In a recent outburst which lasted for 260 days , the black hole candidate GRO J1655-40 exhibited a behaviour similar to its last outburst observed almost eight years ago .
We analyze a total of 150 observational spells in 122 days of data spreaded over the entire outburst phase of Feb. 2005 to Oct. 2005 .
From our study , a comprehensive understanding of the detailed behaviour of this black hole candidate has emerged .
Based on the degree of importance of the black body and the power-law components we divide the entire episode in four spectral states , namely , hard , soft , very soft and intermediate .
Quasi-Periodic oscillations ( QPOs ) were found in two out of these four states , namely , in the hard and the intermediate states .
In the hard state , at the rising phase of the outburst , QPO frequency ranged from 0.034 - 17.78 Hz and the spectra was fitted by a disk black body , power-law and iron emission line at 6.2 - 6.5 keV .
In the intermediate state , QPOs vary from 13.17 Hz to 19.04 Hz and the QPO frequency modulation in this state was not significant .
The spectra in this state are well fitted by the disk black body and the power-law components .
In the hard state of the declining phase of the outburst , we found QPOs of decreasing frequency from 13.14 Hz to 0.034 Hz .
The spectra of this state were fitted by a disk black body and power-law components , but in the initial few days a cooler Comptonized component was required for a better fit .
In the soft and very soft states , the spectral states are mostly dominated by the strong disk black body component .