other faint X-ray transients also can exhibit bright, extended outbursts which would eliminate the need for a separate sub-class of X-ray transients. We discuss our results also in the context of the behavior of X-ray binaries accreting at low levels with luminosities around 10^{35} erg/s, a poorly studied accretion rate regime.