State transitions of GX 339-4 during its outburst rising phase

Abstract

We investigate systematically four outbursts of black hole system GX 339-4 observed by the Rossi X-ray Timing Explorer (RXTE) in both spectral and timing domains and find that these outbursts have some common properties although they experience different 'q' tracks in the hardness-intensity diagram (HID). While the spectral indices are around 1.5 in low hard state (LHS), 2.4 in soft intermediate state (SIMS) and high soft state (HSS), the spectral parameters of thermal, non-thermal and reflection components vary significantly in transitions from LHS to HIMS. Also the quasi periodic oscillation (QPO) shows a peculiar behavior during the state transition between LHS and HIMS: the RMS drop of type C fundamental QPO is accompanied with showing-up of the second harmonic. Interestingly, the QPO RMS is found to have a similar linear relationship with the non-thermal fraction of emission in different outbursts. These findings provide more clues to our understanding the outburst of the black hole X-ray binary system.