Unveiling the nature of INTEGRAL objects through optical spectroscopy. VIII. Identification of 44 newly detected hard X-ray sources

TL;DR

This study used optical spectroscopy to identify and characterize 44 hard X-ray sources detected by INTEGRAL, revealing a diverse population mainly composed of active galactic nuclei, with insights into their physical parameters and the survey's sensitivity.

Contribution

The paper presents the identification and detailed characterization of 44 INTEGRAL sources, expanding the catalog of known hard X-ray emitters with optical spectroscopy and multiwavelength data.

Findings

Active galactic nuclei are the most common hard X-ray sources.

Recent INTEGRAL surveys can detect sources like LINER AGNs and non-magnetic CVs.

Physical parameters of sources were determined using multiwavelength data.

Abstract

(abridged) Hard X-ray surveys performed by the INTEGRAL satellite have discovered a conspicuous fraction (up to 30%) of unidentified objects among the detected sources. Here we continue our identification program by selecting probable optical candidates using positional cross-correlation with soft X-ray, radio, and/or optical archives, and performing optical spectroscopy on them. As a result, we identified or more accurately characterized 44 counterparts of INTEGRAL sources: 32 active galactic nuclei, with redshift 0.019 < z < 0.6058, 6 cataclysmic variables (CVs), 5 high-mass X-ray binaries (2 of which in the Small Magellanic Cloud), and 1 low-mass X-ray binary. This was achieved by using 7 telescopes of various sizes and archival data from two online spectroscopic surveys. The main physical parameters of these hard X-ray sources were also determined using the available multiwavelength information. AGNs are the most abundant population among hard X-ray objects, and our results confirm this tendency when optical spectroscopy is used as an identification tool. The deeper sensitivity of recent INTEGRAL surveys enables one to begin detecting hard X-ray emission above 20 keV from sources such as LINER-type AGNs and non-magnetic CVs.