Mini-outburst of black hole X-ray binary GX 339-4 in 2004

The mini-outburst of black hole X-ray binaries (BHXBs) is a re-bright event of light curve, which is often detected in BHXBs with the low orbital period, such as XTE J1650-500 ($P_{\mathrm{orb}}\approx 7.69\pm 0.02\mathrm{hr}$), GRO J0422+32 ($P_{\mathrm{orb}}\approx 5.091850\pm 0.000005\mathrm{hr}$) and Swift J1753.5-0127 ($P_{\mathrm{orb}}\approx 3.244\pm 0.001\mathrm{hr}$). Because of its low X-ray luminosity, the physics properties of mini-outburst is still unclear. GX 339-4 is a famous BHXBs with the orbital period $P_{\mathrm{orb}}=16.9\mathrm{hr}$ and present many normal outburst and failed outburst over the past decades. However, the mini-outburst is not still detected in GX 339-4. In this work, using the Rossi X-ray Timing Explorer (RXTE) observations, we investigated the energy spectrum properties of the GX 339-4 outburst in 2004 and confirmed that the outburst in 2004 is a mini-outburst. It is very interest that the mini-outburst has been through a whole state transition from Low/Hard state to High/Soft state. We also give a comparison between the normal outburst in 2002 and the mini-outburst in 2004. And we find that the two outburst present a similar Hardness-Intensity diagram and spectral properties, which suggest that the normal outburst and mini-outburst have a similar physics. We think that the mini-outburst of GX 339-4 in 2004 can be well explained by the disk instability model.