Unveiling the nature of INTEGRAL objects through optical spectroscopy. X. A new multi-year, multi-observatory campaign

TL;DR

This study uses optical spectroscopy from multiple observatories to identify and classify 33 high-energy X-ray sources from the INTEGRAL catalog, revealing their nature as AGNs, X-ray binaries, and other objects.

Contribution

It provides a comprehensive multi-year, multi-observatory optical spectroscopic campaign that classifies the nature of INTEGRAL sources, expanding the understanding of their physical properties.

Findings

Majority (23/33) are active galactic nuclei (AGNs).

10 sources are local universe objects, including Galactic binaries and a flare star.

Six AGNs are at high redshift (z > 0.5).

Abstract

Within the framework of our program (running since 2004) of identification of hard X-ray INTEGRAL sources through optical spectroscopy, we present the results concerning the nature of 33 high-energy objects. The data were acquired with the use of six telescopes of different sizes and from one on-line archive. The results indicate that the majority of these objects (23 out of 33) are active galactic nuclei (AGNs), whereas 10 are sources in the local Universe with eight of which in the Galaxy and two in the Small Magellanic Cloud (SMC). Among the identified AGNs, 13 are of Type 1 (i.e., with broad emission lines), eight are of Type 2 (with narrow emissions only), and two are X-ray bright, optically normal galaxies with no apparent nuclear activity in the optical. Six of these AGNs lie at high redshift (z > 0.5). Concerning local objects, we found that five of them are Galactic cataclysmic variables, three are high-mass X-ray binaries (two of which lying in the SMC), one is a low-mass X-ray binary, and one is classified as a flare star that is likely of RS CVn type. The main optical properties and inferred physical characteristics of these sources are presented and discussed.