Morphology and Evolution of the 20 Day Superorbital Modulation in the High-Mass X-ray Binary IGR J16493-4348
Abstract
We report on Nuclear Spectroscopic Telescope Array (NuSTAR), Swift X-ray Telescope (XRT) and Swift Burst Alert Telescope (BAT) observations of IGR J16493-4348, a wind-fed Supergiant X-ray Binary (SGXB) showing significant superorbital variability. From a discrete Fourier transform of the BAT light curve, we refine its superorbital period to be 20.058 ± 0.07 days. The BAT dynamic power spectrum and a fractional root mean square analysis both show strong variations in the amplitude of the superorbital modulation, but no observed changes in the period were found. The superorbital modulation is significantly weaker between MJD 55,700 and MJD 56,300. The joint NuSTAR and XRT observations, which coincide near the minimum and maximum of the superorbital modulation, reveal no significant changes in the ∼1093 s neutron star rotation period on superorbital timescales. We do not observe any significant changes in the pulse profiles in the 3-50 keV band and the 3-40 keV spectral continuum between superorbital minimum and maximum, suggesting a similar accretion regime. At superorbital maximum, we find a possible Fe K_ emission feature at 6.4 keV. The 6.4 keV emission feature is not significant at superorbital minimum. The spectral continuum shows no significant changes as a function of neutron star rotation period. We discuss different mechanisms that might drive the observed superorbital modulation.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E.682C