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

NICOLA MASETTI, P. Parisi, E. Jiménez-Bailón, E. Palazzi, V. Chavushyan, L. Bassani, A. Bazzano, A. J. Bird, A. J. Dean, G. Galaz, R. Landi, A. Malizia, D. Minniti, L. Morelli, F. Schiavone, J. B. Stephen, P. Ubertini

Research output: Contribution to journalArticlepeer-review

41 Citations (Scopus)


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-rys 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 together with data from an online spectroscopic survey, here 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, the large majority (14) is made up of type 1 AGNs (i.e. with broad emission lines); of these, 6 lie at redshift larger than 0.5 and one (IGR J12319-0749) 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 (that is, with narrow emission lines only), and one of the two cases is confirmed as 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, possibly of RS CVn type. The main physical parameters of these hard X-ray sources were also determined using the multiwavelength information available in the literature. 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.

Original languageEnglish
Article numberA123
JournalAstronomy and Astrophysics
Publication statusPublished - 2012


  • X-rays: binaries
  • X-rays: general
  • galaxies:Seyfert
  • novae, cataclysmic variables
  • quasars: emission lines
  • stars: flare

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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