DATA REDUCTION  
2.1. Flaring episodes  
2.2. Data, exposure, and background mosaics  

SIMULATIONS  
3.1. Initial setup  
3.2. Reliability, completeness, and sensitivity  

SOURCE DETECTION  
4.1. Catalog creation  

MATCH WITH XMM - Newton AND Chandra CATALOGS  
5.1. XMM - Newton  
5.2. Chandra  
5.3. Optical counterparts  

OBSCURATION PROPERTIES OF THE NUSTAR UDS97 SAMPLE  
6.1. Extraction of X-ray spectra  
6.2. Broadband spectral fitting  
6.3. Adding the Hardness Ratio information  
6.4. The observed CT fraction  

DISCUSSION ON THE CT FRACTION  

CONCLUSIONS