Abstract:
We present the results obtained from a comprehensive timing and spectral study of two high mass X-ray binary sources using
NuSTAR observations. These two sources, IGR J16320–4751 and IGR J16479–4514 were discovered by INTEGRAL and have
been characterized for the first time in the hard X-ray band (beyond 10 keV) in this work. In these sources, we observe the
occurrence of intense X-ray flares, with average luminosities exceeding 1036 erg s−1. Our analysis reveals that these flares can
be described consistently in the quasi-spherical accretion regime. The orbital phase of the first flare in NuSTAR observation of
IGR J16479–4514 matches with the orbital phases of previous flares (φ = 0.35) in this source detected by other telescopes. We
conclude that, this flare occurs as a result of the periastron passage of the neutron star (NS), rather than due to the presence of
a corotating interaction region. Furthermore, from the energy-resolved pulse profile analysis of IGR J16320–4751, we find that
the pulse fraction is lower in hard X-rays compared to the soft X-rays. We present the hard X-ray spectral parameters of these
two sources using several standard spectral model components. We do not detect a cyclotron absorption feature in either target.
We provide estimates to the surface magnetic field strength of NS in IGR J16320−4751, using two indirect methods. Lastly, we
observe spectral hardening during flaring segments compared to the off-flaring segments which indicates that Comptonization
is more effective during the flaring segments.
