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We present the results obtained from a comprehensive timing and spectralstudy of two high-mass X-ray binary sources using NuSTAR observations. Thesetwo sources, IGR J16320-4751 and IGR J16479-4514, were discovered by INTEGRALand have been characterized for the first time in the hard X-ray band (beyond10~keV) in this work. In these sources, we observe the occurrence of intenseX-ray flares, with average luminosities exceeding 10$^{36}$~erg~s$^{-1}$. Ouranalysis reveals that these flares can be described consistently in thequasi-spherical accretion regime. The orbital phase of the first flare inNuSTAR observation of IGR J16479-4514 matches with the orbital phases ofprevious flares ($\phi=0.35$) in this source detected by other telescopes. Weconclude that this flare occurs as a result of the periastron passage of theneutron star, rather than due to the presence of a corotating interactionregion (CIR). Furthermore, from the energy-resolved pulse profile analysis ofIGR J16320-4751, we find that the pulse fraction is lower in hard X-rayscompared to soft X-rays. We present the hard X-ray spectral parameters of thesetwo sources using several standard spectral model components. We do not detecta cyclotron absorption feature in either target. We provide estimates of thesurface magnetic field strength of NS in IGR J16320-4751 using two indirectmethods. Lastly, we observe spectral hardening during flaring segments comparedto the off-flaring segments which indicates that comptonization is moreeffective during the flaring segments.

NuSTAR investigation of X-ray variability and hard X-ray spectral properties in IGR J16320-4751 and IGR J16479-4514