REVEALING THE NATURE OF NEW UNIDENTIFIED INTEGRAL SOURCES.

Since its launch on October 2002, the INTEGRAL satellite has revolutionized our knowledge of the hard X–ray sky thanks to its unprecedented imaging capabilities and source detection positional accuracy above 20 keV. Nevertheless, many of the newly-detected sources in the INTEGRAL sky surveys are of unknown nature. However, the combined use of available information at longer wavelengths (mainly soft X–rays and radio) and of optical spectroscopy on the putative counterparts of these new hard X–ray objects allows pinpointing their exact nature. Continuing our long-standing program running since 2004 (and with which we identified more than 100 INTEGRAL objects) here we report the classification, through optical spectroscopy, of 25 unidentified high-energy sources, mostly belonging to the recently published 4-th IBIS survey. [ABSTRACT FROM AUTHOR]