Multi-Wavelength Study of X-ray Pulsar 2S 1553-542 During Outburst in
  2021
  We summarize the results of temporal and spectral analysis of the X-ray
pulsar 2S 1553-542 using the Nuclear Spectroscopic Telescope Array (NuSTAR) and
Swift during the outburst in January-February 2021. During the outburst, the
spin period of the neutron star was $P = 9.2822\pm 0.0001$ s based on NuSTAR
data. The temporal evolution of the spin period, pulse profile, and pulse
fraction is studied during the outburst. The spectra of the source are studied
for different days of the outburst and can be well described by a model
consisting of -- a black body emission or a power law. We have investigated the
inter-day evolution of different timing and spectral parameters during the
outburst. The energy dependence of the pulse profile was studied to investigate
the evolution of the individual peaks and emission geometry of the pulsar with
a different energy. The pulse profile of the source shows strong single peak
nature with a hump-like feature of relatively lower intensity and it evolves
significantly with different energy ranges. The evolution of the pulse profile
is studied during different phases of the outburst and the pulse fraction shows
a positive correlation with energy.
