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

TL;DR

This study systematically analyzes four outbursts of GX 339-4, revealing common spectral and timing properties and unique QPO behaviors during state transitions, enhancing understanding of black hole X-ray binary outbursts.

Contribution

It provides a comprehensive analysis of spectral and timing evolution in GX 339-4's outbursts, highlighting consistent patterns and peculiar QPO behaviors during state transitions.

Findings

Spectral indices are around 1.5 (LHS), 2.4 (SIMS and HSS).

QPO RMS drops and second harmonic appear during LHS-HIMS transition.

QPO RMS correlates linearly with non-thermal emission fraction.

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.