XTE J0111.2−7317: a nebula-embedded X-ray binary in the Small Magellanic Cloud

The observed characteristics of the nebulosity surrounding the Small Magellanic Cloud (SMC) high-mass X-ray binary XTE J0111.2−7317 are examined in the context of three possible nebular types: supernova remnant, bowshock and H ii region. Observational evidence is presented which appears to support the interpretation that the nebulosity surrounding XTE J0111.2–7317 is an H ii region. The source therefore appears to be a normal SMC Be X-ray binary (BeXRB) embedded in a locally enhanced interstellar medium which it has photoionized to create an H ii region. This is supported by observations of the X-ray outburst seen with the Burst and Transient Source Experiment (BATSE) and Rossi X-ray Timing Explorer (RXTE) in 1998–1999. It exhibited characteristics typical of a giant or type II outburst in a BeXRB including large spin-up rates, L_X≥ 10³⁸ erg cm⁻² s⁻¹, and a correlation between spin-up rate and pulsed flux. However, the temporal profile of the outburst was unusual, consisting of two similar intensity peaks, with the first peak of shorter duration than the second.