XTE J1701-462 AND ITS IMPLICATIONS FOR THE NATURE OF SUBCLASSES IN LOW-MAGNETIC-FIELD NEUTRON STAR LOW-MASS X-RAY BINARIES
- MIT Kavli Institute for Astrophysics and Space Research, 70 Vassar Street, Cambridge, MA 02139 (United States)
- Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Science Park 904, 1098 XH, Amsterdam (Netherlands)
- Kapteyn Astronomical Institute, Groningen University, 9700 AV, Groningen (Netherlands)
- Centre d'Etude Spatiale des Rayonnements, UMR 5187, 9 Av. du Colonel Roche, BP 44346, 31028 Toulouse Cedex 4 (France)
- School of Physics and Astronomy, University of Southampton, Southampton, Hampshire, SO17 1BJ (United Kingdom)
We report on an analysis of Rossi X-Ray Timing Explorer data of the transient neutron star low-mass X-ray binary (NS-LMXB) XTE J1701-462, obtained during its 2006-2007 outburst. The X-ray properties of the source changed between those of various types of NS-LMXB subclasses. At high luminosities, the source switched between two types of Z source behavior and at low luminosities we observed a transition from Z source to atoll source behavior. These transitions between subclasses primarily manifest themselves as changes in the shapes of the tracks in X-ray color-color (CD) and hardness-intensity diagrams (HID), but they are accompanied by changes in the kHz quasi-periodic oscillations, broadband variability, burst behavior, and/or X-ray spectra. We find that for most of the outburst the low-energy X-ray flux is a good parameter to track the gradual evolution of the tracks in CD and HID, allowing us to resolve the evolution of the source in greater detail than before and relate the observed properties to other NS-LMXBs. We further find that during the transition from Z to atoll, characteristic behavior known as the atoll upper banana can equivalently be described as the final stage of a weakening Z source flaring branch, thereby blurring the line between the two subclasses. Our findings strongly suggest that the wide variety in behavior observed in NS-LXMBs with different luminosities can be linked through changes in a single variable parameter, namely the mass accretion rate, without the need for additional differences in the neutron star parameters or viewing angle. We briefly discuss the implications of our findings for the spectral changes observed in NS-LMXBs and suggest that, contrary to what is often assumed, the position along the color-color tracks of Z sources is not determined by the instantaneous mass accretion rate.
- OSTI ID:
- 21455022
- Journal Information:
- Astrophysical Journal, Vol. 719, Issue 1; Other Information: DOI: 10.1088/0004-637X/719/1/201; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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