Unveiling the nature of INTEGRAL objects through optical spectroscopy. IX. 22 more identifications, and a glance into the far hard X-ray Universe

Abstract

(Abridged) Since its launch in 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. 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 us to pinpoint their exact nature. Continuing our long-standing program that has been running since 2004, and using 6 different telescopes of various sizes, we report the classification through optical spectroscopy of 22 more unidentified or poorly studied high-energy sources detected with the IBIS instrument onboard INTEGRAL. We found that 16 of them are active galactic nuclei (AGNs), while the remaining 6 objects are within our Galaxy. Among the identified extragalactic sources, 14 are Type 1 AGNs; of these, 6 lie at redshift larger than 0.5 and one has z = 3.12, which makes it the second farthest object detected in the INTEGRAL surveys up to now. The remaining AGNs are of type 2, and one of them is a pair of interacting Seyfert 2 galaxies. The Galactic objects are identified as two cataclysmic variables, one high-mass X-ray binary, one symbiotic binary and two chromospherically active stars. We thus still find that AGNs are the most abundant population among hard X-ray objects identified through optical spectroscopy. Moreover, we note that the higher sensitivity of the more recent INTEGRAL surveys is now enabling the detection of high-redshift AGNs, thus allowing the exploration of the most distant hard X-ray emitting sources and possibly of the most extreme blazars.

18 pages, 9 figures, 8 tables, accepted for publication on Astronomy & Astrophysics, main journal

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Cited by in corpus (18)

• High-Mass X-ray Binaries in the Milky Way: A closer look with INTEGRAL
• INTEGRAL/IBIS nine-year Galactic Hard X-Ray Survey
• The INTEGRAL/IBIS AGN catalogue I: X-ray absorption properties versus optical classification
• Unveiling the nature of the unidentified gamma-ray sources II: radio, infrared and optical counterparts of the gamma-ray blazar candidates
• Unveiling the nature of the unidentified gamma-ray sources IV: the $\text{Swift}$ catalog of potential X-ray counterparts
• Hard X-ray Cataclysmic Variables
• Wind-accreting Symbiotic X-ray Binaries
• On the nature of the hard X-ray sources SWIFTJ1907.3-2050, IGRJ12123-5802 and IGRJ19552+0044
• The nature of fifty Palermo Swift-BAT hard X-ray objects through optical spectroscopy
• Optical identification of X-ray source 1RXS J180431.1-273932 as a magnetic cataclysmic variable
• Searching for gamma-ray blazar candidates among the unidentified INTEGRAL sources
• Swift J2218.4+1925: a new hard X-ray selected Polar observed with XMM-Newton
• Stellar population properties for a sample of hard X-ray AGNs
• Swift J0525.6+2416 and IGR J04571+4527: two new hard X-ray selected magnetic cataclysmic variables identified with XMM-Newton
• Hard - X-rays selected Active Galactic Nuclei. I. A radio view at high-frequencies
• Suzaku Observation of the Symbiotic X-Ray Binary IGR J16194-2810
• Identifying four $INTEGRAL$ sources in the Galactic Plane via VLT/optical and $XMM$-$Newton$/X-ray spectroscopy
• Investigating the Optical Counterpart Candidates of Four INTEGRAL Sources localized with Chandra