Spectral evolution of LMXB GX 349+2

Abstract

Z sources are the brightest low-mass X-ray binaries (LMXB) believed to contain magnetized neutron stars. They trace a '2' shaped track in theil X-ray colour-colour diagram. It is thought that the accretion rate increases systematically along this track. According to 'unified model' proposed to explain combined spectral and timing properties of this class of sources, the systematic variation with accretion rate of spectral parameters such as the optical depth and the comptonizution parameter can explain the '2' shaped track. We have made detailed spectral and timing analysis of the 2 source OX 349+2 using RXTE archival data of the period 29 September to 13 October 1998 to investigate the spectral variations along the 2 track. We discuss the results in this paper.