Orbital Period Determinations for Four SMC Be/X-ray Binaries
Abstract
We present an optical and X-ray study of four Be/X-ray binaries located in the Small Magellanic Cloud (SMC). OGLE I-band data of up to 11 years of semi-continuous monitoring has been analysed for SMC X-2, SXP172 and SXP202B, providing both a measurement of the orbital period (Porb = 18.62, 68.90, and 229.9 days for the pulsars respectively) and a detailed optical orbital profile for each pulsar. For SXP172 this has allowed a direct comparison of the optical and X-ray emission seen through regular RXTE monitoring, revealing that the X-ray outbursts precede the optical by around 7 days. Recent X-ray studies by XMM-Newton have identified a new source in the vicinity of SXP15.3 raising doubt on the identification of the optical counterpart to this X-ray pulsar. Here we present a discussion of the observations that led to the proposal of the original counterpart and a detailed optical analysis of the counterpart to the new X-ray source, identifying a 21.7 d periodicity in the OGLE I-band data. The optical characteristics of this star are consistent with that of a SMC Be/X-ray binary. However, this star was rejected as the counterpart to SXP15.3 in previous studies due to the lack of H{\alpha} emission.
Keywords
Cite
@article{arxiv.1010.5621,
title = {Orbital Period Determinations for Four SMC Be/X-ray Binaries},
author = {M. P. E. Schurch and M. J. Coe and V. A. McBride and L. J. Townsend and A. Udalski and F. Haberl and R. H. D. Corbet},
journal= {arXiv preprint arXiv:1010.5621},
year = {2015}
}
Comments
Accepted for publication in MNRAS, 11 pages, 17 figures