Correlated X-ray timing and spectral behavior of GX 349+2: RXTE PCA data

Abstract

We present a detailed and systematic investigation of correlated spectral and timing properties of the Z source GX 349+2, using a huge amount (about 40 ks) of good quality data from September 29, 1998 to October 13, 1998, obtained with the Proportional-Counter-Array on-board RXTE satellite. We, for the first time, give a detailed comparison between the normal-branch-properties and the flaring-branch-properties of this source, as it shows an extended normal branch (which is a rare phenomenon for it) for our case. In our work, the properties of the peaked noise are analyzed as functions of the position on the Z-track (in color-color-diagram), and they are discussed in connection with the peaked noise seen for another Z source Cyg X-2 (at low overall intensities). This will help to construct theoretical models for the peaked noise, as well as to understand the physics behind the Z-shaped tracks traced by these kind of sources in color-color-diagram. We also find a QPO (centroid frequency is about 3.8 Hz) at the upper part of the flaring branch. This is for the first time, a QPO is seen from this source and hence is very important in understanding the nature of its X-ray emitting components.