1 INTRODUCTION
2 SAMPLE SELECTION AND DATA PREPARATION
3 X-RAY EMISSION FROM THE CLUSTER CENTER
3.1 Detection of central X-ray sources
3.2 Spectral analysis
3.3 Upper limit of non-detected GCs
3.4 Nature of the central X-ray sources
4 HYDRODYNAMIC SIMULATION OF IMBH ACCRETION
4.1 The physical picture
4.2 Simulation setup
4.3 Results
5 DISCUSSION
6 SUMMARY