A Suzaku view of IGR J16393-4643

Abstract

The pulsar IGR J16393-4643 belongs to a class of highly absorbed supergiant high-mass X-ray binaries (HMXBs), characterized by a very high column density of absorbing matter. We present the results of simultaneous broad-band pulsation and spectrum analysis from a 44- ks Suzaku observation of the source. The orbital intensity profile created with the Swift Burst Alert Telescope (Swift-BAT) light curve shows an indication of IGR J16393-4643 being an eclipsing system with a short eclipse semi-angle θE ~17°. For a supergiant companion star with a 20-R⊙ radius, this implies an inclination of the orbital plane in the range 39°-57°, whereas for a main-sequence B star as the companion with a 10-R⊙ radius, the inclination of the orbital plane is in the range 60°-77°. Pulse profiles created for different energy bands have complex morphology, which shows some energy dependence and increases in pulse fraction with energy. We have also investigated broad-band spectral characteristics, phase-averaged spectra and resolving the pulse phase into peak and trough phases. The phase-averaged spectrum has a very high NH(~ 3 × 1023 cm-2) and is described by a power law (τ ~ 0.9) with a high-energy cut-off above 20 keV. We find a change in the spectral index in the peak and trough phases, implying an underlying change in the source spectrum.