IGR J17329-2731: The birth of a symbiotic X-ray binary

E. Bozzo, A. Bahramian, C. Ferrigno, A. Sanna, J. Strader, F. Lewis, D. M. Russell, T. Di Salvo, L. Burderi, A. Riggio, A. Papitto, P. Gandhi, P. Romano

Research output: Contribution to journalArticlepeer-review


We report on the results of the multiwavelength campaign carried out after the discovery of the INTEGRAL transient IGR J17329-2731. The optical data collected with the SOAR telescope allowed us to identify the donor star in this system as a late M giant at a distance of 2.7-1.2+3.4 kpc. The data collected quasi-simultaneously with XMM-Newton and NuSTAR showed the presence of a modulation with a period of 6680 ± 3 s in the X-ray light curves of the source. This unveils that the compact object hosted in this system is a slowly rotating neutron star. The broadband X-ray spectrum showed the presence of a strong absorption (â1023 cm-2) and prominent emission lines at 6.4 keV, and 7.1 keV. These features are usually found in wind-fed systems, in which the emission lines result from the fluorescence of the X-rays from the accreting compact object on the surrounding stellar wind. The presence of a strong absorption line around ~21 keV in the spectrum suggests a cyclotron origin, thus allowing us to estimate the neutron star magnetic field as ~2.4 × 1012 G. All evidencethus suggests IGR J17329-2731 is a symbiotic X-ray binary. As no X-ray emission was ever observed from the location of IGR J17329-2731 by INTEGRAL (or other X-ray facilities) during the past 15 yr in orbit and considering that symbiotic X-ray binaries are known to be variable but persistent X-ray sources, we concluded that INTEGRAL caught the first detectable X-ray emission from IGR J17329-2731 when the source shined as a symbiotic X-ray binary. The Swift XRT monitoring performed up to ~3 months after the discovery of the source, showed that it maintained a relatively stable X-ray flux and spectral properties.

Original languageEnglish (US)
Article numberA22
JournalAstronomy and Astrophysics
StatePublished - May 1 2018


  • X-rays: binaries
  • X-rays: individuals: IGR J17329-2731

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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