Revealing the nature of unidentified INTEGRAL sources through optical spectroscopy: an overview

TL;DR

This paper reviews the efforts to identify unknown INTEGRAL hard X-ray sources using optical spectroscopy, significantly reducing the unidentified sources and enabling statistical analysis of their nature.

Contribution

It presents a comprehensive overview of the identification process of INTEGRAL sources and reports on new preliminary results from the 4th IBIS catalog.

Findings

Over 100 sources identified since 2004

Reduced the percentage of unidentified sources

Provided statistical insights into source populations

Abstract

Thanks to the INTEGRAL satellite the way of looking at the hard X-ray sky above 20 keV has changed substantially. Through the unique imaging and spectroscopy capabilities of the IBIS instrument that has formed the basis of the INTEGRAL surveys, this satellite has improved the knowledge on hard X-ray sources in terms of sensitivity and positional accuracy. Many of the sources belonging to these surveys are however of unidentified nature, but the combined use of available information at longer wavelengths (mainly soft X-rays and radio) and above all optical spectroscopy on the putative counterparts of these hard X-ray objects can reveal their exact nature. Since 2004 our group identified more than 100 it INTEGRAL sources, reducing drastically the percentage of unidentified objects in the various IBIS surveys and allowing statistical studies on them. Here we present a summary of this identification work and an outlook of our preliminary results on identification of newly-discovered sources belonging to the 4th IBIS catalog.