The Swift Bulge Survey: Optical and near-IR follow-up featuring a likely symbiotic X-ray binary and a focused wind CV

A. W. Shaw, C. O. Heinke, T. J. MacCarone, G. R. Sivakoff, J. Strader, A. Bahramian, N. Degenaar, J. A. Kennea, E. Kuulkers, A. Rau, L. E. Rivera Sandoval, L. Shishkovsky, S. J. Swihart, A. J. Tetarenko, R. Wijnands, J. J.M. In 'T Zand

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4 Scopus citations

Abstract

The nature of very faint X-ray transients (VFXTs) - transient X-ray sources that peak at luminositiesLX ≤ 1036 erg s-1 - is poorly understood. The faint and often short-lived outbursts make characterizing VFXTs and their multiwavelength counterparts difficult. In 2017 April we initiated the Swift Bulge Survey, a shallow X-ray survey of ∼16 square degrees around the Galactic centre with the Neil Gehrels Swift Observatory. The survey has been designed to detect new and known VFXTs, with follow-up programmes arranged to study their multiwavelength counterparts. Here we detail the optical and near-infrared follow-up of four sources detected in the first year of the Swift Bulge Survey. The known neutron star binary IGR J17445-2747 has a K4III donor, indicating a potential symbiotic X-ray binary nature and the first such source to show X-ray bursts. We also find one nearby M-dwarf (1SXPS J174215.0-291453) and one system without a clear near-IR counterpart (Swift J175233.9-290952). Finally, 3XMM J174417.2-293944 has a subgiant donor, an 8.7 d orbital period, and a likely white dwarf accretor;we argue that this is the first detection of a white dwarf accreting from a gravitationally focused wind. A key finding of our follow-up campaign is that binaries containing (sub)giant stars may make a substantial contribution to the VFXT population.

Original languageEnglish
Pages (from-to)4344-4360
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
DOIs
StatePublished - Mar 1 2020

Keywords

  • Binaries: Symbiotic
  • Infrared: Stars
  • Novae, cataclysmic variables
  • Stars: neutron
  • Surveys
  • X-rays: Binaries

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