The Orbit of IGR J16493-4348: An Eclipsing Supergiant High-Mass X-Ray Binary Pulsar
Abstract
IGR J16493-4348 is a wind-accreting supergiant high-mass X-ray binary (sgHMXB), where the neutron star is eclipsed by its stellar companion every 6.78 days. It is one of only five wind-fed sgHMXBs in which superorbital modulation has been definitely observed. We present an analysis of the system’s X-ray variability and periodic modulation using pointed observations (2.5-25 keV) and Galactic bulge scans (2-10 keV) from the Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA), along with Swift Burst Alert Telescope (BAT) 70-month snapshot (14-195 keV) and transient monitor (15-50 keV) observations. The orbital eclipse profiles from the PCA scan and BAT light curves are modeled using asymmetric and symmetric step and ramp functions. We obtain an improved orbital period measurement of 6.7828 ± 0.0004 days from an observed minus calculated (O-C) analysis of mid-eclipse times derived from the BAT transient monitor and PCA scan data. No evidence is found for the presence of a strong photoionization or accretion wake. We refine the superorbital period to 20.067 ± 0.009 days from the discrete Fourier transform (DFT) of the BAT transient monitor light curve. A pulse period of 1093.1036 ± 0.0004 s is measured from a pulsar timing analysis using pointed PCA observations spanning ~1.4 binary orbits. We present pulse times of arrivals (ToAs), circular and eccentric timing models, and calculations of the system’s Keplerian binary orbital parameters. We derive an X-ray mass function of fx(M) = 13.2+2.4-2.5 M⊙ and find a spectral type of B0.5 Ia for the supergiant companion through constraints on the mass and radius of the donor. We will also discuss additional parameters describing the system geometry, including the eclipse half-angle and binary inclination angle.
- Publication:
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AAS/High Energy Astrophysics Division
- Pub Date:
- March 2019
- Bibcode:
- 2019HEAD...1712104P