Swift J174540.7-290015: A new accreting binary in the Galactic centre

G. Ponti, C. Jin, B. De Marco, N. Rea, A. Rau, F. Haberl, F. Coti Zelati, E. Bozzo, C. Ferrigno, G. C. Bower, P. Demorest

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    © 2016 The Authors. We report on the identification of the new Galactic Centre (GC) transient Swift J174540.7-290015 as a likely low-mass X-ray binary located at only 16 arcsec from Sgr A*. This transient was detected on 2016 February 6, during the Swift GC monitoring, and it showed long-term spectral variations compatible with a hard- to soft-state transition. We observed the field with XMM-Newton on February 26 for 35 ks, detecting the source in the soft state, characterized by a low level of variability and a soft X-ray thermal spectrum with a high energy tail (detected by INTEGRAL up to ~50 keV), typical of either accreting neutron stars or black holes. We observed: (i) a high column density of neutral absorbing material, suggesting that Swift J174540.7-290015 is located near or beyond the GC and; (ii) a sub-Solar iron abundance, therefore we argue that iron is depleted into dust grains. The lack of detection of Fe K absorption lines, eclipses or dipping suggests that the accretion disc is observed at a low inclination angle. Radio (Very Large Array) observations did not detect any radio counterpart to Swift J174540.7-290015. No evidence for X-ray or radio periodicity is found. The location of the transient was observed also in the near-infrared (near-IR) with gamma-ray burst optical near-IR detector at MPG/European Southern Observatory La Silla 2.2 m telescope and VLT/NaCo pre- and post-outburst. Within the Chandra error region, we find multiple objects that display no significant variations.
    Original languageEnglish
    JournalMonthly Notices of the Royal Astronomical Society
    Issue number3
    Publication statusPublished - 21 Sep 2016


    • Methods: observational
    • Techniques: spectroscopic
    • X-rays: binaries


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