Volume 613, May 2018
|Number of page(s)||13|
|Published online||25 May 2018|
IGR J17329-2731: The birth of a symbiotic X-ray binary
Department of Astronomy, Université de Genèva,
Chemin d’Ecogia 16,
2 Department of Physics and Astronomy, Michigan State University, East Lansing, MI, USA
3 Dipartimento di Fisica, Universitá degli Studi di Cagliari, SP Monserrato-Sestu km 0.7, 09042 Monserrato, Italy
4 Faulkes Telescope Project, School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA, UK
5 Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
6 New York University Abu Dhabi, PO Box 129188, Abu Dhabi, UAE
7 Dipartimento di Fisica e Chimica, Universitá di Palermo, via Archirafi 36, 90123 Palermo, Italy
9 INAF - Osservatorio Astronomico di Roma, via Frascati 33, 00078 Monteporzio Catone (RM), Italy
10 Department of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK
10 INAF - Osservatorio Astronomico di Brera, via Emilio Bianchi 46, 23807 Merate (LC), Italy
Accepted: 15 February 2018
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 (≫1023 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.
Key words: X-rays: binaries / X-rays: individuals: IGR J17329-2731
© ESO 2018
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