The Be/neutron star system Swift J004929.5-733107 in the Small Magellanic Cloud-X-ray characteristics and optical counterpart candidates

M. J. Coe, J. A. Kennea, P. A. Evans, L. J. Townsend, A. Udalski, I. M. Monageng, D. A.H. Buckley

Research output: Contribution to journalArticlepeer-review

Abstract

Swift J004929.5-733107 is an X-ray source in the Small Magellanic Cloud (SMC) that has been reported several times, but the optical counterpart has been unclear due to source confusion in a crowded region of the SMC. Previous works proposed [MA93] 302 as the counterpart, however we show here, using data obtained from the S-CUBED project, that the X-ray position is inconsistent with that object. Instead we propose a previously unclassified object which has all the indications of being a newly identified Be star exhibiting strong H α emission. Evidence for the presence of significant I-band variability strongly suggest that this is, in fact, a Be type star with a large circumstellar disc. Over 18 yr worth of optical monitoring by the OGLE project reveal a periodic modulation at a period of 413 d, probably the binary period of the system. A SALT optical spectrum shows strong Balmer emission and supports a proposed spectral classification of B1-3 III-IVe. The X-ray data obtained from the S-CUBED project reveal a time-averaged spectrum well fitted by a photon index Γ = 0.93 ± 0.16. Assuming the known distance to the SMC, the flux corresponds to a luminosity ∼1035 erg s-1. All of these observational facts suggest that this is confirmed as a Be star-neutron star X-ray binary (BeXRB) in the SMC, albeit one with an unusually long binary period at the limits of the Corbet Diagram.

Original languageEnglish (US)
Pages (from-to)1398-1406
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Volume504
Issue number1
DOIs
StatePublished - Jun 1 2021

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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