The Orbital Period of Swift J1626.6-5156

TL;DR

This paper reports the discovery of the orbital period of Swift J1626.6-5156, a Be/X-ray binary, using X-ray data spanning 700 days, revealing a nearly circular orbit of 132.9 days.

Contribution

The study precisely determines the orbital period and eccentricity of Swift J1626.6-5156, providing detailed orbital parameters for this Be/X-ray binary system.

Findings

Orbital period of 132.9 days identified.

Orbit is nearly circular with eccentricity 0.08.

X-ray modulation timescales vary over observation period.

Abstract

We present the discovery of the orbital period of Swift J1626.6-5156. Since its discovery in 2005, the source has been monitored with Rossi X-ray Timing Explorer, especially during the early stage of the outburst and into the X-ray modulating episode. Using a data span of $\sim$700 days, we obtain the orbital period of the system as 132.9 days. We find that the orbit is close to a circular shape with an eccentricity 0.08, that is one of the smallest among Be/X-ray binary systems. Moreover, we find that the timescale of the X-ray modulations varied, which led to earlier suggestions of orbital periods at about a third and half of the orbital period of Swift J1626.6-5156.