The X-ray fast-time variability of Sco X-2 (GX 349+2) with RXTE
Abstract
Sco X-2 (GX 349+2) is a low-mass X-ray binary and Z source. We have analysed ~156 ks of Rossi X-ray Timing Explorer data, obtained in 1998 January, on this source. We investigated the fast-time variability as a function of position on the Z track. During these observations, Sco X-2 traced out the most extensive Z track ever reported from this object, making this the most comprehensive study thus far. We found the broad peaked flaring branch noise that is typical of Sco X-2, with a centroid frequency in the range 3.3-5.8 Hz. We also discovered low-frequency noise, and a new peaked noise feature, with centroid frequencies in the range 5.4-7.6 and 11-54 Hz, respectively. We discuss the phenomenology of these features, their relationship with the power spectral components found in other low-mass X-ray binaries, and the implications for current models. In particular, the low-frequency noise we observed was strongest at intermediate energies, in contrast to the low-frequency noise seen in other Z sources. We also detected very low-frequency noise, and have calculated complex cross-spectra between intensity and hardness. We found that the very low-frequency noise is not entirely a result of motion along the Z track.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 2002
- DOI:
- 10.1046/j.1365-8711.2002.05729.x
- arXiv:
- arXiv:astro-ph/0204362
- Bibcode:
- 2002MNRAS.336..217O
- Keywords:
-
- accretion;
- accretion discs;
- binaries: close;
- stars: individual: Sco X-2;
- stars: individual: GX 349+2;
- stars: neutron;
- X-rays: stars;
- Astrophysics
- E-Print:
- 17 pages, 9 figures, minor improvements, accepted for publication in MNRAS