We present the results obtained from timing and spectral studies of the
accretion powered X-ray pulsar 2S~1417-624 during a giant outburst in 2009 by
using {\it Rossi X-ray Timing Explorer (RXTE)} observations. X-ray pulsations
were detected in the light curves obtained from all epochs of observations. The
pulsar was found to be spinning-up during the outburst. The pulse profiles were
observed to be strongly dependent on photon energy and luminosity. A double
peaked profile at lower luminosity evolved into a triple peaked profile at the
peak of the outburst which is further reverted back to a double peaked
structure during the decay of the outburst. An anti-correlation was also
observed between the pulse fraction and the source flux. The 3-70 keV energy
spectrum of pulsar was well described with a power law modified with high
energy cutoff model along with an iron fluorescence line at 6.4 keV. Based on
the evolution of pulse profile, pulse fraction and spectral parameters across
observed luminosity, we interpret our results in terms of changes in the pulsar
beam configuration from sub-critical to super-critical regimes.Comment: 9 pages,7 figures; Accepted for publication in Monthly Notices of the
Royal Astronomical Society journal on July 2, 201
