X-ray spectral evolution of low-mass X-ray binary GX 349+2

Abstract

We present the results of a systematic investigation of spectral evolution in the Z source GX 349+2, using data obtained during 1998 with Proportional-Counter-Array (PCA) on-board the RXTE satellite. The source traced a extended normal branch (NB) and flaring branch (FB) in the color-color diagram (CD) and hardness-intensity diagram (HID) during these observations. The spectra at different positions of Z-track were best fitted by a model consisting of a disk blackbody and a comptonized spectrum. A broad (gaussian) iron line at $\sim 6.7$ keV is also required to improve the fit. The spectral parameters showed a systematic and significant variation with the position along the Z-track. The evolution in spectral parameters is discussed in the view of increasing mass accretion rate scenario, proposed to explain the motion of Z sources in the CD and HID.

7 pages, 5 figures, 2 tables, accepted for the publication in the MNRAS

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